U-draw bending of DP780 in non-conventional drawing mode using direct-drive digital servo-press

Abstract

The U-draw bending of a DP780 sheet sample was performed using a direct-drive digital servo-press. The drawing tests were conducted in a conventional (pendulum) mode and a non-conventional mode consisting of successive tool holdings during forming. Compared to the conventional mode, the results show that the stepwise mode leads to an insignificant change in springback for the DP780 specimens. In addition, finite element (FE) analyses were conducted in order to evaluate the experimental results. The FE simulations were performed in the two modes to mimic the experiments. To simulate the non-conventional forming mode, the stress relaxation was taken into account whenever the tools were stopped during forming. For this purpose, the relaxation phenomenon was measured and captured using a creep law in simulations. FE simulation results were found to be consistent with the experiments and demonstrate that the effect of stepwise motion is negligible to reduce springback even if the stress level drops after each holding step. (C) 2014 The Authors. Published by Elsevier Ltd.