Shape complexity, metal flow, and dead metal zone in cold extrusion

Nonhomogeneous metal flow through an extrusion die can directly affect product quality, productivity, and die life. The complexity of a die profile is an indicator of how difficult it is to extrude the profile. Some investigations about the effect of die complexity on extrusion pressure, product quality, and die life can be found in the published literature. However, the effect of profile complexity on metal flow through the extrusion die has not been explored much. Such a study can directly contribute toward die design improvement and reduction of extrusion defects related to metal flow. This article investigates the effect of shape complexity on the dead metal zone (DMZ) and metal flow through cold extrusion experiments and finite element simulations on some solid profiles. Experiments were performed using flat-face dies of different complexities and different billet materials. 2D and 3D finite element simulations were carried out. One significant conclusion is that currently existing definitions of extrusion shape complexity cannot satisfactorily explain the variations in DMZ size under different conditions. Factors such as die profile symmetry and extrusion ratio may play significant roles in the formation of DMZ and distortion of metal flow through the die.