Effect of Hardening Rule on Analysis of Forming and Strength of Multistage Cold Forged Bolt without Heat Treatment

Abstract

The isotropic hardening model for an elastic-plastic material have often been used for simulation of cold forging processes, by which, however, it is difficult to represent the Bauschinger effect properly. On the other hand, considering the Bauschinger effect is essential for more precise simulation of the forming process as well as the strength of the forged part without heat treatment. One example is a cold-forged bolt of stainless steel. In the present paper, for two multistage cold forming processes of non-heat-treated stainless steel bolts, the simulations of the forming process and the strength were performed by FE analysis using the YU model that is one of the kinematic hardening models being able to express the Bauschinger effect. As a result, the Bauschinger effect during the forming process can be expressed properly. Moreover, by carrying out the analysis on the tensile test of the forged bolt, the difference in strength by between the isotropic and the kinematic hardening models can be estimated clearly. Furthermore, the effect of the forming process on the strength of the forged bolt can also be evaluated appropriately.