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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.

The robust operating window is a major problem during sheet stamping, but existing practical experience concerning process sensitivity is approximate and qualitative only. In this study, sensitivities of strain, punch force, and draw-in to the process and material parameters were calculated for a given part geometry. To ilustrate the influence and relative importance of n-value, anisotropy, friction, and restraining force selected results are presented, compared, and discussed. It was found that strain is the most sensitive, while punch force is least responsive. The restraining force has the strongest influence, and friction is relatively less important. Sensitivity responses are highly nonlinear, thus not allowing for extrapolation or generalization. The sensitivity calculations were performed following a proposed methodology, based on virtual experiments (numerical simulation). It allows variation of one selected parameter only, and keeps project time and cost lower.

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.