5.1 Definition

Extrusion is a bulk forming process in which the material is made to flow using high pressure. The deformation takes places mainly at room temperature cold extrusion as by this means plate-finished workpieces with close dimensional accuracy are obtained.

The billets are only heated to forging temperature hot extrusion if extreme conditions would be necessary for cold forging (high punch force, high degree of deformation, etc).

Workpieces produced in this way are of low dimensional accuracy and have rough surfaces due to scaling, requiring reworking in most cases.

5.2 Application of the Process

With this process, both solid and hollow parts of various shapes (Figs 5.1, 5.2 and 5.3) are produced.

Figure 5.1: Forward extrusions

Figure 5.2: Backward extrusions

Figure 5.2: a) Typical backward extrusions

Figure 5.3: Typical parts for combined extrusion, a) punch, b) die, c) counter-punch, d) ejector

5.3 Types of Extrusion Process

Direct extrusion (forward extrusion)

The movement of the punch and the flow of the material are in the same direction. During the extrusion process the pressure of the punch forces the material to flow in the direction of the movement of the punch, in the process of which the workpiece being formed takes on the shape of the inside of the die.

Figure 5.4: The principle of forward extrusion

Indirect extrusion (backward extrusion)

The flow of the material is in the opposite direction to the movement of the punch. The material is made to flow by the pressure of...