Influence of material properties and stamping conditions on the stiffness and static dent resistance of automotive panels

The use of thinner sheets and the introduction of new materials has meant that the stiffness and dent resistance of exterior panels has become more focused in the automotive industry during the last years. The objective of this study was to investigate the influence of material choice and the effect of varying stamping process conditions on the stiffness and static dent resistance of automotive panels. The experiments were performed on a double-curved panel. Four different materials were included in the study: an aluminium grade, a mild steel, a high-strength steel and a stainless steel. For each material, two different stamping-process conditions were adopted to obtain different strain, stress and thinning distributions in the panels. The same stamping process conditions were applied to all four materials. It can be concluded that the material grade significantly influences the static dent properties. The high-strength steel showed considerably better dent resistance than the other materials. The aluminium panels had slightly better dent resistance than the mild steel panels, although having much lower stiffness. The stainless steel grade had the lowest dent resistance, despite its high yield stress. An effect of the stamping process conditions was also found. Increased blankholding, with consequent increased strain levels in the panels, was generally beneficial to the static dent resistance. The experiments show very little scatter, indicating that the testing methodology developed worked satisfactorily.