Extrusion, its types and applications

Extrusion is the process by which a block/billet of metal is reduced in cross section by forcing it to flow through a die orifice under high pressure.

•In general, extrusion is used to produce cylindrical bars or hollow tubes or for the starting stock for drawn rod, cold extrusion or forged products.

•Most metals are hot extruded due to large amount of forces required in extrusion. Complex shape can be extruded from the more readily extrudable metals such as aluminium.

•The reaction of the extrusion billet with the container and die results in high compressive stresses which are effective in reducing cracking of materials during primary breakdown from the ingot.

•This helps to increase the utilisation of extrusion in the working of metals that are difficult to form like stainless steels, nickel-based alloys, and other high-temperature materials.

•Similar to forging, lower ram force and a fine grained recrystallised structure are possible in hot extrusion.

•However, better surface finish and higher strengths (strain hardened metals) are provided by cold extrusion.

Extrusion products

Typical parts produced by extrusion are trim parts used in automotive and construction applications, window frame members, railings, aircraft structural parts. Aluminium extrusions are used in commercial and domestic buildings for window and door frame systems, prefabricated houses/building structures, roofing and exterior cladding, curtain walling, shop fronts, etc. Furthermore, extrusions are also used in transport for air frames, road and rail vehicles and in marine applications. 

Classification of extrusion processes 

By direction

Direct / Indirect extrusion 

Forward / backward extrusion

By operating temperature

Hot / cold extrusion

By equipment

Horizontal and vertical extrusion