Modifying strain-hardening of carbon steels for improved finite element simulation of orthogonal machining

The results of finite element simulations of machining three carbon steels (BS970 070M20, 080M40, and 080M46), in the speed range 50-250 m/min and at an uncut chip thickness of 0.25 mm, are presented and compared with experimental results. It is shown that predictions of cutting forces and chip thickness ratios that are better than those obtained in many previous studies can be achieved by systematically changing the measured strain-hardening behaviour of the steels, to create materials with higher initial yield stress but unchanged flow stress at strains greater than 1.0. A justification for the change comes from earlier work that demonstrated an equivalence between that and including an upper yield point in the description of the initial yielding of the steel and which also shows that inclusion of an upper yield point is key to accurate predictions. The practical value of the paper is to show how improved simulations of machining may be obtained with commercial software packages without the need to create upper yield point material models.