Aluminium Extrusion Process Basics

Aluminium billets are the starting point of the extrusion process (see picture below):

aluminium billets

Extrusion process has been first introduced in 1797 to produce lead pipes using forcing the metal to flow through a die by means of a screw operated by hand. In 1820 the process switched from manual to force generated by hydraulic presses. In 1894 Alexander Dick invented the modern hot extrusion process which could be applied to most non-ferrous materials.

For aerospace applications, billets are scalped (in other terms some mm of the outer layer of the billet is removed by means of a milling machine) otherwise are cut to length and the resulting pieces are called extrusion logs (see picture below):

billet logs

Before going into the extrusion process, logs have to be preheated above the recrystallization temperature because the as cast microstructure is not suitable for the extrusion process.

After heat treatment, logs are inserted into the container and then forced to flow through the die opening by compressive forces exerted by a hydraulically operated ram. The basic process is described in the picture below:

Aluminum Extrusion Process Basics

The extrusion profile temperature is monitored during the production in order to achieve a desirable temperature range (function of the aluminium alloy extruded) through the control of the extrusion speed.

A puller and roller conveyor guides the extruded profile exiting the die. Along the roller conveyor a series of fans cool down the profile. When the desired length of the profile is reached, a saw or a shear cut the profile.

Not all the log can be extruded. The final part of it contains oxides from the billet skin that need to be rejected. This part of the log is called butt.