In the extrusion process a heated aluminum billet is pressed through a steel die to take a specific shape. Typically, extruded products are long metal bars or tubular sections used as structure components or body parts in automotive or in a wide range of general engineering applications. Extrusion types are divided into three basic forms, depending on the degree of difficulty in forming the cross section: (i) solid extrusion, (ii) semi-hollow and (iii) hollow extrusions.
Rods and other simple geometric cross-sectional forms without enclosed surfaces are examples for solid extrusions. Semi-hollow extrusions are more difficult to shape to extrude. Hollow extrusions are the most difficult to produce and are characterized by at least one fully enclosed chamber.