Sheet Forming with Pulsating Blankholder Modeling and Experiments

Robust processing window and subsequent quality of part are major concerns during sheet metal stamping. The sheet restraining force is a key parameter controlling metal flow, thus influencing formability and quality of the resulting part. Recent advances in press and die building provided capability of altering the restraining force (RF) during a stamping stroke via pulsating blankholder force (PBF). An outcome of this technology would be an increase in the maximum drawing depth resulting from a decrease in the average blankholder force. In this study, laboratory and numerical experiments were performed in an effort to better understand the effect of various PBF trajectories on stamping performance. A working numerical model using explicit code was successfully developed for time effective simulation of drawn cups with pulsating binder force. Preliminary results of this ongoing project are presented. The pulsating force trajectory was found to have a beneficial effect on drawability. Also, robustness with respect to process parameters such as friction and binder force was increased. The amplitude of the pulsation was found to be a key factor while the frequency was of minor importance to drawability and process robustness. The optimum values of the maximum binder force and amplitude maybe difficult to establish because the results depend on part geometry, among others. This indicates that there is a need for numerical predictive methods to approach individual stamping designs.