Aluminium encyclopaedia

Impact extrusion

In aluminium processing, impact extrusion at room temperature, so-called "cold impact extrusion", is an important method of forming. A circle (also a slug or a billet), which is a disc stamped out of strip, is placed in a steel die. When a steel punch is pressed against the circle with a pressure of up to 1500 newtons per square millimetre, the aluminium deforms plastically. It "flows" through openings in the punch, die or between the two and adopts a shape given by the shape of the tool, such as a cylinder. It is possible to produce rectangular or circular cross sections with diameters from 3-150 millimetres, wall thicknesses of 0.1 millimetres upwards and heights that are up to ten times the diameter (but with a maximum of 450 millimetres) as well as external and internal ribs. Wrought alloys can be used but the best materials are unalloyed aluminium and refined aluminium.

The extrusion process lasts only a fraction of a second, it can be automated to a large extent and the extrusion die has a long service life. The products, especially aluminium packaging like cans or tubes as well as blanks for rivets, screws or shaped parts have high strength as a result of cold working, smooth surfaces and high dimensional accuracy. Hardly any scrap is produced.