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Extrusion

• Extrusion is a process by which a billet or ablock of metal is reduced in cross section byforcing it to flow through a die orifice under high

pressure.• Generally extrusion is used to produce rods,

bars and hollow tubes, though shapes of irregular cross section can also be produced.

• Most metals are extruded in hot condition dueto large reduction in area.

• Cold extrusion is possible for very ductilemetals.

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Extrusion

The two basic types of extrusion are:

Direct extrusion or forward extrusion

Indirect extrusion or backward extrusion

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Direct extrusion

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Indirect extrusion

Hollow

ram

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Direct and Indirect extrusions

• In direct extrusion, the direction of the flowof metal through the die is same as the

direction of movement of ram. In indirectextrusion it is the opposite.

• Since there is no relative motion betweenbillet and container in indirect extrusion, thefrictional forces are less and hence the totalextrusion force is less than in directextrusion.

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Direct and Indirect extrusions

• Because of the requirement of the hollow

ram in indirect extrusion, loads which can

be applied, are less than that can be appliedin direct extrusion.

• Handling of very long products in indirect

extrusion is difficult.

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Indirect extrusion of cans

(Impact extrusion)

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Impact extrusion

• Impact extrusion is a process used to

produce short lengths of hollow tubes (by

indirect extrusion).

• It is usually performed on a high speed

mechanical press.

•

Restricted to softer metals like Pb, Sn, Al,and Cu.

• Considerable heating results due to high-

speed deformation.

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Extrusion of tubes

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Extrusion of tubes

1. A hollow billet is used as the starting material.

2. The hole may be produced by hot piercing.

3. The clearance between mandrel and die

determines the wall thickness of the tube.

4. In one process, piercing and extrusion are

completed in a double action extrusion process.

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Rod/Wire Drawing

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Rod/Wire Drawing

It involves pulling of metal through a die bymeans of a tensile force applied at the exitside of the die.

Plastic flow is caused by combination of applied tensile force and the compressiveforce due to the die.

Diameter of a bar/rod/tube is reduced bysuccessive drawing operations.

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Rod/Wire Drawing

Wire drawing is generally carried out at roomtemperature.

Principle is same in both rod drawing andwire drawing but equipment is different for different sized products.

Rods and tubes which can not be coiled are

drawn on draw benches.Wires (dia less than 5mm) are produced by

block drawing where coiling is possible.

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Rod Drawing

Draw head is moved either by a chain drive or 

a hydraulic mechanism.

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Wire Drawing

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Wire Drawing

Block drawing allows generation of largelengths in smaller floor space.

Max reduction in area that can be achieveddepends on ductility, die angle and friction.

Reduction per drawing pass is generallybelow 30-35%.

If many reductions are required to producefinal wire, multi-pass wire drawing is done.

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Multi-pass Wire Drawing

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Process requirements

Wire/rod should be sufficiently ductile.

The front end of the stock is to be made

pointed to facilitate entry. Cleaning of the wire (by pickling).

• Adequate lubrication

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Materials for Drawing Dies

• Tool steels - suitable for medium die

life, good abrasion resistance.

•Tungsten Carbide

–die life 2 to 3 times that

of alloy steel, large productions, excellent

abrasion resistance.

• Diamond - for very fine wires with

excellent surface finish.