Hydrostatic extrusion of composite rod

Hydrostatic extrusion is a process where the billet is completely immersed in pressurized liquid. Pressure at the die orifice is lower than that at the die entrance, and the resulting pressure differential causes metal flow toward the orifice or die exit. The force required to push the billet through the die is thus provided by the hydrostatic pressure instead of by a direct ram force. Composite rods or wire are composed of two or more different materials, each material having its own distinctive mechanical characteristics. Because a composite rod billet deforms more uniformly in hydrostatic extrusion than in conventional extrusion, it is considered that hydrostatic extrusion is one of the most effective processes to manufacture composite rods and wires. The aim of this work is to propose an analytical model for hydrostatic extrusion. In this model, the liquid surrounding the billet is considered as a kind of hydrodynamic lubrication. On the other hand, the upper-bound theorem is adopted to analyse the deformation of the composite rod or wire. A model describing plastic flow of these clad rods has been established. Work-hardening effects of the materials are taken into account in the model. The results show the deformation behavior of billets in hydrostatic extrusion under different processing conditions. Finally an experiment of hydrostatic extrusion of round rod has been conducted and its results found to be very close to the model analysis.