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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 operating window and subsequent quality of part is a major concern during sheet metal stamping. For a given part geometry, material, and lubrication conditions, the blankholder restraining force is the key parameter controlling metal flow, thus influencing formability and quality of the resulting part. Recent advances in press building provide capability of the blankholder force (BHF) variation during stamping stroke. In this study, a laboratory and numerical experiments were performed in an effort to better understand the effect of various BHF 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. Selected results of these numerical tests, showing strong influence and process design promise, are presented, compared to the experimental results, and discussed.

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.

Recent advances in press and die building have provided the capability of restraining force (RF) variation during a sheet stamping stroke. Even though the commercial presses with VRF capabilities are now available, the full benefits cannot be attained because, for complex industrial stampings, it is difficult to select the VRF trajectory which will improve the stamping quality or achieve even more complex task of arriving at the desired design target. In this paper we demonstrate how numerical modeling can be used to select a proper VRF trajectory to achieve a postulated design target. The working numerical model using explicit LS-Dyna 3D code was successfully developed for time effective simulation of complex parts with variable binder force. Three case studies with the specific design targets of 1) springback, 2) punch force, and 3) maximum strain are presented and discussed. The results show strong nonlinear influence.

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.