Metal Processes

Turning

Turning Turning is the production of cylindrical components using a centre

lathe. The material is held firmly in a rotating chuck whilst a cutting tool is brought towards it to create the required shape. A variety of processes can be carried out on the lathe for example turning cylinders, creating texture (knurling), accurate drilling and threading

Milling

Milling Machine Milling machines are powerful pieces of equipment which use rotating

multi toothed cutters to shape the material. There are two types of milling machine, horizontal and vertical. The machines are named by the position of the cutting tool in relation to the workpiece. Milling machines can be used as side and face cutters and can also be used to cut slots in the material.

Milling consists of machining metal by using rotating cutters which have a number of cutting edges. These tools are known as milling cutters.

Horizontal Milling MachineVertical Milling Machine

Milling CuttersSlot Cutter

Slot

Straddle Milling

Milling Cutter

Dovetail Slot

Dovetail Cutter

Angle Cutter

Angled Face

Milling Cutters

Flat Surface

Slab Cutter

T-Slot

Tee Slot Cutter

Die casting

Die Casting Where large quantities of quality castings are required in industry,

the moulds (‘dies’)need to be permanent. These special, alloy moulds are costly to produce because they are made in sections for easy removal of the components. The high operating costs involved make this process economically viable for high volume mass production where accuracy of shape, size and surface finish is essential.

Gravity Castings

Molten metal is poured into the cavity under its own weight. This produces sound, dense castings with mechanical properties superior to pressure casting (since metal enters the mould with less turbulence). This process also traps less gas than pressure casting does, leading to less porosity.

Die Casting

die

fixed pattern

injection piston

molten metal

release

cavity

‘Hot’ chamber and ‘cold’ chamber processes are used. In both processes molten metal is forced into a metal die by a hydraulic ram. Thin section and complex shapes with fine detail are possible.

1. A measure of molten metal is poured into the charge chamber.

2. An injection piston then forces the metal into a water-cooled die through a system of sprues and runners.

3. The metal solidifies rapidly and the casting is removed, complete with its sprues and runners.

Die Casting Materials

Materials used in this process include low melting temperature alloys, lead, zinc, aluminium and brass alloys.

Identifying Features

Section hair lines, ejector pin marks, flashes caused by leakage left on internal surfaces (these do not interfere with performance or appearance), and sprue and runner marks.

Press Forming

Press Forming Press forming involves squeezing sheet metal between two matched metal moulds (dies). This

gives a very strong, shell-like structure. One die is the mirror image of the other, apart from an allowance for the thickness of the material being formed. The machining of these dies is a specialised skill. They can be complicated and therefore difficult and time consuming to make. This makes them very expensive to produce.

The ProcessThe sheet metal component starts out as a flat sheet or strip

1 A blank is cut to the required size.2 The blank is placed in a press.3 The product is formed using immense force.

The complete forming process may take several additional stages of operations to form, draw (stretch) and pierce the material into its final shape

Press Forming Materials

Sheet metals; various steels, aluminium alloys, brass, copper

Identifying Features

Sudden directional changes, i.e. sharp edges and deep draws, are avoided to minimise overstretching the walls of the product. Different operations, e.g flanges, ribs, piercing, can be identified.

Uses

Products used in many everyday activities are easily identifiable. These range from pans, kettles and stainless steel kitchen sinks to car bodies and aircraft panels.

Sand Casting

Sand Casting

Sand casting is the most frequently used metal casting process. ‘Green, foundry sand is a blend of silica grains, clay and water. The term ‘green’ describes the damp quality which bonds the sand together. Oil-bound sand gives excellent results but is relatively expensive and difficult to reconstitute. There is an element of waste involved as the sand that is in contact with the hot metal will burn. This burned sand needs to be scraped out and disposed of.

The quality of the casting produced depends on the quality of the pattern. These are normally made in wood. The pattern requires radiused corners, drafted sides and a good surface finish. The sand mould is produced around the pattern, which is removed to leave a cavity. Molten metal is poured into the mould and solidifies. When cold, the mould is broken up to retrieve the casting.

Sand Casting

pattern

sprue pins

cope

drag

gates

riserrunner

1. Place the pattern centrally in the drag.

2. Pack sand around the pattern.

3. Turn the drag over and attach the cope.

4. Insert sprue pins and pack sand around them.

5. Remove the sprue pins.

6. Split the moulding box and cut ‘gates’.

7. Remove the pattern to leave a cavity.

8. Reassemble the cope so that the mould is ready to receive the molten metal.

9. Pour the molten metal into the runner. The melt fills the mould and exits, along with any gases, via the riser.

Sand Casting Materials

Iron, aluminium and non-ferrous alloys are most widely used in sand casting. Exceptions include refractory (able to withstand high temperatures) metals such as titanium. Precious metals e.g. gold lend themselves to casting.

Identifying Features

Complex 3-D components. Mainly solid but internal shapes can be produced using cores. Thin sections are difficult to mould. Surface texture can be poor. Draft angles, fillets, rounded corners and strengthening webs will be evident and will echo the pattern requirements. Other recognisable features include bosses and porous surface textures. Fettle marks, due to the removal of runners and risers, may be visible.

Uses

Casting is a versatile process using the material properties in the manufacture of engine parts, tools and decorative jewellery. Multiple mould patterns decrease production time thus lowering production costs.

Casting

Casting Casting in Aluminium

The main reason for casting an object is that the shape of the object is such that it would make matching either very difficult or too expensive.

There are many ways in which an object can be cast, but there are only two ways which are suitable for use in the school workshop.

1. Gravity feed casting

2. Investment casting.

The main difference being that gravity feed casting uses a wooden pattern and so can be used for large numbers, where as investment casting uses either a wax or a polystyrene pattern and therefore only be used once. Both these methods come into the category of Green sand moulding, which gets its name not from the colour of the sand, but because the sand is damp.

Piercing and Blanking

Piercing and Blanking Piercing and blanking are essentially the same process, involving the stamping

of shapes out of sheet metal or metal strip. The differences in the process simply depend on which bit of metal is to be kept: in piercing a shaped hole is made in the metal, whereas in blanking a shape is stamped out of the metal and then used.

The Process

punch

strip

die

Piercing

The punch and die are shown here in the closed position. Notice how the punch fits into the die but does not enter it, stopping instead as soon as the metal has been cut. Accurate alignment of the two is essential.

Blanking

Blanking

The main components used for blanking in mass production are a punch, a die and a stripper plate. The stripper plate prevents the metal ‘riding up’ the die on its upward travel. The die is attached to the main press by means of a bolster plate. The punch is attached to a movable ram.

Blank falling through dieand bolster plate

Bolster plate

Die

Ram

Metal Strip

Punch

Stripper

Progressive Piercing and Blanking

Progressive Piercing and Blanking

Many products requires to be both pierced and blanked. This is often done in the same press by first piercing the metal, and then moving it along to another die and blanking out the desired shape. This process is called progressive piercing and blanking.

1 The metal strip is fed into the first die.

2 A hole is pierced in the metal on the first stroke of the ram.

3 The ram rises and metal is moved into position over the blanking die.

4 Accurate alignment is essential here.

5 The punch descends and the completed component ( in this case a washer) is blanked from the metal strip. At the same time a hole is pierced in the next washer.

6 Piercing is normally done before blanking, as this minimises the risk of fracturing the metal.

Metal StripFinished Washer

Metal Strip

Stripper

Piercing punch

Die

Stop

Scrap

Ram

Blanking punch

Pilot

Piercing and Blanking Materials

Most types of metals can be pierced and blanked in sheet or strip form. The metal is normally annealed first so as to minimise the risk of fracture or tearing.

Identifying Features

A sheared surface will show two distinct areas of deformation and fracture. With the correct clearance angles in the punch, this can be minimised to give a reasonably smooth edge which will require no further finishing.

Uses

Uses of piercing and blanking include component parts for a variety of tool and products. Often products made from sheet metal that have been press formed are pierced to give a decorative finish.

Drop Forging

Drop Forging Impression-die drop forging is an industrial process used in the production of high quality, strong

metal components or products. The main advantages are that components can be accurately repeated using specially shaped dies to control the flow of metal; the need for highly skilled craftsmen is thus eliminated.

PRE

SSU

RE

PRE

SSU

RE

Anvil

Ram

Top Die

Bottom Die

Billet Flash

The Process

The die used are very expensive to produce. High alloy steels are required to prevent heat loss which causes them to wear too quickly under impact loads.

1. A hot metal billet is placed between the dies.

2. The hot metal is forced into the cavity using a power driven hammer. (Note that the process may take more than one operation using a succession of dies.)

3.Excess metal is squeezed out forming a flashing around the parting line of the two dies. The amount of flashing is determined by die wear and the quantity of excess metal.

4. When the forging is complete the flash is removed using a trimming die.

Drop Forging Materials

Most metals are in alloy form are suited to the drop forging process. Alloy steels and copper alloys are most common.

Identifying Features

The function of the product may indicate that drop forging is the most appropriate process for manufacture, i.e. the product or certain parts of the product may require compressive or tensile force to be used. Strength to weight ratio is a consideration. Visually there may well be evidence of flashing and flash removal around the edges of the product. Quality products may have undergone further finishing to eliminate visual evidence of die parting lines.

Uses

Drop forging metal increases its strength. The grain structure of the metal is changed to follow the outer contour of the component. This provides greater scope for the design of high quality metal products. Examples range from hand tools such as spanners and plumbing fittings to high quality cutlery and domestic appliances.

Drawing

Drawing The process of drawing is the main process in the production of three dimensional curved

pressings e.g. drinks cans. The sheet material (blank) is held in place by a pressure ring which has a highly finished surface plus lubrication to minimise friction. A punch is then forced into the material drawing it down to form the required shape. The depth which can be drawn in one punch depends on the type of material, its tensile strength and the tool design.

Pressure ring

Punch

Joining Materials

Joining MaterialsThe manufacture of most products requires joining together of materials. Part of the designer’s role is to select the most appropriate method.

Permanent joining methods include adhesives, arc welding, fitted joints, riveting, spot welding.

Non-permanent methods include nuts, bolts and screws.

Fixings

Mechanical knock down fixings are generally used on square cut butt joints on manufactured boards. No glue is required but accurately drilled holes are essential. Knock-down fixings (fixings) make assembly straight forward and have the added advantage that dismantling a product is possible.

PLASTIC CORNER BLOCK

TWO BLOCK FITTING

RIGID JOINT

Fixings Knock-down fittings are those that can be put together easily, normally using

only a screw driver, a drill, a mallet/hammer and other basic tools. They are temporary joints although many are used to permanently join together items such as cabinets and other pieces of furniture that are purchased in a flat pack

CAM LOCKS

SCAN FITTINGS

Welding Soldering, brazing and welding techniques are used mainly to join metals. Some

thermoplastics can also be joined in this way. Arc Welding

Heat is obtained by an electric arc via a transformer. One lead is attached to the work and the other to a grip holder a welding rod. An arc is formed when the end of the rod is brought near the work. The heat melts the parent metal and the filler rod together. The rod is coated with flux to prevent oxidation.

Spot Welding The metal is heated and fused together between two copper electrodes. Used on

thin gauge mild steel, e.g. car bodies

Riveting There are two methods. The traditional method uses soft iron, aluminium or

copper for snap, countersunk and flat head rivets in conjunction with a hammer and rivet ‘set’.

Traditional

1. 2. 3.

4.5.

Riveting Where the use of a hammer is to be avoided, controlled pressure is applied to a

‘pop rivet’ using a pop-riveting ‘gun’. Also used for ‘blind’ riveting.

1. 2. 3.

The two pieces of plastic or aluminium are drilled to a size slightly larger than the rivet

The pop rivet is passed through both holes in the sheet plastic / aluminium.

The rivet pliers are pushed on to the pin of the rivet and the handles are pulled together. As this happens the pin head is pulled into the rivet and the end of the rivet is expanded. Eventually the pin will break off leaving the rivet permanently fixed in position holding the two pieces of plastic / aluminium together.

Bolts The screw thread has the advantage of enabling items to be taken apart for

inspection or maintenance purposes. Nuts, bolts and set screws can be obtained in various forms. There are numerous designs of spanners for use with square- and hexagonal-headed nuts and bolts, just as there are keys for socket screws.

Screws Screws are used to fasten together boards, panels and fittings such as hinges and

brackets. Pieces can be taken apart and reassembled without damage. Screwdrivers are available in a variety of blade types, e.g. slot and pozidrive. Effort in driving screws home can be minimised by using electrically powered ‘screw guns’

Other Things To Consider Permanent, semi-permanent or temporary? Types(s) of material(s) allow for movement surface area indoor or outdoor? Are cramps to be used? Time (setting time)

Finishing Metal

FinishingFinishing bright steel :

Stage 1 - After shaping with coarse file and smooth file, complete filing by draw-filing. Always work in the same direction along the metal and make sure that each stage removes all marks left by the previous one.

Stage 2 - Finish by using different grades of emery cloth, first coarse, then fine, and finally after all marks have been removed add a little oil to the fine cloth for final finishing

Stage 3 - To protect the metal from rust, smear it with light grease.

Oil finishing black steel:

Stage 1 - Remove all loose scale from forging, grease, etc.

Stage 2 - Either dip the metal in machine oil and burn it into the metal, or heat the metal to dull red heat and quench it in oil.

Stage 3 - Wipe off surplus oil and polish with black boot polish.

Finishing Painting metal:

Stage 1 - Thoroughly clean and degrease the metal. Paraffin or special degreasers will clean badly affected parts while hot water with soda or detergents will remove light oil and dirt.

Stage 2 - Find a dust free place to work, and make arrangements for supporting the work while painting and drying before starting.

Stage 3 - For maximum protection apply primer, undercoat and topcoat. For inside work one or two coats of topcoat alone are adequate. Two thin coats are always better than one thick one.

Lacquering:Stage 1 - Thoroughly clean, polish and degrease the metal.Stage 2 - Apply the lacquer or varnish with a best quality soft brush to preserve the finish.

HEAT TREATMENT

Heat Treatments

Annealing heated above critical temperature and cooled slowly softens structure

Quenching heated above critical temperature and cooled rapidly in water or oil improves hardness and strength

Heat Treatments

Tempering heated below critical temperature, held and quenched improves ductility and toughness while retaining hardness

ENGINEERINGAPPLICATION

Some metals and metal alloys possess high structural strength per unit mass, making them useful materials for carrying large loads or resisting impact damage. Metal alloys can be engineered to have high resistance to shear, torque and deformation. However the same metal can also be vulnerable to fatigue damage through repeated use or from sudden stress failure when a load capacity is exceeded. The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many appliances, tools, pipes, non-illuminated signs and railroad tracks.

The two most commonly used structural metals, iron and aluminium, are also the most abundant metals in the Earth's crust.[13]

Metals are good conductors, making them valuable in electrical appliances and for carrying an electric current over a distance with little energy lost. Electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for the most part, are wired with copper wire for its good conducting properties.

The thermal conductivity of metal is useful for containers to heat materials over a flame. Metal is also used for heat sinks to protect sensitive equipment from overheating.

The high reflectivity of some metals is important in the construction of mirrors, including precision astronomical instruments. This last property can also make metallic jewelry aesthetically appealing.

Some metals have specialized uses; radioactive metals such as uranium and plutonium are used in nuclear power plants to produce energy via nuclear fission. Mercury is a liquid at room temperature and is used in switches to complete a circuit when it flows over the switch contacts. Shape memory alloy is used for applications such as pipes, fasteners and vascular stents

Plain Low-Carbon SteelsPlain Low-Carbon Steels

These alloys are relatively soft and weak but These alloys are relatively soft and weak but have outstanding ductility and toughness; have outstanding ductility and toughness;

They are machinable, weldable, and, of all They are machinable, weldable, and, of all steels, are the least expensive to produce. steels, are the least expensive to produce. Typical applications include automobile body Typical applications include automobile body

components, structural shapes (I-beams, channel and components, structural shapes (I-beams, channel and angle iron), and sheets that are used in pipelines, angle iron), and sheets that are used in pipelines, buildings, bridges, and tin cans.buildings, bridges, and tin cans.

Typically have a yield strength of 275 MPa (40,000 Typically have a yield strength of 275 MPa (40,000 psi), tensile strengths between 415 and 550 MPa psi), tensile strengths between 415 and 550 MPa (60,000 and 80,000 psi), and a ductility of 25%EL.(60,000 and 80,000 psi), and a ductility of 25%EL.

High-strength, Low-alloy High-strength, Low-alloy (HSLA) Steels(HSLA) Steels

they are ductile, formable, and machinable. they are ductile, formable, and machinable. more resistant to corrosion than the plain carbon more resistant to corrosion than the plain carbon

steels,steels, they have replaced plain carbon steels in many they have replaced plain carbon steels in many

applications where structural strength is critical applications where structural strength is critical (e.g., bridges, towers, support columns in high-rise (e.g., bridges, towers, support columns in high-rise

buildings, and pressure vessels).buildings, and pressure vessels).

Low-Carbon SteelsLow-Carbon Steels

Medium-Carbon SteelsMedium-Carbon Steels

Heat-treated alloys are stronger than the Heat-treated alloys are stronger than the low-carbon steels, but at a sacrifice of low-carbon steels, but at a sacrifice of ductility and toughness.ductility and toughness.

Applications:Applications: railway wheels and tracks, railway wheels and tracks, gears, crankshafts, and other machine partsgears, crankshafts, and other machine parts high-strength structural components calling high-strength structural components calling

for a combination of high strength, wear for a combination of high strength, wear resistance, and toughness.resistance, and toughness.

High-Carbon SteelsHigh-Carbon Steels

The tool and die steels are high-carbon The tool and die steels are high-carbon alloys, alloys, usually containing chromium, vanadium, usually containing chromium, vanadium,

tungsten, and molybdenum.tungsten, and molybdenum. These alloying elements + carbon forming very hard and These alloying elements + carbon forming very hard and

wear-resistant carbide compounds (e.g., Crwear-resistant carbide compounds (e.g., Cr2323CC66, V, V44CC33, and , and WC). WC).

These steels are utilized as These steels are utilized as cutting tools and dies for forming and shaping cutting tools and dies for forming and shaping

materials, materials, as well as in knives, razors, hacksaw blades, as well as in knives, razors, hacksaw blades,

springs, and high-strength wire.springs, and high-strength wire.

Copper Alloys: brassesbrasses

Some of the common brasses are:Some of the common brasses are: yellow, naval, and cartridge brass, muntz metal, yellow, naval, and cartridge brass, muntz metal,

and gilding metal.and gilding metal. Some of the common uses for brass alloys:Some of the common uses for brass alloys:

costume jewelry, cartridge casings, automotive costume jewelry, cartridge casings, automotive radiators, musical instruments, electronic radiators, musical instruments, electronic packaging, and coins.packaging, and coins.

Copper Alloys: bronzesCopper Alloys: bronzes

Alloys of copper and several other elements, Alloys of copper and several other elements, including tin, aluminum, silicon, and nickel.including tin, aluminum, silicon, and nickel.

Bronzes are somewhat stronger than the Bronzes are somewhat stronger than the brasses, brasses, Yet they still have a high degree of corrosion Yet they still have a high degree of corrosion

resistance. resistance. Generally bronzes are utilized when, in addition Generally bronzes are utilized when, in addition

to corrosion resistance, good tensile properties to corrosion resistance, good tensile properties are required.are required.

Aluminum and Its Alloys

Some common applications of aluminum Some common applications of aluminum alloys:alloys: aircraft structural parts, beverage cans, bus aircraft structural parts, beverage cans, bus

bodies, and automotive parts (engine blocks, bodies, and automotive parts (engine blocks, pistons, and manifolds).pistons, and manifolds).

Beryllium CoppersBeryllium Coppers The most common heat-treatable copper alloys.The most common heat-treatable copper alloys. Possess a remarkable combination of properties: Possess a remarkable combination of properties:

tensile strengths as high as 1400 MPa (200,000 psi), tensile strengths as high as 1400 MPa (200,000 psi), excellent electrical and corrosion properties, and wear resistance excellent electrical and corrosion properties, and wear resistance

when properly lubricated;when properly lubricated; they may be cast, hot worked, or cold worked. they may be cast, hot worked, or cold worked. High strengths are attained by precipitation-hardening heat High strengths are attained by precipitation-hardening heat

treatments.treatments. These alloys are costly because of the beryllium These alloys are costly because of the beryllium

additions, which range between 1.0 and 2.5 wt%.additions, which range between 1.0 and 2.5 wt%. Applications include:Applications include:

jet aircraft landing gear bearings and bushings,jet aircraft landing gear bearings and bushings, springs, and surgical and dental instruments.springs, and surgical and dental instruments.

Magnesium and Its Alloys Mg alloys are used in aircraft and missile applications. Mg alloys are used in aircraft and missile applications. Recently the demand for Mg alloys has increased.Recently the demand for Mg alloys has increased. For many applications, Mg alloys have replaced For many applications, Mg alloys have replaced

engineering plastics engineering plastics have comparable densities but the magnesium materials are have comparable densities but the magnesium materials are

stiffer, more recyclable, and less costly to produce. stiffer, more recyclable, and less costly to produce. For example, magnesium is now employed in For example, magnesium is now employed in

variety of hand-held devices (e.g., chain saws, power tools), variety of hand-held devices (e.g., chain saws, power tools), automobiles (steering wheels, seat frames, transmission cases), automobiles (steering wheels, seat frames, transmission cases), laptop computers, camcorders, TV sets, cellular telephones.laptop computers, camcorders, TV sets, cellular telephones.

Titanium and Its AlloysTitanium and Its Alloys The major limitation: The major limitation:

chemical reactivity with other materials at elevated temperatures. chemical reactivity with other materials at elevated temperatures. the development of non conventional refining, melting, and the development of non conventional refining, melting, and

casting techniques is necessary; casting techniques is necessary; Titanium alloys are quite expensive.Titanium alloys are quite expensive.

The corrosion resistance of titanium alloys at normal The corrosion resistance of titanium alloys at normal temperatures is unusually high; temperatures is unusually high; virtually immune to air, marine, and a variety of industrial virtually immune to air, marine, and a variety of industrial

environments.environments. Commonly utilized in airplane structures, space vehicles, Commonly utilized in airplane structures, space vehicles,

surgical implants, and in the petroleum and chemical surgical implants, and in the petroleum and chemical industries.industries.

The Refractory MetalsThe Refractory Metals The applications of these metals are varied. The applications of these metals are varied.

For example: tantalum and molybdenum are alloyed with For example: tantalum and molybdenum are alloyed with stainless steel to improve its corrosion resistance. stainless steel to improve its corrosion resistance.

Molybdenum alloys are utilized for Molybdenum alloys are utilized for extrusion dies and structural parts in space vehicles; extrusion dies and structural parts in space vehicles; incandescent light filaments, x-ray tubes, incandescent light filaments, x-ray tubes,

Tungsten alloys Tungsten alloys welding electrodes.welding electrodes.

Tantalum is immune to chemical attack by virtually all Tantalum is immune to chemical attack by virtually all environments at temperatures below 150°C environments at temperatures below 150°C frequently used in applications need a corrosion-resistant frequently used in applications need a corrosion-resistant

material.material.

The Superalloys The superalloys have superlative combinations of The superalloys have superlative combinations of

properties. properties. Most are used in aircraft turbine components,Most are used in aircraft turbine components,

must withstand exposure to severely oxidizing environments and must withstand exposure to severely oxidizing environments and high temperatures for reasonable time periods. high temperatures for reasonable time periods.

density is an important consideration because centrifugal density is an important consideration because centrifugal stresses are function of rotation and density. stresses are function of rotation and density.

Classified according to the predominant metal in the Classified according to the predominant metal in the alloy (Co, Ni, or Fe). alloy (Co, Ni, or Fe).

Other alloying elements include the refractory metals Other alloying elements include the refractory metals (Nb, Mo,W, Ta, Cr, and Ti). (Nb, Mo,W, Ta, Cr, and Ti).

Other applications: nuclear reactors and petrochemical Other applications: nuclear reactors and petrochemical equipment.equipment.

Investment CastingInvestment Casting

This technique is employed when high This technique is employed when high dimensional accuracy, reproduction of fine dimensional accuracy, reproduction of fine detail, and an excellent finish are required—detail, and an excellent finish are required—for example: for example: in jewelry and dental crowns and inlays. in jewelry and dental crowns and inlays. blades for gas turbines and jet engine impellers.blades for gas turbines and jet engine impellers.

Lost Foam CastingLost Foam Casting

With lost foam casting, complex geometries and With lost foam casting, complex geometries and tight tolerances are possible.tight tolerances are possible.

In comparison to sand casting, lost foam is a In comparison to sand casting, lost foam is a simpler, quicker, and less expensive process, simpler, quicker, and less expensive process, and there are fewer environmental wastes. and there are fewer environmental wastes.

Metal alloys that most commonly use this Metal alloys that most commonly use this technique are cast irons and aluminum alloys; technique are cast irons and aluminum alloys; furthermore, applications include automobile furthermore, applications include automobile engine blocks, cylinder heads, crankshafts, engine blocks, cylinder heads, crankshafts, marine engine blocks, and electric motor frames.marine engine blocks, and electric motor frames.

SOURCE OF METALLIC MATERIALS

Almost all metals present in the environment have been biogeochemically cycled since the formation of the Earth. Human activity has introduced additional processes that have increased the rate of redistribution of metals between environmental compartments, particularly since the industrial revolution. However, over most of the Earth's land surface the primary control on the distribution of metals is the geochemistry of the

underlying and local rocks except in all but the worst cases of industrial contamination and some particular geological situations. Fundamental links between chemistry and mineralogy lead to characteristic geochemical signatures for different rock types. As rocks erode and weather to form soils and sediments, chemistry and mineralogy again influence how much metal remains close to the source, how much is translocated greater

distances, and how much is transported in solutions that replenish ground and surface water supplies. In addition, direct processes such as the escape of gases and fluids along major fractures in the Earth's crust, and volcanic related activity, locally can provide significant sources of metals to surface environments, including the atmosphere and sea floor. As a result of these processes the Earth's surface is geochemically inhomogeneous. Regional scale processes lead to large areas with enhanced or depressed metal levels that can cause biological effects due to either toxicity or deficiency if the metals are, or are not, transformed to bioavailable chemical species.