Process Encyclopaedia

Overview

• 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.

Process details

Materials and shapes

• 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.

Economics

• 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 £50,000.
• Dies can cost upwards of £1000 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 +

Typical products

• Tubing
• aluminium window frames
• railings
• trims
• wires

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