Extrusion

Submitted to: submitted by:Asst. Prof. M.P.Gururajan Koduri Srikrishna (2008AMD2922)

Introduction Joseph Bramah, developer of extrusion process.It is a process by which a material is forced to

flow through a die, which is shaped to produce the required cross-section.

It is similar to the squeezing action of tooth paste.

Courtesy: google images(direct extrusion)

Types of extrusion• Hot extrusionAt elevated temperatureNo work hardeningcostly

Cold extrusionAt room temperatureWork hardeningLack of oxidation, good surface finish.

Direct extrusion

Indirect extrusion

Courtesy: google images (indirect extrusion)

Indirect extrusionAdvantages:Reduction of frictionhigh contianer’s lifebillet moves more uniformly. So, less

extrusion defectsDisadvantages:Impurities and defects on surface.Length and area of extrusion depends on

stem.

Hydrostatic extrusion

Extrusion force curves

courtesy: wiki

Fig: relations between forces applied and ram displacement in various processes

Copper alloysComposition of copper used is 55 to 65%As copper content increases, ease of extrusion

decreases.In order to have hot working, Lead content

should be low600-1000oCPressure-690MPaTubes of 11cm outer diameter, with thickness of

2mm.Free cutting brass, hot stamping brassManganese bronze alloys has marine applications

Steels 1100 to1250oCDummy preheated to 800 to 900oCGlass lubricationPlain carbon steels to high alloyed steelsTubes of 20m long, diameter of 10mm,20mm.

Aluminium alloy300 to600oCPress- 500 to 6000TonsBillets of 75mm diameter for small,1100mm

diameter for big presses.A layer of metal remains on the surface after

extrusion.Lubricants- graphite, molybdenum disulphide

Properties of materialsPresence of impurities, gas, dross, etcDepending on degree of deformationDeformation is greater in outer zones.Therefore, differences in properties at these

places.This variation is high, if extrusion ratio is low.Temperature at which work is carried out. Bismuth is brittle in cast state, but, it can be

extruded without difficulty at 40oC

Extrusion defectsSurface crackingPiping defectInternal cracking

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