Sand casting, the most widely used casting process, utilizes expendable sand molds to form complex metal parts that can be made of nearly any alloy. Because the sand mold must be destroyed in order to remove the part, called the casting, sand casting typically has a low production rate. The sand casting process involves the use of a furnace, metal, pattern, and sand mold. The metal is melted in the furnace and then ladled and poured into the cavity of the sand mold, which is formed by the pattern. The sand mold separates along a parting line and the solidified casting can be removed. The steps in this process are described in greater detail in the next section. Sand casting overview Sand casting is used to produce a wide variety of metal components with complex geometries. These parts can vary greatly in size and weight, ranging from a couple ounces to several tons. Some smaller sand cast parts include components as gears, pulleys, crankshafts, connecting rods, and propellers. Larger applications include housings for large equipment and heavy machine bases. Sand casting is also common in producing automobile components, such as engine blocks, engine manifolds, cylinder heads, and transmission cases. Capabilities Typical Feasible Shapes: Thin-walled: Complex Solid: Cylindrical Solid: Cubic Solid: Complex Flat Thin-walled: Cylindrical Thin-walled: Cubic Part size: Weight: 1 oz - 450 ton Materials: Alloy Steel Carbon Steel Cast Iron Stainless Steel Aluminum Copper Magnesium Nickel Lead Tin Titanium Zinc Surface finish: 300 - 600 in 125 - 2000 in
Transcript
Sand casting, the most widely used casting process, utilizes expendable sand molds to form complex metal parts that can be made of nearly any alloy. Because the sand mold must be destroyed in order to remove the part, called the casting, sand casting typically has a low production rate. The sand casting process involves the use of a furnace, metal, pattern, and sand mold. The metal is melted in the furnace and then ladled and poured into the cavity of the sand mold, which is formed by the pattern. The sand mold separates along a parting line and the solidified casting can be removed. The steps in this process are described in greater detail in the next section.
Sand casting overview
Sand casting is used to produce a wide variety of metal components with complex geometries. These parts can vary greatly in size and weight, ranging from a couple ounces to several tons. Some smaller sand cast parts include components as gears, pulleys, crankshafts, connecting rods, and propellers. Larger applications include housings for large equipment and heavy machine bases. Sand casting is also common in producing automobile components, such as engine blocks, engine manifolds, cylinder heads, and transmission cases.
Tolerance: ± 0.03 in. ± 0.015 in. Wall thickness: 0.125 - 5 in. 0.09 - 40 in. Production quantity: 1 - 1000 1 - 1000000 Lead time: Days Hours
Advantages:
Can produce very large parts Can form complex shapes Many material options Low tooling and equipment cost Scrap can be recycled Short lead time possible
Disadvantages:
Poor material strength High porosity possible Poor surface finish and tolerance Seondary machining often required Low production rate High labor cost
Applications: Engine blocks and manifolds, machine bases, gears, pulleys
Process Cycle
The process cycle for sand casting consists of six main stages, which are explained below.
Mold-making - The first step in the sand casting process is to create the mold for the casting. In an expendable mold process, this step must be performed for each casting. A sand mold is formed by packing sand into each half of the mold. The sand is packed around the pattern, which is a replica of the external shape of the casting. When the pattern is removed, the cavity that will form the casting remains. Any internal features of the casting that cannot be formed by the pattern are formed by separate cores which are made of sand prior to the formation of the mold. Further details on mold-making will be described in the next section. The mold-making time includes positioning the pattern, packing the sand, and removing the pattern. The mold-making time is affected by the size of the part, the number of cores, and the type of sand mold. If the mold type requires heating or baking time, the mold-making time is substantially increased. Also, lubrication is often applied to the surfaces of the mold cavity in order to facilitate removal of the casting. The use of a lubricant also improves the flow the metal and can improve the surface finish of the casting. The lubricant that is used is chosen based upon the sand and molten metal temperature.
Clamping - Once the mold has been made, it must be prepared for the molten metal to be poured. The surface of the mold cavity is first lubricated to facilitate the removal of the casting. Then, the cores are positioned and the mold halves are closed and securely clamped together. It is essential that the mold halves remain securely closed to prevent the loss of any material.
Pouring - The molten metal is maintained at a set temperature in a furnace. After the mold has been clamped, the molten metal can be ladled from its holding container in the furnace and poured into the mold. The pouring can be performed manually or by an automated machine. Enough molten metal must be poured to fill the entire cavity and all channels in the mold. The filling time is very short in order to prevent early solidification of any one part of the metal.
Cooling - The molten metal that is poured into the mold will begin to cool and solidify once it enters the cavity. When the entire cavity is filled and the molten metal solidifies, the final shape of the casting is formed. The mold can not be opened until the cooling time has elapsed. The desired cooling time can be estimated based upon the wall thickness of the casting and the temperature of the metal. Most of the possible defects that can occur are a result of the solidification process. If some of the molten metal cools too quickly, the part may exhibit shrinkage, cracks, or incomplete sections. Preventative measures can be taken in designing both the part and the mold and will be explored in later sections.
Removal - After the predetermined solidification time has passed, the sand mold can simply be broken, and the casting removed. This step, sometimes called shakeout, is typically performed by a vibrating machine that shakes the sand and casting out of the flask. Once removed, the casting will likely have some sand and oxide layers adhered to the surface. Shot blasting is sometimes used to remove any remaining sand, especially from internal surfaces, and reduce the surface roughness.
Trimming - During cooling, the material from the channels in the mold solidifies attached to the part. This excess material must be trimmed from the casting either manually via cutting or sawing, or using a trimming press. The time required to trim the excess
material can be estimated from the size of the casting's envelope. A larger casting will require a longer trimming time. The scrap material that results from this trimming is either discarded or reused in the sand casting process. However, the scrap material may need to be reconditioned to the proper chemical composition before it can be combined with non-recycled metal and reused.
Mold In sand casting, the primary piece of equipment is the mold, which contains several components. The mold is divided into two halves - the cope (upper half) and the drag (bottom half), which meet along a parting line. Both mold halves are contained inside a box, called a flask, which itself is divided along this parting line. The mold cavity is formed by packing sand around the pattern in each half of the flask. The sand can be packed by hand, but machines that use pressure or impact ensure even packing of the sand and require far less time, thus increasing the production rate. After the sand has been packed and the pattern is removed, a cavity will remain that forms the external shape of the casting. Some internal surfaces of the casting may be formed by cores. Cores are additional pieces that form the internal holes and passages of the casting. Cores are typically made out of sand so that they can be shaken out of the casting, rather than require the necessary geometry to slide out. As a result, sand cores allow for the fabrication of many complex internal features. Each core is positioned in the mold before the molten metal is poured. In order to keep each core in place, the pattern has recesses called core prints where the core can be anchored in place. However, the core may still shift due to buoyancy in the molten metal. Further support is provided to the cores by chaplets. These are small metal pieces that are fastened between the core and the cavity surface. Chaplets must be made of a metal with a higher melting temperature than that of the metal being cast in order to maintain their structure. After solidification, the chaplets will have been cast inside the casting and the excess material of the chaplets that protrudes must be cut off. In addition to the external and internal features of the casting, other features must be incorporated into the mold to accommodate the flow of molten metal. The molten metal is poured into a pouring basin, which is a large depression in the top of the sand mold. The molten metal funnels out of the bottom of this basin and down the main channel, called the sprue. The sprue then connects to a series of channels, called runners, which carries the molten metal into the cavity. At the end of each runner, the molten metal enters the cavity through a gate which controls the flow rate and minimizes turbulence. Often connected to the runner system are risers. Risers are chambers that fill with molten metal, providing an additional source of metal during solidification. When the casting cools, the molten metal will shrink and additional material is needed. A similar feature that aids in reducing shrinkage is an open riser. The first material to enter the cavity is allowed to pass completely through and enter the open riser. This strategy prevents early solidification of the molten metal and provides a source of material to compensate for shrinkage. Lastly, small channels are included that run from the cavity to the exterior of the mold. These channels act as venting holes to allow gases to escape the cavity. The porosity of the sand also allows air to escape, but additional vents are sometimes needed. The molten metal that flows through all of the channels (sprue, runners, and risers) will solidify attached to the casting and must be separated from the part after it is removed.
Sand Mold - Opened
Sand Mold - Closed
Sand The sand that is used to create the molds is typically silica sand (SiO2) that is mixed with a type of binder to help maintain the shape of the mold cavity. Using sand as the mold material offers several benefits to the casting process. Sand is very inexpensive and is resistant to high temperatures, allowing many metals to be cast that have high melting temperatures. There are different preparations of the sand for the mold, which characterize the following four unique types of sand molds.
Greensand mold - Greensand molds use a mixture of sand, water, and a clay or binder. Typical composition of the mixture is 90% sand, 3% water, and 7% clay or binder. Greensand molds are the least expensive and most widely used.
Skin-dried mold - A skin-dried mold begins like a greensand mold, but additional bonding materials are added and the cavity surface is dried by a torch or heating lamp to increase mold strength. Doing so also improves the dimensional accuracy and surface finish, but will lower the collapsibility. Dry skin molds are more expensive and require more time, thus lowering the production rate.
Dry sand mold - In a dry sand mold, sometimes called a cold box mold, the sand is mixed only with an organic binder. The mold is strengthened by baking it in an oven. The resulting mold has high dimensional accuracy, but is expensive and results in a lower production rate.
No-bake mold - The sand in a no-bake mold is mixed with a liquid resin and hardens at room temperature.
The quality of the sand that is used also greatly affects the quality of the casting and is usually described by the following five measures:
Strength - Ability of the sand to maintain its shape.
Permeability - Ability to allow venting of trapped gases through the sand. A higher permeability can reduce the porosity of the mold, but a lower permeability can result in a better surface finish. Permeability is determined by the size and shape of the sand grains.
Thermal stability - Ability to resist damage, such as cracking, from the heat of the molten metal.
Collapsibility - Ability of the sand to collapse, or more accurately compress, during solidification of the casting. If the sand can not compress, then the casting will not be able to shrink freely in the mold and can result in cracking.
Reusability - Ability of the sand to be reused for future sand molds.
Packing equipment There exists many ways to pack the sand into the mold. As mentioned above, the sand can be hand packed into the mold. However, there are several types of equipment that provide more effective and efficient packing of the sand. One such machine is called a sandslinger and fills the flask with sand by propelling it under high pressure. A jolt-squeeze machine is a common piece of equipment which rapidly jolts the flask to distribute the sand and then uses hydraulic pressure to compact it in the flask. Another method, called impact molding, uses a controlled explosion to drive and compact the sand into the flask. In what can be considered an opposite approach, vacuum molding packs the sand by removing the air between the flask and a thin sheet of plastic that covers the pattern. The packing of the sand is also automated in a process known as flask-less molding. Despite the name of the process, a flask is still used. In conventional sand casting, a new flask is used for each mold. However, flask-less molding uses a single master flask in an automated process of creating sand molds. The flask moves along a conveyor and has sand blown against the pattern inside. This automated process greatly increases the production rate and also has many benefits to the castings. Flask-less molding can produce uniform, high density molds that result in excellent casting quality. Also, the automated process causes little variation between castings.
Tooling
The main tooling for sand casting is the pattern that is used to create the mold cavity. The pattern is a full size model of the part that makes an impression in the sand mold. However, some internal surfaces may not be included in the pattern, as they will be created by separate cores. The pattern is actually made to be slightly larger than the part because the casting will shrink inside the mold cavity. Also, several identical patterns may be used to create multiple impressions in the sand mold, thus creating multiple cavities that will produce as many parts in one casting. Several different materials can be used to fabricate a pattern, including wood, plastic, and metal. Wood is very common because it is easy to shape and is inexpensive, however it can warp and deform easily. Wood also will wear quicker from the sand. Metal, on the other hand, is more expensive, but will last longer and has higher tolerances. The pattern can be reused to create the cavity for many molds of the same part. Therefore, a pattern that lasts longer will reduce tooling costs. A pattern for a part can be made many different ways, which are classified into the following four types:
Solid pattern - A solid pattern is a model of the part as a single piece. It is the easiest to fabricate, but can cause some difficulties in making the mold. The parting line and runner system must be determined separately. Solid patterns are typically used for geometrically simple parts that are produced in low quantities.
Solid pattern
Split pattern - A split pattern models the part as two separate pieces that meet along the parting line of the mold. Using two separate pieces allows the mold cavities in the cope and drag to be made separately and the parting line is already determined. Split patterns are typically used for parts that are geometrically complex and are produced in moderate quantities.
Split pattern
Match-plate pattern - A match-plate pattern is similar to a split pattern, except that each half of the pattern is attached to opposite sides of a single plate. The plate is usually made from wood or metal. This pattern design ensures proper alignment of the mold cavities in the cope and drag and the runner system can be included on the match plate. Match-plate patterns are used for larger production quantities and are often used when the process is automated.
Match-plate pattern
Cope and drag pattern - A cope and drag pattern is similar to a match plate pattern, except that each half of the pattern is attached to a separate plate and the mold halves are made independently. Just as with a match plate pattern, the plates ensure proper alignment of the mold cavities in the cope and drag and the runner system can be included on the plates. Cope and drag patterns are often desirable for larger castings, where a match-plate pattern would be too heavy and cumbersome. They are also used for larger production quantities and are often used when the process is automated.
Cope and drag pattern
Another piece of tooling used in sand casting is a core-box. If the casting requires sand cores, the cores are formed in these boxes, which are similar to a die and can be made of wood, plastic, or metal just like the pattern. The core-boxes can also contain multiple cavities to produce several identical cores.
Materials
Sand casting is able to make use of almost any alloy. An advantage of sand casting is the ability to cast materials with high melting temperatures, including steel, nickel, and titanium. The four most common materials that are used in sand casting are shown below, along with their melting temperatures.
Decrease the maximum wall thickness of a part to shorten the cycle time (cooling time specifically) and reduce the part volume
INCORRECT
Part with thick walls
CORRECT
Part redesigned with thin walls
Uniform wall thickness will ensure uniform cooling and reduce defects. A thick section, often referred to as a hot spot, causes uneven cooling and can result in shrinkage, porosity, or cracking.
INCORRECT
Non-uniform wall thickness (t1 � t2)
CORRECT
Uniform wall thickness (t1 = t2)
Corners
Round corners to reduce stress concentrations and fracture
Inner radius should be at least the thickness of the walls
INCORRECT
Sharp corner
CORRECT
Rounded corner
Draft
Apply a draft angle of 2° - 3° to all walls parallel to the parting direction to facilitate removing the part from the mold.
INCORRECT
No draft angle
CORRECT
Draft angle (�)
Machining allowance
Add 0.0625 - 0.25 in. (0.16 - 0.64 mm) to part dimensions to allow for machining to obtain a smooth surface.
Cost Drivers
Material cost
The material cost for sand casting includes the cost of the metal, melting the metal, the mold sand, and the core sand. The cost of the metal is determined by the weight of the part, calculated from part volume and material density, as well the unit price of the material. The melting cost will also be greater for a larger part weight and is influenced by the material, as some materials are more costly to melt. However, the melting cost in typically insignificant compared to the metal cost. The amount of mold sand that is used, and hence the cost, is also proportional to the weight of the part. Lastly, the cost of the core sand is determined by the quantity and size of the cores used to cast the part.
Production cost
The production cost includes a variety of operations used to cast the part, including core-making, mold-making, pouring, and cleaning. The cost of making the cores depends on the volume of the cores and the quantity used to cast the part. The cost of the mold-making is not greatly influenced by the part geometry when automated equipment is being used. However, the inclusion of cores will slightly slow the process and therefore increase the cost. Lastly, the cost of pouring the metal and cleaning the final casting are both driven by the weight of the part. It will take longer to pour and to clean a larger and heavier casting.
Tooling cost
The tooling cost has two main components - the pattern and the core-boxes. The pattern cost is primarily controlled by the size of the part (both the envelope and the projected area) as well as the part's complexity. The cost of the core-boxes first depends on their size, a
result of the quantity and size of the cores that are used to cast the part. Much like the pattern, the complexity of the cores will affect the time to manufacture this part of the tooling (in addition to the core size), and hence the cost. The quantity of parts that are cast will also impact the tooling cost. A larger production quantity will require the use of a tooling material, for both the pattern and core-boxes, that will not wear under the required number of cycles. The use or a stronger, more durable, tooling material will significantly increase the cost.
Blow Molding
Blow molding is a manufacturing process that is used to create hollow plastic parts by inflating a heated plastic tube until it fills a mold and forms the desired shape. The raw material in this process is a thermoplastic in the form of small pellets or granules, which is first melted and formed into a hollow tube, called the parison. There are various ways of forming the parison, as explained below. The parison is then clamped between two mold halves and inflated by pressurized air until it conforms to the inner shape of the mold cavity. Typical pressures are 25 to 150 psi, far less than for injection molding. Lastly, after the part has cooled, the mold halves are separated and the part is ejected. Parts made from blow molding are plastic, hollow, and thin-walled, such as bottles and containers that are available in a variety of shapes and sizes. Small products may include bottles for water, liquid soap, shampoo, motor oil, and milk, while larger containers include plastic drums, tubs, and storage tanks. Blow molded parts can be formed from a variety of thermoplastic materials, including the following:
Low Density Polyethylene (LDPE)
High Density Polyethylene (HDPE)
Polyethylene Terephtalate (PET)
Polypropylene (PP)
Polyvinyl Chloride (PVC)
As mentioned above, there are different methods used to form the parison which distinguish the following three forms of blow molding:
Extrusion blow molding - An extruder uses a rotating screw to force the molten plastic through a die head that forms the parison around a blow pin. The parison is extruded vertically between the two open mold halves, so they can close on the parison and blow pin. Pressurized air flows through the blow pin to inflate the parison. This is the most common type of blow molding and is used to manufacture large quantities of relatively simple parts.
Injection blow molding - The molten plastic is injection molded around a core inside a parison mold to form the hollow parison. When the parison mold opens, both the parison and core are transferred to the blow mold and securely clamped. The core then opens and allows pressurized air to inflate the parison. This is the least commonly used method because of the lower production rate, but is capable of forming more complicated parts with higher accuracy. Injection blow molding is often preferred for small, complex bottles, such as those in medical applications.
Stretch blow molding - The parison is formed in the same way as injection blow molding. However, once transferred to the blow mold, it is heated and stretched downward by the core before being inflated. This stretching provides greater strength to the plastic. Stretch blow molding is typically used to create parts that must withstand some internal pressure or be very durable, such as soda bottles.
Part size: Envelope: Up to 105 ft³ Materials: Thermoplastics Surface finish: 250 - 500 �in 250 - 500 �in Tolerance: ± 0.04 in. ± 0.01 in. Wall thickness: 0.015 - 0.125 in. 0.01 - 0.24 in. Production quantity: 100000 - 1000000 1000 - 1000000 Lead time: Days Days
Advantages:
Can form complex shapes with uniform wall thickness High production rate Low labor cost Little scrap generated
Disadvantages:
Limited to hollow, thin walled parts with low degree of asymmetry Poor control of wall thickness Poor surface finish Few material options High tooling and equipment cost
Applications: Bottles, containers, ducting
Injection molding is the most commonly used manufacturing process for the fabrication of plastic parts. A wide variety of products are manufactured using injection molding, which vary greatly in their size, complexity, and application. The injection molding process requires the use of an injection molding machine, raw plastic material, and a mold. The plastic is melted in the injection molding
machine and then injected into the mold, where it cools and solidifies into the final part. The steps in this process are described in greater detail in the next section.
Injection molding overview
Injection molding is used to produce thin-walled plastic parts for a wide variety of applications, one of the most common being plastic housings. Plastic housing is a thin-walled enclosure, often requiring many ribs and bosses on the interior. These housings are used in a variety of products including household appliances, consumer electronics, power tools, and as automotive dashboards. Other common thin-walled products include different types of open containers, such as buckets. Injection molding is also used to produce several everyday items such as toothbrushes or small plastic toys. Many medical devices, including valves and syringes, are manufactured using injection molding as well.
Surface finish: 4 - 16 �in 1 - 32 �in Tolerance: ± 0.008 in. ± 0.002 in. Wall thickness: 0.03 - 0.25 in. 0.015 - 0.5 in. Production quantity: 10000 - 1000000 1000 - 1000000 Lead time: Months Weeks Advantages: Can form complex shapes and fine details
Excellent surrface finish Good dimensional accuracy High production rate Low labor cost Scrap can be recycled
Disadvantages: Limited to thin walled parts High tooling and equipment cost Long lead time possible
The process cycle for injection molding is very short, typically between 2 seconds and 2 minutes, and consists of the following four stages:
Clamping - Prior to the injection of the material into the mold, the two halves of the mold must first be securely closed by the clamping unit. Each half of the mold is attached to the injection molding machine and one half is allowed to slide. The hydraulically powered clamping unit pushes the mold halves together and exerts sufficient force to keep the mold securely closed while the material is injected. The time required to close and clamp the mold is dependent upon the machine - larger machines (those with greater clamping forces) will require more time. This time can be estimated from the dry cycle time of the machine.
Injection - The raw plastic material, usually in the form of pellets, is fed into the injection molding machine, and advanced towards the mold by the injection unit. During this process, the material is melted by heat and pressure. The molten plastic is then injected into the mold very quickly and the buildup of pressure packs and holds the material. The amount of material that is injected is referred to as the shot. The injection time is difficult to calculate accurately due to the complex and changing flow of the molten plastic into the mold. However, the injection time can be estimated by the shot volume, injection pressure, and injection power.
Cooling - The molten plastic that is inside the mold begins to cool as soon as it makes contact with the interior mold surfaces. As the plastic cools, it will solidify into the shape of the desired part. However, during cooling some shrinkage of the part may occur. The packing of material in the injection stage allows additional material to flow into the mold and reduce the amount of visible shrinkage. The mold can not be opened until the required cooling time has elapsed. The cooling time can be estimated from several thermodynamic properties of the plastic and the maximum wall thickness of the part.
Ejection - After sufficient time has passed, the cooled part may be ejected from the mold by the ejection system, which is attached to the rear half of the mold. When the mold is opened, a mechanism is used to push the part out of the mold. Force must be applied to eject the part because during cooling the part shrinks and adheres to the mold. In order to facilitate the ejection of the part, a mold release agent can be sprayed onto the surfaces of the mold cavity prior to injection of the material. The time that is required to open the mold and eject the part can be estimated from the dry cycle time of the machine and should include time for the part to fall free of the mold. Once the part is ejected, the mold can be clamped shut for the next shot to be injected.
After the injection molding cycle, some post processing is typically required. During cooling, the material in the channels of the mold will solidify attached to the part. This excess material, along with any flash that has occurred, must be trimmed from the part, typically by using cutters. For some types of material, such as thermoplastics, the scrap material that results from this trimming can be recycled by being placed into a plastic grinder, also called regrind machines or granulators, which regrinds the scrap material into pellets. Due to some degradation of the material properties, the regrind must be mixed with raw material in the proper regrind ratio to be reused in the injection molding process.
Injection molded part
Equipment
Injection molding machines have many components and are available in different configurations, including a horizontal configuration and a vertical configuration. However, regardless of their design, all injection molding machines utilize a power source, injection unit, mold assembly, and clamping unit to perform the four stages of the process cycle.
Injection unit
The injection unit is responsible for both heating and injecting the material into the mold. The first part of this unit is the hopper, a large container into which the raw plastic is poured. The hopper has an open bottom, which allows the material to feed into the barrel. The barrel contains the mechanism for heating and injecting the material into the mold. This mechanism is usually a ram injector or a reciprocating screw. A ram injector forces the material forward through a heated section with a ram or plunger that is usually hydraulically powered. Today, the more common technique is the use of a reciprocating screw. A reciprocating screw moves the material forward by both rotating and sliding axially, being powered by either a hydraulic or electric motor. The material enters the grooves of the screw from the hopper and is advanced towards the mold as the screw rotates. While it is advanced, the material is melted by pressure, friction, and additional heaters that surround the reciprocating screw. The molten plastic is then injected very quickly into the mold through the nozzle at the end of the barrel by the buildup of pressure and the forward action of the screw. This increasing pressure allows the material to be packed and forcibly held in the mold. Once the material has solidified inside the mold, the screw can retract and fill with more material for the next shot.
Injection molding machine - Injection unit
Clamping unit
Prior to the injection of the molten plastic into the mold, the two halves of the mold must first be securely closed by the clamping unit. When the mold is attached to the injection molding machine, each half is fixed to a large plate, called a platen. The front half of the mold, called the mold cavity, is mounted to a stationary platen and aligns with the nozzle of the injection unit. The rear half of the mold, called the mold core, is mounted to a movable platen, which slides along the tie bars. The hydraulically powered clamping motor actuates clamping bars that push the moveable platen towards the stationary platen and exert sufficient force to keep the mold securely closed while the material is injected and subsequently cools. After the required cooling time, the mold is then opened by the clamping motor. An ejection system, which is attached to the rear half of the mold, is actuated by the ejector bar and pushes the solidified part out of the open cavity.
Injection molding machine - Clamping unit
Machine specifications
Injection molding machines are typically characterized by the tonnage of the clamp force they provide. The required clamp force is determined by the projected area of the parts in the mold and the pressure with which the material is injected. Therefore, a larger part will require a larger clamping force. Also, certain materials that require high injection pressures may require higher tonnage machines. The size of the part must also comply with other machine specifications, such as shot capacity, clamp stroke, minimum mold thickness, and platen size.
Injection molded parts can vary greatly in size and therefore require these measures to cover a very large range. As a result, injection molding machines are designed to each accommodate a small range of this larger spectrum of values. Sample specifications are shown below for three different models (Babyplast, Powerline, and Maxima) of injection molding machine that are manufactured by Cincinnati Milacron.
Babyplast Powerline Maxima Clamp force (ton) 6.6 330 4400 Shot capacity (oz.) 0.13 - 0.50 8 - 34 413 - 1054 Clamp stroke (in.) 4.33 23.6 133.8 Min. mold thickness (in.) 1.18 7.9 31.5 Platen size (in.) 2.95 x 2.95 40.55 x 40.55 122.0 x 106.3
Injection molding machine
Tooling
The injection molding process uses molds, typically made of steel or aluminum, as the custom tooling. The mold has many components, but can be split into two halves. Each half is attached inside the injection molding machine and the rear half is allowed to slide so that the mold can be opened and closed along the mold's parting line. The two main components of the mold are the mold core and the mold cavity. When the mold is closed, the space between the mold core and the mold cavity forms the part cavity, that will be filled with molten plastic to create the desired part. Multiple-cavity molds are sometimes used, in which the two mold halves form several identical part cavities.
Mold overview
Mold base
The mold core and mold cavity are each mounted to the mold base, which is then fixed to the platens inside the injection molding machine. The front half of the mold base includes a support plate, to which the mold cavity is attached, the sprue bushing, into which the material will flow from the nozzle, and a locating ring, in order to align the mold base with the nozzle. The rear half of the mold base includes the ejection system, to which the mold core is attached, and a support plate. When the clamping unit separates the mold halves, the ejector bar actuates the ejection system. The ejector bar pushes the ejector plate forward inside the ejector box, which in turn pushes the ejector pins into the molded part. The ejector pins push the solidified part out of the open mold cavity.
Mold base
Mold channels
In order for the molten plastic to flow into the mold cavities, several channels are integrated into the mold design. First, the molten plastic enters the mold through the sprue. Additional channels, called runners, carry the molten plastic from the sprue to all of the cavities that must be filled. At the end of each runner, the molten plastic enters the cavity through a gate which directs the flow. The molten plastic that solidifies inside these runners is attached to the part and must be separated after the part has been ejected from the mold. However, sometimes hot runner systems are used which independently heat the channels, allowing the contained material to be melted and detached from the part. Another type of channel that is built into the mold is cooling channels. These channels allow water to flow through the mold walls, adjacent to the cavity, and cool the molten plastic.
Mold channels
Mold design
In addition to runners and gates, there are many other design issues that must be considered in the design of the molds. Firstly, the mold must allow the molten plastic to flow easily into all of the cavities. Equally important is the removal of the solidified part from the mold, so a draft angle must be applied to the mold walls. The design of the mold must also accommodate any complex features on the part, such as undercuts or threads, which will require additional mold pieces. Most of these devices slide into the part cavity through the side of the mold, and are therefore known as slides, or side-actions. The most common type of side-action is a side-core which enables an external undercut to be molded. Other devices enter through the end of the mold along the parting direction, such as internal core lifters, which can form an internal undercut. To mold threads into the part, an unscrewing device is needed, which can rotate out of the mold after the threads have been formed.
Mold - Closed
Mold - Exploded view
Materials
There are many types of materials that may be used in the injection molding process. Most polymers may be used, including all thermoplastics, some thermosets, and some elastomers. When these materials are used in the injection molding process, their raw form is usually small pellets or a fine powder. Also, colorants may be added in the process to control the color of the final part. The selection of a material for creating injection molded parts is not solely based upon the desired characteristics of the final part. While each material has different properties that will affect the strength and function of the final part, these properties also dictate the parameters used in processing these materials. Each material requires a different set of processing parameters in the injection molding process, including the injection temperature, injection pressure, mold temperature, ejection temperature, and cycle time. A comparison of some commonly used materials is shown below (Follow the links to search the material library).
Material name Abbreviation Trade names Description Applications
Flow rate of material too low Sink marks Injection pressure too low
Non-uniform cooling rate
Ejector marks Cooling time too short
Ejection force too high
Many of the above defects are caused by a non-uniform cooling rate. A variation in the cooling rate can be caused by non-uniform wall thickness or non-uniform mold temperature.
Design Rules
Maximum wall thickness
Decrease the maximum wall thickness of a part to shorten the cycle time (injection time and cooling time specifically) and reduce the part volume
INCORRECT
Part with thick walls
CORRECT
Part redesigned with thin walls
Uniform wall thickness will ensure uniform cooling and reduce defects
INCORRECT
Non-uniform wall thickness (t1 � t2)
CORRECT
Uniform wall thickness (t1 = t2)
Corners
Round corners to reduce stress concentrations and fracture
Inner radius should be at least the thickness of the walls
INCORRECT
Sharp corner
CORRECT
Rounded corner
Draft
Apply a draft angle of 1° - 2° to all walls parallel to the parting direction to facilitate removing the part from the mold.
INCORRECT
No draft angle
CORRECT
Draft angle (�)
Ribs
Add ribs for structural support, rather than increasing the wall thickness
INCORRECT
Thick wall of thickness t
CORRECT
Thin wall of thickness t with ribs
Orient ribs perpendicular to the axis about which bending may occur
INCORRECT
Incorrect rib direction under load F
CORRECT
Correct rib direction under load F
Thickness of ribs should be 50-60% of the walls to which they are attached
Height of ribs should be less than three times the wall thickness
Round the corners at the point of attachment
Apply a draft angle of at least 0.25°
INCORRECT
Thick rib of thickness t
CORRECT
Thin rib of thickness t
Close up of ribs
Bosses
Wall thickness of bosses should be no more than 60% of the main wall thickness
Radius at the base should be at least 25% of the main wall thickness
Should be supported by ribs that connect to adjacent walls or by gussets at the base.
INCORRECT
Isolated boss
CORRECT
Isolated boss with ribs (left) or gussets (right)
If a boss must be placed near a corner, it should be isolated using ribs.
INCORRECT
Boss in corner
CORRECT
Ribbed boss in corner
Undercuts
Minimize the number of external undercuts
External undercuts require side-cores which add to the tooling cost
Some simple external undercuts can be molded by relocating the parting line
Simple external undercut
Mold cannot separate
New parting line allows undercut
Redesigning a feature can remove an external undercut
Part with hinge
Hinge requires side-core
Redesigned hinge
New hinge can be molded
Minimize the number of internal undercuts
Internal undercuts often require internal core lifters which add to the tooling cost
Designing an opening in the side of a part can allow a side-core to form an internal undercut
Internal undercut accessible from the side
Redesigning a part can remove an internal undercut
Part with internal undercut
Mold cannot separate
Part redesigned with slot
New part can be molded
Minimize number of side-action directions
Additional side-action directions will limit the number of possible cavities in the mold
Threads
If possible, features with external threads should be oriented perpendicular to the parting direction.
Threaded features that are parallel to the parting direction will require an unscrewing device, which greatly adds to the tooling cost.
Cost Drivers
Material cost
The material cost is determined by the weight of material that is required and the unit price of that material. The weight of material is clearly a result of the part volume and material density; however, the part's maximum wall thickness can also play a role. The weight of material that is required includes the material that fills the channels of the mold. The size of those channels, and hence the amount of material, is largely determined by the thickness of the part.
Production cost
The production cost is primarily calculated from the hourly rate and the cycle time. The hourly rate is proportional to the size of the injection molding machine being used, so it is important to understand how the part design affects machine selection. Injection molding machines are typically referred to by the tonnage of the clamping force they provide. The required clamping force is determined by the projected area of the part and the pressure with which the material is injected. Therefore, a larger part will require a
larger clamping force, and hence a more expensive machine. Also, certain materials that require high injection pressures may require higher tonnage machines. The size of the part must also comply with other machine specifications, such as clamp stroke, platen size, and shot capacity. The cycle time can be broken down into the injection time, cooling time, and resetting time. By reducing any of these times, the production cost will be lowered. The injection time can be decreased by reducing the maximum wall thickness of the part and the part volume. The cooling time is also decreased for lower wall thicknesses, as they require less time to cool all the way through. Several thermodynamic properties of the material also affect the cooling time. Lastly, the resetting time depends on the machine size and the part size. A larger part will require larger motions from the machine to open, close, and eject the part, and a larger machine requires more time to perform these operations.
Tooling cost
The tooling cost has two main components - the mold base and the machining of the cavities. The cost of the mold base is primarily controlled by the size of the part's envelope. A larger part requires a larger, more expensive, mold base. The cost of machining the cavities is affected by nearly every aspect of the part's geometry. The primary cost driver is the size of the cavity that must be machined, measured by the projected area of the cavity (equal to the projected area of the part and projected holes) and its depth. Any other elements that will require additional machining time will add to the cost, including the feature count, parting surface, side-cores, lifters, unscrewing devices, tolerance, and surface roughness. The quantity of parts also impacts the tooling cost. A larger production quantity will require a higher class mold that will not wear as quickly. The stronger mold material results in a higher mold base cost and more machining time. One final consideration is the number of side-action directions, which can indirectly affect the cost. The additional cost for side-cores is determined by how many are used. However, the number of directions can restrict the number of cavities that can be included in the mold. For example, the mold for a part which requires 3 side-action directions can only contain 2 cavities. There is no direct cost added, but it is possible that the use of more cavities could provide further savings.
Metal Injection Molding (MIM) is a variation on traditional plastic injection molding that enables the fabrication of solid metal parts utilizing injection molding technology. In this process, the raw material, referred to as the feedstock, is a powder mixture of metal and polymer. For this reason, MIM is sometimes referred to as Powder Injection Molding (PIM). Using a standard injection molding machine, the powder is melted and injected into a mold, where it cools and solidifies into the shape of the desired part. Subsequent heating processes remove the unwanted polymer and produce a high-density metal part. Metal injection molding is best suited for the high-volume production of small metal parts. As with injection molding, these parts may be geometrically complex and have thin walls and fine details. The use of metal powders enables a wide variety of ferrous and non ferrous alloys to be used and for the material properties (strength, hardness, wear resistance, corrosion resistance, etc.) to be close to those of wrought metals. Also, because the metal is not melted in the MIM process (unlike metal casting processes), high temperature alloys can be used without any negative affect on tool life. Metals commonly used for MIM parts include the following:
Low alloy steels
Stainless steels
High-speed steels
Irons
Cobalt alloys
Copper alloys
Nickel alloys
Tungsten alloys
Titanium alloys
Metal parts manufactured from the MIM process are found in numerous industries, including aerospace, automotive, consumer products, medical/dental, and telecommunications. MIM components can be found in cell phones, sporting goods, power tools, surgical instruments, and various electronic and optical devices. The metal injection molding process consists of the following steps:
Feedstock preparation - The first step is to create a powder mixture of metal and polymer. The powder metals used here are much finer (typically under 20 microns) than those used in traditional powder metallurgy processes. The powder metal is mixed with a hot thermoplastic binder, cooled, and then granulated into a homogenous feedstock in the form of pellets. The resulting feedstock is typically 60% metal and 40% polymer by volume.
MIM Feedstock Preparation
Injection molding - The powder feedstock is molded using the same equipment and tooling that are used in plastic injection molding. However, the mold cavities are designed approximately 20% larger to account for the part shrinkage during sintering. In the injection molding cycle, the feedstock is melted and injected into the mold cavity, where it cools and solidifies into the shape of the part. The molded "green" part is ejected and then cleaned to remove all flash.
MIM Injection Molding
Debinding - This step removes the polymer binder from the metal. In some cases, solvent debinding is first performed in which the "green" part is placed in a water or chemical bath to dissolve most of the binder. After (on in place of) this step, thermal debinding or pre-sintering is performed. The "green" part is heated in a low temperature oven, allowing the polymer binder to be removed via evaporation. As a result, the remaining "brown" metal part will contain approximately 40% empty space by volume.
MIM Debinding
Sintering - The final step is to sinter the "brown" part in a high temperature furnace (up to 2500°F) in order to reduce the empty space to approximately 1-5%, resulting in a high-density (95-99%) metal part. The furnace uses an atmosphere of inert gases and attains temperatures close to 85% of the metal's melting point. This process removes pores from the material, causing the part to shrink to 75-85% of its molded size. However, this shrinkage occurs uniformly and can be accurately predicted. The resulting part retains the original molded shape with high tolerances, but is now of much greater density.
MIM Sintering
After the sintering process, no secondary operations are required to improve tolerance or surface finish. However, just like a cast metal part, a number of secondary processes can be performed to add features, improve material properties, or assemble other components. For example, a MIM part can be machined, heat treated, or welded.
Metal Injection Molding (MIM)
Design rules
When designing parts to be manufactured using MIM, most of the design rules for plastic injection molding still apply. However, there are some exceptions or additions, such as the following:
Wall thickness - Just as with plastic injection molding, wall thickness should be minimized and kept uniform throughout the part. It is worth noting that in the MIM process, minimizing wall thickness not only reduces material volume and cycle time, but also reduces the debinding and sintering times as well.
Draft - Unlike plastic injection molding, many MIM parts do not require any draft. The polymer binder used in the powder material releases more easily from the mold than most injection molded polymers. Also, MIM parts are ejected before they fully cool and shrink around the mold features because the metal powder in the mixture takes longer to cool.
Sintering support - During sintering, MIM parts must be properly supported or they may distort as they shrink. By designing parts with flat surfaces on the same plane, standard flat support trays can be used. Otherwise, more expensive custom supports may be required.
Surface finish: 25 - 35 �in 16 - 80 �in Tolerance: ± 0.005 in. ± 0.0015 in. Wall thickness: 0.04 - 0.25 in. 0.01 - 1.2 in. Production quantity: 10000 - 1000000 1000 - 1000000 Lead time: Weeks Weeks
Advantages:
Can form complex shapes and fine details Good surface finish Good mechanical properties High production rate
Disadvantages:
Limited part size Limited to thin walled parts High tooling and equipment cost Long lead time possible
Applications: Metal components in electronics, surgical instruments, consumer products
Thermoforming
Thermoforming describes the process of heating a thermoplastic sheet to its softening point, stretching it over or into a single-sided mold, and holding it in place while it cools and solidifies into the desired shape. The thermoplastic sheet is clamped into a holding device and heated by an oven using either convection or radiant heat until it is softened. The sheet is then held horizontally over a mold and pressed into or stretched over the mold using vacuum pressure, air pressure, or mechanical force. The softened sheet conforms to the shape of the mold and is held in place until it cools. The excess material is then trimmed away and the formed part is released. Excess material can be reground, mixed with unused plastic, and reformed into thermoplastic sheets. Thermoforming is commonly used for food packaging, but has many applications from plastic toys to aircraft windscreens to cafeteria trays. Thin-gauge (less than 0.060 inches) sheets are mostly used for rigid or disposable packaging, while thick-gauge (greater than 0.120 inches) sheets are typically used for cosmetic permanent surfaces on automobiles, shower enclosures, and electronic equipment. A variety of thermoplastic materials can be used in this process, including the following:
Acrylic (PMMA)
Acrylonitrile Butadiene Styrene (ABS)
Cellulose Acetate
Low Density Polyethylene (LDPE)
High Density Polyethylene (HDPE)
Polypropylene (PP)
Polystyrene (PS)
Polyvinyl Chloride (PVC)
As mentioned above, there are different methods of forcing the thermoplastic sheet to conform to the mold. These types of thermoforming include the following:
Vacuum forming - A vacuum is formed between the mold cavity and the thermoplastic sheet. The vacuum pressure (typically 14 psi) forces the sheet to conform to the mold and form the part shape.
Vacuum Forming
Pressure forming - In addition to utilizing a vacuum underneath the sheet, air pressure (typically 50 psi, but up to 100 psi) is applied on the back side of the sheet to help force it onto the mold. This additional force allows the forming of thicker sheets and creating finer details, textures, undercuts, and sharp corners.
Pressure Forming
Mechanical forming - The thermoplastic sheet is mechanically forced into or around the mold by direct contact. Typically, a core plug will push the sheet into the mold cavity and force it into the desired shape.
Part size: Area: 0.04 in² - 300 ft² Materials: Thermoplastics Surface finish: 60 - 120 �in 16 - 120 �in Tolerance: ± 0.04 in. ± 0.008 in. Wall thickness: 0.015 - 0.15 in. 0.002 - 0.25 in. Production quantity: 10 - 1000 1 - 100000 Lead time: Days Days
Advantages: Can produce very large parts High production rate Low cost
Disadvantages:
Limited shape complexity Limited to thin walled parts Scrap cannot be recycled Trimming is required
Applications: Packaging, open containers, panels, cups, signs
Die casting is a manufacturing process that can produce geometrically complex metal parts through the use of reusable molds, called dies. The die casting process involves the use of a furnace, metal, die casting machine, and die. The metal, typically a non-ferrous alloy such as aluminum or zinc, is melted in the furnace and then injected into the dies in the die casting machine. There are two main types of die casting machines - hot chamber machines (used for alloys with low melting temperatures, such as zinc) and cold chamber machines (used for alloys with high melting temperatures, such as aluminum). The differences between these machines will be detailed in the sections on equipment and tooling. However, in both machines, after the molten metal is injected into the dies, it rapidly cools and solidifies into the final part, called the casting. The steps in this process are described in greater detail in the next section.
Die casting hot chamber machine overview
Die casting cold chamber machine overview
The castings that are created in this process can vary greatly in size and weight, ranging from a couple ounces to 100 pounds. One common application of die cast parts are housings - thin-walled enclosures, often requiring many ribs and bosses on the interior. Metal housings for a variety of appliances and equipment are often die cast. Several automobile components are also manufactured using die casting, including pistons, cylinder heads, and engine blocks. Other common die cast parts include propellers, gears, bushings, pumps, and valves.
The process cycle for die casting consists of five main stages, which are explained below. The total cycle time is very short, typically between 2 seconds and 1 minute.
Clamping
- The first step is the preparation and clamping of the two halves of the die. Each die half is first cleaned from the previous injection and then lubricated to facilitate the ejection of the next part. The lubrication time increases with part size, as well as the number of cavities and side-cores. Also, lubrication may not be required after each cycle, but after 2 or 3 cycles, depending upon the material. After lubrication, the two die halves, which are attached inside the die casting machine, are closed and securely clamped together. Sufficient force must be applied to the die to keep it securely closed while the metal is injected. The time required to close and clamp the die is dependent upon the machine - larger machines (those with greater clamping forces) will require more time. This time can be estimated from the dry cycle time of the machine.
Injection
- The molten metal, which is maintained at a set temperature in the furnace, is next transferred into a chamber where it can be injected into the die. The method of transferring the molten metal is dependent upon the type of die casting machine, whether a hot chamber or cold chamber machine is being used. The difference in this equipment will be detailed in the next section. Once transferred, the molten metal is injected at high pressures into the die. Typical injection pressure ranges from 1,000 to 20,000 psi. This pressure holds the molten metal in the dies during solidification. The amount of metal that is injected into the die is referred to as the shot. The injection time is the time required for the molten metal to fill all of the channels and cavities in the die. This time is very short, typically less than 0.1 seconds, in order to prevent early solidification of any one part of the metal. The proper injection time can be determined by the thermodynamic properties of the material, as well as the wall thickness of the casting. A greater wall thickness will require a longer injection time. In the case where a cold chamber die casting machine is being used, the injection time must also include the time to manually ladle the molten metal into the shot chamber.
Cooling
- The molten metal that is injected into the die will begin to cool and solidify once it enters the die cavity. When the entire cavity is filled and the molten metal solidifies, the final shape of the casting is formed. The die can not be opened until the cooling time has elapsed and the casting is solidified. The cooling time can be estimated from several thermodynamic properties of the metal, the maximum wall thickness of the casting, and the complexity of the die. A greater wall thickness will require a longer cooling time. The geometric complexity of the die also requires a longer cooling time because the additional resistance to the flow of heat.
Ejection
- After the predetermined cooling time has passed, the die halves can be opened and an ejection mechanism can push the casting out of the die cavity. The time to open the die can be estimated from the dry cycle time of the machine and the ejection time is determined by the size of the casting's envelope and should include time for the casting to fall free of the die. The ejection mechanism must apply some force to eject the part because during cooling the part shrinks and adheres to the die. Once the casting is ejected, the die can be clamped shut for the next injection.
Trimming
- During cooling, the material in the channels of the die will solidify attached to the casting. This excess material, along with any flash that has occurred, must be trimmed from the casting either manually via cutting or sawing, or using a trimming press. The time required to trim the excess material can be estimated from the size of the casting's envelope. The scrap material that results from this
trimming is either discarded or can be reused in the die casting process. Recycled material may need to be reconditioned to the proper chemical composition before it can be combined with non-recycled metal and reused in the die casting process.
Die cast part
Equipment
The two types of die casting machines are a hot chamber machine and cold chamber machine.
Hot chamber die casting machine
- Hot chamber machines are used for alloys with low melting temperatures, such as zinc, tin, and lead. The temperatures required to melt other alloys would damage the pump, which is in direct contact with the molten metal. The metal is contained in an open holding pot which is placed into a furnace, where it is melted to the necessary temperature. The molten metal then flows into a shot chamber through an inlet and a plunger, powered by hydraulic pressure, forces the molten metal through a gooseneck channel and into the die. Typical injection pressures for a hot chamber die casting machine are between 1000 and 5000 psi. After the molten metal has been injected into the die cavity, the plunger remains down, holding the pressure while the casting solidifies. After solidification, the hydraulic system retracts the plunger and the part can be ejected by the clamping unit. Prior to the injection of the molten metal, this unit closes and clamps the two halves of the die. When the die is attached to the die casting machine, each half is fixed to a large plate, called a platen. The front half of the die, called the cover die, is mounted to a stationary platen and aligns with the gooseneck channel. The rear half of the die, called the ejector die, is mounted to a movable platen, which slides along the tie bars. The hydraulically powered clamping unit actuates clamping bars that push this platen towards the cover die and exert enough pressure to keep it closed while the molten metal is injected. Following the solidification of the metal inside the die cavity, the clamping unit releases the die halves and simultaneously causes the ejection system to push the casting out of the open cavity. The die can then be closed for the next injection.
Hot chamber die casting machine - Opened
Hot chamber die casting machine - Closed
Cold chamber die casting machine
- Cold chamber machines are used for alloys with high melting temperatures that can not be cast in hot chamber machines because they would damage the pumping system. Such alloys include aluminum, brass, and magnesium. The molten metal is still contained in an open holding pot which is placed into a furnace, where it is melted to the necessary temperature. However, this holding pot is kept separate from the die casting machine and the molten metal is ladled from the pot for each casting, rather than being pumped. The metal is poured from the ladle into the shot chamber through a pouring hole. The injection system in a cold chamber machine functions similarly to that of a hot chamber machine, however it is usually oriented horizontally and does not include a gooseneck channel. A plunger, powered by hydraulic pressure, forces the molten metal through the shot chamber and into the injection sleeve in the die. The typical injection pressures for a cold chamber die casting machine are between 2000 and 20000 psi. After the molten metal has been injected into the die cavity, the plunger remains forward, holding the pressure while the casting solidifies. After solidification, the hydraulic system retracts the plunger and the part can be ejected by the clamping unit. The clamping unit and mounting of the dies is identical to the hot chamber machine. See the above paragraph for details.
Cold chamber die casting machine - Opened
Cold chamber die casting machine - Closed
Machine specifications
Both hot chamber and cold chamber die casting machines are typically characterized by the tonnage of the clamp force they provide. The required clamp force is determined by the projected area of the parts in the die and the pressure with which the molten metal is injected. Therefore, a larger part will require a larger clamping force. Also, certain materials that require high injection pressures may require higher tonnage machines. The size of the part must also comply with other machine specifications, such as maximum shot volume, clamp stroke, minimum mold thickness, and platen size. Die cast parts can vary greatly in size and therefore require these measures to cover a very large range. As a result, die casting machines are designed to each accommodate a small range of this larger spectrum of values. Sample specifications for several different hot chamber and cold chamber die casting machines are given below.
Type Clamp force (ton)
Max. shot volume (oz.)
Clamp stroke (in.)
Min. mold thickness (in.)
Platen size (in.)
Hot chamber 100 74 11.8 5.9 25 x 24 Hot chamber 200 116 15.8 9.8 29 x 29 Hot chamber 400 254 21.7 11.8 38 x 38 Cold chamber 100 35 11.8 5.9 23 x 23
Cold chamber 400 166 21.7 11.8 38 x 38
Cold chamber 800 395 30.0 15.8 55 x 55
Cold chamber 1600 1058 39.4 19.7 74 x 79
Cold chamber 2000 1517 51.2 25.6 83 x 83
Tooling
The dies into which the molten metal is injected are the custom tooling used in this process. The dies are typically composed of two halves - the cover die, which is mounted onto a stationary platen, and the ejector die, which is mounted onto a movable platen. This design allows the die to open and close along its parting line. Once closed, the two die halves form an internal part cavity which is filled with the molten metal to form the casting. This cavity is formed by two inserts, the cavity insert and the core insert, which are inserted into the cover die and ejector die, respectively. The cover die allows the molten metal to flow from the injection system, through an opening, and into the part cavity. The ejector die includes a support plate and the ejector box, which is mounted onto the platen and inside contains the ejection system. When the clamping unit separates the die halves, the clamping bar pushes the ejector plate forward inside the ejector box which pushes the ejector pins into the molded part, ejecting it from the core insert. Multiple-cavity dies are sometimes used, in which the two die halves form several identical part cavities.
Die channels
The flow of molten metal into the part cavity requires several channels that are integrated into the die and differs slightly for a hot chamber machine and a cold chamber machine. In a hot chamber machine, the molten metal enters the die through a piece called a sprue bushing (in the cover die) and flows around the sprue spreader (in the ejector die). The sprue refers to this primary channel of molten metal entering the die. In a cold chamber machine, the molten metal enters through an injection sleeve. After entering the die, in either type of machine, the molten metal flows through a series of runners and enters the part cavities through gates, which direct the flow. Often, the cavities will contain extra space called overflow wells, which provide an additional source of molten metal during solidification. When the casting cools, the molten metal will shrink and additional material is needed. Lastly, small channels are included that run from the cavity to the exterior of the die. These channels act as venting holes to allow air to escape the die cavity. The molten metal that flows through all of these channels will solidify attached to the casting and must be separated from the part after it is ejected. One type of channel that does not fill with material is a cooling channel. These channels allow water or oil to flow through the die, adjacent to the cavity, and remove heat from the die.
Die assembly - Open
Die assembly - Closed
Die assembly - Exploded view
(Hot chamber) (Hot chamber) (Hot chamber)
Die assembly - Opened (Cold chamber)
Die assembly - Closed (Cold chamber)
Die assembly - Exploded view (Cold chamber)
Die Design
In addition to these many types of channels, there are other design issues that must be considered in the design of the dies. Firstly, the die must allow the molten metal to flow easily into all of the cavities. Equally important is the removal of the solidified casting from the die, so a draft angle must be applied to the walls of the part cavity. The design of the die must also accommodate any complex features on the part, such as undercuts, which will require additional die pieces. Most of these devices slide into the part cavity through the side of the die, and are therefore known as slides, or side-actions. The most common type of side-action is a side-core which enables an external undercut to be molded. Another important aspect of designing the dies is selecting the material. Dies can be fabricated out of many different types of metals. High grade tool steel is the most common and is typically used for 100-150,000 cycles. However, steels with low carbon content are more resistant to cracking and can be used for 1,000,000 cycles. Other common materials for dies include chromium, molybdenum, nickel alloys, tungsten, and vanadium. Any side-cores that are used in the dies can also be made out of these materials.
Materials
Die casting typically makes use of non-ferrous alloys. The four most common alloys that are die cast are shown below, along with brief descriptions of their properties. (Follow the links to search the material library).
Materials Properties
Aluminum alloys
Low density
Good corrosion resistance
High thermal and electrical conductivity
High dimensional stability
Relatively easy to cast
Requires use of a cold chamber machine
Copper alloys
High strength and toughness
High corrosion and wear resistance
Materials Properties High dimensional stability
Highest cost
Low die life due to high melting temperature
Requires use of a cold chamber machine
Magnesium alloys
Very low density
High strength-to-weight ratio
Excellent machinability after casting
Use of both hot and cold chamber machines
Zinc alloys
High density
High ductility
Good impact strength
Excellent surface smoothness allowing for painting or plating
Requires such coating due to susceptibility to corrosion
Easiest to cast
Can form very thin walls
Long die life due to low melting point
Use of a hot chamber machine
The selection of a material for die casting is based upon several factors including the density, melting point, strength, corrosion resistance, and cost. The material may also affect the part design. For example, the use of zinc, which is a highly ductile metal, can allow for thinner walls and a better surface finish than many other alloys. The material not only determines the properties of the final casting, but also impacts the machine and tooling. Materials with low melting temperatures, such as zinc alloys, can be die cast in a hot chamber machine. However, materials with a higher melting temperature, such as aluminum and copper alloys, require the use of cold chamber machine. The melting temperature also affects the tooling, as a higher temperature will have a greater adverse effect on the life of the dies.
Possible Defects
Defect Causes
Flash Injection pressure too high
Clamp force too low
Unfilled sections
Insufficient shot volume
Slow injection
Low pouring temperature
Defect Causes
Bubbles Injection temperature too high
Non-uniform cooling rate
Hot tearing Non-uniform cooling rate
Ejector marks Cooling time too short
Ejection force too high
Many of the above defects are caused by a non-uniform cooling rate. A variation in the cooling rate can be caused by non-uniform wall thickness or non-uniform die temperature.
Design Rules
Maximum wall thickness
Decrease the maximum wall thickness of a part to shorten the cycle time (injection time and cooling time specifically) and reduce the part volume
INCORRECT
Part with thick walls
CORRECT
Part redesigned with thin walls
Uniform wall thickness will ensure uniform cooling and reduce defects
INCORRECT
Non-uniform wall thickness (t1 � t2)
CORRECT
Uniform wall thickness (t1 = t2)
Corners
Round corners to reduce stress concentrations and fracture
Inner radius should be at least the thickness of the walls
INCORRECT
Sharp corner
CORRECT
Rounded corner
Draft
Apply a draft angle to all walls parallel to the parting direction to facilitate removing the part from the die.
Aluminum: 1° for walls, 2° for inside cores
Magnesium: 0.75° for walls, 1.5° for inside cores
Zinc: 0.5° for walls, 1° for inside cores
INCORRECT
No draft angle
CORRECT
Draft angle (�)
Undercuts
Minimize the number of external undercuts
External undercuts require side-cores which add to the tooling cost
Some simple external undercuts can be cast by relocating the parting line
Simple external undercut
Die cannot separate
New parting line allows undercut
Redesigning a feature can remove an external undercut
Part with hinge
Hinge requires side-core
Redesigned hinge
New hinge can be cast
Remove all internal undercuts that require lifters - Jamming of these devices often occurs in die casting
Designing an opening in the side of a part can allow a side-core to form an internal undercut
Internal undercut accessible from the side
Redesigning a part can remove an internal undercut
Part with internal undercut
Die cannot separate
Part redesigned with slot
New part can be cast
Minimize number of side-action directions
Additional side-action directions will limit the number of possible cavities in the die
Cost Drivers
Material cost
The material cost is determined by the weight of material that is required and the unit price of that material. The weight of material is clearly a result of the part volume and material density; however, the part's maximum wall thickness can also play a role. The weight of material that is required includes the material that fills the channels of the die. A part with thinner walls will require a larger system of channels to ensure that the entire part fills quickly and evenly, and therefore will increase the amount of required material. However, this additional material is typically less than the amount of material saved from the reduction in part volume, a result of thinner walls. Therefore, despite the larger channels, using thinner walls will typically lower the material cost.
Production cost
The production cost is primarily calculated from the hourly rate and the cycle time. The hourly rate is proportional to the size of the die casting machine being used, so it is important to understand how the part design affects machine selection. Die casting machines are typically referred to by the tonnage of the clamping force they provide. The required clamping force is determined by the projected area of the part and the pressure with which the molten metal is injected. Therefore, a larger part will require a larger clamping force, and hence a more expensive machine. Also, certain materials that require high injection pressures may require higher tonnage machines. The size of the part must also comply with other machine specifications, such as clamp stroke, platen size, and shot capacity. In addition to the size of the machine, the type of machine (hot chamber vs. cold chamber) will also affect the cost. The use of materials with high melting temperatures, such as aluminum, will require cold chamber machines which are typically more expensive. The cycle time can be broken down into the injection time, cooling time, and resetting time. By reducing any of these times, the production cost will be lowered. The injection time can be decreased by reducing the maximum wall thickness of the part. Also, certain materials can be injected faster than others, but the injection times are so short that the cost saving are negligible. Substantial time can be saved by using a hot chamber machine because in cold chamber machines the molten metal must be ladled into the machine. This ladling time is dependent upon the shot weight. The cooling time is also decreased for lower wall thicknesses, as they require less time to cool all the way through. Several thermodynamic properties of the material also affect the cooling time. Lastly, the resetting time depends on the machine size and the part size. A larger part will require larger motions from the machine to open, close, and eject the part, and a larger machine requires more time to perform these operations. Also, the use of any side-cores will slow this process.
Tooling cost
The tooling cost has two main components - the die set and the machining of the cavities. The cost of the die set is primarily controlled by the size of the part's envelope. A larger part requires a larger, more expensive, die set. The cost of machining the cavities is affected by nearly every aspect of the part's geometry. The primary cost driver is the size of the cavity that must be machined, measured by the projected area of the cavity (equal to the projected area of the part and projected holes) and its depth. Any other elements that will require additional machining time will add to the cost, including the feature count, parting surface, side-cores, tolerance, and surface roughness. The quantity of parts and material used will affect the tooling life and therefore impact the cost. Materials with high casting temperatures, such as copper, will cause a short tooling life. Zinc, which can be cast at lower temperatures, allows for a much longer tooling life. This effect becomes more cost prohibitive with higher production quantities. One final consideration is the number of side-action directions, which can indirectly affect the cost. The additional cost for side-cores is determined by how many are used. However, the number of directions can restrict the number of cavities that can be included in the die. For example, the die for a part which requires 3 side-core directions can only contain 2 cavities. There is no direct cost added, but it is possible that the use of more cavities could provide further savings.
Centrifugal Casting
Centrifugal casting, sometimes called rotocasting, is a metal casting process that uses centrifugal force to form cylindrical parts. This differs from most metal casting processes, which use gravity or pressure to fill the mold. In centrifugal casting, a permanent mold made from steel, cast iron, or graphite is typically used. However, the use of expendable sand molds is also possible. The casting process is usually performed on a horizontal centrifugal casting machine (vertical machines are also available) and includes the following steps:
Mold preparation - The walls of a cylindrical mold are first coated with a refractory ceramic coating, which involves a few steps (application, rotation, drying, and baking). Once prepared and secured, the mold is rotated about its axis at high speeds (300-3000 RPM), typically around 1000 RPM.
Pouring - Molten metal is poured directly into the rotating mold, without the use of runners or a gating system. The centrifugal force drives the material towards the mold walls as the mold fills.
Cooling - With all of the molten metal in the mold, the mold remains spinning as the metal cools. Cooling begins quickly at the mold walls and proceeds inwards.
Casting removal - After the casting has cooled and solidified, the rotation is stopped and the casting can be removed.
Finishing - While the centrifugal force drives the dense metal to the mold walls, any less dense impurities or bubbles flow to the inner surface of the casting. As a result, secondary processes such as machining, grinding, or sand-blasting, are required to clean and smooth the inner diameter of the part.
Centrifugal casting is used to produce axi-symmetric parts, such as cylinders or disks, which are typically hollow. Due to the high centrifugal forces, these parts have a very fine grain on the outer surface and possess mechanical properties approximately 30% greater than parts formed with static casting methods. These parts may be cast from ferrous metals such as low alloy steel, stainless steel, and iron, or from non-ferrous alloys such as aluminum, bronze, copper, magnesium, and nickel. Centrifugal casting is performed in wide variety of industries, including aerospace, industrial, marine, and power transmission. Typical parts include bearings, bushings, coils, cylinder liners, nozzles, pipes/tubes, pressure vessels, pulleys, rings, and wheels.
Surface finish: 63 - 500 �in 32 - 500 �in Tolerance: ± 0.01 in. ± 0.002 in. Wall thickness: 0.1 - 5.0 in. 0.1 - 5.0 in. Production quantity: 100 - 10000 1 - 10000 Lead time: Weeks Days
Advantages:
Can form very large parts Good mechanical properties Good surface finish and accuracy Low equipment cost Low labor cost Little scrap generated
Disadvantages: Limited to cylindrical parts Secondary machining is often required for inner diameter Long lead time possible
Applications: Pipes, wheels, pulleys, nozzles
Investment casting is one of the oldest manufacturing processes, dating back thousands of years, in which molten metal is poured into an expendable ceramic mold. The mold is formed by using a wax pattern - a disposable piece in the shape of the desired part. The pattern is surrounded, or "invested", into ceramic slurry that hardens into the mold. Investment casting is often referred to as "lost-wax casting" because the wax pattern is melted out of the mold after it has been formed. Lox-wax processes are one-to-one (one pattern creates one part), which increases production time and costs relative to other casting processes. However, since the mold is destroyed during the process, parts with complex geometries and intricate details can be created. Investment casting can make use of most metals, most commonly using aluminum alloys, bronze alloys, magnesium alloys, cast iron, stainless steel, and tool steel. This process is beneficial for casting metals with high melting temperatures that can not be molded in plaster or metal. Parts that are typically made by investment casting include those with complex geometry such as turbine blades or firearm components. High temperature applications are also common, which includes parts for the automotive, aircraft, and military industries. Investment casting requires the use of a metal die, wax, ceramic slurry, furnace, molten metal, and any machines needed for sandblasting, cutting, or grinding. The process steps include the following:
Pattern creation - The wax patterns are typically injection molded into a metal die and are formed as one piece. Cores may be used to form any internal features on the pattern. Several of these patterns are attached to a central wax gating system (sprue, runners, and risers), to form a tree-like assembly. The gating system forms the channels through which the molten metal will flow to the mold cavity.
Mold creation - This "pattern tree" is dipped into a slurry of fine ceramic particles, coated with more coarse particles, and then dried to form a ceramic shell around the patterns and gating system. This process is repeated until the shell is thick enough to withstand the molten metal it will encounter. The shell is then placed into an oven and the wax is melted out leaving a hollow ceramic shell that acts as a one-piece mold, hence the name "lost wax" casting.
Pouring - The mold is preheated in a furnace to approximately 1000°C (1832°F) and the molten metal is poured from a ladle into the gating system of the mold, filling the mold cavity. Pouring is typically achieved manually under the force of gravity, but other methods such as vacuum or pressure are sometimes used.
Cooling - After the mold has been filled, the molten metal is allowed to cool and solidify into the shape of the final casting. Cooling time depends on the thickness of the part, thickness of the mold, and the material used.
Casting removal - After the molten metal has cooled, the mold can be broken and the casting removed. The ceramic mold is typically broken using water jets, but several other methods exist. Once removed, the parts are separated from the gating system by either sawing or cold breaking (using liquid nitrogen).
Finishing - Often times, finishing operations such as grinding or sandblasting are used to smooth the part at the gates. Heat treatment is also sometimes used to harden the final part.
Surface finish: 50 - 125 �in 16 - 300 �in Tolerance: ± 0.005 in. ± 0.002 in. Wall thickness: 0.06 - 0.80 in. 0.025 - 5.0 in. Production quantity: 10 - 1000 1 - 1000000 Lead time: Weeks Days
Advantages:
Can form complex shapes and fine details Many material options High strength parts Very good surface finish and accuracy Little need for secondary machining
Disadvantages:
Time-consuming process High labor cost High tooling cost Long lead time possible
Permanent mold casting is a metal casting process that shares similarities to both sand casting and die casting. As in sand casting, molten metal is poured into a mold which is clamped shut until the material cools and solidifies into the desired part shape. However, sand casting uses an expendable mold which is destroyed after each cycle. Permanent mold casting, like die casting, uses a metal mold (die) that is typically made from steel or cast iron and can be reused for several thousand cycles. Because the molten metal is poured into the die and not forcibly injected, permanent mold casting is often referred to as gravity die casting. Permanent mold casting is typically used for high-volume production of small, simple metal parts with uniform wall thickness. Non-ferrous metals are typically used in this process, such as aluminum alloys, magnesium alloys, and copper alloys. However, irons and steels can also be cast using graphite molds. Common permanent mold parts include gears and gear housings, pipe fittings, and other automotive and aircraft components such as pistons, impellers, and wheels. The permanent mold casting process consists of the following steps:
Mold preparation - First, the mold is pre-heated to around 300-500°F (150-260°C) to allow better metal flow and reduce defects. Then, a ceramic coating is applied to the mold cavity surfaces to facilitate part removal and increase the mold lifetime.
Mold assembly - The mold consists of at least two parts - the two mold halves and any cores used to form complex features. Such cores are typically made from iron or steel, but expendable sand cores are sometimes used. In this step, the cores are inserted and the mold halves are clamped together.
Pouring - The molten metal is poured at a slow rate from a ladle into the mold through a sprue at the top of the mold. The metal flows through a runner system and enters the mold cavity.
Cooling - The molten metal is allowed to cool and solidify in the mold.
Mold opening - After the metal has solidified, the two mold halves are opened and the casting is removed.
Trimming - During cooling, the metal in the runner system and sprue solidify attached to the casting. This excess material is now cut away.
Permanent Mold Casting
Using these basic steps, other variations on permanent mold casting have been developed to accommodate specific applications. Examples of these variations include the following:
Slush Casting - As in permanent mold casting, the molten metal is poured into the mold and begins to solidify at the cavity surface. When the amount of solidified material is equal to the desired wall thickness, the remaining slush (material that has yet to completely solidify) is poured out of the mold. As a result, slush casting is used to produce hollow parts without the use of cores.
Low Pressure Permanent Mold Casting - Instead of being poured, the molten metal is forced into the mold by low pressure air (< 1 bar). The application of pressure allows the mold to remain filled and reduces shrinkage during cooling. Also, finer details and thinner walls can be molded.
Vacuum Permanent Mold Casting - Similar to low pressure casting, but vacuum pressure is used to fill the mold. As a result, finer details and thin walls can be molded and the mechanical properties of the castings are improved.
Shell mold casting is a metal casting process similar to sand casting, in that molten metal is poured into an expendable mold. However, in shell mold casting, the mold is a thin-walled shell created from applying a sand-resin mixture around a pattern. The pattern, a metal piece in the shape of the desired part, is reused to form multiple shell molds. A reusable pattern allows for higher production rates, while the disposable molds enable complex geometries to be cast. Shell mold casting requires the use of a metal pattern, oven, sand-resin mixture, dump box, and molten metal. Shell mold casting allows the use of both ferrous and non-ferrous metals, most commonly using cast iron, carbon steel, alloy steel, stainless steel, aluminum alloys, and copper alloys. Typical parts are small-to-medium in size and require high accuracy, such as gear housings, cylinder heads, connecting rods, and lever arms. The shell mold casting process consists of the following steps:
Pattern creation - A two-piece metal pattern is created in the shape of the desired part, typically from iron or steel. Other materials are sometimes used, such as aluminum for low volume production or graphite for casting reactive materials.
Mold creation - First, each pattern half is heated to 175-370°C (350-700°F) and coated with a lubricant to facilitate removal. Next, the heated pattern is clamped to a dump box, which contains a mixture of sand and a resin binder. The dump box is inverted, allowing this sand-resin mixture to coat the pattern. The heated pattern partially cures the mixture, which now forms a shell around the pattern. Each pattern half and surrounding shell is cured to completion in an oven and then the shell is ejected from the pattern.
Mold assembly - The two shell halves are joined together and securely clamped to form the complete shell mold. If any cores are required, they are inserted prior to closing the mold. The shell mold is then placed into a flask and supported by a backing material.
Pouring - The mold is securely clamped together while the molten metal is poured from a ladle into the gating system and fills the mold cavity.
Cooling - After the mold has been filled, the molten metal is allowed to cool and solidify into the shape of the final casting.
Casting removal - After the molten metal has cooled, the mold can be broken and the casting removed. Trimming and cleaning processes are required to remove any excess metal from the feed system and any sand from the mold.
Surface finish: 50 - 300 �in 32 - 500 �in Tolerance: ± 0.015 in. ± 0.006 in. Wall thickness: 0.06 - 2.0 in. 0.06 - 2.0 in. Production quantity: 1000 - 1000000 100 - 1000000 Lead time: Weeks Days
Advantages:
Can form complex shapes and fine details Very good surface finish High production rate Low labor cost Low tooling cost Little scrap generated
Disadvantages: High equipment cost
Applications: Cylinder heads, connecting rods
Milling
Milling is the most common form of machining, a material removal process, which can create a variety of features on a part by cutting away the unwanted material. The milling process requires a milling machine, workpiece, fixture, and cutter. The workpiece is a piece of pre-shaped material that is secured to the fixture, which itself is attached to a platform inside the milling machine. The cutter is a cutting tool with sharp teeth that is also secured in the milling machine and rotates at high speeds. By feeding the workpiece into the rotating cutter, material is cut away from this workpiece in the form of small chips to create the desired shape. Milling is typically used to produce parts that are not axially symmetric and have many features, such as holes, slots, pockets, and even three dimensional surface contours. Parts that are fabricated completely through milling often include components that are used in limited quantities, perhaps for prototypes, such as custom designed fasteners or brackets. Another application of milling is the fabrication of tooling for other processes. For example, three-dimensional molds are typically milled. Milling is also commonly used as a secondary process to add or refine features on parts that were manufactured using a different process. Due to the high tolerances and surface finishes that milling can offer, it is ideal for adding precision features to a part whose basic shape has already been formed.
The time required to produce a given quantity of parts includes the initial setup time and the cycle time for each part. The setup time is composed of the time to setup the milling machine, plan the tool movements (whether performed manually or by machine), and install the fixture device into the milling machine. The cycle time can be divided into the following four times:
Load/Unload time - The time required to load the workpiece into the milling machine and secure it to the fixture, as well as the time to unload the finished part. The load time can depend on the size, weight, and complexity of the workpiece, as well as the type of fixture.
Cut time - The time required for the cutter to make all the necessary cuts in the workpiece for each operation. The cut time for any given operation is calculated by dividing the total cut length for that operation by the feed rate, which is the speed of the cutter relative to the workpiece.
Idle time - Also referred to as non-productive time, this is the time required for any tasks that occur during the process cycle that do not engage the workpiece and therefore remove material. This idle time includes the tool approaching and retracting from the workpiece, tool movements between features, adjusting machine settings, and changing tools.
Tool replacement time - The time required to replace a tool that has exceeded its lifetime and therefore become to worn to cut effectively. This time is typically not performed in every cycle, but rather only after the lifetime of the tool has been reached. In determining the cycle time, the tool replacement time is adjusted for the production of a single part by multiplying by the frequency of a tool replacement, which is the cut time divided by the tool lifetime.
Following the milling process cycle, there is no post processing that is required. However, secondary processes may be used to improve the surface finish of the part if it is required. The scrap material, in the form of small material chips cut from the workpiece, is propelled away from the workpiece by the motion of the cutter and the spraying of lubricant. Therefore, no process cycle step is required to remove the scrap material, which can be collected and discarded after the production. Cutting parameters In milling, the speed and motion of the cutting tool is specified through several parameters. These parameters are selected for each operation based upon the workpiece material, tool material, tool size, and more.
Cutting feed - The distance that the cutting tool or workpiece advances during one revolution of the spindle and tool, measured in inches per revolution (IPR). In some operations the tool feeds into the workpiece and in others the workpiece feeds into the tool. For a multi-point tool, the cutting feed is also equal to the feed per tooth, measured in inches per tooth (IPT), multiplied by the number of teeth on the cutting tool.
Cutting speed - The speed of the workpiece surface relative to the edge of the cutting tool during a cut, measured in surface feet per minute (SFM).
Spindle speed - The rotational speed of the spindle and tool in revolutions per minute (RPM). The spindle speed is equal to the cutting speed divided by the circumference of the tool.
Feed rate - The speed of the cutting tool's movement relative to the workpiece as the tool makes a cut. The feed rate is measured in inches per minute (IPM) and is the product of the cutting feed (IPR) and the spindle speed (RPM).
Axial depth of cut - The depth of the tool along its axis in the workpiece as it makes a cut. A large axial depth of cut will require a low feed rate, or else it will result in a high load on the tool and reduce the tool life. Therefore, a feature is typically machined in several passes as the tool moves to the specified axial depth of cut for each pass.
Radial depth of cut - The depth of the tool along its radius in the workpiece as it makes a cut. If the radial depth of cut is less than the tool radius, the tool is only partially engaged and is making a peripheral cut. If the radial depth of cut is equal to the tool diameter, the cutting tool is fully engaged and is making a slot cut. A large radial depth of cut will require a low feed rate, or else it will result in a high load on the tool and reduce the tool life. Therefore, a feature is often machined in several steps as the tool moves over the step-over distance, and makes another cut at the radial depth of cut.
Peripheral cut
Slot cut
Operations
During the process cycle, a variety of operations may be performed to the workpiece to yield the desired part shape. The following operations are each defined by the type of cutter used and the path of that cutter to remove material from the workpiece.
End milling - An end mill makes either peripheral or slot cuts, determined by the step-over distance, across the workpiece in order to machine a specified feature, such as a profile, slot, pocket, or even a complex surface contour. The depth of the feature may be machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes.
Chamfer milling - A chamfer end mill makes a peripheral cut along an edge of the workpiece or a feature to create an angled surface, known as a chamfer. This chamfer, typically with a 45 degree angle, can be machined on either the exterior or interior of a part and can follow either a straight or curved path.
Face milling - A face mill machines a flat surface of the workpiece in order to provide a smooth finish. The depth of the face, typically very small, may be machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes.
Drilling - A drill enters the workpiece axially and cuts a hole with a diameter equal to that of the tool. A drilling operation can produce a blind hole, which extends to some depth inside the workpiece, or a through hole, which extends completely through the workpiece.
Boring - A boring tool enters the workpiece axially and cuts along an internal surface to form different features. The boring tool is a single-point cutting tool, which can be set to cut the desired diameter by using an adjustable boring head. Boring is commonly performed after drilling a hole in order to enlarge the diameter or obtain more precise dimensions.
Counterboring - An counterbore tool enters the workpiece axially and enlarges the top portion of an existing hole to the diameter of the tool. Counterboring is often performed after drilling to provide space for the head of a fastener, such as a bolt, to sit below the surface of a part. The counterboring tool has a pilot on the end to guide it straight into the existing hole.
Reaming - A reamer enters the workpiece axially and enlarges an existing hole to the diameter of the tool. Reaming removes a minimal amount of material and is often performed after drilling to obtain both a more accurate diameter and a smoother internal finish.
Tapping - A tap enters the workpiece axially and cuts internal threads into an existing hole. The existing hole is typically drilled by the required tap drill size that will accommodate the desired tap. Threads may be cut to a specified depth inside the hole (bottom tap) or the complete depth of a through hole (through tap).
Equipment
Milling machines can be found in a variety of sizes and designs, yet they still possess the same main components that enable the workpiece to be moved in three directions relative to the tool. These components include the following:
Base and column - The base of a milling machine is simply the platform that sits on the ground and supports the machine. A large column is attached to the base and connects to the other components.
Table - The workpiece that will be milled is mounted onto a platform called the table, which typically has "T" shaped slots along its surface. The workpiece may be secured in a fixture called a vise, which is secured into the T-slots, or the workpiece can be clamped directly into these slots. The table provides the horizontal motion of the workpiece in the X-direction by sliding along a platform beneath it, called the saddle.
Saddle - The saddle is the platform that supports the table and allows its longitudinal motion. The saddle is also able to move and provides the horizontal motion of the workpiece in the Y-direction by sliding transversely along another platform called the knee.
Knee - The knee is the platform that supports the saddle and the table. In most milling machines, sometimes called column and knee milling machines, the knee provides the vertical motion (Z direction) of the workpiece. The knee can move vertically along the column, thus moving the workpiece vertically while the cutter remains stationary above it. However, in a fixed bed machine, the knee is fixed while the cutter moves vertically in order to cut the workpiece.
Manual vertical milling machine
The above components of the milling machine can be oriented either vertically or horizontally, creating two very distinct forms of milling machine. A horizontal milling machine uses a cutter that is mounted on a horizontal shaft, called an arbor, above the workpiece. For this reason, horizontal milling is sometimes referred to as arbor milling. The arbor is supported on one side by an overarm, which is connected to the column, and on the other side by the spindle. The spindle is driven by a motor and therefore rotates the arbor. During milling, the cutter rotates along a horizontal axis and the side of the cutter removes material from the workpiece. A vertical milling machine, on the other hand, orients the cutter vertically. The cutter is secured inside a piece called a collet, which is
then attached to the vertically oriented spindle. The spindle is located inside the milling head, which is attached to the column. The milling operations performed on a vertical milling machine remove material by using both the bottom and sides of the cutter. Milling machines can also be classified by the type of control that is used. A manual milling machine requires the operator to control the motion of the cutter during the milling operation. The operator adjusts the position of the cutter by using hand cranks that move the table, saddle, and knee. Milling machines are also able to be computer controlled, in which case they are referred to as a computer numerical control (CNC) milling machine. CNC milling machines move the workpiece and cutter based on commands that are preprogrammed and offer very high precision. The programs that are written are often called G-codes or NC-codes. Many CNC milling machines also contain another axis of motion besides the standard X-Y-Z motion. The angle of the spindle and cutter can be changed, allowing for even more complex shapes to be milled.
Tooling
The tooling that is required for milling is a sharp cutter that will be rotated by the spindle. The cutter is a cylindrical tool with sharp teeth spaced around the exterior. The spaces between the teeth are called flutes and allow the material chips to move away from the workpiece. The teeth may be straight along the side of the cutter, but are more commonly arranged in a helix. The helix angle reduces the load on the teeth by distributing the forces. Also, the number of teeth on a cutter varies. A larger number of teeth will provide a better surface finish. The cutters that can be used for milling operations are highly diverse, thus allowing for the formation of a variety of features. While these cutters differ greatly in diameter, length, and by the shape of the cut they will form, they also differ based upon their orientation, whether they will be used horizontally or vertically. A cutter that will be used in a horizontal milling machine will have the teeth extend along the entire length of the tool. The interior of the tool will be hollow so that it can be mounted onto the arbor. With this basic form, there are still many different types of cutters that can be used in horizontal milling, including those listed below.
Plane (helical) mill
Form relieved mill
Staggered tooth mill
Double angle mill
Another operation known as a straddle milling is also possible with a horizontal milling machine. This form of milling refers to the use of multiple cutters attached to the arbor and used simultaneously. Straddle milling can be used to form a complex feature with a single cut. For vertical milling machines, the cutters take a very different form. The cutter teeth cover only a portion of the tool, while the remaining length is a smooth surface, called the shank. The shank is the section of the cutter that is secured inside the collet, for attachment to the spindle. Also, many vertical cutters are designed to cut using both the sides and the bottom of the cutter. Listed below are several common vertical cutters.
Flat end mill
Ball end mill
Chamfer mill
Face mill
Twist drill
Reamer
Tap
All cutters that are used in milling can be found in a variety of materials, which will determine the cutter's properties and the workpiece materials for which it is best suited. These properties include the cutter's hardness, toughness, and resistance to wear. The most common cutter materials that are used include the following:
High-speed steel (HSS)
Carbide
Carbon steel
Cobalt high speed steel
The material of the cutter is chosen based upon a number of factors, including the material of the workpiece, cost, and tool life. Tool life is an important characteristic that is considered when selecting a cutter, as it greatly affects the manufacturing costs. A short tool life will not only require additional tools to be purchased, but will also require time to change the tool each time it becomes too worn. The cutters listed above often have the teeth coated with a different material to provide additional wear resistance, thus extending the life of the tool. Tool wear can also be reduced by spraying a lubricant and/or coolant on the cutter and workpiece during milling. This fluid is used to reduce the temperature of the cutter, which can get quite hot during milling, and reduce the friction at the interface between the cutter and the workpiece, thus increasing the tool life. Also, by spraying a fluid during milling, higher feed rates can be used, the surface finish can be improved, and the material chips can be pushed away. Typical cutting fluids include mineral, synthetic, and water soluble oils.
Materials
In milling, the raw form of the material is a piece of stock from which the workpieces are cut. This stock is available in a variety of shapes such as flat sheets, solid bars (rectangular, cylindrical, hexagonal, etc.), hollow tubes (rectangular, cylindrical, etc.), and shaped beams (I-beams, L-beams, T-beams, etc.). Custom extrusions or existing parts such as castings or forgings are also sometimes used.
Flat sheet
Rectangular bar
Rectangular tube
I-beam
Milling can be performed on workpieces in variety of materials, including most metals and plastics. Common materials that are used in milling include the following:
Aluminum
Brass
Magnesium
Nickel
Steel
Thermoset plastics
Titanium
Zinc
When selecting a material, several factors must be considered, including the cost, strength, resistance to wear, and machinability. The machinability of a material is difficult to quantify, but can be said to posses the following characteristics:
Results in a good surface finish
Promotes long tool life
Requires low force and power to mill
Provides easy collection of chips
Possible Defects
Most defects in milling are inaccuracies in a feature's dimensions or surface roughness. There are several possible causes for these defects, including the following:
Incorrect cutting parameters - If the cutting parameters such as the feed rate, spindle speed, or axial depth of cut are too high, the surface of the workpiece will be rougher than desired and may contain scratch marks or even burn marks. Also, a large depth of cut may result in vibration of the cutter and cause inaccuracies in the cut.
Dull cutter - As a cutter is used, the teeth will wear down and become dull. A dull cutter is less capable of making precision cuts.
Unsecured workpiece - If the workpiece is not securely clamped in the fixture, the friction of milling may cause it to shift and alter the desired cuts.
Design Rules
Workpiece
Select a material that minimizes overall cost. An inexpensive workpiece may result in longer cut times and more tool wear, increasing the total cost
Minimize the amount of milling that is required by pre-cutting the workpiece close to the desired size and shape
Select the size of the workpiece such that a large enough surface exists for the workpiece to be securely clamped. Also, the clamped surface should allow clearance between the tool and the fixture for any cuts
Features
Minimize the number of setups that are required by designing all features on one side of the workpiece, if possible
Design features, such as holes and threads, to require tools of standard sizes
Minimize the number of tools that are required
Ensure that the depth of any feature is less than the tool length and therefore will avoid the collet contacting the workpiece
Lower requirements for tolerance and surface roughness, if possible, in order to reduce costs
Design internal vertical edges to have a corner radius equal to that of a standard tool. If another component with an external sharp edge must fit, then drill a hole to provide a relief area
Avoid very long and thin features
Use chamfers rather than a corner radius for outside horizontal edges
Avoid undercuts
Cost Drivers
Material cost
The material cost is determined by the quantity of material stock that is required and the unit price of that stock. The amount of stock is determined by the workpiece size, stock size, method of cutting the stock, and the production quantity. The unit price of the material stock is affected by the material and the workpiece shape. Also, any cost attributed to cutting the workpieces from the stock also contributes to the total material cost.
Production cost
The production cost is a result of the total production time and the hourly rate. The production time includes the setup time, load time, cut time, idle time, and tool replacement time. Decreasing any of these time components will reduce cost. The setup time and load time are dependent upon the skill of the operator. The cut time, however, is dependent upon many factors that affect the cut length and feed rate. The cut length can be shortened by optimizing the number of operations that are required and reducing the feature size if possible. The feed rate is affected by the operation type, workpiece material, tool material, tool size, and various cutting parameters such as the axial depth of cut. Lastly, the tool replacement time is a direct result of the number of tool replacements which is discussed regarding the tooling cost.
Tooling cost
The tooling cost for machining is determined by the total number of cutting tools required and the unit price for each tool. The quantity of tools depends upon the number of unique tools required by the various operations to be performed and the amount of wear that each of those tools experience. If the tool wear exceeds the lifetime of a tool, then a replacement tool must be purchased. The lifetime of a tool is dependant upon the tool material, cutting parameters such as cutting speed, and the total cut time. The unit price of a tool is affected by the tool type, size, and material.
Turning
Turning is a form of machining, a material removal process, which is used to create rotational parts by cutting away unwanted material. The turning process requires a turning machine or lathe, workpiece, fixture, and cutting tool. The workpiece is a piece of pre-shaped material that is secured to the fixture, which itself is attached to the turning machine, and allowed to rotate at high speeds. The cutter is typically a single-point cutting tool that is also secured in the machine, although some operations make use of multi-point tools. The cutting tool feeds into the rotating workpiece and cuts away material in the form of small chips to create the desired shape.
Turning is used to produce rotational, typically axi-symmetric, parts that have many features, such as holes, grooves, threads, tapers, various diameter steps, and even contoured surfaces. Parts that are fabricated completely through turning often include components that are used in limited quantities, perhaps for prototypes, such as custom designed shafts and fasteners. Turning is also commonly used as a secondary process to add or refine features on parts that were manufactured using a different process. Due to the high tolerances and surface finishes that turning can offer, it is ideal for adding precision rotational features to a part whose basic shape has already been formed.
The time required to produce a given quantity of parts includes the initial setup time and the cycle time for each part. The setup time is composed of the time to setup the turning machine, plan the tool movements (whether performed manually or by machine), and install the fixture device into the turning machine. The cycle time can be divided into the following four times:
Load/Unload time
- The time required to load the workpiece into the turning machine and secure it to the fixture, as well as the time to unload the finished part. The load time can depend on the size, weight, and complexity of the workpiece, as well as the type of fixture.
Cut time
- The time required for the cutting tool to make all the necessary cuts in the workpiece for each operation. The cut time for any given operation is calculated by dividing the total cut length for that operation by the feed rate, which is the speed of the tool relative to the workpiece.
Idle time
- Also referred to as non-productive time, this is the time required for any tasks that occur during the process cycle that do not engage the workpiece and therefore remove material. This idle time includes the tool approaching and retracting from the workpiece, tool movements between features, adjusting machine settings, and changing tools.
Tool replacement time
- The time required to replace a tool that has exceeded its lifetime and therefore become to worn to cut effectively. This time is typically not performed in every cycle, but rather only after the lifetime of the tool has been reached. In determining the cycle time, the tool replacement time is adjusted for the production of a single part by multiplying by the frequency of a tool replacement, which is the cut time divided by the tool lifetime.
Following the turning process cycle, there is no post processing that is required. However, secondary processes may be used to improve the surface finish of the part if it is required. The scrap material, in the form of small material chips cut from the workpiece, is propelled away from the workpiece by the motion of the cutting tool and the spraying of lubricant. Therefore, no process cycle step is required to remove the scrap material, which can be collected and discarded after the production. Cutting parameters In turning, the speed and motion of the cutting tool is specified through several parameters. These parameters are selected for each operation based upon the workpiece material, tool material, tool size, and more.
Cutting feed - The distance that the cutting tool or workpiece advances during one revolution of the spindle, measured in inches per revolution (IPR). In some operations the tool feeds into the workpiece and in others the workpiece feeds into the tool. For a multi-point tool, the cutting feed is also equal to the feed per tooth, measured in inches per tooth (IPT), multiplied by the number of teeth on the cutting tool.
Cutting speed - The speed of the workpiece surface relative to the edge of the cutting tool during a cut, measured in surface feet per minute (SFM).
Spindle speed - The rotational speed of the spindle and the workpiece in revolutions per minute (RPM). The spindle speed is equal to the cutting speed divided by the circumference of the workpiece where the cut is being made. In order to maintain a constant cutting speed, the spindle speed must vary based on the diameter of the cut. If the spindle speed is held constant, then the cutting speed will vary.
Feed rate - The speed of the cutting tool's movement relative to the workpiece as the tool makes a cut. The feed rate is measured in inches per minute (IPM) and is the product of the cutting feed (IPR) and the spindle speed (RPM).
Axial depth of cut - The depth of the tool along the axis of the workpiece as it makes a cut, as in a facing operation. A large axial depth of cut will require a low feed rate, or else it will result in a high load on the tool and reduce the tool life. Therefore, a feature is typically machined in several passes as the tool moves to the specified axial depth of cut for each pass.
Radial depth of cut - The depth of the tool along the radius of the workpiece as it makes a cut, as in a turning or boring operation. A large radial depth of cut will require a low feed rate, or else it will result in a high load on the tool and reduce the tool life. Therefore, a feature is often machined in several steps as the tool moves over at the radial depth of cut.
Operations
During the process cycle, a variety of operations may be performed to the workpiece to yield the desired part shape. These operations may be classified as external or internal. External operations modify the outer diameter of the workpiece, while internal operations modify the inner diameter. The following operations are each defined by the type of cutter used and the path of that cutter to remove material from the workpiece.
External operations
Turning - A single-point turning tool moves axially, along the side of the workpiece, removing material to form different features, including steps, tapers, chamfers, and contours. These features are typically machined at a small radial depth of cut and multiple passes are made until the end diameter is reached.
Facing - A single-point turning tool moves radially, along the end of the workpiece, removing a thin layer of material to provide a smooth flat surface. The depth of the face, typically very small, may be machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes.
Grooving - A single-point turning tool moves radially, into the side of the workpiece, cutting a groove equal in width to the cutting tool. Multiple cuts can be made to form grooves larger than the tool width and special form tools can be used to create grooves of varying geometries.
Cut-off (parting) - Similar to grooving, a single-point cut-off tool moves radially, into the side of the workpiece, and continues until the center or inner diameter of the workpiece is reached, thus parting or cutting off a section of the workpiece.
Thread cutting - A single-point threading tool, typically with a 60 degree pointed nose, moves axially, along the side of the workpiece, cutting threads into the outer surface. The threads can be cut to a specified length and pitch and may require multiple passes to be formed.
Internal operations
Drilling - A drill enters the workpiece axially through the end and cuts a hole with a diameter equal to that of the tool.
Boring - A boring tool enters the workpiece axially and cuts along an internal surface to form different features, such as steps, tapers, chamfers, and contours. The boring tool is a single-point cutting tool, which can be set to cut the desired diameter by using an adjustable boring head. Boring is commonly performed after drilling a hole in order to enlarge the diameter or obtain more precise dimensions.
Reaming - A reamer enters the workpiece axially through the end and enlarges an existing hole to the diameter of the tool. Reaming removes a minimal amount of material and is often performed after drilling to obtain both a more accurate diameter and a smoother internal finish.
Tapping - A tap enters the workpiece axially through the end and cuts internal threads into an existing hole. The existing hole is typically drilled by the required tap drill size that will accommodate the desired tap.
Equipment
Turning machines, typically referred to as lathes, can be found in a variety of sizes and designs. While most lathes are horizontal turning machines, vertical machines are sometimes used, typically for large diameter workpieces. Turning machines can also be classified by the type of control that is offered. A manual lathe requires the operator to control the motion of the cutting tool during the turning operation. Turning machines are also able to be computer controlled, in which case they are referred to as a computer numerical control (CNC) lathe. CNC lathes rotate the workpiece and move the cutting tool based on commands that are preprogrammed and offer very high precision. In this variety of turning machines, the main components that enable the workpiece to be rotated and the cutting tool to be fed into the workpiece remain the same. These components include the following:
Manual lathe
Bed
- The bed of the turning machine is simply a large base that sits on the ground or a table and supports the other components of the machine.
Headstock assembly
- The headstock assembly is the front section of the machine that is attached to the bed. This assembly contains the motor and drive system which powers the spindle. The spindle supports and rotates the workpiece, which is secured in a workpiece holder or fixture, such as a chuck or collet.
Tailstock assembly
- The tailstock assembly is the rear section of the machine that is attached to the bed. The purpose of this assembly is to support the other end of the workpiece and allow it to rotate, as it's driven by the spindle. For some turning operations, the workpiece is not supported by the tailstock so that material can be removed from the end.
Carriage
- The carriage is a platform that slides alongside the workpiece, allowing the cutting tool to cut away material as it moves. The carriage rests on tracks that lay on the bed, called "ways", and is advanced by a lead screw powered by a motor or hand wheel.
Cross slide
- The cross slide is attached to the top of the carriage and allows the tool to move towards or away from the workpiece, changing the depth of cut. As with the carriage, the cross slide is powered by a motor or hand wheel.
Compound
- The compound is attached on top of the cross slide and supports the cutting tool. The cutting tool is secured in a tool post which is fixed to the compound. The compound can rotate to alter the angle of the cutting tool relative to the workpiece.
Turret
- Some machines include a turret, which can hold multiple cutting tools and rotates the required tool into position to cut the workpiece. The turret also moves along the workpiece, feeding the cutting tool into the material. While most cutting tools are stationary in the turret, live tooling can also be used. Live tooling refers to powered tools, such as mills, drills, reamers, and taps, which rotate and cut the workpiece.
Tooling
The tooling that is required for turning is typically a sharp single-point cutting tool that is either a single piece of metal or a long rectangular tool shank with a sharp insert attached to the end. These inserts can vary in size and shape, but are typically a square, triangle, or diamond shaped piece. These cutting tools are inserted into the turret or a tool holder and fed into the rotating workpiece to cut away material. These single point cutting tools are available in a variety of shapes that allow for the formation of different features. Some common types of tools are as follows:
Style A - 0 degree lead-angle turning tools
Style B - 15 degree lead-angle turning tools
Style C - 0 degree square nose tools
Style D - 80 degree included angle pointed-nose tools
Style E - 60 degree included angle pointed-nose tools
Cutoff tools
Form tools
The above tools are often specified as being right or left handed, which indicates in which direction they move along the workpiece while making a cut. As described in the previous section, live tooling can also be used for turning, which includes the use of mills, drills, reamers, and taps. These are cylindrical multi-point cutting tools that have sharp teeth spaced around the exterior. The spaces between the teeth are called flutes and allow the material chips to move away from the workpiece. The teeth may be straight along the side of the cutter, but are
more commonly arranged in a helix. The helix angle reduces the load on the teeth by distributing the forces. Also, the number of teeth on a cutter varies. A larger number of teeth will provide a better surface finish. The cutter teeth cover only a portion of the tool, while the remaining length is a smooth surface, called the shank. The shank is the section of the cutter that is secured inside the tool holder. All cutting tools that are used in turning can be found in a variety of materials, which will determine the tool's properties and the workpiece materials for which it is best suited. These properties include the tool's hardness, toughness, and resistance to wear. The most common tool materials that are used include the following:
High-speed steel (HSS)
Carbide
Carbon steel
Cobalt high speed steel
The material of the tool is chosen based upon a number of factors, including the material of the workpiece, cost, and tool life. Tool life is an important characteristic that is considered when selecting a tool, as it greatly affects the manufacturing costs. A short tool life will not only require additional tools to be purchased, but will also require time to change the tool each time it becomes too worn.
Materials
In turning, the raw form of the material is a piece of stock from which the workpieces are cut. This stock is available in a variety of shapes such as solid cylindrical bars and hollow tubes. Custom extrusions or existing parts such as castings or forgings are also sometimes used.
Round bar
Round tube
Custom extrusions
Turning can be performed on a variety of materials, including most metals and plastics. Common materials that are used in turning include the following:
Aluminum
Brass
Magnesium
Nickel
Steel
Thermoset plastics
Titanium
Zinc
When selecting a material, several factors must be considered, including the cost, strength, resistance to wear, and machinability. The machinability of a material is difficult to quantify, but can be said to posses the following characteristics:
Results in a good surface finish
Promotes long tool life
Requires low force and power to turn
Provides easy collection of chips
Possible Defects
Most defects in turning are inaccuracies in a feature's dimensions or surface roughness. There are several possible causes for these defects, including the following:
Incorrect cutting parameters
- If the cutting parameters such as the feed rate, spindle speed, or depth of cut are too high, the surface of the workpiece will be rougher than desired and may contain scratch marks or even burn marks. Also, a large depth of cut may result in vibration of the tool and cause inaccuracies in the cut.
Dull cutting tool
- As a tool is used, the sharp edge will wear down and become dull. A dull tool is less capable of making precision cuts.
Unsecured workpiece
- If the workpiece is not securely clamped in the fixture, the friction of turning may cause it to shift and alter the desired cuts.
Design Rules
Workpiece
Select a material that minimizes overall cost. An inexpensive workpiece may result in longer cut times and more tool wear, increasing the total cost
Minimize the amount of turning that is required by pre-cutting the workpiece close to the desired size and shape
Select the size of the workpiece such that a large enough surface exists for the workpiece to be securely clamped. Also, the clamped surface should allow clearance between the tool and the fixture for any cuts
Features
Minimize the number of setups that are required by designing all features to be accessible from one setup
Design features, such as holes and threads, to require tools of standard sizes
Minimize the number of tools that are required
Ensure that the depth of any feature is less than the tool length and therefore will avoid the tool holder contacting the workpiece
Lower requirements for tolerance and surface roughness, if possible, in order to reduce costs
Avoid undercuts
Cost Drivers
Material cost
The material cost is determined by the quantity of material stock that is required and the unit price of that stock. The amount of stock is determined by the workpiece size, stock size, method of cutting the stock, and the production quantity. The unit price of the material stock is affected by the material and the workpiece shape. Also, any cost attributed to cutting the workpieces from the stock also contributes to the total material cost.
Production cost
The production cost is a result of the total production time and the hourly rate. The production time includes the setup time, load time, cut time, idle time, and tool replacement time. Decreasing any of these time components will reduce cost. The setup time and load time are dependent upon the skill of the operator. The cut time, however, is dependent upon many factors that affect the cut length and feed rate. The cut length can be shortened by optimizing the number of operations that are required and reducing the feature size if possible. The feed rate is affected by the operation type, workpiece material, tool material, tool size, and various cutting parameters such as the radial depth of cut. Lastly, the tool replacement time is a direct result of the number of tool replacements which is discussed regarding the tooling cost.
Tooling cost
The tooling cost for machining is determined by the total number of cutting tools required and the unit price for each tool. The quantity of tools depends upon the number of unique tools required by the various operations to be performed and the amount of wear that each of those tools experience. If the tool wear exceeds the lifetime of a tool, then a replacement tool must be purchased. The lifetime of a tool is dependant upon the tool material, cutting parameters such as cutting speed, and the total cut time. The unit price of a tool is affected by the tool type, size, and material.
Drilling
Hole-making is a class of machining operations that are specifically used to cut a hole into a workpiece. Machining, a material removal process, creates features on a part by cutting away the unwanted material and requires a machine, workpiece, fixture, and cutting tool. Hole-making can be performed on a variety of machines, including general machining equipment such as CNC milling machines or CNC turning machines. Specialized equipment also exists for hole-making, such as drill presses or tapping machines. The workpiece is a piece of pre-shaped material that is secured to the fixture, which itself is attached to a platform inside the machine. The cutting tool is a cylindrical tool with sharp teeth that is secured inside a piece called a collet, which is then attached to the spindle, which rotates the tool at high speeds. By feeding the rotating tool into the workpiece, material is cut away in the form of small chips to create the desired feature. Hole-making operations are typically performed amongst many other operations in the machining of a part. However, hole-making
may be performed as a secondary machining process for an existing part, such as a casting or forging. This can be done to add features that were too costly to form during the primary process or to improve the tolerance or surface finish of existing holes.
Machined holes
In machining, a hole is a cylindrical feature that is cut from the workpiece by a rotating cutting tool that enters the workpiece axially. The hole will have the same diameter of the cutting tool and match the geometry (which may include a pointed end). Non-cylindrical features, or pockets, can also be machined, but they require end milling operations not hole-making operations. While all machined holes have the same basic form they can still differ in many ways to best suit a given application. A machined hole can be characterized by several different parameters or features which will determine the hole-making operation and tool that is required.
Diameter - Holes can be machined in a wide variety of diameters, determined by the selected tool. The cutting tools used for hole-making are available in standard sizes that can be as small as 0.0019 inches and as large as 3 inches. Several standards exist including fractional sizes, letter sizes, number sizes, and metric sizes. A custom tool can be created to machine a non-standard diameter, but it is more cost effective to use the closest standard sized tool.
Tolerance - In any machining operation, the precision of a cut can be affected by several factors, including the sharpness of the tool, any vibration of the tool, or the build up of chips of material. The specified tolerance of a hole will determine the method of hole-making used, as some methods are suited for tight-tolerance holes.
Depth - A machined hole may extend to a point within the workpiece, known as a blind hole, or it may extend completely through the workpiece, known as a through hole. A blind hole may have a flat bottom, but typically ends in a point due to the pointed end of the tool. When specifying the depth of a hole, one may reference the depth to the point or the depth to the end of the full diameter portion of the hole. The total depth of the hole is limited by the length of the cutting tool.
Recessed top - A common feature of machined holes is to recess the top of the hole into the workpiece. This is typically done to accommodate the head of a fastener and allow it to sit flush with the workpiece surface. Two types of recessed holes are a counterbore, which has a cylindrical recess, and a countersink, which has a cone-shaped recess.
Threads - Threaded holes are machined to accommodate a threaded fastener and are typically specified by their outer diameter and pitch. The pitch is a measure of the spacing between threads and may be expressed in the English standard, as the number of threads per inch (TPI), or in the metric standard, as the distance in millimeters (mm) between threads.
Hole-making operations
Several hole-making operations exist, each using a different type of cutting tool and forming a different type of hole.
Drilling - A drill bit enters the workpiece axially and cuts a blind hole or a through hole with a diameter equal to that of the tool. A drill bit is a multi-point tool and typically has a pointed end. A twist drill is the most commonly used, but other types of drill bits, such as a center drill, spot drill, or tap drill can be used to start a hole that will be completed by another operation
Reaming - A reamer enters the workpiece axially and enlarges an existing hole to the diameter of the tool. A reamer is a multi-point tool that has many flutes, which may be straight or in a helix. Reaming removes a minimal amount of material and is often performed after drilling to obtain both a more accurate diameter and a smoother internal finish.
Tapping - A tap enters the workpiece axially and cuts internal threads into an existing hole. The existing hole is typically drilled by the required tap drill size that will accommodate the desired tap. The tap is selected based on the major diameter and pitch of the threaded hole. Threads may be cut to a specified depth inside the hole (bottom tap) or the complete depth of a through hole (through tap). Boring - A boring tool enters the workpiece axially and cuts along the internal surface of an existing hole to enlarge the diameter or obtain more precise dimensions. The boring tool is a single-point cutting tool, which can be set to cut the desired diameter by using an adjustable boring head.
Counterboring - A counterbore tool enters the workpiece axially and enlarges the top portion of an existing hole to the diameter of the tool. Counterboring is often performed after drilling to provide space for the head of a fastener, such as a bolt, to sit flush with the workpiece surface. The counterboring tool has a pilot on the end to guide it straight into the existing hole. Countersinking - A countersink tool enters the workpiece axially and enlarges the top portion of an existing hole to a cone-shaped opening. Countersinking is often performed after drilling to provide space for the head of a fastener, such as a screw, to sit flush with the workpiece surface. Common included angles for a countersink include 60, 82, 90, 100, 118, and 120 degrees.
rill Size Chart The drill size chart provides a list of standard size drill bits in several measurement systems, including fractional, metric, wire gauge number, and letter. The decimal equivalents of the diameters are shown in both English and Metric units. Fractional sizes are measured in inches, while metric sizes are measured in millimeters. The wire gauge and letter systems refer to tool diameters that increase as the wire gauge decreases from #107 to #1 and then continues from A to Z. The drill size chart contains tools up to 1.5 inches in diameter, but larger tools are also commonly used. Download charts: English Metric
Drill size standard: Fractional Letter Wire Gauge Metric
Drill size Diameter (in) Diameter (mm) #59 0.0410 1.0414 #58 0.0420 1.0668 #57 0.0430 1.0922 1.1 mm 0.0433 1.1000 #56 0.0465 1.1811 3/64 in 0.0469 1.1906 1.2 mm 0.0472 1.2000 1.3 mm 0.0512 1.3000 #55 0.0520 1.3208 #54 0.0550 1.3970 1.4 mm 0.0551 1.4000 1.5 mm 0.0591 1.5000 #53 0.0595 1.5113 1/16 in 0.0625 1.5875 1.6 mm 0.0630 1.6000 #52 0.0635 1.6129 1.7 mm 0.0669 1.7000 #51 0.0670 1.7018 #50 0.0700 1.7780 1.8 mm 0.0709 1.8000 #49 0.0730 1.8542 1.9 mm 0.0748 1.9000 #48 0.0760 1.9304 5/64 in 0.0781 1.9844 #47 0.0785 1.9939 2 mm 0.0787 2.0000 #46 0.0810 2.0574 #45 0.0820 2.0828 2.1 mm 0.0827 2.1000 #44 0.0860 2.1844 2.2 mm 0.0866 2.2000 #43 0.0890 2.2606 2.3 mm 0.0906 2.3000 #42 0.0935 2.3749 3/32 in 0.0938 2.3813 2.4 mm 0.0945 2.4000 #41 0.0960 2.4384 #40 0.0980 2.4892 2.5 mm 0.0984 2.5000 #39 0.0995 2.5273 #38 0.1015 2.5781 2.6 mm 0.1024 2.6000 #37 0.1040 2.6416 2.7 mm 0.1063 2.7000 #36 0.1065 2.7051 7/64 in 0.1094 2.7781 #35 0.1100 2.7940 2.8 mm 0.1102 2.8000
Drill size Diameter (in) Diameter (mm) #34 0.1110 2.8194 #33 0.1130 2.8702 2.9 mm 0.1142 2.9000 #32 0.1160 2.9464 3 mm 0.1181 3.0000 #31 0.1200 3.0480 3.1 mm 0.1221 3.1000 1/8 in 0.1250 3.1750 3.2 mm 0.1260 3.2000 #30 0.1285 3.2639 3.3 mm 0.1299 3.3000 3.4 mm 0.1339 3.4000 #29 0.1360 3.4544 3.5 mm 0.1378 3.5000 #28 0.1405 3.5687 9/64 in 0.1406 3.5719 3.6 mm 0.1417 3.6000 #27 0.1440 3.6576 3.7 mm 0.1457 3.7000 #26 0.1470 3.7338 #25 0.1495 3.7973 3.8 mm 0.1496 3.8000 #24 0.1520 3.8608 3.9 mm 0.1535 3.9000 #23 0.1540 3.9116 5/32 in 0.1563 3.9688 #22 0.1570 3.9878 4 mm 0.1575 4.0000 #21 0.1590 4.0386 #20 0.1610 4.0894 4.1 mm 0.1614 4.1000 4.2 mm 0.1654 4.2000 #19 0.1660 4.2164 4.3 mm 0.1693 4.3000 #18 0.1695 4.3053 11/64 in 0.1719 4.3656 #17 0.1730 4.3942 4.4 mm 0.1732 4.4000 #16 0.1770 4.4958 4.5 mm 0.1772 4.5000 #15 0.1800 4.5720 4.6 mm 0.1811 4.6000 #14 0.1820 4.6228 #13 0.1850 4.6990 4.7 mm 0.1850 4.7000 3/16 in 0.1875 4.7625 4.8 mm 0.1890 4.8000 #12 0.1890 4.8006
Drill size Diameter (in) Diameter (mm) #11 0.1910 4.8514 4.9 mm 0.1929 4.9000 #10 0.1935 4.9149 #9 0.1960 4.9784 5 mm 0.1969 5.0000 #8 0.1990 5.0546 5.1 mm 0.2008 5.1000 #7 0.2010 5.1054 13/64 in 0.2031 5.1594 #6 0.2040 5.1816 5.2 mm 0.2047 5.2000 #5 0.2055 5.2197 5.3 mm 0.2087 5.3000 #4 0.2090 5.3086 5.4 mm 0.2126 5.4000 #3 0.2130 5.4102 5.5 mm 0.2165 5.5000 7/32 in 0.2188 5.5563 5.6 mm 0.2205 5.6000 #2 0.2210 5.6134 5.7 mm 0.2244 5.7000 #1 0.2280 5.7912 5.8 mm 0.2284 5.8000 5.9 mm 0.2323 5.9000 A 0.2340 5.9436 15/64 in 0.2344 5.9531 6 mm 0.2362 6.0000 B 0.2380 6.0452 6.1 mm 0.2402 6.1000 C 0.2420 6.1468 6.2 mm 0.2441 6.2000 D 0.2460 6.2484 6.3 mm 0.2480 6.3000 1/4 in 0.2500 6.3500 E 0.2500 6.3500 6.4 mm 0.2520 6.4000 6.5 mm 0.2559 6.5000 F 0.2570 6.5278 6.6 mm 0.2598 6.6000 G 0.2610 6.6294 6.7 mm 0.2638 6.7000 17/64 in 0.2656 6.7469 H 0.2660 6.7564 6.8 mm 0.2677 6.8000 6.9 mm 0.2717 6.9000 I 0.2720 6.9088 7 mm 0.2756 7.0000 J 0.2770 7.0358
Drill size Diameter (in) Diameter (mm) 7.1 mm 0.2795 7.1000 K 0.2810 7.1374 9/32 in 0.2813 7.1438 7.2 mm 0.2835 7.2000 7.3 mm 0.2874 7.3000 L 0.2900 7.3660 7.4 mm 0.2913 7.4000 M 0.2950 7.4930 7.5 mm 0.2953 7.5000 19/64 in 0.2969 7.5406 7.6 mm 0.2992 7.6000 N 0.3020 7.6708 7.7 mm 0.3032 7.7000 7.8 mm 0.3071 7.8000 7.9 mm 0.3110 7.9000 5/16 in 0.3125 7.9375 8 mm 0.3150 8.0000 O 0.3160 8.0264 8.1 mm 0.3189 8.1000 8.2 mm 0.3228 8.2000 P 0.3230 8.2042 8.3 mm 0.3268 8.3000 21/64 in 0.3281 8.3344 8.4 mm 0.3307 8.4000 Q 0.3320 8.4328 8.5 mm 0.3347 8.5000 8.6 mm 0.3386 8.6000 R 0.3390 8.6106 8.7 mm 0.3425 8.7000 11/32 in 0.3438 8.7313 8.8 mm 0.3465 8.8000 S 0.3480 8.8392 8.9 mm 0.3504 8.9000 9 mm 0.3543 9.0000 T 0.3580 9.0932 9.1 mm 0.3583 9.1000 23/64 in 0.3594 9.1281 9.2 mm 0.3622 9.2000 9.3 mm 0.3661 9.3000 U 0.3680 9.3472 9.4 mm 0.3701 9.4000 9.5 mm 0.3740 9.5000 3/8 in 0.3750 9.5250 V 0.3770 9.5758 9.6 mm 0.3780 9.6000 9.7 mm 0.3819 9.7000 9.8 mm 0.3858 9.8000 W 0.3860 9.8044
Drill size Diameter (in) Diameter (mm) 9.9 mm 0.3898 9.9000 25/64 in 0.3906 9.9219 10 mm 0.3937 10.0000 X 0.3970 10.0838 Y 0.4040 10.2616 13/32 in 0.4063 10.3188 Z 0.4130 10.4902 10.5 mm 0.4134 10.5000 27/64 in 0.4219 10.7156 11 mm 0.4331 11.0000 7/16 in 0.4375 11.1125 11.5 mm 0.4528 11.5000 29/64 in 0.4531 11.5094 15/32 in 0.4688 11.9063 12 mm 0.4724 12.0000 31/64 in 0.4844 12.3031 12.5 mm 0.4921 12.5000 1/2 in 0.5000 12.7000 13 mm 0.5118 13.0000 33/64 in 0.5156 13.0969 17/32 in 0.5313 13.4938 13.5 mm 0.5315 13.5000 35/64 in 0.5469 13.8906 14 mm 0.5512 14.0000 9/16 in 0.5625 14.2875 14.5 mm 0.5709 14.5000 37/64 in 0.5781 14.6844 15 mm 0.5906 15.0000 19/32 in 0.5938 15.0813 39/64 in 0.6094 15.4781 15.5 mm 0.6102 15.5000 5/8 in 0.6250 15.8750 16 mm 0.6299 16.0000 41/64 in 0.6406 16.2719 16.5 mm 0.6496 16.5000 17 mm 0.6693 17.0000 43/64 in 0.6719 17.0656 11/16 in 0.6875 17.4625 17.5 mm 0.6890 17.5000 45/64 in 0.7031 17.8594 18 mm 0.7087 18.0000 23/32 in 0.7188 18.2563 18.5 mm 0.7284 18.5000 47/64 in 0.7344 18.6531 19 mm 0.7480 19.0000 3/4 in 0.7500 19.0500 49/64 in 0.7656 19.4469 19.5 mm 0.7677 19.5000
Drill size Diameter (in) Diameter (mm) 25/32 in 0.7813 19.8438 20 mm 0.7874 20.0000 51/64 in 0.7969 20.2406 20.5 mm 0.8071 20.5000 13/16 in 0.8125 20.6375 21 mm 0.8268 21.0000 53/64 in 0.8281 21.0344 27/32 in 0.8438 21.4313 21.5 mm 0.8465 21.5000 55/64 in 0.8594 21.8281 22 mm 0.8661 22.0000 7/8 in 0.8750 22.2250 22.5 mm 0.8858 22.5000 57/64 in 0.8906 22.6219 23 mm 0.9055 23.0000 29/32 in 0.9063 23.0188 21/23 in 0.9130 23.1913 59/64 in 0.9219 23.4156 23.5 mm 0.9252 23.5000 15/16 in 0.9375 23.8125 24 mm 0.9449 24.0000 61/64 in 0.9531 24.2094 24.5 mm 0.9646 24.5000 31/32 in 0.9688 24.6063 25 mm 0.9843 25.0000 63/64 in 0.9844 25.0031 1 in 1.0000 25.4000 25.5 mm 1.0039 25.5000 1 1/64 in 1.0156 25.7969 26 mm 1.0236 26.0000 1 1/32 in 1.0313 26.1938 26.5 mm 1.0433 26.5000 1 3/64 in 1.0469 26.5906 1 1/16 in 1.0625 26.9875 27 mm 1.0630 27.0000 1 5/64 in 1.0781 27.3844 27.5 mm 1.0827 27.5000 1 3/32 in 1.0938 27.7813 28 mm 1.1024 28.0000 1 7/64 in 1.1094 28.1781 28.5 mm 1.1221 28.5000 1 1/8 in 1.1250 28.5750 1 9/64 in 1.1406 28.9719 29 mm 1.1417 29.0000 1 5/32 in 1.1563 29.3688 29.5 mm 1.1614 29.5000 1 11/64 in 1.1719 29.7656 30 mm 1.1811 30.0000
Drill size Diameter (in) Diameter (mm) 1 3/16 in 1.1875 30.1625 30.5 mm 1.2008 30.5000 1 13/64 in 1.2031 30.5594 1 7/32 in 1.2188 30.9563 31 mm 1.2205 31.0000 1 15/64 in 1.2344 31.3531 31.5 mm 1.2402 31.5000 1 1/4 in 1.2500 31.7500 32 mm 1.2598 32.0000 1 17/64 in 1.2656 32.1469 32.5 mm 1.2795 32.5000 1 9/32 in 1.2813 32.5438 1 19/64 in 1.2969 32.9406 33 mm 1.2992 33.0000 1 5/16 in 1.3125 33.3375 33.5 mm 1.3189 33.5000 1 21/64 in 1.3281 33.7344 34 mm 1.3386 34.0000 1 11/32 in 1.3438 34.1313 34.5 mm 1.3583 34.5000 1 23/64 in 1.3594 34.5281 1 3/8 in 1.3750 34.9250 35 mm 1.3780 35.0000 1 25/64 in 1.3906 35.3219 35.5 mm 1.3976 35.5000 1 13/32 in 1.4063 35.7188 36 mm 1.4173 36.0000 1 27/64 in 1.4219 36.1156 36.5 mm 1.4370 36.5000 1 7/16 in 1.4375 36.5125 1 29/64 in 1.4531 36.9094 37 mm 1.4567 37.0000 1 15/32 in 1.4688 37.3063 37.5 mm 1.4764 37.5000 1 31/64 in 1.4844 37.7031 38 mm 1.4961 38.0000 1 1/2 in 1.5000 38.1000
Tap Size Chart The tap size chart provides a list of standard size taps, specifying the diameter and thread spacing, for fractional, metric, and screw sizes. The decimal equivalents of the diameters are shown in both English and Metric units. Fractional sizes are listed in inches, while metric sizes are listed in millimeters following the letter "M". A screw size number corresponds to a diameter which is larger for a higher screw size. The thread spacing, which may be coarse or fine, is listed after the diameter. In the fractional and screw size systems, the thread count is used, measured in threads per inch. The metric system uses the thread pitch, which is the distance between threads, measured in millimeters. For each thread count, the equivalent thread pitch is provided and for metric taps, the approximate thread count is shown based on the pitch. Lastly, the recommended tap drill size is provided for each standard tap size. This size drill bit should be used for drilling the initial hole that will then be tapped. Download charts: English Metric
Tap size Diameter (in) Diameter (mm) Thread count (TPI) Thread pitch (mm) Tap drill size M4.5x0.5 0.1772 4.5000 ~51 0.500 4 mm M4.5x0.75 0.1772 4.5000 ~34 0.750 3.8 mm #10-32 0.1900 4.8260 32 0.794 #21 #10-24 0.1900 4.8260 24 1.058 #25 M5x0.5 0.1969 5.0000 ~51 0.500 4.5 mm M5x0.8 0.1969 5.0000 ~32 0.800 4.2 mm #12-24 0.2160 5.4864 24 1.058 #17 #12-28 0.2160 5.4864 28 0.907 #15 M5.5x0.5 0.2165 5.5000 ~51 0.500 5 mm M6x0.5 0.2362 6.0000 ~51 0.500 5.5 mm M6x0.75 0.2362 6.0000 ~34 0.750 5.2 mm M6x1 0.2362 6.0000 ~26 1.000 5 mm 1/4-20 0.2500 6.3500 20 1.270 #7 1/4-28 0.2500 6.3500 28 0.907 #3 M7x0.75 0.2756 7.0000 ~34 0.750 6.2 mm M7x1 0.2756 7.0000 ~26 1.000 6 mm 5/16-18 0.3125 7.9375 18 1.411 F 5/16-24 0.3125 7.9375 24 1.058 I M8x0.5 0.3150 8.0000 ~51 0.500 7.5 mm M8x0.75 0.3150 8.0000 ~34 0.750 7.2 mm M8x1 0.3150 8.0000 ~26 1.000 7 mm M8x1.25 0.3150 8.0000 ~21 1.250 6.8 mm M9x0.75 0.3543 9.0000 ~34 0.750 8.2 mm M9x1 0.3543 9.0000 ~26 1.000 8 mm M9x1.25 0.3543 9.0000 ~21 1.250 7.8 mm 3/8-24 0.3750 9.5250 24 1.058 Q 3/8-16 0.3750 9.5250 16 1.588 5/16 in M10x0.75 0.3937 10.0000 ~34 0.750 9.2 mm M10x1.5 0.3937 10.0000 ~17 1.500 8.5 mm M10x1.25 0.3937 10.0000 ~21 1.250 8.8 mm M10x1 0.3937 10.0000 ~26 1.000 9 mm M11x0.75 0.4331 11.0000 ~34 0.750 10.2 mm M11x1 0.4331 11.0000 ~26 1.000 10 mm M11x1.5 0.4331 11.0000 ~17 1.500 9.5 mm 7/16-14 0.4375 11.1125 14 1.814 U 7/16-20 0.4375 11.1125 20 1.270 25/64 in M12x1.5 0.4724 12.0000 ~17 1.500 10.5 mm M12x1.75 0.4724 12.0000 ~15 1.750 10.2 mm M12x0.75 0.4724 12.0000 ~34 0.750 11.25 mm M12x1 0.4724 12.0000 ~26 1.000 11 mm M12x1.25 0.4724 12.0000 ~21 1.250 10.8 mm 1/2-20 0.5000 12.7000 20 1.270 29/64 in 1/2-13 0.5000 12.7000 13 1.954 27/64 in M14x1.5 0.5512 14.0000 ~17 1.500 12.5 mm M14x1.25 0.5512 14.0000 ~21 1.250 12.8 mm M14x1 0.5512 14.0000 ~26 1.000 13 mm M14x2 0.5512 14.0000 ~13 2.000 12 mm 9/16-18 0.5625 14.2875 18 1.411 33/64 in
Tap size Diameter (in) Diameter (mm) Thread count (TPI) Thread pitch (mm) Tap drill size 9/16-12 0.5625 14.2875 12 2.117 31/64 in M15x1 0.5906 15.0000 ~26 1.000 14 mm M15x1.5 0.5906 15.0000 ~17 1.500 13.5 mm 5/8-18 0.6250 15.8750 18 1.411 37/64 in 5/8-11 0.6250 15.8750 11 2.309 17/32 in M16x2 0.6299 16.0000 ~13 2.000 14 mm M16x1.5 0.6299 16.0000 ~17 1.500 14.5 mm M16x1 0.6299 16.0000 ~26 1.000 15 mm M17x1 0.6693 17.0000 ~26 1.000 16 mm M17x1.5 0.6693 17.0000 ~17 1.500 15.5 mm M18x2.5 0.7087 18.0000 ~11 2.500 15.5 mm M18x1 0.7087 18.0000 ~26 1.000 17 mm M18x1.5 0.7087 18.0000 ~17 1.500 16.5 mm M18x2 0.7087 18.0000 ~13 2.000 16 mm 3/4-16 0.7500 19.0500 16 1.588 11/16 in 3/4-10 0.7500 19.0500 10 2.540 21/32 in M20x2 0.7874 20.0000 ~13 2.000 18 mm M20x1.5 0.7874 20.0000 ~17 1.500 18.5 mm M20x1 0.7874 20.0000 ~26 1.000 19 mm M20x2.5 0.7874 20.0000 ~11 2.500 17.5 mm M22x2 0.8661 22.0000 ~13 2.000 20 mm M22x1.5 0.8661 22.0000 ~17 1.500 20.5 mm M22x1 0.8661 22.0000 ~26 1.000 21 mm M22x2.5 0.8661 22.0000 ~11 2.500 19.5 mm 7/8-9 0.8750 22.2250 9 2.822 49/64 in 7/8-14 0.8750 22.2250 14 1.814 13/16 in M24x3 0.9449 24.0000 ~9 3.000 21 mm M24x1 0.9449 24.0000 ~26 1.000 23 mm M24x1.5 0.9449 24.0000 ~17 1.500 22.5 mm M24x2 0.9449 24.0000 ~13 2.000 22 mm M25x2 0.9843 25.0000 ~13 2.000 23 mm M25x1 0.9843 25.0000 ~26 1.000 24 mm M25x1.5 0.9843 25.0000 ~17 1.500 23.5 mm 1-14 1.0000 25.4000 14 1.814 15/16 in 1-8 1.0000 25.4000 8 3.175 7/8 in M26x1.5 1.0236 26.0000 ~17 1.500 24.5 mm M27x1.5 1.0630 27.0000 ~17 1.500 25.5 mm M27x3 1.0630 27.0000 ~9 3.000 24 mm M27x1 1.0630 27.0000 ~26 1.000 26 mm M27x2 1.0630 27.0000 ~13 2.000 25 mm M28x2 1.1024 28.0000 ~13 2.000 26 mm M28x1 1.1024 28.0000 ~26 1.000 27 mm M28x1.5 1.1024 28.0000 ~17 1.500 26.5 mm 1 1/8-12 1.1250 28.5750 12 2.117 1 3/64 in 1 1/8-7 1.1250 28.5750 7 3.629 63/64 in M30x1.5 1.1811 30.0000 ~17 1.500 28.5 mm M30x3.5 1.1811 30.0000 ~8 3.500 26.5 mm M30x2 1.1811 30.0000 ~13 2.000 28 mm
Tap size Diameter (in) Diameter (mm) Thread count (TPI) Thread pitch (mm) Tap drill size 1 1/4-12 1.2500 31.7500 12 2.117 1 11/64 in 1 1/4-7 1.2500 31.7500 7 3.629 1 7/64 in M33x2 1.2992 33.0000 ~13 2.000 31 mm M33x3.5 1.2992 33.0000 ~8 3.500 29.5 mm M36x3 1.4173 36.0000 ~9 3.000 33 mm M36x4 1.4173 36.0000 ~7 4.000 32 mm 1 1/2 -12 1.5000 38.1000 12 2.117 1 27/64 in 1 1/2-6 1.5000 38.1000 6 4.233 1 11/32 in M39x4 1.5354 39.0000 ~7 4.000 35 mm M39x3 1.5354 39.0000 ~9 3.000 36 mm M42x4.5 1.6535 42.0000 ~6 4.500 37.5 mm 1 3/4-12 1.7500 44.4500 12 2.117 1 43/64 in 1 3/4-5 1.7500 44.4500 5 5.080 1 35/64 in M45x4.5 1.7717 45.0000 ~6 4.500 40.5 mm M48x5 1.8898 48.0000 ~6 5.000 43 mm 2-12 2.0000 50.8000 12 2.117 1 59/64 in 2-4 1/2 2.0000 50.8000 4.5 5.644 1 25/32 in M52x5 2.0472 52.0000 ~6 5.000 47 mm M56x5.5 2.2047 56.0000 ~5 5.500 50.5 mm M60x5.5 2.3622 60.0000 ~5 5.500 54.5 mm M64x6 2.5197 64.0000 ~5 6.000 58 mm M68x6 2.6772 68.0000 ~5 6.000 62 mm
Sheet Metal Fabrication
Sheet metal fabrication is a classification of manufacturing processes that shape a piece of sheet metal into the desired part through material removal and/or material deformation. Sheet metal, which acts as the workpiece in these processes, is one of the most common forms of raw material stock. The material thickness that classifies a workpiece as sheet metal is not clearly defined. However, sheet metal is generally considered to be a piece of stock between 0.006 and 0.25 inches thick. A piece of metal much thinner is considered to be "foil" and any thicker is referred to as a "plate". The thickness of a piece of sheet metal is often referred to as its gauge, a number typically ranging from 3 to 38. A higher gauge indicates a thinner piece of sheet metal, with exact dimensions that depend on the material. Sheet metal stock is available in a wide variety of materials, which include the following:
Aluminum
Brass
Bronze
Copper
Magnesium
Nickel
Stainless steel
Steel
Tin
Titanium
Zinc
Sheet metal can be cut, bent, and stretched into a nearly any shape. Material removal processes can create holes and cutouts in any 2D geometric shape. Deformation processes can bend the sheet numerous times to different angles or stretch the sheet to create complex contours. The size of sheet metal parts can range from a small washer or bracket, to midsize enclosures for home appliances, to large airplane wings. These parts are found in a variety of industries, such as aircraft, automotive, construction, consumer products, HVAC, and furniture. Sheet metal fabrication processes can mostly be placed into two categories - forming and cutting. Forming processes are those in which the applied force causes the material to plastically deform, but not to fail. Such processes are able to bend or stretch the sheet into the desired shape. Cutting processes are those in which the applied force causes the material to fail and separate, allowing the material to be cut or removed. Most cutting processes are performed by applying a great enough shearing force to separate the material, and are therefore sometimes referred to as shearing processes. Other cutting processes remove material by using heat or abrasion, instead of shearing forces.
Forming
Bending
Roll forming
Spinning
Deep Drawing
Stretch forming
Cutting with shear
Shearing
Blanking
Punching
Cutting without shear
Laser beam cutting
Plasma cutting
Water jet cutting
Sheet Metal Forming
Sheet metal forming processes are those in which force is applied to a piece of sheet metal to modify its geometry rather than remove any material. The applied force stresses the metal beyond its yield strength, causing the material to plastically deform, but not to fail. By doing so, the sheet can be bent or stretched into a variety of complex shapes. Sheet metal forming processes include the following:
Bending
Roll forming
Spinning
Deep Drawing
Stretch forming
Bending
Bending is a metal forming process in which a force is applied to a piece of sheet metal, causing it to bend at an angle and form the desired shape. A bending operation causes deformation along one axis, but a sequence of several different operations can be performed to create a complex part. Bent parts can be quite small, such as a bracket, or up to 20 feet in length, such as a large enclosure or chassis. A bend can be characterized by several different parameters, shown in the image below.
Bending diagram
Bend line - The straight line on the surface of the sheet, on either side of the bend, that defines the end of the level flange and the start of the bend.
Outside mold line - The straight line where the outside surfaces of the two flanges would meet, were they to continue. This line defines the edge of a mold that would bound the bent sheet metal.
Flange length - The length of either of the two flanges, extending from the edge of the sheet to the bend line.
Mold line distance - The distance from either end of the sheet to the outside mold line.
Setback - The distance from either bend line to the outside mold line. Also equal to the difference between the mold line distance and the flange length.
Bend axis - The straight line that defines the center around which the sheet metal is bent.
Bend length - The length of the bend, measured along the bend axis.
Bend radius - The distance from the bend axis to the inside surface of the material, between the bend lines. Sometimes specified as the inside bend radius. The outside bend radius is equal to the inside bend radius plus the sheet thickness.
Bend angle - The angle of the bend, measured between the bent flange and its original position, or as the included angle between perpendicular lines drawn from the bend lines.
Bevel angle - The complimentary angle to the bend angle.
The act of bending results in both tension and compression in the sheet metal. The outside portion of the sheet will undergo tension and stretch to a greater length, while the inside portion experiences compression and shortens. The neutral axis is the boundary line inside the sheet metal, along which no tension or compression forces are present. As a result, the length of this axis remains constant. The changes in length to the outside and inside surfaces can be related to the original flat length by two parameters, the bend allowance and bend deduction, which are defined below.
Neutral axis
Neutral axis - The location in the sheet that is neither stretched nor compressed, and therefore remains at a constant length.
K-factor - The location of the neutral axis in the material, calculated as the ratio of the distance of the neutral axis (measured from the inside bend surface) to the material thickness. The K-factor is dependent upon several factors (material, bending operation, bend angle, etc.) and is typically greater than 0.25, but cannot exceed 0.50.
Bend allowance - The length of the neutral axis between the bend lines, or in other words, the arc length of the bend. The bend allowance added to the flange lengths is equal to the total flat length.
Bend deduction - Also called the bend compensation, the amount a piece of material has been stretched by bending. The value equals the difference between the mold line lengths and the total flat length.
When bending a piece of sheet metal, the residual stresses in the material will cause the sheet to springback slightly after the bending operation. Due to this elastic recovery, it is necessary to over-bend the sheet a precise amount to achieve the desired bend radius and bend angle. The final bend radius will be greater than initially formed and the final bend angle will be smaller. The ratio of the final bend angle to the initial bend angle is defined as the springback factor, KS. The amount of springback depends upon several factors, including the material, bending operation, and the initial bend angle and bend radius.
Springback
Bending is typically performed on a machine called a press brake, which can be manually or automatically operated. For this reason, the bending process is sometimes referred to as press brake forming. Press brakes are available in a range of sizes (commonly 20-200 tons) in order to best suit the given application. A press brake contains an upper tool called the punch and a lower tool called the die,
between which the sheet metal is located. The sheet is carefully positioned over the die and held in place by the back gauge while the punch lowers and forces the sheet to bend. In an automatic machine, the punch is forced into the sheet under the power of a hydraulic ram. The bend angle achieved is determined by the depth to which the punch forces the sheet into the die. This depth is precisely controlled to achieve the desired bend. Standard tooling is often used for the punch and die, allowing a low initial cost and suitability for low volume production. Custom tooling can be used for specialized bending operations but will add to the cost. The tooling material is chosen based upon the production quantity, sheet metal material, and degree of bending. Naturally, a stronger tool is required to endure larger quantities, harder sheet metal, and severe bending operations. In order of increasing strength, some common tooling materials include hardwood, low carbon steel, tool steel, and carbide steel.
Press Brake (Open)
Press Brake (Closed)
While using a press brake and standard die sets, there are still a variety of techniques that can be used to bend the sheet. The most common method is known as V-bending, in which the punch and die are "V" shaped. The punch pushes the sheet into the "V" shaped groove in the V-die, causing it to bend. If the punch does not force the sheet to the bottom of the die cavity, leaving space or air underneath, it is called "air bending". As a result, the V-groove must have a sharper angle than the angle being formed in the sheet. If the punch forces the sheet to the bottom of the die cavity, it is called "bottoming". This technique allows for more control over the angle because there is less springback. However, a higher tonnage press is required. In both techniques, the width of the "V" shaped groove, or die opening, is typically 6 to 18 times the sheet thickness. This value is referred to as the die ratio and is equal to the die opening divided by the sheet thickness.
V Bending
In addition to V-bending, another common bending method is wipe bending, sometimes called edge bending. Wipe bending requires the sheet to be held against the wipe die by a pressure pad. The punch then presses against the edge of the sheet that extends beyond the die and pad. The sheet will bend against the radius of the edge of the wipe die.
Wipe Bending
Design rules
Bend location - A bend should be located where enough material is present, and preferably with straight edges, for the sheet to be secured without slipping. The width of this flange should be equal to at least 4 times the sheet thickness plus the bend radius.
Bend radius
Use a single bend radius for all bends to eliminate additional tooling or setups
Inside bend radius should equal at least the sheet thickness
Bend direction - Bending hard metals parallel to the rolling direction of the sheet may lead to fracture. Bending perpendicular to the rolling direction is recommended.
Any features, such as holes or slots, located too close to a bend may be distorted. The distance of such features from the bend should be equal to at least 3 times the sheet thickness plus the bending radius.
In the case of manual bending, if the design allows, a slot can be cut along the bend line to reduce the manual force required.
Roll forming
Roll forming, sometimes spelled rollforming, is a metal forming process in which sheet metal is progressively shaped through a series of bending operations. The roll forming process is performed on a roll forming line in which the metal stock is fed through a series of roll stations. Each station has a roller, referred to as a roller die, positioned on both sides of the sheet. The shape and size of the roller die may be unique to that station, or several identical roller dies may be used in different positions. The roller dies may be above and below the sheet, along the sides, at an angle, etc. As the sheet is forced through the roller die in a roll station, it plastically deforms and bends. Each roll station performs one stage in the complete bending of the sheet to form the desired part. The roll dies are lubricated to reduce friction between the die and the sheet, thus reducing the tool wear. Also, lubricant can allow for a higher production rate, which will also depend on the material thickness, number of roll stations, and radius of each bend. The roll forming line can also include other sheet metal fabrication operations before or after the roll forming, such as punching or shearing. The roll forming process can be used to form a sheet into a wide variety of cross-section profiles. An open profile is most common, but a closed tube-like piece can be created as well. Because the final form is achieved through a series of bends, the part does not require a uniform or symmetric cross-section along its length. Roll forming is used to create very long sheet metal parts with typical widths of 1-20 inches and thicknesses of 0.004-0.125 inches. However wider and thicker sheets can be formed, some up to 5 ft wide and 0.25 inches thick. The roll forming process is capable of producing parts with tolerances as tight as ±0.005 inches. Typical roll formed parts include panels, tracks, shelving, etc. These parts are commonly used in industrial and commercial buildings for roofing, lighting, storage units, and HVAC applications.
Spinning
Spinning, sometimes called spin forming, is a metal forming process used to form cylindrical parts by rotating a piece of sheet metal while forces are applied to one side. A sheet metal disc is rotated at high speeds while rollers press the sheet against a tool, called a mandrel, to form the shape of the desired part. Spun metal parts have a rotationally symmetric, hollow shape, such as a cylinder, cone, or hemisphere. Examples include cookware, hubcaps, satellite dishes, rocket nose cones, and musical instruments. Spinning is typically performed on a manual or CNC lathe and requires a blank, mandrel, and roller. The blank is the disc-shaped piece of sheet metal that is pre-cut from stock material and will be formed into the part. The mandrel is a solid form of the internal shape of the part, against which the blank will be pressed. For more complex parts, such as those with reentrant surfaces, multi-piece mandrels can be used. Because the mandrel does not experience much wear in this process, it can be made from wood or plastic. However, high volume production typically utilizes a metal mandrel. The mandrel and blank are clamped together and secured in the center of the lathe to be rotated at high speeds. While the blank and mandrel rotate, force is applied to the sheet by a tool, causing the sheet to bend and form around the mandrel. The tool may make several passes to complete the shaping of the sheet. This tool is usually a roller wheel attached to a lever. Rollers are available in different diameters and thicknesses and are usually made from steel or brass. The rollers are inexpensive and experience little wear allowing for low volume production of parts.
Deep Drawing
Deep drawing is a metal forming process in which sheet metal is stretched into the desired part shape. A tool pushes downward on the sheet metal, forcing it into a die cavity in the shape of the desired part. The tensile forces applied to the sheet cause it to plastically deform into a cup-shaped part. Deep drawn parts are characterized by a depth equal to more than half of the diameter of the part. These parts can have a variety of cross sections with straight, tapered, or even curved walls, but cylindrical or rectangular parts are most common. Deep drawing is most effective with ductile metals, such as aluminum, brass, copper, and mild steel. Examples of parts formed with deep drawing include automotive bodies and fuel tanks, cans, cups, kitchen sinks, and pots and pans. The deep drawing process requires a blank, blank holder, punch, and die. The blank is a piece of sheet metal, typically a disc or rectangle, which is pre-cut from stock material and will be formed into the part. The blank is clamped down by the blank holder over the die, which has a cavity in the external shape of the part. A tool called a punch moves downward into the blank and draws, or stretches, the material into the die cavity. The movement of the punch is usually hydraulically powered to apply enough force to the blank. Both the die and punch experience wear from the forces applied to the sheet metal and are therefore made from tool steel or carbon steel. The process of drawing the part sometimes occurs in a series of operations, called draw reductions. In each step, a punch forces the part into a different die, stretching the part to a greater depth each time. After a part is completely drawn, the punch and blank holder can be raised and the part removed from the die. The portion of the sheet metal that was clamped under the blank holder may form a flange around the part that can be trimmed off.
Deep Drawing
Deep Drawing Sequence
Stretch Forming
Stretch forming is a metal forming process in which sheet metal is stretched and bent simultaneously to form large contoured parts. Stretch forming in performed on a stretch press, in which a piece of sheet metal is securely gripped along its edges. The tooling used in this process is a stretch form block, which is a solid contoured piece against which the sheet metal will be pressed. The form block is slowly driven into the sheet by pneumatic or hydraulic force causing it to deform. The most common stretch presses are vertical with the form block being raised from below the sheet, but other machine configurations involve the form block descending into the sheet or even moving from the side. As this tool presses against the sheet, which is gripped tightly at its edges, the tensile forces increase and the sheet plastically deforms into a new shape. Stretch formed parts are typically large and possess large radius bends. The shapes that can be produced vary from a simple curved surface to complex non-uniform cross sections. Stretch forming is capable of shaping parts with very high accuracy and smooth surfaces. Ductile materials are preferable, the most commonly used being aluminum, steel, and titanium. Typical stretch formed parts are large curved panels such as door panels in cars or wing panels on aircraft. Other stretch formed parts can be found in window frames and enclosures.
Sheet Metal Cutting (Shearing)
Cutting processes are those in which a piece of sheet metal is separated by applying a great enough force to caused the material to fail. The most common cutting processes are performed by applying a shearing force, and are therefore sometimes referred to as shearing processes. When a great enough shearing force is applied, the shear stress in the material will exceed the ultimate shear strength and the material will fail and separate at the cut location. This shearing force is applied by two tools, one above and one below the sheet. Whether these tools are a punch and die or upper and lower blades, the tool above the sheet delivers a quick downward blow to the sheet metal that rests over the lower tool. A small clearance is present between the edges of the upper and lower tools, which facilitates the fracture of the material. The size of this clearance is typically 2-10% of the material thickness and depends upon several factors, such as the specific shearing process, material, and sheet thickness. The effects of shearing on the material change as the cut progresses and are visible on the edge of the sheared material. When the punch or blade impacts the sheet, the clearance between the tools allows the sheet to plastically deform and "rollover" the edge. As the tool penetrates the sheet further, the shearing results in a vertical burnished zone of material. Finally, the shear stress is too great and the material fractures at an angle with a small burr formed at the edge. The height of each of these portions of the cut depends on several factors, including the sharpness of the tools and the clearance between the tools.
Sheared edge
A variety of cutting processes that utilize shearing forces exist to separate or remove material from a piece of sheet stock in different ways. Each process is capable of forming a specific type of cut, some with an open path to separate a portion of material and some with a closed path to cutout and remove that material. By using many of these processes together, sheet metal parts can be fabricated with cutouts and profiles of any 2D geometry. Such cutting processes include the following:
Shearing - Separating material into two parts
Blanking - Removing material to use for parts
Conventional blanking
Fine blanking
Punching - Removing material as scrap
Piercing
Slotting
Perforating
Notching
Nibbling
Lancing
Slitting
Parting
Cutoff
Trimming
Shaving
Dinking
Shearing
As mentioned above, several cutting processes exist that utilize shearing force to cut sheet metal. However, the term "shearing" by itself refers to a specific cutting process that produces straight line cuts to separate a piece of sheet metal. Most commonly, shearing is used to cut a sheet parallel to an existing edge which is held square, but angled cuts can be made as well. For this reason, shearing is primarily used to cut sheet stock into smaller sizes in preparation for other processes. Shearing has the following capabilities:
The shearing process is performed on a shear machine, often called a squaring shear or power shear, that can be operated manually (by hand or foot) or by hydraulic, pneumatic, or electric power. A typical shear machine includes a table with support arms to hold the sheet, stops or guides to secure the sheet, upper and lower straight-edge blades, and a gauging device to precisely position the sheet. The sheet is placed between the upper and lower blade, which are then forced together against the sheet, cutting the material. In most devices, the lower blade remains stationary while the upper blade is forced downward. The upper blade is slightly offset from the lower blade, approximately 5-10% of the sheet thickness. Also, the upper blade is usually angled so that the cut progresses from one end to the other, thus reducing the required force. The blades used in these machines typically have a square edge rather than a knife-edge and are available in different materials, such as low alloy steel and high-carbon steel.
Shearing
Blanking
Blanking is a cutting process in which a piece of sheet metal is removed from a larger piece of stock by applying a great enough shearing force. In this process, the piece removed, called the blank, is not scrap but rather the desired part. Blanking can be used to cutout parts in almost any 2D shape, but is most commonly used to cut workpieces with simple geometries that will be further shaped in subsequent processes. Often times multiple sheets are blanked in a single operation. Final parts that are produced using blanking include gears, jewelry, and watch or clock components. Blanked parts typically require secondary finishing to smooth out burrs along the bottom edge. The blanking process requires a blanking press, sheet metal stock, blanking punch, and blanking die. The sheet metal stock is placed over the die in the blanking press. The die, instead of having a cavity, has a cutout in the shape of the desired part and must be custom made unless a standard shape is being formed. Above the sheet, resides the blanking punch which is a tool in the shape of the desired part. Both the die and punch are typically made from tool steel or carbide. The hydraulic press drives the punch downward at high speed into the sheet. A small clearance, typically 10-20% of the material thickness, exists between the punch and die. When the punch impacts the sheet, the metal in this clearance quickly bends and then fractures. The blank which has been sheared from the stock now falls freely into the gap in the die. This process is extremely fast, with some blanking presses capable of performing over 1000 strokes per minute.
Blanking
Fine blanking Fine blanking is a specialized type of blanking in which the blank is sheared from the sheet stock by applying 3 separate forces. This technique produces a part with better flatness, a smoother edge with minimal burrs, and tolerances as tight as ±0.0003. As a result, high quality parts can be blanked that do not require any secondary operations. However, the additional equipment and tooling does add to the initial cost and makes fine blanking better suited to high volume production. Parts made with fine blanking include automotive parts, electronic components, cutlery, and power tools. Most of the equipment and setup for fine blanking is similar to conventional blanking. The sheet stock is still placed over a blanking die inside a hydraulic press and a blanking punch will impact the sheet to remove the blank. As mentioned above, this is done by the application of 3 forces. The first is a downward holding force applied to the top of the sheet. A clamping system holds a guide plate tightly against the sheet and is held in place with an impingement ring, sometimes called a stinger, that surrounds the perimeter of the blanking location. The second force is applied underneath the sheet, directly opposite the punch, by a "cushion". This cushion provides a counterforce during the blanking process and later ejects the blank. These two forces reduce bending of the sheet and improve the flatness of the blank. The final force is provided by the blanking punch impacting the sheet and shearing the blank into the die opening. In fine blanking, the clearance between the punch and the die is smaller, around 0.001 inches, and the blanking is performed at slower speeds. As a result, instead of the material fracturing to free the blank, the blank flows and is extruded from the sheet, providing a smoother edge.
Fine blanking
Punching
Punching is a cutting process in which material is removed from a piece of sheet metal by applying a great enough shearing force. Punching is very similar to blanking except that the removed material, called the slug, is scrap and leaves behind the desired internal feature in the sheet, such as a hole or slot. Punching can be used to produce holes and cutouts of various shapes and sizes. The most common punched holes are simple geometric shapes (circle, square, rectangle, etc.) or combinations thereof. The edges of these punched features will have some burrs from being sheared but are of fairly good quality. Secondary finishing operations are typically performed to attain smoother edges. The punching process requires a punch press, sheet metal stock, punch, and die. The sheet metal stock is positioned between the punch and die inside the punch press. The die, located underneath the sheet, has a cutout in the shape of the desired feature. Above the sheet, the press holds the punch, which is a tool in the shape of the desired feature. Punches and dies of standard shapes are typically used, but custom tooling can be made for punching complex shapes. This tooling, whether standard or custom, is usually made from tool steel or carbide. The punch press drives the punch downward at high speed through the sheet and into the die below. There is a small clearance between the edge of the punch and the die, causing the material to quickly bend and fracture. The slug that is punched out of the sheet falls freely through the tapered opening in the die. This process can be performed on a manual punch press, but today computer numerical controlled (CNC) punch presses are most common. A CNC punch press can be hydraulically, pneumatically, or electrically powered and deliver around 600 punches per minute. Also, many CNC punch presses utilize a turret that can hold up to 100 different punches which are rotated into position when needed.
Punching
A typical punching operation is one in which a cylindrical punch tool pierces the sheet metal, forming a single hole. However, a variety of operations are possible to form different features. These operations include the following:
Piercing - The typical punching operation, in which a cylindrical punch pierces a hole into the sheet.
Slotting - A punching operation that forms rectangular holes in the sheet. Sometimes described as piercing despite the different shape.
Perforating - Punching a close arrangement of a large number of holes in a single operation.
Notching - Punching the edge of a sheet, forming a notch in the shape of a portion of the punch.
Nibbling - Punching a series of small overlapping slits or holes along a path to cutout a larger contoured shape. This eliminates the need for a custom punch and die but will require secondary operations to improve the accuracy and finish of the feature.
Lancing - Creating a partial cut in the sheet, so that no material is removed. The material is left attached to be bent and form a shape, such as a tab, vent, or louver.
Slitting - Cutting straight lines in the sheet. No scrap material is produced.
Parting - Separating a part from the remaining sheet, by punching away the material between parts.
Cutoff - Separating a part from the remaining sheet, without producing any scrap. The punch will produce a cut line that may be straight, angled, or curved.
Trimming - Punching away excess material from the perimeter of a part, such as trimming the flange from a drawn cup.
Shaving - Shearing away minimal material from the edges of a feature or part, using a small die clearance. Used to improve accuracy or finish. Tolerances of ±0.001 inches are possible.
Dinking - A specialized form of piercing used for punching soft metals. A hollow punch, called a dinking die, with beveled, sharpened edges presses the sheet into a block of wood or soft metal.
Sheet Metal Cutting
Cutting processes are those in which a piece of sheet metal is separated by applying a great enough force to caused the material to fail. The cut being formed may follow an open path to separate a portion of material or a closed path to cutout and remove that material. The geometric possibilities for a cutting process depend on the technology used, but most are capable of cutting out any 2D shape. Some of the most common sheet metal cutting processes use shearing forces to separate the material. A description of those processes can be found in the previous section. In this section, cutting processes that use other forces, such thermal energy or abrasion, will be discussed. Some common methods of sheet metal cutting that use such forces include the following:
Laser beam cutting
Plasma cutting
Water jet cutting
Laser beam cutting
Laser cutting uses a high powered laser to cut through sheet metal. A series of mirrors and lenses direct and focus a high-energy beam of light onto the surface of the sheet where it is to be cut. When the beam strikes the surface, the energy of the beam melts and vaporizes the metal underneath. Any remaining molten metal or vapor is blown away from the cut by a stream of gas. The position of the laser beam relative to the sheet is precisely controlled to allow the laser to follow the desired cutting path. This process is carried out on laser cutting machines that consist of a power supply, laser system, mirrors, focusing lens, nozzle, pressurized gas, and a workpiece table. The laser most commonly used for sheet metal cutting is a CO2 based laser with approximately 1000-2000 watts of power. However, Nd and Nd-YAG lasers are sometimes used for very high power applications. The laser beam is directed by a series of mirrors and through the "cutting head" which contains a lens and nozzle to focus the beam onto the cutting location. The beam diameter at the cutting surface is typically around 0.008 inches. In some machines, the cutting head is able to move in the X-Y plane over the workpiece which is clamped to a stationary table below. In other laser cutting machines, the cutting head remains stationary, while the table moves underneath it. Both systems allow the laser beam to cut out any 2D shape in the workpiece. As mentioned above, pressurized gas is also used in the process to blow away the molten metal and vapor as the cut is formed. This assist gas, typically oxygen or nitrogen, feeds into the cutting head and is blown out the same nozzle as the laser beam. Laser cutting can be preformed on sheet metals that are both ferrous and non-ferrous. Materials with low reflectivity and conductivity allow the laser beam to be most effective - carbon steel, stainless steel, and titanium are most common. Metals that reflect light and conduct heat, such as aluminum and copper alloys, can still be cut but require a higher power laser. Laser cutting can also be used beyond sheet metal applications, to cut plastics, ceramics, stone, wood, etc. As previously mentioned, laser cutting can be used to cut nearly any 2D shape. However, the most common use is cutting an external profile or complex features. Simple internal features, such as holes or slots are usually punched out using other sheet metal processes. But highly complex shapes and outer part boundaries are well suited for laser cutting. The fact that laser cutting does not require any physical contact with the material offers many benefits to the quality of the cuts. First, minimal burrs are formed, creating a smooth edge that may not require any finishing. Secondly, no tool contact means only minimal distortion of the sheet will occur. Also, only a small amount of heat distortion is present in the narrow zone affected by the laser beam. Lastly, no contaminates will be embedded into the material during cutting. Although not a quality issue, it is worth noting that the lack of physical tool wear will reduce costs and make laser cutting cost effective for low volume production.
Capabilities
Sheet thickness: 0.02-0.50 in.
Cutting speed: 30-500 IPM (1000 IPM feasible)
Kerf width: 0.006-0.016 in. (0.004 in. feasible)
Tolerance: ±0.005 in. (±0.001 in. feasible)
Surface finish: 125-250 �in
Design rules
Edges - Burrs are minimal, but can be further reduced by using a thinner sheet stock.
Corners - Rounded corners are preferred to sharp corners. Interior corners must have a minimum radius equal to the laser beam radius.
Holes - Minimum hole diameter should be approximately 20% of sheet thickness, down to 0.010 inches. Laser-cut holes will have a slight natural taper.
Multiple sheets can be cut at once to reduce cost
Plasma cutting
Plasma cutting uses a focused stream of ionized gas, or plasma, to cut through sheet metal. The plasma flows at extremely high temperatures and high velocity and is directed toward the cutting location by a nozzle. When the plasma contacts the surface below, the metal melts into a molten state. The molten metal is then blown away from the cut by the flow of ionized gas from the nozzle. The position of the plasma stream relative to the sheet is precisely controlled to follow the desired cutting path. Plasma cutting is performed with a plasma torch that may be hand held or, more commonly, computer controlled. CNC (computer numerically controlled) plasma cutting machines enable complex and precision cuts to made. In either type of plasma torch, the flow of plasma is created by first blowing an inert gas at high speed though a nozzle pointed at the cutting surface. An electrical arc, formed through the flow of gas, ionizes the gas into plasma. The nozzle then focuses the flow of plasma onto the cut location. As with laser cutting, this process does not require any physical tooling which reduces initial costs and allows for cost effective low volume production. The capabilities of plasma cutting vary slightly from laser cutting. While both processes are able to cut nearly any 2D shape out of sheet metal, plasma cutting cannot achieve the same level of precision and finish. Edges may be rough, especially with thicker sheets, and the surface of the material will have an oxide layer that can be removed with secondary processes. However, plasma cutting is capable of cutting through far thicker sheets than laser cutting and is often used for workpieces beyond sheet metal.
Water jet cutting
Water jet cutting uses a high velocity stream of water to cut through sheet metal. The water typically contains abrasive particles to wear the material and travels in a narrow jet at high speeds, around 2000 ft/sec. As a result, the water jet applies very high pressure (around 60,000 psi) to the material at the cut location and quickly erodes the material. The position of the water jet is typically computer controlled to follow the desired cutting path. Water jet cutting can be used to cut nearly any 2D shape out of sheet metal. The width of the cuts is typically between 0.002 and 0.06 inches and the edges are of good quality. Because no burrs are formed, secondary finishing is usually not required. Also, by not using heat to melt the material, like laser and plasma cutting, heat distortion is not a concern.
Additive Fabrication
Contents
1. Process Cycle
2. Technologies
3. Applications
Additive fabrication refers to a class of manufacturing processes, in which a part is built by adding layers of material upon one another. These processes are inherently different from subtractive processes or consolidation processes. Subtractive processes, such as milling, turning, or drilling, use carefully planned tool movements to cut away material from a workpiece to form the desired part. Consolidation processes, such as casting or molding, use custom designed tooling to solidify material into the desired shape. Additive processes, on the other hand, do not require custom tooling or planned tool movements. Instead, the part is constructed directly from a digital 3-D model created through Computer Aided Design (CAD) software. The 3-D CAD model is converted into many thin layers and the manufacturing equipment uses this geometric data to build each layer sequentially until the part is completed. Due to this approach, additive fabrication is often referred to as layered manufacturing, direct digital manufacturing, or solid freeform fabrication. The most common term for additive fabrication is rapid prototyping. The term "rapid" is used because additive processes are performed much faster than conventional manufacturing processes. The fabrication of a single part may only take a couple hours, or can take a few days depending on the part size and the process. However, processes that require custom tooling, such as a mold, to be designed and built may require several weeks. Subtractive processes, such as machining, can offer more comparable production times, but those times can increase substantially for highly complex parts. The term "prototyping" is used because these additive processes were initially used solely to fabricate prototypes. However, with the improvement of additive technologies, these processes are becoming increasingly capable of high-volume production manufacturing, as will be explored in the section on applications. Additive fabrication offers several advantages, listed below.
Speed - As described above, these "rapid" processes have short build times. Also, because no custom tooling must be developed, the lead time in receiving parts is greatly reduced.
Part complexity - Because no tooling is required, complex surfaces and internal features can be created directly when building the part. Also, the complexity of a part has little effect on build times, as opposed to other manufacturing processes. In molding and casting processes, part complexity may not affect the cycle times, but can require several weeks to be spent on creating the mold. In machining, complex features directly affect the cycle time and may even require more expensive equipment or fixtures.
Material types - Additive fabrication processes are able to produce parts in plastics, metals, ceramics, composites, and even paper with properties similar to wood. Furthermore, some processes can build parts from multiple materials and distribute the material based on the location in the part.
Low-volume production - Other more conventional processes are not very cost effective for low-volume productions because of high initial costs due to custom tooling and lengthy setup times. Additive fabrication requires minimal setup and builds a part directly from the CAD model, allowing for low per-part costs for low-volume productions.
With all of these advantages, additive fabrication will still not replace more conventional manufacturing processes for every application. Processes such as machining, molding, and casting are still preferred in specific instances, such as the following:
Large parts - Additive processes are best suited for relatively small parts because build times are largely dependent upon part size. A larger part in the X-Y plane will require more time to build each layer and a taller part (in the Z direction) will require more layers to be built. This limitation on part size is not shared by some of the more common manufacturing methods. The cycle times in molding and casting processes are typically controlled by the part thickness, and machining times are dependent upon the material and part complexity. Manufacturing large parts with additive processes is also not ideal due to the current high prices of material for these processes.
High accuracy and surface finish - Currently, additive fabrication processes can not match the precision and finishes offered by machining. As a result, parts produced through additive fabrication may require secondary operations depending on their intended use.
High-volume production - While the production capabilities of additive processes are improving with technology, molding and casting are still preferred for high-volume production. At very large quantities, the per-part cost of tooling is insignificant and the cycle times remain shorter than those for additive fabrication.
Material properties - While additive fabrication can utilize various material types, individual material options are somewhat limited. As a result, materials that offer certain desirable properties may not be available. Also, due to the fabrication methods, the properties of the final part may not meet certain design requirements. Lastly, the current prices for materials used in additive processes are far greater than more commonly used materials for other processes.
Process Cycle
Several different additive fabrication processes are commercially available or are currently being developed. Each process may use different materials and different techniques for building the layers of a part. However, each process employs the same basic steps, listed below.
Create CAD model - For all additive processes, the designer must first use Computer-Aided Design (CAD) software to create a 3-D model of the part.
Convert CAD model into STL model - Each form of CAD software saves the geometric data representing the 3-D model in different ways. However, the STL format (initially developed for Stereolithography) has become the standard file format for additive processes. Therefore, CAD files must be converted to this file format. The STL format represents the surfaces of the 3-D model as a set of triangles, storing the coordinates for the vertices and normal directions for each triangle.
Slice STL model into layers - Using specialized software, the user prepares the STL file to be built, first designating the location and orientation of the part in the machine. Part orientation impacts several parameters, including build time, part strength, and accuracy. The software then slices the STL model into very thin layers along the X-Y plane. Each layer will be built upon the previous layer, moving upward in the Z direction.
Build part one layer at a time - The machine builds the part from the STL model by sequentially forming layers of material on top of previously formed layers. The technique used to build each layer differs greatly amongst the additive process, as does the material being used. Additive processes can use paper, polymers, powdered metals, or metal composites, depending upon the process.
Post-processing of part - After being built, the part and any supports are removed from the machine. If the part was fabricated from a photosensitive material, it must be cured to attain full strength. Minor cleaning and surface finishing, such as sanding, coating, or painting, can be performed to improve the part's appearance and durability.
Technologies
The technologies that can be used to build a part one layer at a time are quite varied and in different stages of development. In order to accommodate different materials, as well as improve build times or part strength, numerous technologies have emerged. Some technologies are commercially available methods of fabricating prototypes, others are quickly becoming viable forms of production manufacturing, and newer technologies are continuously being developed. These different methods of additive fabrication can be classified by the type of material that is employed.
Liquid-based processes - These additive technologies typically use photocurable polymer resins and cure selected portions of the resin to form each part layer. The most common liquid-based additive process is Stereolithography (SLA), which was the first commercially available additive process. Parts produced using this technology offer high accuracy and an appearance similar to molded parts. However, photocurable polymers offer somewhat poor mechanical properties which may worsen over time. Other liquid-based processes include Ink Jet Printing, which may use a single jet or multiple jets.
Powder-based processes - In powder-based processes, such as Selective Laser Sintering (SLS), a selected portion of powdered material is melted or sintered to form each part layer. The use of powdered material enables parts to be fabricated using polymers, metals, or ceramics. Also, the mechanical properties of these parts are better and more stable than a photocured polymer part. Other powder-based processes include Direct Metal Laser Sintering (DMLS) and Three Dimensional Printing (3DP).
Solid-based processes - Solid-based processes use a variety of solid, non-powder, materials and each process differs in how it builds the layers of a part. Most solid-based processes use sheet-stacking methods, in which very thin sheets of material are layered on top of one another and the shape of the layer is cut out. The most common sheet-stacking process is Laminated Object Manufacturing (LOM), which uses thin sheets of paper, but other processes make use of polymer or metal sheets. Other solid-based processes use solid strands of polymer, not sheets, such as Fused Deposition Modeling (FDM) which extrudes and deposits the polymer into layers.
Aside from the material type, additive fabrication processes can also be characterized by the number of dimensions of movement that are required to build the part. For example, a process like Stereolithography or Selective Laser Sintering requires movement in the X, Y, and Z directions. In these processes, a laser cures only a small region of a layer at a time. Therefore, the build mechanism (a laser in this case) or the part must move in X and Y direction to allow an entire layer to be formed, and then in the Z direction to allow the next layer to be built. Most additive processes operate in this way, requiring 3 dimensions of movement. However, some processes may only require 2 dimensions of movement. As an example, some ink-jet processes use an array of jets that form a "strip" of a layer at a time. Therefore, movement is only required in the Y direction to form a layer, and then the Z direction to build the next layer. Finally, some emerging technologies are using a two dimensional array of mirrors to form an entire part layer at once, requiring movement in only one direction, the Z direction. Such technologies are appealing because fewer dimensions of movement results in faster build times and lower cost.
Applications
Additive fabrication processes initially yielded parts with few applications due to limited material options and mechanical properties. However, improvements to the processing technologies and material options have expanded the possibilities for these layered parts. Now, additive fabrication is used in a variety of industries, including the aerospace, architectural, automotive, consumer product, medical product, and military industries. The application of parts in these industries is quite vast. For example, some parts are merely aesthetic such as jewelry, sculptures, or 3D architectural models. Others are customized to meet the user's personal needs such as
specially fitted sports equipment, dental implants, or prosthetic devices. The following three categories are often used to describe the different application of additive fabrication and may be applied to all of the above industries.
Rapid prototyping - Prototypes for visualization, form/fit testing, and functional testing
Rapid tooling - Molds and dies fabricated using additive processes
Rapid manufacturing - Medium-to-high volume production runs of end-use parts
Rapid prototyping Additive processes are primarily used for the fabrication of prototypes. Initially, this was because the production of end-use products demanded better mechanical properties and lower costs. While these layered parts now offer higher quality and lower costs, other reasons still exist for using additive processes for the fabrication of prototypes. Firstly, prototypes are needed during the design stage and must be produced quickly. Additive processes have short build times and do not require any custom tooling to be created. Secondly, additive fabrication is more cost effective for low quantities than other processes. Again, this is primarily because no costly tooling is required. The prototypes created through additive fabrication can serve many purposes. The prototype may simply be used for form testing, which is visually assessing the 3D form and design of the part and being able to communicate redesign or manufacturing requirements to other engineers. Prototypes are also frequently used for fit testing, in which the part's compatibility with other components of an assembly can be evaluated. In such form and fit applications, the material and mechanical properties are usually of little concern. Some additive processes produce prototypes used for functional testing, in which the part is tested under the operating conditions of the final product. For this application, the material and mechanical properties are significant and therefore only some additive fabrication processes are used towards this end. By using additive fabrication to produce prototypes, much time and money can be saved in the product design process. The quick fabrication of a prototype means that more designs can be considered and tested in a shorter period of time. Also, potential manufacturing problems that are caused by the part design can be identified before full production begins. Not only does the design process move quicker, but the quality of the design is likely to improve as well. Rapid tooling Mold and dies, the custom tooling for molding and casting processes, are geometrically complex parts that require high accuracy, low surface roughness, and strong mechanical properties. Machining these tools using CNC milling or EDM can be the most time consuming and costly step in the molding or casting process. As a result, using additive fabrication to create the tooling offers a fast and cheap alternative known as rapid tooling. As previously explained, additive fabrication excels at producing highly complex parts without great impact on build time. Also, the highly skilled and expensive labor required to machine a mold is not required. As a result, rapid tooling can enable high-volume production of quality parts without the large initial cost and lead time for the tooling. Rapid tooling also offers the potential for many improvements to the mold design, including complex cooling channels that are more efficient, the use of multiple materials, and functionally grading materials to optimize performance. Some limitations still exist in using rapid tooling. First, additive fabrication does not offer the high accuracy or finishes of machining, so secondary operations are typically required. Also, unlike additive fabrication, machining is able to use hard materials that offer great durability. As a result, rapid tooling is typically only used for low-to-medium volume productions. Lastly, as explained earlier, additive fabrication processes have smaller part size limitations and are unable to produce very large tooling. The most common method of rapid tooling uses additive processes to fabricate the tooling indirectly by first creating a pattern. This pattern is then used to form the mold or die. Patterns are already used in manufacturing processes that use non-permanent molds, such as sand casting and investment casting. In these processes, a pattern is traditionally machined from wood, plastic, or soft metal and used to form the mold. Additive fabrication offers a fast alternative for creating these patterns, which can be re-used many times and offer similar properties to wood or plastic patterns. Indirect tooling from additive fabrication can also be used to form re-usable molds for processes like vacuum casting or injection molding. Vacuum casting can use molds formed by pouring silicon rubber or room temperature vulcanizing (RTV) rubber around the rapid tooling pattern and allowing it to harden into the shape of the mold. These rubber molds can be used to form up to 50 plastic parts out of various polymers. Rapid tooling patterns can also be used to form metal/ceramic composite molds for injection molding
which can produce up to 1,000 plastic parts. Another type of rapid tooling is direct tooling, which is the use of additive fabrication to directly produce the mold without the need for a pattern. This approach was initially not viable because of the high accuracy and durability required for molds. However, with improvements in additive technologies and materials, direct rapid tooling is now possible. For example, Selective Laser Sintering and Electron Beam Melting have been used to directly fabricate metal molds, capable of producing hundreds of thousands of parts. However, secondary operations are still typically required to improve the finishes and tolerances of the mold. Rapid manufacturing Rapid manufacturing, a relatively new application for additive fabrication, is the medium-to-high volume production of end-use products using additive technologies. Initially, these processes weren't considered for large scale production due to limitations in the mechanical properties and surface finishes that they could attain. However, with improvements to additive technologies and materials, most additive processes are capable of, or being considered for, producing end-use products out of plastics, metals, composites, and ceramics. Rapid manufacturing does have its limitations and is best suited for parts that take advantage of the additive process. As explained earlier, additive technologies excel at producing highly complex geometries, relatively small parts, using multiple materials, and functionally grading materials to improve performance. For parts that are very large, geometrically simple, or require high tolerances and surface finishes, other more conventional processes are still preferred. Assuming that the desired part quality can be achieved, rapid manufacturing can offer many cost benefits over conventional manufacturing. Firstly, additive fabrication does not require any tooling which can be very costly and time consuming to produce for molding and casting processes. Also, additive processes typically have lower labor costs than conventional processes. This is due to the fact that parts are built directly from the CAD model and the process is highly automated. The labor costs are mainly attributed to the setup process, which becomes less significant with higher volume productions. Despite the above advantages, at a certain production volume conventional processes remain the more cost effective choice. This cut-off for rapid manufacturing exists for several reasons. First, the cost benefit of not incurring tooling costs becomes less significant at high production volumes. When manufacturing hundreds of thousands of parts, the per-part cost of tooling becomes less of an issue. Next, the material cost for rapid manufacturing can be quite high because additive processes use less widely available materials. However, as rapid manufacturing becomes more commonplace, these material prices will drop. Lastly, part build times can not compete with the short cycle times of molding and casting processes, which are of great advantage at large production volumes. As additive technologies improve, rapid manufacturing will become more viable for large scale productions. A short time ago, additive manufacturing processes were only cost effective for production volumes of 100-500 parts. Now, production volumes of 10,000-15,000 parts are being seen.
Stereolithography
Stereolithography (SLA) is the most widely used rapid prototyping technology. It can produce highly accurate and detailed polymer parts. It was the first rapid prototyping process, introduced in 1988 by 3D Systems, Inc., based on work by inventor Charles Hull. It uses a low-power, highly focused UV laser to trace out successive cross-sections of a three-dimensional object in a vat of liquid photosensitive polymer. As the laser traces the layer, the polymer solidifies and the excess areas are left as liquid. When a layer is completed, a leveling blade is moved across the surface to smooth it before depositing the next layer. The platform is lowered by a distance equal to the layer thickness (typically 0.003-0.002 in), and a subsequent layer is formed on top of the previously completed layers. This process of tracing and smoothing is repeated until the build is complete. Once complete, the part is elevated above the vat and drained. Excess polymer is swabbed or rinsed away from the surfaces. In many cases, a final cure is given by placing the part in a UV oven. After the final cure, supports are cut off the part and surfaces are polished, sanded or otherwise finished.
Stereolithography (SLA)
Capabilities
Abbreviation: SLA Material type: Liquid (Photopolymer) Materials: Thermoplastics (Elastomers) Max part size (LxWxH): 59.00 x 29.50 x 19.70 in.
Min feature size: 0.004 in. Min layer thickness: 0.0010 in. Accuracy: 0.0050 in. Surface finish: Smooth Build speed: Average
Applications: Form/fit testing, Functional testing, Rapid tooling patterns, Snap fits, Very detailed parts, Presentation models, High heat applications
Fused Deposition Modeling (FDM)
Fused Deposition Modeling (FDM) was developed by Stratasys in Eden Prairie, Minnesota. In this process, a plastic or wax material is extruded through a nozzle that traces the part's cross sectional geometry layer by layer. The build material is usually supplied in filament form, but some setups utilize plastic pellets fed from a hopper instead. The nozzle contains resistive heaters that keep the plastic at a temperature just above its melting point so that it flows easily through the nozzle and forms the layer. The plastic hardens immediately after flowing from the nozzle and bonds to the layer below. Once a layer is built, the platform lowers, and the extrusion nozzle deposits another layer. The layer thickness and vertical dimensional accuracy is determined by the extruder die diameter, which ranges from 0.013 to 0.005 inches. In the X-Y plane, 0.001 inch resolution is achievable. A range of materials are available including ABS, polyamide, polycarbonate, polyethylene, polypropylene, and investment casting wax.
Fused Deposition Modeling (FDM)
Capabilities
Abbreviation: FDM Material type: Solid (Filaments) Materials: Thermoplastics such as ABS, Polycarbonate, and Polyphenylsulfone; Elastomers Max part size (LxWxH): 36.00 x 24.00 x 36.00 in.
Min feature size: 0.005 in. Min layer thickness: 0.0050 in. Accuracy: 0.0050 in. Surface finish: Rough Build speed: Slow
Applications: Form/fit testing, Functional testing, Rapid tooling patterns, Small detailed parts, Presentation models, Patient and food applications, High heat applications
Selective Laser Sintering
Selective Laser Sintering (SLS) was developed at the University of Texas in Austin, by Carl Deckard and colleagues. The technology was patented in 1989 and was originally sold by DTM Corporation. DTM was acquired by 3D Systems in 2001. The basic concept of SLS is similar to that of SLA. It uses a moving laser beam to trace and selectively sinter powdered polymer and/or metal composite materials into successive cross-sections of a three-dimensional part. As in all rapid prototyping processes, the parts are built upon a platform that adjusts in height equal to the thickness of the layer being built. Additional powder is deposited on top of each solidified layer and sintered. This powder is rolled onto the platform from a bin before building the layer. The powder is maintained at an elevated temperature so that it fuses easily upon exposure to the laser. Unlike SLA, special support structures are not required because the excess powder in each layer acts as a support to the part being built. With the metal composite material, the SLS process solidifies a polymer binder material around steel powder (100 micron diameter) one slice at a time, forming the part. The part is then placed in a furnace, at temperatures in excess of 900 °C, where the polymer binder is burned off and the part is infiltrated with bronze to improve its density. The burn-off and infiltration procedures typically take about one day, after which secondary machining and finishing is
performed. Recent improvements in accuracy and resolution, and reduction in stair-stepping, have minimized the need for secondary machining and finishing. SLS allows for a wide range of materials, including nylon, glass-filled nylon, SOMOS (rubber-like), Truform (investment casting), and the previously discussed metal composite.
Selective Laser Sintering (SLS)
Capabilities
Abbreviation: SLS Material type: Powder (Polymer) Materials: Thermoplastics such as Nylon, Polyamide, and Polystyrene; Elastomers; Composites Max part size (LxWxH): 22.00 x 22.00 x 30.00 in.
Min feature size: 0.005 in. Min layer thickness: 0.0040 in. Accuracy: 0.0100 in. Surface finish: Average Build speed: Fast
Applications: Form/fit testing, Functional testing, Rapid tooling patterns, Less detailed parts, Parts with snap-fits & living hinges, High heat applications
Direct Metal Laser Sintering
Direct Metal Laser Sintering (DMLS) was developed jointly by Rapid Product Innovations (RPI) and EOS GmbH, starting in 1994, as the first commercial rapid prototyping method to produce metal parts in a single process. With DMLS, metal powder (20 micron diameter), free of binder or fluxing agent, is completely melted by the scanning of a high power laser beam to build the part with properties of the original material. Eliminating the polymer binder avoids the burn-off and infiltration steps, and produces a 95% dense steel part compared to roughly 70% density with Selective Laser Sintering (SLS). An additional benefit of the DMLS process
compared to SLS is higher detail resolution due to the use of thinner layers, enabled by a smaller powder diameter. This capability allows for more intricate part shapes. Material options that are currently offered include alloy steel, stainless steel, tool steel, aluminum, bronze, cobalt-chrome, and titanium. In addition to functional prototypes, DMLS is often used to produce rapid tooling, medical implants, and aerospace parts for high heat applications. The DMLS process can be performed by two different methods, powder deposition and powder bed, which differ in the way each layer of powder is applied. In the powder deposition method, the metal powder is contained in a hopper that melts the powder and deposits a thin layer onto the build platform. In the powder bed method (shown below), the powder dispenser piston raises the powder supply and then a recoater arm distributes a layer of powder onto the powder bed. A laser then sinters the layer of powder metal. In both methods, after a layer is built the build piston lowers the build platform and the next layer of powder is applied. The powder deposition method offers the advantage of using more than one material, each in its own hopper. The powder bed method is limited to only one material but offers faster build speeds.
Direct Metal Laser Sintering (DMLS)
Capabilities
Abbreviation: DMLS Material type: Powder (Metal)
Materials: Ferrous metals such as Steel alloys, Stainless steel, Tool steel; Non-ferrous metals such as Aluminum, Bronze, Cobalt-chrome, Titanium; Ceramics
Max part size (LxWxH): 10.00 x 10.00 x 8.70 in.
Min feature size: 0.005 in. Min layer thickness: 0.0010 in. Accuracy: 0.0100 in. Surface finish: Average Build speed: Fast Applications: Form/fit testing, Functional testing, Rapid tooling, High heat applications, Medical implants, Aerospace parts
3D Printing
Three Dimensional Printing (3DP) technology was developed at the Massachusetts Institute of Technology and licensed to several corporations. The process is similar to the Selective Laser Sintering (SLS) process, but instead of using a laser to sinter the material, an ink-jet printing head deposits a liquid adhesive that binds the material. Material options, which include metal or ceramic powders, are somewhat limited but are inexpensive relative to other additive processes. 3D Printing offers the advantage of fast build speeds, typically 2-4 layers per minute. However, the accuracy, surface finish, and part strength are not quite as good as some other additive processes. 3D Printing is typically used for the rapid prototyping of conceptual models (limited functional testing is possible). The 3D printing process begins with the powder supply being raised by a piston and a leveling roller distributing a thin layer of powder to the top of the build chamber. A multi-channel ink-jet print head then deposits a liquid adhesive to targeted regions of the powder bed. These regions of powder are bonded together by the adhesive and form one layer of the part. The remaining free standing powder supports the part during the build. After a layer is built, the build platform is lowered and a new layer of powder added, leveled, and the printing repeated. After the part is completed, the loose supporting powder can be brushed away and the part removed. 3D printed parts are typically infiltrated with a sealant to improve strength and surface finish.
Three Dimensional Printing (3DP)
Capabilities
Abbreviation: 3DP Material type: Powder
Materials: Ferrous metals such as Stainless steel; Non-ferrous metals such as Bronze; Elastomers; Composites; Ceramics
Max part size (LxWxH): 59.00 x 29.50 x 27.60 in.
Min feature size: 0.008 in. Min layer thickness: 0.0020 in. Accuracy: 0.0040 in.
The additive fabrication technique of inkjet printing is based on the 2D printer technique of using a jet to deposit tiny drops of ink onto paper. In the additive process, the ink is replaced with thermoplastic and wax materials, which are held in a melted state. When printed, liquid drops of these materials instantly cool and solidify to form a layer of the part. For this reason, the process if often referred to as thermal phase change inkjet printing. Inkjet printing offers the advantages of excellent accuracy and surface finishes. However, the limitations include slow build speeds, few material options, and fragile parts. As a result, the most common application of inkjet printing is prototypes used for form and fit testing. Other applications include jewelry, medical devices, and high-precisions products. Several manufactures have developed different inkjet printing devices that use the basic technique described above. Inkjet printers from Solidscape Inc., such as the ModelMaker (MM), use a single jet for the build material and another jet for support material. 3D Systems has implemented their MultiJet Moldeling (MJM) technology into their ThermoJet Modeler machines that utilize several hundred nozzles to enable faster build times. The inkjet printing process, as implemented by Solidscape Inc., begins with the build material (thermoplastic) and support material (wax) being held in a melted state inside two heated reservoirs. These materials are each fed to an inkjet print head which moves in the X-Y plane and shoots tiny droplets to the required locations to form one layer of the part. Both the build material and support material instantly cool and solidify. After a layer has been completed, a milling head moves across the layer to smooth the surface. The particles resulting from this cutting operation are vacuumed away by the particle collector. The elevator then lowers the build platform and part so that the next layer can be built. After this process is repeated for each layer and the part is complete, the part can be removed and the wax support material can be melted away.
Inkjet Printing
Capabilities
Abbreviation: MM, MJM Material type: Liquid Materials: Thermoplastics such as Polyester Max part size (LxWxH): 12.00 x 6.00 x 6.00 in. Min feature size: 0.005 in. Min layer thickness: 0.0005 in. Accuracy: 0.0010 in. Surface finish: Very Smooth Build speed: Slow Applications: Form/fit testing, Very detailed parts, Rapid tooling patterns, Jewelry and fine items, Medical devices
Jetted Photopolymer
Jetted photopolymer is an additive process that combines the techniques used in Inkjet Printing and Stereolithography. The method of building each layer is similar to Inkjet Printing, in that it uses an array of inkjet print heads to deposit tiny drops of build material and support material to form each layer of a part. However, as in Stereolithography, the build material is a liquid acrylate-based photopolymer that is cured by a UV lamp after each layer is deposited. For this reason, Jetted Photopolymer is sometimes referred to as Photopolymer Inkjet Printing. The advantages of this process are very good accuracy and surface finishes. However, the feature detail and material properties are not quite as good as Stereolithography. As with Inkjet Printing, the most common application of this technology is prototypes used for form and fit testing. Other applications include rapid tooling patterns, jewelry, and medical devices. Two companies that have developed jetted photopolymer devices include Objet Geometries Ltd. and 3D Systems. The equipment designed by both companies deposits the photopolymer build material as described above, but differs in the application of support material. Objet, an Israeli company, commercialized their PolyJet technology in 2000. In the PolyJet system, the support material is also a photopolymer that is deposited from a second print head and cured by the UV lamp. This support material does not cure the same as the build material and can later be washed away with pressurized water. 3D systems commercialized their InVision systems in 2003. These jetted photopolymer devices use a separate print head to deposit a wax support material. After the part is completed, the wax is melted away.
Jetted Photopolymer
Capabilities
Abbreviation: JP Material type: Liquid (Photopolymer) Materials: Thermoplastics such as Acrylic (Elastomers) Max part size (LxWxH): 19.30 x 15.40 x 7.90 in. Min feature size: 0.006 in. Min layer thickness: 0.0006 in. Accuracy: 0.0010 in. Surface finish: Smooth Build speed: Fast Applications: Form/fit testing, Very detailed parts, Rapid tooling patterns, Presentation models, Jewelry and fine items
Laminated Object Manufacturing (LOM)
The first commercial Laminated Object Manufacturing (LOM) system was shipped in 1991. LOM was developed by Helisys of Torrance, CA. The main components of the system are a feed mechanism that advances a sheet over a build platform, a heated roller to apply pressure to bond the sheet to the layer below, and a laser to cut the outline of the part in each sheet layer. Parts are produced by stacking, bonding, and cutting layers of adhesive-coated sheet material on top of the previous one. A laser cuts the outline of the part into each layer. After each cut is completed, the platform lowers by a depth equal to the sheet thickness (typically 0.002-0.020 in), and another sheet is advanced on top of the previously deposited layers. The platform then rises slightly and the heated roller applies pressure to bond the new layer. The laser cuts the outline and the process is repeated until the part is completed. After a layer is cut, the extra material remains in place to support the part during build.
Laminated Object Manufacturing (LOM)
Capabilities
Abbreviation: LOM Material type: Solid (Sheets) Materials: Thermoplastics such as PVC; Paper; Composites (Ferrous metals; Non-ferrous metals; Ceramics) Max part size (LxWxH): 32.00 x 22.00 x 20.00 in. Min feature size: 0.008 in. Min layer thickness: 0.0020 in. Accuracy: 0.0040 in. Surface finish: Rough Build speed: Fast Applications: Form/fit testing, Less detailed parts, Rapid tooling patterns
Metals
Almost 75% of all elements are metals. Metals are used in electronics for wires and in cookware for pots and pans because they conduct electricity and heat well. Most metals are malleable and ductile and are, in general, heavier than the other elemental substances. Two or more metals can be alloyed to create materials with properties that do not exist in a pure metal. All metals can be classified as either ferrous or non-ferrous. Ferrous metals contain iron and non-ferrous metals do not. All ferrous metals are magnetic and have poor corrosion resistance while non-ferrous metals are typically non-magnetic and have more corrosion resistance. An overview of the most common ferrous and non-ferrous metals is shown below.
Ferrous Metals
Material name Composition Properties Applications Low Carbon Steels
Up to 0.30% Carbon Good formability, good weld-ability, low cost
0.1%-0.2% carbon: Chains, stampings, rivets, nails, wire, pipe, and where very soft, plastic steel is needed. 0.2%-0.3% carbon: Machine and structural parts
Medium Carbon Steels
0.30% to 0.80% Carbon
A good balance of properties, fair formability
0.3%-0.4% carbon: Lead screws, gears, worms, spindles, shafts, and machine parts. 0.4%-0.5% carbon: Crankshafts, gears, axles, mandrels, tool shanks, and heat-treated machine parts 0.6%-0.8% carbon: "Low carbon tool steel" and is used where shock strength is wanted. Drop hammer dies, set screws, screwdrivers, and arbors. 0.7%-0.8% carbon: Tough and hard steel. Anvil faces, band saws, hammers, wrenches, and cable wire.
High Carbon Steels
0.80% to ~2.0% Carbon
Low toughness, formability, and weld-ability, high hardness and wear resistance, fair formability
0.8%-0.9% carbon: Punches for metal, rock drills, shear blades, cold chisels, rivet sets, and many hand tools. 0.9%-1.0% carbon: Used for hardness and high tensile strength, springs, cutting tools
1.0%-1.2% carbon: Drills, taps, milling cutters, knives, cold cutting dies, wood working tools. 1.2%-1.3% carbon: Files, reamers, knives, tools for cutting wood and brass. 1.3%-1.4% carbon: Used where a keen cutting edge is necessary (razors, saws, etc.) and where wear resistance is important.
Stainless steel is a family of corrosion resistant steels. They contain at least 10.5% chromium, with or without other elements. The Chromium in the alloy forms a self-healing protective clear oxide layer. This oxide layer gives stainless steels their corrosion resistance.
Good corrosion resistance, appearance, and mechanical properties
Austenitic Steels: Contains chromium and nickel. The typical chromium content is in the range of 16% to 26%; nickel content is commonly less than 35%.
Good mechanical and corrosion resisting properties, high hardness and yield strength as well as excellent ductility and are usually non-magnetic
Kitchen sinks, architectural applications such as roofing, cladding, gutters, doors and windows; Food processing equipment; Heat exchangers; Ovens; Chemical tanks
Ferritic Steels: Magnetic with a high chromium and low nickel content usually alloyed with other elements such as aluminum or titanium.
Good ductility, weld-ability, and formability; reasonable thermal conductivity, and corrosion resistance with a good bright surface appearance
Automotive trim, catalytic converters, radiator caps, fuel lines, cooking utensils, architectural and domestic appliance trim applications
Stainless Steel
Martensitic Steels: Typically contains 11.0% to 17.0% chromium, no nickel, and 0.10% to 0.65% carbon levels. The high carbon enables the material to be hardened by heating to a high temperature, followed by rapid cooling (quenching).
Good combination of corrosion resistance and excellent mechanical properties, produced by heat treatment, to develop maximum hardness, strength, and resistance to abrasion and erosion.
Cutlery, scissors, surgical instruments, wear plates, garbage disposal shredder lugs, industrial knives, vanes for steam turbines, fasteners, shafts, and springs
Non-Ferrous Metals
Material name Composition Properties Applications
Aluminum / Aluminum alloys
Pure metal / Easily alloyed with small amounts of copper, manganese, silicone, magnesium, and other elements
Low density, good electrical conductivity (approx. 60% of copper), nonmagnetic, noncombustible, ductile, malleable, corrosion resistance; easily formed, machined, or cast
Lead Pure metal Heaviest common metal, ductile, and malleable, good corrosion resistance
Pipes, batteries, roofing, protection against X-Rays
Magnesium / Magnesium Alloys
Pure metal / Used as an alloy element for aluminum, lead, zinc, and other nonferrous alloys; alloyed with aluminum to improve the mechanical, fabrication, and welding characteristics
Lightest metallic material (density of about 2/3 of that of aluminum), strong and tough, most machinable metal, good corrosion resistance, easily cast
Automobile, portable electronics, appliances, power tools, sporting goods parts, and aerospace equipment
Nickel / Nickel Alloys
Pure metal / Alloys very well with large amounts of other elements, chiefly chromium, molybdenum, and tungsten
Very good corrosion resistance (can be alloyed to extend beyond stainless steels), good high temperature and mechanical performance, fairly good conductor of heat and electricity
The major use of nickel is in the preparation of alloys or plating - frequently used as an undercoat in decorative chromium plating and to improve corrosion resistance; applications include electronic lead wires, battery components, heat exchangers in corrosive environments
Titanium / Titanium Alloys
Pure metal / Easily alloys with aluminum, nickel, chromium, and other elements
Low density, low coefficient of thermal expansion, high melting point, excellent corrosion resistance, nontoxic and generally biologically compatible with human tissues and bones, high strength, stiffness, good toughness
Aerospace structures and other high-performance applications, chemical and petrochemical applications, marine environments, and biomaterial applications
Zinc / Zinc Alloys
Pure metal/ Metal is employed to form numerous alloys with other metals. Alloys of primarily zinc with small amounts of copper, aluminum, and magnesium are useful in die-casting. The most widely used alloy of zinc is brass
Excellent corrosion resistance, light weight, reasonable conductor of electricity
Used principally for galvanizing iron (more than 50% of metallic zinc goes into galvanizing steel), numerous automotive applications because of its light weight
Plastics
Plastic is a commercial name for a group of materials that while being processed, can be pushed or formed into almost any desired shape and then retain that shape. Plastics can be cast, molded, or pressed into an unlimited variety of shapes. They are one of the most used materials on a volume basis in industrial and commercial life. Plastics are on par with metals, wood, and ceramics and are essential to the needs of virtually the entire spectrum of business. Plastics, properly applied, will perform functions at a cost that other materials cannot match. Most plastics can be classified as either thermoplastic or thermosetting materials. Thermoplastic materials can be formed into desired shapes under heat and pressure and become solids on cooling. If they are subjected to the same conditions of heat and pressure, they can be reprocessed into new shapes. Thermosetting materials are like concrete, once processed and shaped, they cannot be reshaped. Today, the vast majority of plastics are thermoplastics. Plastics are made up of polymers. Polymeric materials are characterized by long chains of repeated molecule units known as "mers". These long chains intertwine to form the bulk of the plastic. The ways in which the chains intertwine determine the plastic's macroscopic properties. Typically, the polymer chain orientations are random and give the plastic an amorphous structure. Amorphous plastics have good impact strength and toughness. Examples include acrylonitrile-butadiene-styrene (ABS), styrene-acrylonitrile copolymer (SAN), polyvinyl chloride (PVC), polycarbonate (PC), and polystyrene (PS). If instead the polymer chains take an orderly, densely packed arrangement, the plastic is said to be crystalline. Crystalline plastics share many properties with crystals, and typically will have lower elongation and flexibility than amorphous plastics, and better chemical resistance. Examples of crystalline plastics include acetal, polyamide (PA; nylon), polyethylene (PE), polypropylene (PP), polyester (PET, PBT), and polyphenylene sulfide (PPS). Advances in chemistry have made the distinction between crystalline and amorphous less clear, since some materials like nylon are formulated both as a crystalline material and as an amorphous material.
Thermoplastics and Thermosets
Material name Abbreviation Trade names Description Applications
Tough, flexible, high cost Bushings, electrical components, seals, washers
Introduction
Steve works in a small ten person company. For the last two years, he has been designing sheet metal battery housings for a bio-medical product designed and marketed by his company. Steve's company's main client would like them to explore the possibility of replacing the sheet metal housing with a plastic housing. Steve has a good idea about how the plastic housing will look. He has seen an example of a plastic housing being used in a competitive product. However, his boss wants to learn about the cost before deciding to switch to the plastic. He asks Steve to figure out the cost of making an injection molded plastic housing. Steve is really excited about this project.
Traditional Cost Analysis Approach
Steve sets out to get an estimate for the injection molded battery housing, but encounters many obstacles. He tries multiple approaches recommended by his co-workers, but after each attempt, Steve still does not have an answer and grows more frustrated with the project.
First Attempt: Steve does research on the Internet and finds a molder that looks very promising. Their website says that they are extremely cost competitive and very experienced with the latest injection molding technology. They also have great customer testimonials on the web site. Steve calls the molder. The molder says that Steve should send them the engineering drawing of the part and they will provide him a quote within forty eight hours. Unfortunately, Steve does not have a detailed engineering design yet. So, he cannot send them the drawing. To make the matter worse, once Steve mentions that the project is exploratory and he does not have a detailed drawing, the molder looses interest. Even if Steve had the engineering drawing, his boss would never approve sending drawings of a key product to an unknown molder.
Second Attempt: Steve contacts his college roommate John who now works at a very large company and has access to the best-in-class cost estimation software. John invites Steve to visit him and try his cost estimation software. Steve visits John's company and starts using the software. The first three questions are relatively simple and Steve has no trouble answering them. But then the questions start getting increasingly harder and becoming very specific about the molding process. Steve has no idea whether he needs insulated runners or not. All he wants to do is to run away. John suggests that Steve attend a highly informative training session by the software vendor. Steve comes back to his office and talks to the software vendor. It turns out that the software costs $24,950 and the two day training session is only available if he buys the software. Steve does not want to ask his boss to spend 25K on this software.
Third Attempt: Another friend, Bill, suggests to Steve that he buy a book that only costs $90 and has a very detailed method for calculating cost. So, Steve orders the book from Amazon - it has great reviews. Steve cannot wait for the book to arrive. Finally, two days later the book arrives. Steve starts working through the formulas. It is a pain to use them. But, it is certainly better than nothing. Suddenly, Steve notices that the book mentions that the data is based on a survey done over 15 years ago. He is very upset. He thinks about writing an angry review but it won't help his project.
Fourth Attempt: Steve calls his brother-in-law Greg to discuss his problem. Fortunately, Greg's company has ordered ten new plastic parts in the last three months. Greg shows those new parts to Steve. One of them turns out to be close to Steve's specifications for his part. Fortunately, Greg works in a company that is in a different enough market from Steve's company. So, Greg has no trouble in sharing the cost data with Steve. Finally, Steve has a rough estimate for his injection molded part. However, Steve would like to find out how the cost would be different if he changed the part to his exact specifications. Unfortunately, Greg cannot help him with that question.
Cost Analysis with CustomPartNet
Hearing about Steve's difficulty in acquiring an estimate, a co-worker informs Steve that he has recently heard about a website called CustomPartNet that he should investigate. Steve locates the website and finds that he can easily browse through an extensive reference part library for injection molded parts. He quickly identifies a housing that meets his specifications, shown below.
Steve is even able to change the material and wall thickness for the reference part to exactly match his specifications.
The system produces a detailed cost estimate based on the up-to-date market information.
Steve also performs several what-if scenarios to see how changing the part size, quantity, and material would affect the cost.
In addition, an extensive glossary helps him understand the specialized terminology used in the injection molding community. Steve is able to invite his brother-in-law Bill to add comments and help refine his analysis. He presents a very detailed cost analysis report to his boss and his boss decides that they should switch to the plastic part. The system also allows Steve to search for qualified molders, based on the part parameters, who can mold the part for Steve.
Introduction
Bill is a mechanical engineering student that is currently taking the senior design course at his university. As part of this course, Bill and the other members of a 5-person design team must fully design a new product. They must specify the material, manufacturing process, and estimated cost of each component. Students in this course who produce successful designs often go on to apply for patents and sell their products. Bill and his team have completed their preliminary designs and now must estimate the cost of each component. Bill tells his team that they can use the tools at CustomPartNet to generate estimates for each of their parts and proceeds to show them how to estimate the cost of the plastic housing for their device, shown below.
Initial cost analysis
Bill and his team have learned about a variety of manufacturing processes in their design course and have decided that the housing will be injection molded. Using the custom estimate form on CustomPartNet, Bill enters the necessary parameters of the housing. For the parameters that he is unfamiliar with, the glossary pop-ups explain what information is required.
After completing the form, Bill saves his part and is able to view the cost analysis. As shown below, Bill sees an estimate of $1.294 for each part.
Knowledge center and part redesign
Bill and his team previously determined that for their product to be affordable, it would need to be manufactured for under $3.00 per part. After seeing that this single component contributes to over 40% of the cost, Bill needs to find a way to cut cost. Bill clicks on the link to CustomPartNet's knowledge center to look for answers and finds that the information provided on injection molding explains the cost drivers for this process and the proper design guidelines for creating a part.
In his design course, Bill learned about a large number of manufacturing processes, but there was not enough time in a single semester to cover the correct design practices for each process. At CustomPartNet's knowledge center, Bill learns that injection molded parts must have thin walls in order to cool quickly and that adding ribs to flat surfaces will add the necessary strength. Bill also learns that undercuts in the part will substantially add to the tooling cost. Using this information, Bill and his team redesign the plastic housing for their product. As shown below, the new design has thinner walls, with ribs for added strength. Also, the hinges and latch have been redesigned to remove undercuts.
Bill now returns to his saved estimate and enters the new parameters of the redesigned housing. He and his team are amazed to see that their new design will cost $0.698 per part, a reduction in cost of 46%.
Material selection
With the design now complete, Bill decides to explore the effect of material on the cost. His team had initially chosen ABS as the material for the housing because they had learned in class that ABS is a commonly used material for small injection molded housings. However, in CustomPartNet's knowledge center, Bill finds several alternative materials that are also commonly used for housings. These materials include nylon, polycarbonate, polyethylene, and polypropylene. Using CustomPartNet's cost analysis page to conduct live cost comparisons, Bill is able to immediately see the effect of each of these materials on the cost of his part. He quickly determines that using High Density Polyethylene (HDPE) will yield a cost of $0.491 per part, a further 30% reduction in cost. Furthermore, Bill is able to view how this reduction in cost is possible. HDPE has a lower density and unit price compared to ABS, which lowers the material cost. Additionally, the thermodynamic properties of the material allow the production rate to increase from 133 to 277 parts per hour.
Using the tools at CustomPartNet, Bill and his team were able to quickly estimate their own parts, view material properties and up-to-date pricing, and learn about the DFM guidelines and cost drivers for injection molding. Using these tools, Bill and his team were able to redesign their part for easy manufacture and dramatically reduce the cost. Bill and his team continue to use CustomPartNet for design tips and cost estimates for the rest of the components. At the end of the semester, their professor is impressed with their design and recommends that the team apply for a patent and pursue developing their design into a marketable product.
AISI
The American Iron and Steel Institute.
AISI Steels
Steel designations defined by of the American Iron and Steel Institute. AISI carbon and alloy steels are essentially the same as those designated by the Society of Automotive Engineers (SAE). The AISI system is more comprehensive than the SAE in that letters precede the alloy number indicating the manufacturing method: A represents basic open-hearth alloy steel, B acid Bessemer carbon steel, C basic open-hearth carbon steel, CB either acid Bessemer or basic open-hearth carbon steel, E electric furnace alloy steel.
ASTM
The American Society for Testing Materials.
Acetal
Acetal resins, whose chemical name is polyoxymethylene, are formed from the polymerization of formaldehyde. Acetals tend to have a high degree of crystallinity, giving them superior strength and stiffness compared with other thermoplastics, while retaining good toughness at low temperatures. Acetals are known for their high strength, fatigue and corrosion resistance, surface hardness, lubricity, and resilience.
Acrylic
Acrylic resins are widely known for their superior impact resistance and clarity. Acrylates and methacrylates comprise the two main groups of acrylics, which enjoy widespread use in aerospace, automotive and optical applications.
Acrylonitrile Butadiene Styrene (ABS)
Introduced in the late 1940s ABS has a wide range of good properties. It's very stiff, tough, thermal and chemically resistant, it is easy to process and has an excellent surface appearance. ABS is used in many impact-resistant applications from motorcycle fairings to lawn mower housings.
Acrylonitrile Chlorinated PE-styrene
Like ABS, it is a terpolymer, but of acrylinitrile and chlorinated polystyrene, and has better flame-retardency and weatherability than ABS.
Acrylonitrile Styrene Acrylate (ASA)
ASA is produced either by a patented, proprietary process or by graft process. ASA has superior weatherability compared with ABS and because of an absence of double bonds resists yellowing and embrittlement better than other polymers.
Additional costs per operation
The total cost of any material, components, or equipment used in a single operation. The additional cost per part is equal to these costs per operation amortized over the number of parts per operation.
Additive
A substance that is added to the raw material used in a process in order to alter some material property. Examples of additives include colorants, flame retardants, and UV protectants. The additives ratio describes the weight of additives that may be added relative to the weight of raw material.
Alloy Steel
Steels containing alloying elements and with qualities superior to those of carbon steels. An alloy steel is defined as meeting one or more of the following conditions: having a manganese content greater than 1.65%, a silicon content greater than 0.5%, a copper content greater than 0.6%, or specified minimum quantities of chromium, molybdenum, nickel, tungsten, or vanadium. Alloys with a total of less than 5% of such elements are considered low alloy steels. Alloys with more than 11% chromium are generally considered stainless steels. Most alloy steel is medium- or high-carbon steel.
Aluminum
Chemical symbol Al. Element No. 13 on the periodic chart. Aluminum is a white-silver metal with an atomic weight 26.97, a melting point of 660°C (1220 °F), and a boiling point of approximately 2270°C (4118 °F). It is stable against normal atmospheric corrosion, but attacked by both acids and alkalis. Aluminum is light weight, ductile, malleable, and conducts electricity with very little resistance. Aluminum is often alloyed with other metals to improve its tensile strength and resistance to acids and alkalis. Pure aluminum is refined from alumina, a common oxide found in bauxite ore. Aluminum is second only to steel in consumption. Aluminum is heavily used in the transportation, packaging, building, electronics industries. Its principle uses in steel making include: deoxidation, restricting grain growth (by forming dispersed oxides or nitrides), and as an alloying element in nitriding steel.
Automatic tool change time
The time required for an automatic tool changer to position a new tool. In a milling machine, this includes the time to stop and orient the spindle, remove the current tool, insert the new tool, and start the spindle again. In a turning machine, this time describes the turret rotating to a new tool position.
Automatic tool changer
A device that stores several tools, each in its own pocket or tool holder, and can automatically move the required tool into position. In a milling machine, this device removes the tool from the spindle, places it back in the correct pocket, and inserts a new tool into the spindle. In a turning machine, this device (known as a turret) rotates the required tool into position and continues to hold it during the cut.
Axial depth of cut
The depth of the tool along its axis in the workpiece as it makes a cut. In turning, a facing operation has an axial depth of cut relative to the workpiece axis. A large axial depth of cut will require a low feed rate, or else it will result in a high load on the tool and reduce the tool life. Therefore, a feature is typically machined in several passes as the tool moves to the specified axial depth of cut for each pass.
End milling (Milling machine) Facing (Turning machine)
Bar advance time
When a bar feeder is used as the fixture, one piece of bar stock is loaded and simply advanced into position before each cycle, rather than loading a new workpiece. The bar advance time is the amount of time (in minutes) required to advance the bar into position for the next part to be machined.
Bar end
The material at the end of a piece of bar stock that will not be used. The bar end, or bar remnant, is typically the result of a device holding the bar while the stock is cut. The bar end is used in determining how many workpieces a single piece of bar stock will yield.
Bar stock
Bar load time
When a bar feeder is used as the fixture, one piece of bar stock is loaded and simply advanced into position before each cycle, rather than loading a new workpiece. The bar load time is the amount of time (in minutes) required to load the bar, which occurs everytime the number of workpieces per bar have been machined.
Bases
Structures that act as the bottom support for other parts. (Includes: feet, foundations, pedestals, platforms, shelves, stands, structures, supports, trays, etc)
Beams
Long, rigid structures that are attached at one or both ends to a surface to provide support. (Includes: arms, axles, bars, columns, cylinders, pillars, poles, posts, rails, rods, shafts, spokes, structures, struts, supports, trusses, etc)
Bend allowance
The length of the neutral axis between the bend lines, or in other words, the arc length of the bend. The bend allowance added to the flange lengths is equal to the total flat length.
Bending diagram
Neutral axis
Bend angle
The angle to which a piece of material has been bent. The bend angle can be measured between the bent material and its original position, or as the included angle between perpendicular lines drawn from the bend lines.
Bending diagram
Bend deduction
The bend deduction, sometimes called the bend compensation, describes the amount a piece of material has been stretched by bending. The value equals the difference between the mold line lengths and the total flat length. The mold line lengths are the distances measured to the outside mold line and are equal to the flange lengths plus the setback.
Bending diagram
Bend length
The length of a bend formed in a piece of sheet metal. This length is measured along the bend axis, which is typically a straight line.
Bending diagram
Bend radius
The radius of a bend in a piece of material that occurs between the bend lines. The radius is measured from the bend axis to the inside surface of the material and is therefore sometimes specified as the inside bend radius.
Bending diagram
Bending force
The amount of force required to bend a piece of material into a new permanent shape. The bending force must create enough stress in the material to exceed the yield strength, allowing the material to plastically deform. In bending, the applied force will cause tension on side of the material and compression on the other.
V bending
Wipe bending
Blank
A piece of sheet metal that is used as an initial workpiece on which other sheet metal operations will be performed. Blanks are cut from a larger piece of sheet stock in the blanking process and typically have a simple geometric shape, such as a rectangle or circle.
Rectangular blanks
Round blanks
Boring
An operation in which a boring tool enters the workpiece axially and cuts along an internal surface to form different features. The boring tool is a single-point cutting tool, which can be set to cut the desired diameter by using an adjustable boring head. Boring is commonly performed after drilling a hole in order to enlarge the diameter or obtain more precise dimensions. On a turning machine, a variety of features can be formed, including steps, tapers, chamfers, and contours. These features are typically machined at a small radial depth of cut and multiple passes are made until the end diameter is reached. For a finish turning operation, the cutting feed is calculated based on the desired surface roughness and the tool nose radius.
Boring (Milling machine)
Bored hole
Boring (Turning machine)
Bored step
Bored taper
Bored chamfer
Bored contour
Boss
A cylindrical protrusion on a part that is used for aligning or fastening another part by accepting a screw or other insert through a hole in the center.
Box type
The type of box recommended for packing may be a corrugated cardboard box or a wood crate. Corrugated cardboard boxes are characterized by their wall thickness and test strength, which both determine the maximum weight the box can hold. The test strength listed here is the bursting strength measured in pounds per square inch.
Brackets
Structures that can be fastened between two adjacent surfaces to provide support. (Includes: braces, hinges, structures, supports, etc)
Brinell Hardness Test
ASTM E10. A common standard method of measuring the hardness of metallic materials. A hardened steel or tungsten carbide ball is pressed into the smooth surface of the material with a specific load. A microscope in used to measure the diameter of the indentation in the material surface and then compared to the corresponding Brinell Hardness Number (BHN) on a chart or calculated from a prescribed formula, the applied load in kilograms divided by the surface area of the resulting impression in square millimeters. The Brinell hardness test for steel involves impressing a 10 mm diameter hardened steel or tungsten carbide ball with a load of 3000 kilograms. The Vickers hardness scale is preferred for steels with a hardness over 500 BHN.
Caps
Removable covers that are used to close the opening of a container. (Includes: closures, covers, lids, plugs, stoppers, tops, etc)
Captured cavity
A pocket in a part which has inward curving surfaces, but are not completely enclosed. A solid object that fills such a cavity could not be removed. Many manufacturing processes are incapable of producing parts with such a feature.
Bottle with captured cavity (Cross-section shown in red)
Carbon Steel
Steel made from molten iron or ferrous scrap with carbon, manganese, sulfur, silicon, and phosphorous. Carbon steel contains up to about 2% carbon, up to 1.65% manganese, and 0.60% or less silicon. Its mechanical properties are primarily determined by the amount of carbon present. Aside from carbon, only residual quantities of other elements (nickel, chromium, molybdenum, etc.) are present, except those added for deoxidization or to counter the deleterious effects of residual sulfur. Carbon steel is also called plain or straight carbon steel, and ordinary steel.
Cast Iron
1) Iron with a carbon content that exceeds the solubility limit of carbon in austenite (approximately 1.8%) at the eutectic temperature. Cast Irons typically contain 1.8-4.5% carbon, plus silicon, sulfur, and phosphorus; they may also have other alloying elements such as chromium, manganese, nickel, and vanadium. 2) A generic term for a large family of cast ferrous alloys like gray cast iron, white cast iron, malleable cast iron and ductile cast iron. Sometimes the word "cast" is left out, resulting in "gray iron," "white iron," "malleable iron," and "ductile iron," respectively.
Cavity
The enclosed space between two mold halves which forms the shape of the desired part. Often times, molds are designed with more than one cavity, allowing multiple identical parts to be molded in one cycle. The most common number of cavities are 1, 2, 4, or 8.
Cavity pressure
The pressure inside the mold cavities caused by the injection of molten material during the mold filling stage. Cavity pressure depends on the material, injection pressure, and the geometry of the cavities and runner system. For most polymers, the cavity pressure is between 4,000 and 10,000 psi.
Centigrade
Also known as the Celsius scale, a temperature scale which sets the freezing point of water at 0° and the boiling point at 100°. To convert centigrade to Fahrenheit multiply by 1.8 and add 32, e.g., (100° x 1.8) + 32 = 212°F.
Ceramic
A man-made solid produced by the fusion of inorganic substances. A more specific definition within the slip casting industry is that the term 'ceramics' has come to signify the use of talc-ball clay slurries to cast ware for firing at low temperatures, where as the term 'pottery' is used to refer to ware fabricated by individuals and companies using plastic clays of all types and at all temperature ranges.
Chamfer milling
An operation in which a chamfer mill makes a peripheral cut along an edge of the workpiece or a feature to create an angled surface, known as a chamfer. It is assumed that the angle of the chamfer is 45 degrees, so that the chamfer width is equal to its height. The chamfer length can be the complete perimeter of a workpiece or feature, just one side, or even a part of a side. Also, a chamfer can be machined on either the exterior or interior of a part and can follow either a straight or curved path.
Chamfer milling operation
Complete chamfer
Side chamfers (0 ends, 1 end, 2 ends)
Clamp force
The force that is applied to a mold by the molding machine in order to keep it securely closed while the material is injected. The clamp force is typically some factor of safety greater than the separating force, which is the outward force exerted on the mold halves by the injected material.
Clamping force
Clamp stroke
The distance that the rear mold half must travel in order to be securely clamped to the front mold half. The clamp stroke must be large enough to allow the part to be ejected from the mold.
Clamps
Removable fasteners that hold a part in place by exerting force on its sides. (Includes: clips, clasps, grips, locks, snaps, ties, vises, etc)
Clarity
The measure clearness in a transparent or translucent polymer.
Coefficient Of Linear Thermal Expansion (CTE)
The change in a unit of length of a material per unit change in temperature. Expressed in in/in-°F or cm/cm-°C. The CTE is not constant, but varies with temperature, so it is often expressed as an average over a temperature range. The ASTM test measuring the CTE in polymers is D696.
Coefficient of Expansion
Abbreviated CTE for Coefficient of Thermal Expansion. The change in length per unit length, area per unit area, or volume per unit volume for each degree change in temperature. Typical units for linear CTE are cm/cm°C or in/in°F, or expressed as millionths of unit length change per unit length per degree (microns/(meter ºC)).
Complex features
Protrusions or depressions occurring in multiple directions on a part, including those opposing the tooling direction, such as undercuts.
Complexity
The complexity of a part is determined by several parameters, so 5 preset configurations are available. In a custom configuration, the user may specify the feature count and the mold requirements, which may include side-cores, lifters, unscrewing devices, and parting surface complexity.
Compressive Strength
The amount of compressive stress that a material is capable of sustaining before buckling or being crushed. If a material fails in compression by a brittle fracture, the compressive strength has a very definite value. Materials such as clay brick, cast iron, and concrete can exhibit great compressive strengths, but brittle failure results in a catastrophic failure. The crushing strength of concrete, called the cube strength because the test involves crushing a concrete cube, is around 6000 psi, granite is 20,000 psi, and cast iron ranges from 60,000 - 120,000 psi. In the case of ductile, malleable, or semiviscous materials (which buckle rather than shatter), the value obtained for compressive strength is an arbitrary value dependent on the degree of distortion that is indicative as failure of the material. Such arbitrary values are referred to as compressive yield strengths whereas complete compressive failure is termed ultimate compressive strength.
Conductivity
The measure of a materials ability to transmit electricity or heat. The reciprocal of conductivity is resistivity.
Connectors
Fasteners that connects two or more parts together by attaching at each end. (Includes: adapters, couplings, joints, junctions, links, etc)
Containers and covers
Parts whose primary function is to store and/or protect other parts or materials
Cooling time
In molding and casting processes, the cooling time is the time required for the molten material to cool and solidify in the mold before the part is ejected. The theoretical cooling time can be calculated from material properties, but a correction factor is often applied to account for how the mold geometry and cooling lines affect heat flow.
Copper
Chemical symbol Cu. Element No. 29 of the periodic system, atomic weight 63.57. A characteristically reddish metal of bright luster, highly malleable and ductile and having high electrical and heat conductivity; melting point 1981 (degrees) F.; boiling point 4327 F.; specific gravity 8.94. Used in the pure state or alloyed by other elements to make brasses and bronzes consumed in building construction, electric and electronic products, industrial machinery, transportation equipment, and numerous consumer and general products. Used in the pure state as sheet, tube, rod and wire and also as alloyed by other elements and an alloy with other metals.
Core
An additional mold piece that is used to form features that cannot be formed by the two mold halves, such as an undercut. A core can be placed in the mold cavity or actuated through the side (side-core).
Core defect rate
The percentage of expendable cores, such as those made from sand, that are defective from the core-making or core-setting processes.
Core-box
A box used to form expendable cores, such as those made from sand.
Corrosion Resistance
The intrinsic ability of a material to resist degradation by corrosion. This ability can be enhanced by application of "special" coatings on the surface of the material.
Counterboring
An operation in which a counterbore tool enters the workpiece axially and enlarges the top portion of an existing hole to the diameter of the tool. Counterboring is often performed after drilling to provide space for the head of a fastener, such as a bolt, to sit below the surface of a part. The counterboring tool has a pilot on the end to guide it straight into the existing hole.
Counterboring operation
Counterbored hole
Countersinking
An operation in which a countersink tool enters the workpiece axially and enlarges the top portion of an existing hole to a cone-shaped opening. Countersinking is often performed after drilling to provide space for the head of a fastener, such as a screw, to sit flush with the workpiece surface. Common included angles for a countersink include 60, 82, 90, 100, 118, and 120 degrees.
Countersinking operation
Cut charge
The cost of cutting a workpiece from a piece of stock.
Cut diameter
The diameter of the workpiece at the location of a cut in a turning operation. The cutting speed and spindle speed can both be calculated for this diameter. Depending on the form of speed control, only one of these values will remain constant as the cut proceeds and the diameter changes.
Cut length
The length that the cutting tool travels at a specified feed rate in order to perform an operation. The cut length can be calculated based on the operation type, feature dimensions, and cutting parameters. The cut length includes the distance to engage and exit the workpiece, but does not include any distances that are traversed at a rapid travel rate.
Cut power
The amount of power, typically measured in horsepower (hp) or kilowatts (kW), which is required by a machine to perform a cutting operation. This power can be calculated from the material removal rate and the specific cutting energy of the material. The cut power for all operations must be less than the maximum power available from the machine.
Cut time
The time required for the tool to travel the cut length at a specified feed rate.
Cut-off
A turning operation, also known as parting, in which a single-point cut-off tool moves radially, into the side of the workpiece, and continues until the center or inner diameter of the workpiece is reached, thus parting or cutting off a section of the workpiece. A part catcher is often used to catch the removed part.
Cut-off to center
Cut-off to inner diameter
Cutoff width
The width of the cut when cutting a workpiece from a piece of bar stock. The cutoff width is used in determining how many workpieces a single piece of bar stock will yield.
Bar stock
Cutterpath type
The cutterpath describes the path of the tool while it travels the cut length in order to complete an operation. For some operations, the required cutterpath will involve not only cutting away all the material (roughing) but also cutting along the perimeter to leave a smooth finish (profiling). While a “Rough & Profile” operation will complete the desired feature, it is sometimes preferable to use a “Rough only” operation followed by a “Profile only” operation that uses different cutting parameters.
Cutting feed
The distance that the cutting tool or workpiece advances during one revolution of the spindle, measured in inches per revolution (IPR). In some operations the tool feeds into the workpiece and in others the workpiece feeds into the tool. For a multi-point tool, the cutting feed is also equal to the cutting feed per tooth, measured in inches per tooth (IPT), multiplied by the number of teeth on the cutting tool.
Cutting feed per tooth
The distance that the workpiece feeds into each tooth on a multi-point cutting tool as it rotates. This distance, also called the chip load per tooth, describes the size of the material chip that each tooth will cut. The feed per tooth, measured in inches per tooth (IPT), multiplied by the number of teeth on the cutting tool is equal to the cutting feed, measured in inches per revolution (IPR).
Cutting speed
The speed of the workpiece surface relative to the edge of the cutting tool during a cut, measured in surface feet per minute (SFM).
Cycle time
The time that is required for one complete cycle of a manufacturing process. Typically, the cycle time is the time required to produce a single part. However, many processes allow for the production of multiple parts per cycle. For example, a mold may contain multiple cavities or machining can be performed on multiple parts at once.
D
Deep drawing force
The amount of force required to deep draw a sheet metal blank to a smaller diameter determined by the punch. The required force will depend upon the material, sheet thickness, and drawing ratio. The drawing force will create enough stress in the material to exceed the tensile yield strength, allowing the material to plastically deform to the new shape.
Deep drawing
Defect rate
The percentage of the production quantity of parts that are defective. These parts can be discarded or recycled.
Density
The ratio of a material's mass to its volume at a given temperature and pressure, typically measured in kg/m^3, g/cm^3, or lb/in^3. Water is 1.0 g/cm³ at 25°C and 1 atmosphere of pressure.
Die casting machine type
Die casting machines can be classified as one of two types – a hot chamber or a cold chamber machine. Hot chamber machines are used for alloys with low melting temperatures, such as zinc. Cold chamber machines are required for alloys with high melting temperatures, such as aluminum, and have longer cycle times and higher hourly rates.
Die life
The number of cycles performed during the casting process before the wear on the die is too much for it to be used anymore. If the die life is shorter than the number of cycles needed to produce the production quantity of parts, additional dies will be needed. However, a die can be repaired to slightly extend its lifetime. The die life is affected by both the material of the die and the material being injected.
Dielectric Constant
Also called the permittivity and denoted DK, or Er. The ratio of the capacitance of an insulator to the capacitance of a vacuum or dry air (the dielectric constant of a vacuum is 1.00000, dry air is 1.00054). Capacitors release charge when a circuit is broken. Capacitance is the ratio of charge absorbed to the potential (voltage applied). A dielectric constant of 3 means an insulator will absorb 3 times more electrical charge than a vacuum.
Dielectric Strength
The maximum voltage an insulating material can withstand before breakdown occurs. Imperial units are in volts per Mil and Metric units are in kilovolts per mm.
Draft
The offset of the walls of a part by a slight angle, referred to as the draft angle. A draft angle is often required on the surfaces of a part that are parallel to the tooling direction in order to facilitate removal from a mold. However, some processes do not require a part to have any draft.
Draft angle
Draw reduction
The percent reduction of the diameter of a sheet metal blank to the draw diameter (or punch diameter) through a deep drawing operation. The complete deep drawing of a part is often achieved by a series of draw reductions.
Deep drawing reduction
Drawing ratio
A measure of the severity of a deep drawing operation, calculated as the ratio of the blank diameter to the punch diameter. The limiting drawing ratio (LDR) is a measure of a material's deep drawability and is calculated from the largest blank that can be completely deep drawn for a given punch diameter.
Drilling
An operation in which a drill enters the workpiece axially and cuts a hole with a diameter equal to that of the tool. On a milling machine, an end milling operation is required to produce a hole with a tool smaller than the hole diameter. A drilling operation typically produces a blind hole, which extends to some depth inside the workpiece, measured to the point made by the tool or to the end of the full diameter portion. On a milling machine, a hole that extends completely through the workpiece (through hole) can also be drilled.
Drilling (Milling machine)
Drilling (Turning machine)
Blind hole
Through hole
Dry cycle time
The cycle time of a process that results from no material or workpiece being used. The dry cycle time is typically a measure of machine performance that indicates the time for the machine to perform the actions necessary to manufacture a part, without the part actually being produced. This time will always be less than the actual cycle time.
E
Ejection temperature
The temperature of the material at which a part can safely be ejected from the mold. Ejection of the part before it reaches this temperature may cause warping or other defects.
Ejector marks
A part defect in the form of small indentations that are made where the ejection system pushed the part out of the mold.
Elastomer
A material that at room temperature can be stretched repeatedly to at least twice its original length and, upon immediate release of the stress, will return with force to its approximate original length.
Elongation
The percent change in length of a specimen under a given load. Elongation is usually measured within a fixed distance (50 mm or 2 in.) near the point of yield or failure, not over the entire length of the specimen.
Enclosures
Protective covers, or part of such a cover, that fully encloses other parts and may hold them in place. (Includes: boxes, casings, containers, covers, housings, shells, etc)
End milling
An operation in which an end mill makes either peripheral or slot cuts across the workpiece, determined by the step-over distance, in order to machine a specified feature. The depth of the feature may be machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes. For a rough operation, the recommended cutting speed and feed are selected for a peripheral or slot cut. A finish operation will lower the cutting feed according to the finish requirements.
End milling (Profile)
End milling (Slot)
End milling (Pocket)
End milling features
An end milling operation can produce a variety of features, including profiles, slots, and pockets. A profile is a peripheral cut along an external or internal edge of the workpiece with a length equal to the complete perimeter, just one side, or even a part of a side. A slot is a slot cut in the workpiece that can form a complete loop, run through two sides, run through one side, or be contained. Profiles and slots can be machined with multiple steps and by following straight or curved paths. A pocket is a contained feature of any shape that can be machined by either peripheral or slot cuts. Four possible pocket shapes include a cuboid, pyramid, cylinder, and cone. An end milling operation is capable of producing any custom shape, however the total cut length must be known in order to estimate the cost.
Profile: Complete
Profile: Side (0 ends, 1 ends, 2 ends)
Slot: Complete
Slot: Through (2 sides, 1 side, 0 sides)
Pocket: Cuboid, Pyramid
Pocket: Cylinder, Cone
Envelope
The smallest box, sometimes called a bounding box, that is able to contain the part. The X-Y-Z dimensions of this box describe the maximum length, width, and height of the part. In molding processes, the Z-axis (describing the part's height) is the parting direction of the mold.
Hot glue gun housing (4.38 x 3.75 x 0.59)
Tongs (6.09 x 2.12 x 2.00)
Trigger (1.13 x 2.66 x 0.94)
External undercut
A feature on the exterior of a part that will not allow a mold that contains it to slide away along the parting direction. An external undercut can be either a protrusion or a depression (hole or pocket) and requires an additional mold piece called a side-core to form its shape.
Part with external protrusion
Mold cannot separate
Part with external hole
Mold cannot separate
G
Gate
An opening at the end of a runner, which directs the flow of molten material into the mold cavity.
Gears
Cylindrical parts with teeth around their perimeter which can mesh with other toothed parts to transmit motion. (Includes: cogs, pinions, sprockets, etc)
Glass Transition Temperature (Tg)
he approximate midpoint of the brittle to rubbery temperature range of a polymer. The glass transition temperature of a polymer will often appear as a spike on a difference scanning calorimeter (DSC).
Gray Cast Iron
A cast iron that gives a gray fracture due to the presence of flake graphite. Often called gray iron.
Grooving
A turning operation in which a single-point tool moves radially, into the side of the workpiece, cutting a groove equal in width to the cutting tool. If the desired groove width is larger than the tool width, multiple adjacent grooves will be cut. A profiling cut can be performed to smooth the surface of multiple grooves. Special form tools can also be used to create grooves of varying geometries.
Grooving
Grooving (Form tools)
Gusset
A thin triangular support structure that joins the vertical side of a protrusion to the horizontal base from which it protrudes.
F
Face milling
An operation in which a face mill machines a flat surface of the workpiece in order to provide a smooth finish. The depth of the face, typically very small, may be machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes. For a rough operation, the recommended cutting speed and feed for face milling are used. A finish operation will lower the cutting feed according to the finish requirements.
Face milling operation
Face
Facing
A turning operation in which a single-point tool moves radially, along the end of the workpiece, removing a thin layer of material to provide a smooth flat surface. The cutting tool moves from the outer diameter to the center or inner diameter of the workpiece or can move in the opposite direction. The depth of the face, typically very small, may be machined in a single pass or may be reached by machining at a smaller axial depth of cut and making multiple passes. For a finish operation, the cutting feed is calculated based on the desired surface roughness and the tool nose radius.
Facing to center
Facing to inner diameter
Facing stock
The amount of material that will be removed from the end of a piece of bar stock by a facing or face milling operation, before the next workpiece is cut. The facing stock is used in determining how many workpieces a single piece of bar stock will yield.
Bar stock
Factor of safety
A multiplier that is applied to a calculated force requirement to arrive at a greater amount of force that is deemed safe.
Fasteners
Parts whose primary function is to hold two or more parts together.
Feature count
An estimate of how many features occur on a part. Any protrusion or depression on the main body of the part can count as a feature, including holes, slots, pockets, pins, ribs, bosses, etc. The feature count is the primary indicator of a part's complexity.
Knob (<10 features)
Toy Brick (<25 features)
Carrying Case (<50 features)
Stapler Housing (<100 features)
Rear Monitor Housing (<200 features)
Jewel Case Lid (<400 features)
Internet Router Housing (>400 features)
Feature quantity
The number of features with identical dimensions that are to be manufactured in the same way.
Feature spacing
The distance between two identical features, measured from the end of one feature to the start of the next. If multiple identical features exist at varied spacing, then the average distance between two neighboring features should be used.
Feature spacing (Milling)
Feature spacing (Turning)
Feed rate
The speed of the cutting tool's movement relative to the workpiece as the tool makes a cut. In some operations the tool feeds into the workpiece and in others the workpiece feeds into the tool. The feed rate is measured in inches per minute (IPM) and is the product of the cutting feed (IPR) and the spindle speed (RPM).
Feed system
Sometimes called the runner system or gating system, the feed system describes all of the channels in a mold that allow the molten material to feed into the cavities. This system may include the pouring basin, sprue, runner, riser, gate, etc.
Ferrous
Related to iron; derived from the Latin, ferrum. Ferrous metals are, therefore, iron-based metals.
Filler
A lightweight packing material, such as foam packing peanuts, that is used to fill empty space in the box and protect the packed parts.
Fittings
Parts that attach to the end of a pipe to redirect the flow of fluid. (Includes: attachments, connections, couplings, crosses, elbows, nozzles, reducers, tees, etc)
Fixture
The device used to secure the workpiece in the machine. The type of fixture selected will depend upon the workpiece size and shape, as well as the operations to be performed. Sometimes, a custom fixture must be designed and constructed to accommodate the workpiece. Also, the fixture setup time and workpiece load time may depend on the fixture type.
Fixture setup time
The time required to setup the fixture inside the machine. This time is added to the machine setup time.
Flanges
Flat disks or rings that are fastened around the perimeter, or at the end of, a pipe. (Includes: collars, disks, plates, rims, rings, etc)
Flash
The occurrence of molten material seeping out of the mold cavity and solidifying. Once the part is ejected, a thin layer of material will have formed attached to the part along the parting line.
Flexural Strength
The measure of a materials ability to withstand failure due to bending. Units of Flexural Strength are psi (English) and MPa (Metric).
Flute
A groove on the side of a cutting tool, such as an end mill or drill bit, that is between the cutting teeth. These grooves may be vertical, but typically form a helix to allow the material chips to be pulled away from the workpiece.
Fracture Toughness
A generic term for measures of resistance to extension of a crack. The term is sometimes restricted to results of fracture mechanics tests, which are directly applicable in fracture control. However, the term commonly includes results from simple tests of notched or precracked specimens not based on fracture mechanics analysis. Results from tests of the latter type are often useful for fracture control, based on either service experience or empirical correlations with fracture mechanics tests. See also stress-intensity factor.
Frames
Structures that surround empty space or non-structural elements and support connecting parts. (Includes: bodies, cages, structures, supports, etc)
H
Handles
Interfaces that are attached to another part and designed to be grasped by the user’s hand. (Includes: arms, cranks, grips, knobs, latches, levers, etc)
Hot tearing
A part defect, sometimes called hot cracking, which describes cracks that result from shrinkage. If a part is not allowed to shrink freely and encounters an obstruction, the solidified material will crack.
Hourly rate
The burdened hourly cost of manufacturing parts, manufacturing the tooling, or performing a secondary operation. This rate may include direct and indirect labor costs, overhead costs, as well as profit.
I
Idle operation
An operation in which the tool is not engaged in the workpiece. Such an operation may include a rapid tool movement, a tool replacement, repositioning the workpiece, inspecting the workpiece, etc.
Idle time
The time required for any tool movements that occur during an operation that do not engage the workpiece. This time includes approaching and retracting from the workpiece, moving between features, and changing tools. Most of these tool movements occur at the rapid travel rate.
Injection pressure
The pressure at which molten material is injected into a mold. Each material has a recommended injection pressure. However, the injection pressure may be adjusted based upon the machine being used and the geometry of the part.
Injection temperature
Sometimes referred to as the processing temperature or melt temperature, this property describes the temperature at which molten material is injected into the mold. The injection temperature is determined by the material being injected.
Inserts
Fasteners, typically cylindrical, that are inserted through a part, sometimes by force, to secure it in place. (Includes: anchors, keys, nails, pins, rivets, etc)
Interfaces
Parts whose primary function is to act as a point of contact for the user.
Internal core lifter
An additional mold piece that is used to form an internal undercut that cannot be accessed from the side of the part. Unlike a side-core, an internal core lifter enters the mold along the parting direction, not through the side, and is actuated by the ejection system.
Molding an internal protrusion - Step 1
Molding an internal protrusion - Step 2
Molding an internal protrusion - Step 3
Molding an internal hole - Step 1
Molding an internal hole - Step 2
Molding an internal hole - Step 3
Internal undercuts requiring lifters
Internal undercut
A feature on the interior of a part that will not allow a mold that contains it to slide away along the parting direction. An internal undercut can be either a protrusion or a depression (hole or pocket) and requires an additional mold piece to form its shape. Most internal undercuts require an internal core lifter. However, if the feature can be accessed through an open side of the part, a side-core can be used.
Part with internal protrusion
Mold cannot separate
Part with internal pocket
Mold cannot separate
Izod Impact Test
To measure impact strength or notch toughness, a test specimen, usually of square crossed section, is notched and held between a pair of jaws, then broken by a swinging or falling weight. When the pendulum of the Izod testing machine is released it swings with a downward movement and when it reaches the vertical the hammer makes contact with the specimen which is broken by the force of the blow. The hammer continues its upward motion but the energy absorbed in breaking the test piece reduces its momentum. A graduated scale enables a reading to be taken of the energy used to fracture the test piece. To obtain a representative result the average of three tests is used and to ensure that the results conform to those of the steel specification the test specimens should meet the standard dimensions laid down in BS 131. Contrast with Charpy test.
K
K-factor
In bending, the k-factor defines the location of the neutral axis in the material and is dependent upon several factors, such as the material, bending operation, bend angle, etc. The k-factor is calculated as the ratio of the distance of the neutral axis (measured from the inside bend surface) to the material thickness. Values for the k-factor are typically greater than 0.25 and cannot exceed 0.50.
Neutral axis
Bending diagram
L
Labor rate
The hourly rate that is paid to any workers for a specific task in the manufacturing process, such as setup, machine operation, or post-processing. The labor rate does not include any costs associated with material, equipment, or overhead. If the number of workers is not specified, the labor rate is the amount paid to all workers for an hour.
Labor rate per pound
The rate that is paid to any workers for a specific task based on the weight of material processed during that task. This rate does not include any costs associated with material, equipment, or overhead. If the number of workers is not specified, the labor rate is the amount paid to all workers.
Labor usage
The percentage of time for a task, such as the setup time or production time, where workers are paid at the specified labor rate. A manual labor task will have a usage of 100%, while a partially automated tasks will have a lower labor usage.
Linear Low Density Polyethylene (LLDPE)
A plastic predominantly used for film applications because of its toughness, flexibility and relative transparency. Typical products include grocery bags, garbage bags and landfill liners.
Liquid containers
Containers, typically cylindrical, that are used for storing liquids. (Includes: basins, beakers, bottles, bowls, buckets, cans, containers, cups, flasks, jars, jugs, mugs, pails, pitchers, pots, tanks, tubs, vials, vessels, etc)
Low Density Polyethylene (LDPE)
A low melting point polymer that is tough, flexible, transparent, and has stable electrical properties. Applications include flexible films like dry cleaning and grocery bags, flexible lids and bottles, wire and cable applications, and heat sealing applications.
M
Machine rate
The hourly rate that is charged for running a piece of manufacturing equipment, excluding any labor costs. The machine rate may include the equipment cost, auxiliary costs, maintenance, plant overhead, etc.
Magnesium
Chemical symbol Mg, Atomic number 12, atomic weight 24.312. A silvery, moderately hard, strong, and light metal. Used in ductile iron production, steel desulfurization, and chemical reduction. Growing use as substitute for aluminum and zinc in die castings, due to light weight, high strength and low cost.
Manual tool change time
The time required to manually change a tool in the spindle or tool changer, which includes the time to stop the spindle, remove the current tool, insert the new tool, and start the spindle again. A manual tool change is performed if the machine does not use an automatic tool changer, as well as for replacing a worn tool.
Material markup
A markup to the cost of purchased material that may include overhead costs of storing the material, any labor costs in handling or transporting the material, as well as profit.
Material removal rate
The rate at which material is cut away from the workpiece during a machining operation, measured as a volume per unit time, typically cubic inches per minute.
Material yield
The percentage of material used that yields finished parts. In one molding cycle, this describes the percentage of the shot that fills the part cavities.
Maximum Service Temperature
The highest recommended temperature that a polymer can withstand under no load and without a degradation of its properties. The Deflection Temperature measures the maximum temperature a polymer can withstand under load. The Maximum Service Temperature is also called the Maximum Operating Temperature.
Maximum wall thickness
The thickest wall or feature of a part. In molding processes, the maximum wall thickness is used to determine the cooling time because that section will require the most time to cool. In some parts, the thickest section can be easily identified (Trigger), but often several sections should be checked (Button). When measuring the maximum wall thickness of a given section, the smaller dimension is considered the thickness (Knob).
Trigger (t=0.19)
Stop Watch Button 2 (t=0.06)
Knob (t=0.50)
Mechanical Properties
Those properties of a material that reveal the elastic and inelastic reaction when force is applied, or that involve the relationship between stress and strain; for example, the modulus of elasticity, tensile strength, and fatigue limit. These properties have often been designated as "physical properties," but the term "mechanical properties" is preferred.
Melt loss
The percentage of material that becomes unusable, and hence lost, during the melting process. Melt loss is typically a result of oxidation during the melting and holding of the material.
Melting price
The price per pound of melting raw material in a foundry, which includes direct and indirect labor costs, equipment costs, and overhead.
Milling machine
A machine that rotates a cutting tool at high speeds and moves it into a fixed workpiece to cut away chips of material. A milling machine may be operated manually or by computer numerical control (CNC) to perform a series of operations. Such operations may include face milling, end milling, chamfer milling, drilling, boring, counterboring, reaming, tapping, or an idle operation.
Modulus of Elasticity
Also called elastic modulus and coefficient of elasticity. A measure of the rigidity of metal. The ratio of stress, below the proportional limit, to corresponding strain. Specifically, the modulus obtained in tension or compression is Young's modulus, stretch modulus or modulus of extensibility; the modulus obtained in torsion or shear is modulus of rigidity, shear modulus or modulus of torsion; the modulus covering the ratio of the mean normal stress to the change in volume per unit is the bulk modulus. The tangent modulus and secant modulus are not restricted within the proportional limit; the former is the slope of the stress-strain curve at a specified point; the latter is the slope of a line from the origin to a specified point on the stress-strain curve.
Mold class
Mold class refers to an industry standard provided by the Society of Plastics Industry (SPI) for classifying the quality and lifetime of molds. Class 105 (<=500 cycles): The least expensive type of mold, which can be constructed from cast metal or epoxy, and is to be used for prototypes only. Class 104 (<=100,000 cycles): A low priced mold with mold cavities typically constructed from aluminum or mild steel. Class 103 (<=500,000 cycles): A moderately priced mold, also the most common, requiring cavity and cores to be of a hardness of 28 R/C or higher. Class 102 (<=1,000,000 cycles): A high priced and high quality mold, requiring cavity and cores be hardened to 48 R/C and all other mold components be heat treated. Class 101 (>1,000,000 cycles): The most expensive and highest quality mold, requiring cavities and cores be hardened to at least 48 R/C and all other mold components be made of hardened tool steel.
Mold cost
The total cost of a mold or die, which may include the material, machining, auxiliaries, maintenance, etc.
Mold temperature
The temperature of the interior mold surfaces before the molten material is injected. Usually, cooling lines inside the mold keep this temperature low and aid in cooling the molten material.
Motor horsepower
The power required from a machine's motor to rotate the spindle during a machining operation. The spindle horsepower will typically be less than the machine's motor horsepower due to the machine efficiency being less than 100%. The motor horsepower required for any operation must be less than the rated horsepower of the machine.
Moving parts
Parts whose primary function requires that it be in motion
N
Neutral axis
In bending, the neutral axis describes the location in the material that is neither stretched nor compressed, and therefore remains at a constant length.
Neutral axis
Bending diagram
Nickel
Chemical symbol Ni. Element No. 28 of the periodic system; atomic weight 58.69. Melting point 1455ºC (2651ºF.); boiling point about 2900ºC (5250ºF.), specific gravity 8.90. Hard, silvery-white metal known primarily as an alloy to improve strength and corrosion resistance of other metals, notably steel. Nickel is a slightly magnetic metal, of medium hardness and high degree of ductility and malleability, with high resistance to chemical and atmospheric corrosion. Pure nickel is used in galvanic plating, where objects must be coated with nickel before they can be plated with chrome. When used as an alloying agent, it is of great importance in iron-based alloys in stainless steels and in copper-based alloys such as cupro-nickel as well as in nickel-based alloys such as Monel. About 65% of all nickel is used in the making of stainless steel. Its principal functions as an alloy in steel making: (1) Strengthens unquenched or annealed steels. (2) Toughens pearlitic-ferritic steels (especially at low temperature). (3) Renders high-chromium iron alloys austenitic. In amounts 0.50% to 5.00% its use in alloy steels increases the toughness and tensile strength without detrimental effect on the ductility. Nickel also increases the hardenability, thus permitting the steel to be oil- hardened instead of water quenched. In larger quantities, 8.00% and upwards, nickel is the constituent, together with chromium, of many corrosion resistant and stainless austenitic steels.
Non-ferrous Metals
Metals or alloys that are free of iron or comparatively so.
O
Operation
A specific task or step during the production of parts in a manufacturing process. Many processes, such as machining, sheet metal fabrication, or assembly require a carefully planned sequence of operations.
Operation time
The total time required to complete an operation. In machining, this includes both the cut time and idle time.
Order quantity
The order quantity or yield quantity is the number of parts required from a manufacturing process to fill a buyer’s total or annual order or to be used in a subsequent process. Due to the defect rates that are inherent to many manufacturing processes, a larger production quantity or run quantity must be manufactured to yield the desired order quantity.
Over-run distance
When machining a feature that is open on one or more sides, the tool may be allowed to move beyond the edge of the workpiece. This over-run distance (D) is measured from the edge of the workpiece to the center of the tool. Therefore, an over-run distance of zero will still allow the full feature to be machined.
Over-run distance (D)
Overflow well
A chamber which is attached to the mold cavity that fills with molten metal during injection. The first material to enter the mold is allowed to pass completely through and enter the overflow wells. This strategy prevents early solidification of the molten metal and provides a source of material to compensate for shrinkage. When the part cools, the molten material will shrink and additional material is needed.
P
Pack time
The average time required to pack a single part into a box. The average pack time should be based on the total time to pack the box, including the time to load the parts, add filler if needed, and seal the box. The pack time can reflect the time to manually pack the part or the time required from a machine that automatically performs the packing operations.
Pallet changer
The pallet is the moveable platform in a milling machine to which the fixture and workpiece are attached. A pallet changer allows another pallet to be loaded with a workpiece and then automatically changed with the pallet supporting a finished part. The pallet change time describes the complete time between the end of a machining cycle and start of the next cycle. Because workpieces are loaded while others are being machined, the workpiece load time need not be included in the machining cycle.
Panels
Thin, flat covers that are fastened to a surface to protect it or to seal an opening. (Includes: backings, covers, guards, etc)
Part catcher
A device that may be used in turning machines to catch a part after it is separated from the workpiece by a cut-off operation. The part catch time ( a component of the idle time) refers to any additional time required in the use of this device, such as moving in or out of position and catching the part.
Part spacing
The amount of spacing to be left between the parts when packed into a box, as well as the space adjacent to the side walls of the box. This space can be used to add filler.
Parting direction
The axis along which the two halves of a mold will separate to allow the part to be ejected.
Parting line
The line along a part where the mold halves separate. In a simple mold, this line will be straight. However, more complex molds may have a stepped or curved parting line.
Parting surface
The surface where the mold halves meet. In a simple mold, this surface will be flat. However, more complex molds may have many stepped or curved surfaces.
Parts per operation
The number of parts completed in a single operation when the operation acts on multiple parts at once or one part representing many. For example, a painting operation that paints 10 parts at once will complete 10 parts per operation. An inspection operation that weighs a single part out of every 10 parts will also "complete" 10 parts per operation. The "time per part" is equal to the operation time amortized over the parts per operation.
Pattern
A pattern is a replica of the desired part, used as tooling in many expendable mold processes. The pattern is used to form the shape of the cavity in the mold.
Pedals
Interfaces that are attached to another part and designed to be pushed by the user's foot.
Perimeter
The outer perimeter of the projected area of a part. The perimeter of any projected holes is not included.
Physical Properties
Properties other than mechanical properties, that pertain to the physics of a material and can usually be measured without the application of force; e.g., density, electrical conductivity, thermal expansion, reflectivity, magnetic susceptibility, lattice parameters, etc. This term often has been used to describe mechanical properties, but this usage is not recommended.
Pipes
Long, hollow cylindrical parts that allow the flow of fluid through their interior. (Includes: channels, conduits, hoses, tubes, etc)
Piping elements
Parts whose primary function is to allow the flow of fluid or attach to such a part.
Platen
A large plate onto which a mold half is mounted. Typically, one platen is stationary, while the other is movable. A larger machine typically has larger platen dimensions and can therefore accommodate a larger mold.
Poisson Ratio
The absolute value of the ratio of the transverse strain to the corresponding axial strain, in a body subjected to uniaxial stress; usually applied to elastic conditions. If a square bar is stressed in a testing machine in the direction of its length so that the length increases, there is a contraction in each opposite direction, which produces a decrease in the thickness of the bar. The ratio between the contraction at right angles to a stress and the direct extension is called the Poisson's ratio. Its value in steel is in the order of 0.28.
Polyethylene Terephthalate
Polyethylene Terephthalate (PET or PETE) has excellent toughness and good gas and moisture barrier properties. PET is used to make blow molded food and non-food containers (soda bottles), sheet applications, carpet and textile yarns, strapping, and molding compounds.
Post processing
Post processing refers to any operations that are performed after the primary process has been completed and before any secondary processes are performed. This may include inspecting, trimming, cleaning, or moving the parts.
Production markup
A markup to the production cost, which may be used for any costs not covered by the machine and labor rates, which is typically only the profit.
Production quantity
The production quantity or run quantity refers to the total number of parts that are manufactured, which may include any incomplete or defective parts. The defect rate for a given manufacturing process will determine the required production quantity to yield the desired order quantity.
Production rate
The amount of non-defective parts produced by a manufacturing process within a set time period. Typically, the production rate is given as the number of parts per hour.
Production time
The amount of time required for all machines in use to manufacture the production quantity of parts. The production time includes time when the machines are running (run time or uptime) and when they are down for maintenance or other tasks (down time). The production time does not include any setup time or post processing time.
Programming or layout time
The amount of time (hours) required to program (CNC) or manually layout the instructions for a series of machining operations. This time may include performing calculations, developing the program or instructions, and any testing or inspection that is required.
Projected area
The area of a part or feature that is projected onto the X-Y plane. In molding processes, this is the area projected onto the mold surface because the Z-axis is the parting direction. The projected area can be approximated by a percentage of the X-Y side of the envelope.
Connecting Rod (�25% of envelope)
Bobbin (�50% of envelope)
Small Paint Roller Cylinder (�75% of envelope)
Rear Monitor Housing (�100% of envelope)
Projected corner
Any corner that occurs on the projected area of a part. The corner does not need to be 90 degrees, but can be any angle or sharp curve. The number of these corners determine the complexity of the die needed to trim to the part.
Handle
Connecting Rod
Projected holes
Projected holes are through-holes that project empty space onto the X-Y plane and therefore appear as gaps in the projected area of the part. If the area projected by these holes is very small compared to that of the part, it can be ignored (Servo lever). For holes that project a larger area (Monitor housing), the area can be approximated as a percentage of the X-Y side of the envelope.
Servo Lever (Area can be ignored)
Front Monitor Housing (54% of envelope)
Propellers
Cylindrical parts with two or more blades that rotate to cause fluid flow and/or propulsion. (Includes: blades, fans, impellers, etc)
Punch
A punch is a tool that is forced into a piece of sheet metal in order to shear or deform the material. Punches are available in many shapes and sizes and can be used for a variety of processes. Many punches are cylindrical and the punch diameter determines the size of the hole or pocket being formed. In shearing processes (blanking or punching), the punch has a square edge to shear the material. In forming processes (bending or deep drawing), the punch has an edge radius.
Purchase weight
The total weight of material that must be purchased in order to manufacture the production quantity of parts.
R
Radial depth of cut
The depth of the tool along its radius in the workpiece as it makes a cut. If the radial depth of cut is less than the tool radius, the tool is only partially engaged and is making a peripheral cut. If the radial depth of cut is equal to the tool diameter, the cutting tool is fully engaged and is making a slot cut. In turning and boring operations, a single-point tool cuts at a depth relative to the workpiece radius. A large radial depth of cut will require a low feed rate, or else it will result in a high load on the tool and reduce the tool life. Therefore, a feature is often machined in several steps as the tool moves over the step-over distance, and makes another cut at the radial depth of cut.
Milling (Peripheral cut)
Milling (Slot cut)
Turning
Rapid tooling
Tooling for molding or casting processes that is quickly manufactured through high speed machining of aluminum or soft steel, or by using additive fabrication techniques, such as FDM or DMLS. Rapid tooling is often used in low volume production, where low cost tooling greatly reduces the part cost and a lower tool life is not a factor.
Rapid travel rate
The speed of the cutting tool, measured in inches per minute (IPM), when it is not engaged in the workpiece and rapidly moves from one position to another. The rapid travel rate is used to move between features as well as moving to and from the tool changing position.
Reaming
An operation in which a reamer enters the workpiece axially and enlarges an existing hole to the diameter of the tool. Reaming removes a minimal amount of material and is often performed after drilling to obtain both a more accurate diameter and a smoother internal finish. A finish reaming operation will use a slower cutting feed and cutting speed to provide an even better finish.
Reaming (Milling machine)
Reaming (Turning machine)
Reamed hole
Reconditioning cost
The cost of reconditioning scrap material to the proper chemical composition before it is reused, measured as a percentage of the original material cost.
Recycle ratio
In many processes, scrap material is generated from mold feed systems or defective parts and can be recycled by mixing it with unused material. The recycle ratio is the amount of scrap allowed to be recycled relative to virgin material. The scrap allowed to be recycled by this ratio is often less than the available scrap, resulting is some material waste.
Refractory
The ability to withstand heat without deforming or melting. Many clays, minerals, and even some metals are considered refractory materials.
Regrind ratio
Regrind refers to scrap material that is reground into pellets and then mixed with unused material for reuse. The regrind ratio is the allowable amount of regrind relative to virgin material. The scrap used for regrind can be generated from the mold runners and defective parts. The cost to regrind this material may include both equipment and labor, but should be less than the cost of raw material.
Remelt
Remelt refers to scrap material that is remelted and then mixed with unused material for reuse. The remelt ratio is the allowable amount of remelt relative to virgin material. The scrap used for remelt can be generated from the mold runners and defective parts. The cost to remelt this material may include both equipment and labor, but should be less than the cost of raw material.
Rib
A thin wall protrusion on a flat surface of a part, usually found in parallel clusters, that adds bending stiffness to the part.
Riser
A chamber attached to the runner system that fills with molten metal during injection to provide an additional source of material during cooling. When the part cools, the molten material will shrink and additional material is needed.
Rockwell Hardness
Measure of resistance to penetration when material is exposed to a pointed load. The Rockwell Hardness measurement produces hardness numbers related to the depth of residual penetration of a steel ball or diamond cone (brale) after a minor load of 10 kilograms has been applied to hold the penetrator in position. Under this condition, the major load is applied (either 60, 100 or 150 kilograms). This residual penetration is automatically registered on a dial when the major load is removed from the penetrator but the minor load is still applied. Various dial readings combined with different major loads, five scales designated by letters varying from A to H; the B and C scales are most commonly in use. For testing hard steels, a sphero-conical diamond is used with a 150 kg load, the result is read from the black scale on the dial and is prefixed with the letter C. A hardened tool steel would typically give a reading of 62Rc. For softer metals Scale B is used with a 1/16" diameter steel ball and a standard load of 100 kgs.
Runner
A channel in a mold that delivers the molten material to the mold cavities.
S
Scallop
In an end milling operation, a small cusp of material, called a scallop, sometimes remains between adjacent cuts. Scallops along vertical walls can be removed through a profiling operation. Scallops on horizontal surfaces result from using a ball end mill and can be minimized by using a smaller step-over distance relative to the tool diameter.
Scallop
Separating force
The outward force exerted on the mold halves caused by the injection of molten material during the mold filling stage. The separating force is the product of the cavity pressure and the projected area of the shot. The clamp force applied to the mold must be greater than this separating force in order to keep it securely closed while the material is injected.
Separating force
Setback
In bending, the setback refers to the distance from the bend line to the outside mold line.
Bending diagram
Setup time
The amount of time required to setup a process before production begins. The setup time may include the preparation of the material, machine, and tooling, as well as any testing or calibration that is needed.
Shear strength
The amount of shear stress a material can sustain, measured in units of force per unit area. Shear strength is commonly expressed as megapascals (MPa) or pounds per square inch (psi) of original cross section. The maximum shear stress that a material can withstand before eventually failing is called the ultimate shear strength.
Shearing force
The amount of force required to cut or remove a piece of material through shear, as is done in cutting, blanking or punching operations. The applied force must create enough shear stress in the material to exceed the ultimate shear strength, causing the material to fail and separate.
Shearing
Punching
Sheet border
The sheet border, or stock border, refers to the space between the edge of a piece of sheet stock and the blanks or parts closest to the edge that will be cut. This border may be different along the length and width of the sheet. After all parts have been cut, the sheet border will remain as scrap material. The sheet border is used in determining how many parts a single piece of sheet stock will yield.
Sheet stock (Rectangular blanks)
Sheet stock (Round blanks)
Shot
The amount of material that is injected or poured into a mold. The shot volume includes the volume of all part cavities, as well as the feed system which delivers the material. The amount of material forming the parts relative to the total shot volume is the material yield. The shot volume must be less than the shot capacity of the machine being used. The projected area of the shot describes the projected area of all mold space that fills with material.
Shrinkage
When a part is formed from molten material, the part will shrink as the material cools and solidifies. As a result, a shrinkage allowance is usually added to the size of the part.
Side-action
An additional mold device, such as a side-core, that is actuated through one of the four sides of the mold. One or more side-actions can act through any of the four sides of the mold. The number of sides with such a device, referred to as side-action directions, limits the number of possible cavities in the mold.
4 side-actions in 2 directions
Side-core
An additional mold piece that is used to form features that cannot be formed by the two mold halves, such as an external undercut. A side-core slides into the mold along one of its four sides and forms the shape of the undercut. A single side-core can be used to form multiple undercuts if they are accessible along the same side of the mold and are close together. An internal undercut can be formed by a side-core if it is accessible from the side of the part.
Molding an external protrusion
Molding an external hole
2 undercuts requiring 1 side-core
Internal undercut requiring side-cores
Sink marks
When molten material is injected into a mold, voids can occur if certain sections solidify first, caused by a low injection pressure or non-uniform wall thickness. The remaining material will fill these voids as it continues to cool and shrink. This shrinkage causes marks on the part where the material sunk into the void.
Spacers
Components that are placed between a fastener and a part to create a more precise or secure fit. (Includes: bushings, collars, grommets, rings, seals, sleeves, washers, etc)
Specific cutting energy
The amount of energy per unit volume to remove material from the workpiece during a machining operation, measured in horsepower per cubic inches per minute. The specific cutting energy, also known as unit power, is a material property but is also affected by the type of machining operation and the material and sharpness of the cutting tool. Values for specific cutting energy are typically in the range of 0.1 -2.5 hp/in^3/min (most steels have a value of 1.0-1.5 hp/in^3/min).
Specific heat
Specific heat capacity, or just specific heat, is the amount of energy that is required to raise the temperature of a given amount of material by one degree, typically measured in J/g-K or BTU/lb-F.
Speed control
In some turning operations, the diameter of the workpiece changes so the spindle speed (RPM) and cutting speed (SFM) can not both remain constant. Constant RPM will cause the cutting speed to decrease as the tool moves towards the center of the workpiece. In order to maintain constant SFM, the RPM is increased as the diameter decreases.
Spindle horsepower
The power required from the spindle to rotate a cutting tool (milling machine) or workpiece (turning machine) during a machining operation. The spindle horsepower is typically less than the machine's motor horsepower due to the machine efficiency being less than 100%.
Spindle speed
The rotational speed of the spindle in revolutions per minute (RPM). In a milling machine, the spindle speed describes the rotation of the attached cutting tool. In a turning machine, it describes the rotation of the attached workpiece.
Spindle torque
The torque produced by the spindle based upon the spindle horsepower and the spindle speed at which it is rotating.
Springback
In bending, residual stresses cause the material to spring back slightly after the bending operation. Due to this elastic recovery, it is necessary to over-bend a precise amount to achieve the desired bend radius and bend angle. The final bend radius will be greater than initially formed and the final bend angle will be smaller. The ratio of the final bend angle to the initial bend angle is defined as the springback factor, Ks. The amount of springback depends upon several factors, including the material, bending operation, and the initial bend angle and bend radius.
Springback
Sprue
The main channel through which molten material enters a mold. The sprue often connects to a series of runners that deliver the material into the mold cavities.
Stainless Steel
Strictly speaking, stainless steel is a trade name, an alloy originally patented in 1916 by English metallurgist Harry Brearley, containing a maximum of 0.70% carbon and 9-16% chromium. In the United States, American Stainless Steel Co. of Pittsburgh, PA, produces a chrome-iron alloy under the "stainless steel" patent which it owns. In more general terms, stainless steel is a corrosion resistant steel containing at least 10% chromium. According to the American Iron and Steel Institure (AISI), a steel is considered "Stainless" if it contains 4% or more chromium. Stainless Steels are characterized by their resistance to organic acids, weak mineral acids, and atmospheric oxidation, and their ability to retain their strength at high temperatures. The most common grades of stainless steel in the US are: Type 304, austenitic (chromium-nickel); Type 316, austenitic with 2%-3% molybdenum; Type 409, ferritic (low chromium) for high-temperature use; Type 410, heat-treatable martensitic (medium chromium) with a high strength level; and Type 430, a ferritic general-purpose grade with some corrosion resistance.
Step-over distance
In order to machine a feature that is wider than the width of a single cut, the tool must make several cuts, stepping to the side after each one. This step-over distance is equal to the radial depth of cut for each cut and must be less than or equal to the tool diameter. The size of the step-over distance will determine the scallop height between each step.
Peripheral cut
Slot cut
Stock
The piece of material from which the workpieces or blanks are cut. If the workpieces are available in the desired size, the stock dimensions will equal those of the workpiece. However, a larger piece of bar stock or sheet stock is typically purchased and the workpieces are cut from it. The number of workpieces that can be cut from a piece of stock depend on the workpiece size and other spacing parameters (sheet border, web width, bar end, cutoff width, facing stock).
Sheet stock (Rectangular blanks)
Bar stock
Sheet stock (Round blanks)
Stock utilization
The percentage of material from a piece of stock that is used as a workpiece/blank or final part. When cutting from a piece of stock, any material left attached to the stock or lost in the cutting process is considered scrap. Such scrap material includes the sheet border and web width in the case of sheet stock, and the bar end and cutoff width in the case of bar stock.
Storage containers
Large containers that are used for storing multiple items. (Includes: baskets, bins, boxes, cases, containers, crates, drawers, receptacles, etc)
Stress
Force per unit area. True stress denotes stress determined by measuring force and area at the same time. Conventional stress, as applied to tension and compression tests, is force divided by original area. Nominal stress is stress computed by simple elasticity formula. It can be divided into components, normal and parallel to the plane, called normal stress and shear stress, receptively. Nominal stress, ignoring stress raisers and disregarding plastic flow, in a notch bend test, for example, it is bending moment divided by minimum section modulus. See also residual stress.
Stress Strain Curve
A graph in which stress (load divided by the original cross sectional area of the test piece) is plotted against strain (the extension divided by the length over which it is measured). The slope of the sress strain curve, in the elastic region, is used to determine the modulus of elasticity.
Structural elements
Parts whose primary function is to form the shape of a product and/or support the weight of other parts.
Surface area
The total area of all surfaces that compose a part.
Surface patch
A portion of a part’s surface that is either flat or smoothly curved. The boundary of a surface patch is a sharp corner or curve, where another surface patch begins. The number of surface patches that comprise a part is an indication of the part’s complexity.
Surface roughness
The roughness of a part's surface resulting from a manufacturing process. Surface roughness is typically measured as the arithmetic average (Ra) or root mean square (RMS) of the surface variations, measured in microinches or micrometers. A typical primary manufacturing process results in a surface roughness of 32-250 microinches and finishing operations can lower the roughness to 1-32 microinches.
Switches
Small interfaces that are designed to be pushed or rotated by the user’s fingers or hand. (Includes: buttons, dials, knobs, triggers, wheels, etc)
T
Tapping
An operation in which a tap enters the workpiece axially and cuts internal threads into an existing hole. The existing hole is typically drilled by the required tap drill size that will accommodate the desired tap. On a milling machine, the threads may be cut to a specified depth inside the hole (bottom tap) or the complete depth of a through hole (through tap).
Tapping (Milling machine)
Tapping (Turning machine)
Tapped hole
Tensile Strength
The amount of longitudinal stress a material can sustain when in tension, measured in units of force per unit area. Tensile strength is commonly expressed as megapascals (MPa) or pounds per square inch (psi) of original cross section. The amount of stress that a material can withstand before it yields and plastically deforms is referred to as the tensile yield strength. The maximum stress that a material can withstand before eventually failing is called the ultimate tensile strength. Tensile strength is measured by placing a standard test piece in the jaws of a tensile machine, gradually separating the jaws, and measuring the stretching force necessary to break the test piece.
Thermal Conductivity
The measure of how rapidly heat is conducted through a material, measured in W/m-K or BTU-in/hr-ft2-F.
Thermal diffusivity
A measure of the rate at which heat flows through a material. Thermal diffusivity, typically measured in mm^2/s or in^2/hr, is equal to the thermal conductivity divided by the product of specific heat and density. The thermal diffusivity of most common polymers ranges from 0.09 to 0.14 mm^2/s (0.50 - 0.78 in^2/hr).
Thread cutting
A turning operation in which a single-point tool, typically with a 60 degree pointed nose, moves axially, along the side of the workpiece, cutting threads into the outer surface. The threads can be cut to a specified length and pitch and may require multiple passes to be formed.
Thread cutting operation
Thread pitch
Pitch is a measure of the spacing between threads. The English standard is to measure pitch as the number or threads per inch (TPI), while the Metric standard is the distance in millimeters (mm) between threads.
Threaded fasteners
Fasteners with either external or internal threads. (Includes: bolts, nuts, screws, etc)
Through-hole
A hole that extends completely through a portion of a part and therefore is open at both ends.
Titanium
Chemical symbol Ti. Element No. 22 of the periodic system; atomic weight 47.90; melting point about 1668ºC (3270ºF.); boiling point over 3287ºC (5430ºF.); specific gravity 4.5. A bright white metal; very malleable and ductile. Its principal function has been as an alloy in steel making, but now is being used extensively (especially in aviation and aerospace) because of its high strength, light weight, and good corrosion resistance. As an alloying element in steel, tin: (a) reduces martensitic hardness and hardnability in medium chromium steels. (b) prevents formation of austenite in high-chromium steels. (c) prevents localized depletion of chromium in stainless steel during long heating. (d) added in small amounts give a finer grain size. (e) acts as a carbide stabilizer in austenitic stainless steels and is used to prevent intercrystalline corrosion, commonly termed "weld decay". Titanium carbide is also used with tungsten carbide in the manufacture of hard metal tools.
Tolerance
Also referred to as dimensional accuracy, tolerance is the amount of deviation in a particular dimension of a part, which results from the manufacturing process.
Tool change distance
The distance that the tool must travel between the workpiece and the location that is required for a tool change. This distance is traversed at the rapid travel rate before and after a tool change. This distance depends upon both the workpiece and the tool, so the average distance should be used.
Tool diameter
The diameter of the cutting portion of a cylindrical cutting tool. The cutting portion is the length of the tool containing the flutes or teeth that cut the material.
Tool nose radius
In some turning operations, the single-point tool used for finishing has a rounded front corner or "nose". The radius of the tool nose, along with the cutting feed, will determine the surface roughness formed by the finishing operation. For a given cutting feed, a larger nose radius will provide a better finish.
Turning operation
Tools
Parts that are held in the user's hand and used to perform a task. (Includes: implements, instruments, utensils, etc)
Tooth
A sharp edge along the circumference of a cutting tool, such as an end mill or drill bit, that cuts into the workpiece. Cutting tools may have one or many teeth, but 2 or 4 teeth are the most common.
Toughness
(1) Capacity of a metal to absorb energy and deform plastically before fracturing. Usually measured in a notch impact test, high impact values indicating high toughness, but the area under the stress-strain curve in tensile testing is also a measure of toughness. (2) The ability of a metal to rapidly distribute within itself both the stress and strain caused by a suddenly applied load, or more simply expressed, the ability of a material to withstand shock loading. It is the exact opposite of "brittleness" which carries the implication of sudden failure. A brittle material has little resistance to failure once the elastic limit has been reached.
Turning
A turning operation in which a single-point tool moves axially, along the side of the workpiece, removing material to form different features, including steps, tapers, chamfers, and contours. These features are typically machined at a small radial depth of cut and multiple passes are made until the end diameter is reached. For a finish operation, the cutting feed is calculated based on the desired surface roughness and the tool nose radius.
Step
Taper
Chamfer
Contour
Turning machine
A machine, also called a lathe, which feeds a cutting tool into a rotating workpiece to cut away chips of material. A turning machine may be operated manually or by computer numerical control (CNC) to perform a series of operations. External operations which modify the outer diameter of the workpiece include facing, turning, grooving, cut-off, and thread cutting. Internal operations which modify the inner diameter of a part include drilling, boring, reaming, and tapping.
U
Undercut
A feature on a part that will not allow a mold that contains it to slide away along the parting direction. An undercut can be either a protrusion or a depression (hole or pocket) and is described as being either external or internal. An undercut requires an additional mold piece, such as a side-core or an internal core lifter, to form its shape.
Uniform cross section
A part whose cross section does not change along any one axis, disregarding any draft angle.
Unit power
The amount of power required to remove one cubic inch of material from the workpiece during a machining operation, measured in horsepower per cubic inches per minute. Unit power, also known as specific cutting energy, is a material property but is also affected by the type of machining operation and the material and sharpness of the cutting tool. Values for unit power are typically in the range of 0.1-2.5 hp/in^3/min (most steels have a value of 1.0-1.5 hp/in^3/min).
Unscrewing device
An additional mold piece that is used to form threaded features (internal or external). External threads on a feature perpendicular to the parting direction can be formed by the two mold halves. However, other external threads and all internal threads require an unscrewing device. The device is inserted into the mold to allow the threaded feature to form and is then unscrewed to be removed.
External threads on Y axis
Mold can form threads
External threads on Z axis
Mold cannot separate
Internal threads
Mold cannot separate
Uptime
The amount of time that machines are running during the manufacture of parts, also called the run time. The uptime is often expressed as a percentage of the total production time, which includes the down time.
V
V bending
A sheet metal bending method in which a V-shaped punch presses a piece of sheet metal into the die opening of a V-die. The die opening is a V-shaped groove in the die plate. The width of this opening divided by the sheet thickness is called the die ratio and typically ranges from 6 to 18.
V bending
Volume The amount of space inhabited by a part. The volume of a part can be approximated by the percentage of the envelope volume.
Stereo Handle (�5% of envelope)
Bracket (�15% of envelope)
Dust Collection Turbine (�25% envelope)
Single Gear (�35% envelope)
Warping
The permanent bending of a part that occurs when certain section of the part shrink faster than others, as result of a non-uniform cooling rate.
Web width
The space between adjacent blanks or parts that are to be cut from a piece of sheet stock. When all parts are cut, this web of material remains attached to the sheet border and is scrap material. The web width is used in determining how many parts a single piece of sheet stock will yield.
Sheet stock (Rectangular blanks)
Sheet stock (Round blanks)
Wheels
Smooth, cylindrical parts that rotate. (Includes: bearings, cams, casters, disks, pulleys, rings, rollers, tires, etc)
Wipe bending
Wipe bending, also called edge bending, is a sheet metal bending method in which a sheet is held between a wipe die and pressure pad, and a punch presses against the edge of the sheet. The sheet will bend against the radius of the edge of the wipe die.
Wipe bending
Workpiece
A piece of material that is secured in a fixture and machined into the final part. The workpiece is often cut from a larger piece of stock material and can be a sheet (blank), a standard extruded shape (solid bar, hollow tube, or shaped beam), a custom extrusion, or any prefabricated part such as a casting or forging. Each workpiece shape has certain dimensions that are used in planning the machining operations.
Flat sheet
Round bar
Rectangular bar
Hexagonal bar
Round tube
Rectangular tube
I-beam
L-beam
T-beam
U-beam
Z-beam Custom extrusions
Workpiece clearance
The safe distance away from the workpiece at which the cutting tool can switch from the cutting feed rate to a rapid travel rate. This distance traveled before engaging the workpiece, as well as exiting from the workpiece, is included in the cut length.
Side approach
Top approach
Workpiece load time
The time required to load the workpiece into the machine and secure it to the fixture. The load time can depend on the size, weight, and complexity of the workpiece, as well as the type of fixture.
Yield
Evidence of plastic deformation in structural materials. Also called plastic flow or creep.
Youngs Modulus
The coefficient of elasticity of stretching. Within the limits of elasticity, the ratio of the linear stress to the linear strain is termed the modulus of elasticity or Young's Modulus and may be written Young's Modulus, Modulus of Elasticity or E =(Stress/Strain). It is this property that determines how much a bar will sag under its own weight or under a loading when used as a beam within its limit of proportionality. For steel, Young's Modulus is of the order of 200,000 N/mm^2 or 200 MPa.
Zinc
Chemical Symbol Zn. Element No. 30 of the periodic system; atomic weight 65.38. Blue-white metal; when pure, malleable and ductile even at ordinary temperatures; melting point 419ºC (787ºF.), specific gravity 7.14. Can be electrodeposited; it is extensively used as a coating for steel, especially steel destined for use in construction, transportation, and electrical equipment. Sheet zinc finds many outlets, such as dry batteries, etc. Its most important alloy is brass. Of great importance in die casting, although new ZA (zinc-aluminum) alloy is becoming a major force in die casting. Compounds and dusts used by agricultural, chemical, paint, and rubber industries.
