THE THEORY OF EXTRUSION

Abstract

Extrusion is essentially a process in which a slug of material or a billet is forced through a suitably shaped die and converted into a continuous product of uniform cross-section. Specialized developments, such as the extrusion of taper sections and the manufacture of extrusion forgings, retain the essentials of the basic process. Two methods of extrusion are commonly employed, namely, direct and inverted. In direct extrusion, the die is locked in the end of the chamber and the billet is forced through the die aperture by the ram, relative motion occurring between the billet and the chamber wall. In the inverted process, the billet is placed in the chamber and the die is rammed into it, with no relative motion taking place at the chamber/billet interface (see Fig. 1). The choice of which press components are held stationary, is a matter of convenience of design.