TERM PAPER MEC-104

THE GRINDING PROCESS

SUMMITTED TO: SUBMITTED BY:

MR. RAKESH KUMAR. . HAZRAT BELAL

. ROLL NO:RB4903-B43.

REGISTRATIONID:10901869

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CONTENTS ITEMS PAGES NO:

1. ACKNOWLEDGEMENT 3

2. INTRODUCTION 4

3. THE GRINDING MACHINE. 5

4. THE GRINDING WHEEL. 5

5. THE TYPES OF GRINDING WHEEL. 6

6. MECHANISM OF THE GRINDING. 6

7. TEMPERATURE 7

8. SPARKS 7

9. EFFECT OF TEMPERATURE. 7

10. SUFACE GRINDING PROCESS 8

11. CYLINDRICAL GRINDING PROCESS 9

12. OD GRINDING PROCESS 9

13. ID GRINDING PROCESS 10

14. CENTRELESS GRINDING PROCESS 10

15. BENCH GRINDING PROCESS 11

16. ANGLE GRINDING PROCESS. 12

17. TOOL AND CUTTER GRINDING PROCESS 12

18. RADIUS GRINDING PROCESS 13

19. CONCLUSON 14

20. REFERENCE 15

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ACKNOWLEDGEMENT

I HAVE GREAT SENSE OF HAPPINESS AND PRIDE IN WRITING THIS TERM PAPER. I HAVE WITNESSED THE UNTIRING EFFORTS MADE BY MY MANUFACTURING TEACHER MR.RAKESH KUMAR. I WOULD LIKE TO THANK MY FATHER IN GIVING ME IDEAS FOR MAKING THIS TERM PAPER. I WOULD LIKE TO THANK THE AUTHOR OF THE BOOKS WHICH I USED FOR REFERENCE. I WOULD LIKE TO THANK THE HOST AND CREATOR OF THE WEB SITES FROM WHICH I GOT THE INFORMATION ABOUT THE TERM PAPER.

HAZRAT BELAL

B.TECH (ME)

10901869

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THE GRINDING PROCESS

INTRODUCTION:

The grinding is a mechanical process that uses an abrasive wheel as the cutting tools. Dynamic analysis of the grinding process necessary to reduce the surface waviness and roughness induced by vibrations and to offer a machining accuracy in the order of nanometres. Grinding practice is a large and diverse area of manufacturing and tool making. It can produce very fine and accurate finishes and dimensions. It is basically used for machining very hard materials i.e. cutting larger chips with cutting tools such as tool bits or milling cutters and until recent decades it was the only practical way to machine such materials as hardened steels. It is usually better suited to taking very shallow cuts such as reducing a shaft's diameter by half.

The grinding is a subset of cutting as the grinding is a true metal cutting process. Each grain of abrasive functions as a microscopic single-point cutting edge and shears a tiny chip that is conventionally called a cut chip as in turning, milling, drilling, tapping, etc. However, among people who work in the machining fields, the term cutting is often understood to refer to the macroscopic cutting operations and grinding is often mentally categorized as a separate process. This is why the terms grinding are usually used in contradistinction in shop-floor practice, even though technically grinding is a subset of cutting.

The similar abrasive cutting processes are lapping and sanding. Lapping is process in two surfaces are rubbed together with an abrasive between them by hand movement or by way of a machine. And Sandpaper is a form of paper that is used where an abrasive material has been fixed to its surface.

Abrasive machining and advanced machining processes are often necessary and economical when the workpiece hardness is high , the materials are brittle or flexible, part shapes are complex and surface finish and dimensional tolerance requirement is high. The conventional abrasive basically of aluminium oxide and silicon carbide and super abrasive consisting of cubic boron nitrite and diamond. Friability of the abrasive grains is an important factor as the shape and size of the grains.

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The grinding process is a mechanic process in different types machines are used for cutting different work-piece. The grinding process is used for large scale material removal by varying process parameters. However this is a rough grinding operation with possibly detrimental effect on the workpiece surface and its integrity. It can be economical in specific application and compete favourably with the machining process.

THE GRINDING MACHINE:

A grinding machine is a machine tool used for grinding, which is a type of machining using an abrasive wheel as the cutting tool. Each grain of abrasive on the wheel's surface cuts a small chip from the workpiece via shear deformation. The grinding machine consists of a power driven grinding wheel spinning at the required speed (which is determined by the wheel’s diameter and manufacturer’s rating, usually by a formula) and a bed with a fixture to guide and hold the work-piece. The grinding head can be controlled to travel across a fixed work piece or the workpiece can be moved whilst the grind head stays in a fixed position. Very fine control of the grinding head or table’s position is possible using a vernier calibrated hand wheel, or using the features of NC or CNC controls.

Grinding machines remove material from the workpiece by abrasion, which can generate substantial amounts of heat; they therefore incorporate a coolant to cool the workpiece so that it does not overheat and go outside its tolerance. The coolant also benefits the machinist as the heat generated may cause burns in some cases. In very high-precision grinding machines (most cylindrical and surface grinders) the final grinding stages are usually set up so that they remove about 200nm (less than 1/100000 in) per pass - this generates so little heat that even with no coolant, the temperature rise is negligible.

THE GRINDING WHEEL:

It is an expandable wheel that is composed of an abrasive compound. These wheels are used in grinding machines. The wheel is made from a matrix of coarse particles pressed and bonded together to form a solid, circular shape, various profiles and cross sections are available depending on the intended usage for the wheel. They may also be made from a solid steel or aluminium disc with particles bonded to the surface.

Materials used are generally silicon carbide and diamond with a vitrified bonding agent. In production grinding wheel a wide array of materials is used. Wheels with different abrasives, structure, bond, grade, and grain sizes are available. The abrasive is the actual cutting material such as zirconium aluminum cubic boron nitride, oxide, manufactured diamonds, ceramic aluminum oxide, aluminum oxide etc. The abrasive is selected based on the hardness of the material being cut. The structure of the wheel refers to the density of the wheel i.e. bond and abrasive versus airspace.

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A less-dense wheel will cut freely and has a large effect on the surface finish of the workpiece. A less dense wheel is able to take a deeper or wider cut with less consumption of coolant as the chip clearance on the wheel is greater. The grade of the wheel determines how tightly the bond holds the abrasive. Grade affects almost all considerations of grinding, such as wheel speed, coolant flow, maximum and minimum feed rates and grinding depth. Grain size determines the physical abrasive size in the wheel. A larger grain will cut freely, allowing fast cutting but with a poor surface finish. Ultra-fine grain sizes are for precision finish work where a fine surface finish is required. The wheel bonding agent determines how the wheel holds the abrasives. This affects finish, coolant, and minimum/maximum wheel speed.

The manufacture of these wheels is a precise and tightly controlled process, due not only to the inherent safety risks of a spinning disc, but also the composition and uniformity required to prevent that disc from exploding due to the high stresses produced on rotation.

THE TYPES OF GRINDING WHEEL:

The selection of the grinding wheel depends on the grinding operation to be performed by the wheel. There are arrays of wheel to be select.

(1) Straight wheel.

(2) Cylinder wheel.

(3) Tamper wheel.

(4) Saucer wheel.

(5) Straight cup.

(6) Dish cup.

(7) Diamond wheel.

MECHANISM OF THE GRINDING PROCESS:Grinding is basically a chip removal process in which the cutting tool is an individual abrasive grain. The following are the major factors that differentiate the action of a single grain from that of a single-point tool:

(a) The individual grain has an irregular geometry and is spaced randomly along the periphery of the wheel.

(b) The average rake angle of the grains is highly negative:-60 degree or even lower. Consequently, the shear angle is very low.

(c) The radial positions of the grains in the grinding wheel vary.

(d) The cutting seeds of the grinding wheels are very high, typically 30 m/s(6000ft/min).Page | 6

The mechanics of the grinding and its variables can be best studied by analysing the surface-grinding operation. A grinding wheel of diameter d is removing a layer of the metal at a depth d which is known as the wheel depth of cut. An individual grain on the periphery of the wheel is moving at a tangential velocity V and the work piece is moving with a velocity v.

TEMPERATURE:Temperature rise in the grinding process is an important consideration because it can adversely affect the surface properties and cause residual stresses on the work piece. Furthermore temperature gradients in the work piece can cause distortion by different thermal expansion and contraction. When a portion of the heat generated is conducted into the workpiece the heat expands the part being ground, thus making it difficult to control dimension accuracy. The work piece expands in grinding is mainly converted into heat.

The surface temperature rise has been found to be a function of the total ratio of the total input to the to the surface area ground.

SPARKS:

The sparks observed in the metal grinding are actually glowing chips, the glowing occurs because of the exothermic reaction of the hot chips with the oxygen in the atmosphere. Sparks have not been observed with any metal ground in an oxygen-free environment. The colour, intensity and shape of the spark depends on the composition of the metal being ground. It is suggested that some of the spherical particles may also be produced by plastic deformation and rolling of the chips at the grit-workpiece interface during grinding.

EFFECT OF TEMPERATURE:(A) TEMPERING: Excessive temperature rise cause by grinding can temper and soften the

surface of the steel component which is often ground in the hardened state.

(B) BURNING: if the temperature is excessive the surface may burn. The burning produces a bluish colour on steels which indicates oxidation at high temperature. A burn may not be objectionable in itself. However the surface layers may undergo metallurgical in it. High temperature in grinding may also lead to thermal cracking of the surface of the workpiece.

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(C) RESIDUAL: Temperature changes and gradients within the workpiece are mainly responsible for residual stresses in grinding. The residual stress can usually be lowered by using softer grade wheels, lower wheel speeds and higher work speeds.

THE TYPES OF GRINDING PROCESS

The selection of the grinding operations is determined by the size, shape, features and desired production rate required for the process:

1. Surface grinding process.2. Cylindrical grinding process.3. Bench grinding process.4. Angle grinding process.5. Tool and cutter grinding process.6. Angle grinding process.7. Radius grinding process.

SURFACE GRINDING PROCESS:Surface grinding is the most well-known process of the grinding operations. A rotating wheel is used in the surface grinding which is used for grinding flat surfaces. However, the grinding wheel is not limited to just a cylindrical shape but it can have a myriad of options that are useful in transferring different designs to the object being worked on. When surface grinding an object takes the shape of the wheel will be transferred to the material of the object like a mirror image. The diamonds are used to remove the abrasive material which is unwanted and to give the desired geometry to the work piece. Surface grinding is a finishing process that smooths the surface of metallic or non metallic materials and gives them a more refined look. The surface grinder is comprised of an abrasive wheel, a work-holding device known as a chuck either electromagnetic or vacuum and a reciprocating table. Depending on the material being worked on and the desired surface finish the wheel's abrasive material can vary from aluminium oxide to silicon carbide and from diamond to cubic boron nitride. The chuck is a device that is used to hold the material in place while it is being worked on. It can do this one of two ways- metallic pieces are held in place by a magnetic chuck while non-metallic pieces are vacuumed in place. During the grinding process, the work piece must be flooded with a coolant so as to keep it cool and also to keep the excess shavings from building up. There are different types of coolants that are used depending on the material that

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is being worked on. The most common are: water-soluble chemical fluids, water-soluble oils and synthetic oils. In applying the coolant, care should be taken to apply the liquid directly to the location of the grind. It must be ensured the coolant reaches the material and is not deflected by the grinder wheels at high speeds. Typical work piece materials include cast iron and minor steel. These two materials don't tend to clog the grinding wheel while being processed. Other materials are aluminium, stainless steel, brass and plastics. The three most important factors to consider when surface grinding is: the material of the grinding wheel, the material of the piece being worked on, and the grinding fluid. If proper grinding fluid is not used then the surface finish will not be completely smooth. When grinding at high temperatures, the material tends to become weakened and is more inclined to be corroded. This can also result in a loss of magnetism in materials where this is applicable. The tolerances that are normally achieved with grinding are 2 × 10−4inches for a grinding a flat material and 3 × 10−4inches for a parallel surface. When working with any type of grinder, one should always be cognizant of safety procedures in order to avoid injury.

CYLINDRICAL GRINDING PROCESS:The cylindrical grinder are the class of grinding machine which are used on the work piece that are symmetrical about an axis of rotation i.e. cylinder. The cylindrical grinding is also known as the centre-type grinding called which used in the removing the cylindrical surfaces and shoulders of the work piece. The work piece is mounted and thus rotated by a work piece holder also known as centre driver. Both the tools and the work piece are rotated with the help of separate motors and at different speeds. The axes of rotation tool can be adjusted to produce the desired variety of shapes.

THE TYPES OF CYLINDRICAL GRINDING PROCESS:

1. OD GRINDING PROCESS.

2. ID GRINDING PROCESS.

3. CENTERLESS GRINDING PROCESS.

OD GRINDING PROCESS:

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An OD grinder grinds the outer diameter (OD) of the work piece which held on one or both ends of the work piece. Usually, the work piece is held between centres and rotated by a faster spinning grinding wheel. Great care should be taken when the OD comes closer to finished size as the tool can be over grinded.

ID GRINDING PROCESS:

An ID grinder is that which grinds the inside diameter (ID) of a work piece but this process tends to be a longer process than OD grinding process as the ID grinding stone is smaller in size and requires the operator to make smaller cuts from the tool to ensure perfect size of the work piece.

CENTRELESS GRINDING PROCESS:

The Centreless grinding is a method of material removal through grinding. A centerless grinder is a type of OD grinder where the work piece is supported on the either end and held against the grinding wheel by a second grinding wheel which is smaller in size which is turning at a slower rpm and is known as a regulating wheel while resting the work piece on a work blade. These machines can be used in feed and through feed mode. It's the relationship among these three basic components i.e. the grinding wheel, the regulating wheel and work blade which that makes the difference between a successful centerless grinding application and bad grinded parts.

CENTRELESS GRINDING MACHINE.

Centerless grinding is much easier to combine with automatic loading procedures than the centered grinding through feed grinding process where the regulating wheel is held at a slight angle from the horizontal to the part so that there is a force feeding the part through the grinder which is particularly very efficient in this process. An angular adjustment of 0 to 8 degrees is provided in the machine for the very purpose. Unlike in the centre-type or chucker-type grinding process the parts

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are made using a centerless process that does not require centre holes drivers or work head fixtures. Instead of that the workpiece is supported on its own outer diameter by a work blade located between a high speed grinding wheel and a slower speed regulating wheel which has a smaller diameter. Centerless grinding is found in shops in which high volume production runs. It is an important segment for the technology. Centerless grinding is successfully applied to manufacture of parts ranging from hypodermic needles to bowling balls. The principles of the process remain the same regardless of the workpiece.

The Centerless Grinding is classified into the following types:

1. Through feed grinding process.

2. Plunge grinding process.

THROUGHFEED GRINDING PROCESS:

In the Throughfeed grinding the regulating wheel is inclined creating an angle relative to the grinding wheel. This angle allows the regulating wheel to perform the specific dual purpose of rotating the work piece against the grinding wheel. And driving the workpiece across the grinding wheel to perform the operation. The work piece is fed into the machine along the work blade. The regulating wheel can be swiveled relatively to the grinding wheel. To accomplish the job and to use the full width of the grinding wheel, line contact between the workpiece, grinding wheel and regulating wheel should be maintained. Therefore, the regulating wheel must be trued with a diamond block located on the truing attachment. The diamond block is a device that adjusts the diamond contact relative to the workpiece height above the grinding and regulating wheel centerline.

PLUNGE GRINDING PROCESS:

Plunge grinding is a centred form of grinding in which the wheel plunges radically into the part. The work piece is placed between the wheels on a work blade and grinding wheel is plunged into the workpiece. Grinding of cylindrical parts in cylindrical or centerless grinding, where the infeed of the grinding wheel is limited to radial movements and no cross slide movement.

BENCH GRINDING PROCESS:It is also known as pedestal grinder is a machine used to drive an abrasive wheel. Depending on the grade of the grinding wheel it may be used for sharpening cutting tools such as lathe tools or drill bits. Alternatively it may be used to roughly shape metal prior to welding or fitting. A wire brush wheel or buffing wheels can be interchanged with the grinding wheels in order to clean or polish

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work-pieces. Contrast this with the angle grinder and grinding machine. Grinding wheels designed for steel should not be used for grinding softer metals, like aluminium. The soft metal gets lodged in the pores of the wheel and expands with the heat of grinding. This can dislodge pieces of the grinding wheel.

ANGLE GRINDING PROCESS:It is also known as a side grinder is a handheld power tool used for cutting, grinding and polishing operations. Angle grinders can be powered by an electric motor, petrol engine or compressed air as per the application. The motor drives a geared head at a right-angle on which is mounted an abrasive disc that can be renewed form time to time. Angle grinders typically have an adjustable guard and a side-handle for two-handed operation. The angle grinding may be used both for removing excess material off a piece of material or simply cutting the workpiece. There are many different kinds of discs that are used for various materials and tasks such as cut-off discs (diamond blade), abrasive grinding discs, grinding stones, wire brush wheels and polishing pads. The angle grinder has large bearings to counter side forces generated during cutting unlike a power drill.

Angle grinders are widely used in metalworking, construction and emergency rescues. They are commonly found in workshops, service garages and auto body repair shops. There are a large variety of angle grinders to choose from when trying to find the right one for the job. The most important factors in choosing the right grinder are the disc size and the powerful of the motor. Other factors include power source, rpm, and arbour size. Generally disc size and power increase together. Disc size is usually measured in inches or millimetres Common disc sizes for angle grinders are 4, 4.5, 5, 6, 7, 9 and 12 inches. Discs for pneumatic grinders are smaller in size. Pneumatic grinders are generally used for lighter duty jobs where more precision is required. This is likely because pneumatic grinders can be small but powerful while it is harder for an electric grinder to maintain adequate power with smaller size. Electric grinders are used for larger and heavy duty jobs. There are small electric grinders and large pneumatic grinders.

TOOL AND CUTTER GRINDING PROCESS:A tool and cutter grinder is used to sharpen milling cutters and tool bits along with a host of other cutting tools. It is an extremely versatile machine used to perform a variety of grinding operations: surface, cylindrical, or complex shapes. The image shows a manually operated setup, however highly automated Computer Numerical Control (CNC) machines are becoming increasingly common due to the complexities involved in the process.

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A typical tool and cutter grinder

The operation of this machine (in particular, the manually operated variety) requires a high level of skill. The two main skills needed understand of the relationship between the grinding wheel and the metal being cut and knowledge of tool geometry. The illustrated set-up is only one of many combinations available. The huge variety in shapes and types of machining cutters requires flexibility in usage. A variety of dedicated fixtures are included that allow cylindrical grinding operations or complex angles to be ground. The vise shown can swivel in three planes.

The table moves longitudinally and laterally, the head can swivel as well as being adjustable in the horizontal plane, as visible in the first image. This flexibility in the head allows the critical clearance angles required by the various cutters to be achieved.

RADIUS GRINDING PROCESS:A radius grinder it is also known as the radius tool grinder is a special grinder used for grinding the most complex tool forms and is the historical predecessor to the CNC tool and cutter grinder. Like the CNC grinder, it may be used for other tasks where grinding spherical surfaces is necessary. The tool itself consists of three parts: The grinder head, work table and holding fixture. The grinder head has three degrees of freedom. Vertical movement, movement into the workpiece, and tilt. These are generally set statically and left fixed throughout operations. The work table is a T-slotted X-axis table mounted on top of a radial fixture. Mounting the X axis on top of the radius table as opposed to the other way around and allows for complex and accurate radius grinding. The holding fixtures can be anything one can mount on a slotted table but most commonly used is a collector or chuck fixture that index and has a separate Y movement to allow accurate depth setting and end mill sharpening. The dressers used on these grinders are usually quite expensive and can dress the grinding wheel itself with a particular radius.

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CONCLUSION

Thus, the grinding operation is carried out with a variety of wheel – workpiece configurations. The selection of a grinding process for a particular application depends on part shape, part size, ease of fixturing and the production rate required. The basics types of the grinding operation are surface, cylindrical, internal, and centerless grinding. The relative motion of the wheel may be along the surface or it may be radially into the workpiece. The surface grinders constitute the largest percentage of grinders in the industries followed by the bench grinder, cylindrical grinders and tool and cutter grinder. The least used type of the grinder is the internal grinder.

The grinding machines are available for various work-piece geometries and sizes. Modern grinding machines may be computer controlled, with features such as automatic workpiece loading and unloading, clamping, cycling, gaging, dressing and wheel shaping. The grinders can also be equipped with probes and gages for determining the relative position of the wheel and the workpiece surfaces, as well as with tactile during the dressing cycle. Because the grinding wheels are brittle and are operated at high speeds, certain procedures must be carefully followed in their in their handling. Storage , and use. Failure to follow these rules and the instructions and warnings printed on individual wheel labels may result in serious injury or death.

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REFERENCE

(1) MANUFACTURING PROCESS FOR ENGNEERING MATERIALS.

(2) WIKIPEDIA.

(3) A TEXT BOOK OF THE MANUFACTURING TECHNOLOGY BY R.K.RAJPUT.

(4) PROCESS AND MATERIALS OF MANUFACTURING BY ROY A LINDERG.

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