Aluminium Extrusion: Bars, Tubes and Profiles

Almost every aluminium bar, tube, angle and T-slot profile is extruded: a cylinder of aluminium, the billet, is heated to about 350–500 °C, placed in a heavy-walled container and pushed by a ram through a steel die whose opening is the shape of the product, like toothpaste from a tube. Presses range from about 230 to 11,000 tonnes. Hollow shapes such as tube pass round a mandrel or through a die that splits and rejoins the metal. The long extrusion is cooled, stretched to straighten it, cut to length and, for the stronger alloys, heat treated. This is an industrial process; it explains how the stock that makers buy is made.