In this paper, the reliability-based parameter study is carried out for the stamping process of a front rail roof member with the ultra high strength steel, considering the scatters of the material properties and the process parameters. With the reliability-based design optimization (RBDO) scheme, the springback tendency is investigated from the perturbation of the process parameters such as the sheet thickness, ultimate tensile strength, yield strength, Coulomb friction coefficient, and applied padding force. The amount of the elastic recovery along the height direction is quantified to describe the springback tendency from the analysis. The analysis shows the springback-amount scattering is not ignorable when the yield stress scatters within the similar range of the ultimate tensile strength. The analysis results fully explain the importance of controlling the scatters as well as the average yield-strength amount in the mass production of the stamped products.

In this paper, the shape accuracy of the stamped hat-type product is quantified and analyzed with ultra high strength steel (UHSS) sheets. The shape of the hat-type product is designed in order to simplify the geometry of the side sill and the stamping methodology is proposed in order to verify the effect of the stamping procedure on the springback amount. Experiments and finite element analyses are conducted with four kinds of the forming sequences. The springback amounts are measured and compared according to the forming procedure with the embossing shape. Experimental result in company with analysis one illustrate that the springback amount is reduced with embossing in the padding operation. They also fully demonstrates the proposed forming procedure and the analysis method can be effectively applied to the process design for producing parts with ultra high strength steel.