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Robust operating window and subsequent quality of part are major concerns during sheet metal stamping. For a given part geometry, material, and lubrication conditions, the sheet restraining force is the key parameter controlling metal flow, thus influencing formability and quality of the resulting part. Recent advances in press and die building provide capability of the restraining force (RF) variation during a stamping stroke. In this study, a laboratory and numerical experiments were performed in an effort to better understand the effect of various VRF trajectories on stamping performance. The working numerical model using explicit LS-Dyna 3D code was successfully developed for time effective simulation of complex parts with variable binder force. Several trajectories are proposed and tested, showing strong nonlinear influence. This indicates the need for predictive approaches capable of establishing robust and optimal trajectories for individual complex industrial stamping designs.

Springback is a serious problem in sheet metal stamping. It measures the difference between the final shape of the part and the shape of the forming die. Sheet metal forming simulation has made significant progress in predicting springback and several computer simulation codes are commercially available to predict and compensate for it in tool design. The accurate prediction of springback is important and there is a need to validate and verify those predictions with experimental results. Current validation techniques lack standardized procedures, require measurement fixtures that may impose unrealistic restraint on the part, require profiling equipment such as CMM or laser scanning and for the most part produce small springback which reduces measurement accuracy and increases experimental error. A benchmark test has been developed which addresses all these concerns and compares springback predictions by various numerical simulation codes with each other and with experimental results.

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.