Disc upsetting between spherical dies and its application to the determination of forming limit curves

Abstract

The plastic upsetting of a disc with spherical dies is investigated experimentally and theoretically to determine points on a forming limit curve. For steel specimens of various dimensions, it is found from experimental study that fracture occurs at the free surface of the specimens. Simple theoretical calculations based on the obtained experimental results are performed to determine the state of stress and strain leading to fracture initiation. An advantage of the theoretical approach proposed is that considerations of friction on the die-workpiece interface are excluded. The fracture conditions obtained are used to predict the shape of the forming limit curve at large values of the triaxiality factor.