6 Unit 2- Metal Forming Processes

8/13/2019 6 Unit 2- Metal Forming Processes

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MANUFACTURINGTECHNOLOGY ISUBCODE: MEC230

Unit 2Welding (Metal Joining) Processes

Metal Forming Processes


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Unit 2 : Metal Forming Processes


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Metal Forming Processes : The importance of metals in modern technology is due to theease with which they may be formed into useful shapes liketubes, rods and sheetsThe useful shape may be generated by two basic ways

Plastic deformation processes:- The volume and mass of metalare conserved and metal is displaced from one location to

another

Metal removal or Machining processes:- In which material isremoved in order to give the required shape


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Metal Forming Processes : Forming can be defined as the process in which the desired size

and shape of the objects are obtained through plasticdeformation of material The stresses induced during the process are greater than yield

strengthbut should be lessthan the fracture strengthDifferent types of loading may be used depending on the process

Tensile

Compressive

Shear

Bending


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Classification of Metal Forming Process:Metal forming process may be classified on the basis of type of forcesappliedto the work piece as it is formed into direct shape Direct compression type process (e.g.-Forging, Rolling)

Indirect compression process (e.g.-Extrusion, Wire Drawing)

Tension type process (e.g.-Stretch forming)

Bending process

Shearing process


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Direct Compression type Process (Forging)


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Direct Compression type Process (Rolling)


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Indirect Compression Process (Extrusion)


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Indirect Compression Process (Drawing)


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Indirect Compression Process (Deep Drawing)


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Tension type process (Stretch forming)


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Bending process


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Shearing Process


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Classification of Metal Forming Process


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Classification of Metal Forming Process


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Classification of Metal Forming Process:Metal forming may also be classified on the basis of workingtemperature. Hot Working Processes

Cold working Processes

Warm Working Processes


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Hot Working: Hot working processes the metals are heated aboverecrystallization temperatureto given desired shape Eg rolling, extrusion or forging are used in the first step of

converting a cast ingot into a wrought products.

The metals are given desired shape by subjecting them to forces

which cause them to undergo plastic deformation when heated

above recrystallization temperature.


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Advantages of Hot Working Processes Hot working results in decrease in energy requiredto deform the

metal and increased ability to flow without cracking. Casting defects like blowholes and porosity are eliminatedby the

welding together of these cavities.

Coarse columnar grains of the casting are broken down andrefined into smaller equiaxed recrystallized grains.

Due to refinement of grains mechanical properties such astoughness, ductility elongation and reduction in area areimproved.

These changes in structure from hot working result in an

increase in ductility and toughness over the cast state.


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Cold Working: Cold working processes the metals are done at roomtemperatureto given desired shape Cold working of a metal results in an increase in strength or

hardness and decrease in ductility.

When the cold working is excessive the metal will fracture,

before reaching the desired shape and size.

Need of annealing operations increase the cost of forming by

cold working


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Advantages of Cold Working:- Produces an improved surface finish, scale free and bright

surface and closer dimensional tolerances.

Residual stresses are set up in the metals which remain unless

they are removed by subsequent heat treatment.

Cold working results in loss of ductility and increase of strength

and hardness of metal.


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Limitations of Cold Working:- Only small sized components can be easily cold worked as

greater forces are required for larger sections.

Grain structure is not refined and residual stresses have harmful

effects on certain properties of metals.

Many of the metals having les ductility cannot be worked at

room temperature. It is therefore limited to ductile metals.

Tooling costs are higher and is used when large quantities of

similar components are required.


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Warm Working: It is the plastic deformation of a metal at temperature below the

recrystallization and above room temperature.

It attempts to combine the advantages of both hot and cold

working into one operation.

Warm working has been applied most extensively to the forgingof steel, where it offers fewer forging steps, reduced forging load,

and energy savings compared with cold forgings.

When compared with hot working it offers advantage of

Improved dimensional control,

Higher quality surface and

Lower energy costs.


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Advantages of (Mechanical) Metal Working Processes:- Defects in metals such as blow holes and porosity find to get

filled due to plastic deformation

Mechanically worked components exhibit superior mechanical

properties

Provides grain refinement and improved metallurgical structure

of metal

Cold working with subsequent annealing can produce good

surface finish and close dimensional tolerances Process is ideal for producing small sized components


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Limitations of (Mechanical) Metal Working Processes:- Difficult to produce large components

Produces internal stresses, which are to be relieved

Formation of scale by oxidation and decarburization of surface

may take place Cold working may reduce ductility and induces brittleness

Heavy equipments, machineries and manpower are required


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Wrought Products:- A product is said to be wrought if it is manipulated in the solidstate from a cast shape The choice of manipulation depends upon the material to be

manipulated, the shape required, the accuracy required and the

quantity involved Wrought forms can be, drawn bars, rolled sections, sheet, plate,

tube, wire, extruded sections

A cast metal posses local differences of metallurgical structure

and chemical composition, and contains blowholes and the cast

metals have inferior mechanical properties

Wrought metals are subjected to hot working, this improves the

properties of metal


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Characteristics of Wrought Products:- Hot working imparts directional properties to the metals caused

by the deformation of grains along the direction of working

The minor defects like blow holes at the sub surface and surface

level get eliminated by welding effect when formed

The wrought metals generally exhibit superior mechanical

properties like strength, ductility and toughness

They normally have rough surface finish

The surface may undergo oxidation and result in scale formation

They may undergo decarburization at the outer surface

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6 Unit 2- Metal Forming Processes