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The CAE analysis revealed that a stamping component required extremely high yield strength steel in order to pass the safety requirements. However, springback with this component could cause assembly distortions. The formability prediction was compared with the actual nominal die stamping for splits and wrinkles. The predicted free state springback was compared to the measurements. A compensated die was engineered based on the springback dimensions of the free state stamping. Morphing the negative residual surface created the dimensional compensation. Then a new compensated die face was created. A CAE prediction was used to confirm and adjust the compensated die using iterations of predictions and corrections.

The use of aluminum alloys as automotive body materials increases the need for springback control because of their higher yield strength-to-elastic modulus ratios. Math-based tools can be used to predict the amount of springback of sheet metal parts after stamping, and to further compensate the die face, based on the prediction, to reduce springback. In this study, analysis was conducted with LS-DYNA [1] on an aluminum hood inner to verify the accuracy of springback prediction. This was used as a basis for the die face compensation through a morphing procedure [2, 3]. Reasonably accurate springback prediction was obtained in the rear region of the hood inner, while in the front center region, LS-DYNA over-predicted springback. Gravity loading, appropriate mesh size and adaptive level can all affect springback prediction. Material models have a significant effect on springback prediction of this part.

Previously-reported draw-bend tests showed large discrepancies in springback angles from those predicted by two-dimensional finite element modeling (FEM). In some cases, the predicted angle was several times the measured angle. With more careful 3-D simulation taking into account anticlastic curvature, a significant discrepancy persisted. In order to evaluate the role of the Bauschinger Effect in springback, a transient hardening model was constructed based on novel tension-compression tests for for three sheet materials: drawing-quality steel (baseline material), high-strength low-alloy steel, and 6022-T4 aluminum alloy. This model reproduces the main features of hardening following a strain reversal: low yield stress, rapid strain hardening, and, optionally, permanent softening or hardening relative to the monotonic hardening law. The hardening law was implemented and 3-D FEM was carried out for comparison with the draw-bend springback results.