Formability in extrusion forging: The influence of die geometry and friction conditions

The correct design of forging devices in industrial practice is extremely important. In particular, the die geometries, which greatly influence the plastic material flow, can give rise to unsatisfactory final shapes, e.g. ductile fractures or incomplete die filling. The present paper, which compliments previous works on this subject, shows some results obtained when studying the influence of die geometries and lubrication conditions in extrusion-forging operations, simulating the initial phases of closed-die forging. In particular, attention is focused on ductile fracture phenomenon and material flow, taking these two features as formability indexes. The study is carried out coupling the plastic strain with the stress fields as indicated in the McClintock fracture criterion. This criterion is implemented in the F.E.M. program developed by the authors to furnish a useful tool in die design.