Process Encyclopaedia

Metal extrusion was developed in the late 18th century for making lead pipe. The basic process of forcing a round billet through a shaped die is still used today.
Modern variants can produce clad products in one go - e.g. copper clad with silver.
Wire drawing is related to extrusion but is used for smaller (round) sections and the metal is pulled through the die rather than pushed.

Mainly used with the softer metals, e.g. aluminium, copper, zinc.
Generally speaking, the softer the metal, the more intricate the shapes that can be made.
Useful for long thin parts with constant cross-section.
Possible cross-sections are usually less than 100mm across.
Dimensional tolerance and surface finish may be poor with hot extrusion.
Cold extrusion is possible for some metals giving better properties.

Although extrusion appears to be a continuous process, it is really a batch process as it needs to be interrupted to load new billets.
Typical machine prices are in excess of Ł50,000.
Dies can cost upwards of Ł1000 to make (depending on size), but a lot more to design well.
More frequent die replacement is needed for higher strength metals.
Production rates from 5-10metres/minute are possible.
Usually only economic for several thousand metres +