FORMABILITY IN EXTRUSION FORGING - THE INFLUENCE OF DIE GEOMETRY AND FRICTION CONDITIONS

The correct design of forging devices in industrial practice is extrem ely important. In particular, the die geometries, which greatly influe nce the plastic material flow, can give rise to unsatisfactory final s hapes, e.g. ductile fractures or incomplete die filling. The present p aper, which compliments previous works on this subject, shows some res ults obtained when studying the influence of die geometries and lubric ation conditions in extrusion-forging operations, simulating the initi al phases of closed-die forging. In particular, attention is focused o n ductile fracture phenomenon and material flow, taking these two feat ures as formability indexes. The study is carried out coupling the pla stic strain with the stress fields as indicated in the McClintock frac ture criterion. This criterion is implemented in the F.E.M. program de veloped by the authors to furnish a useful tool in die design.