A sharp character of automobiles is required to express its sporty appearance. A sharp character is, however, prone to a type of defect called the “skid line” as one of the surface defects caused during press forming. Dealing with skid lines requires repeated die repairs, which have been a major problem in the press shops. We clarified the mechanism of skid line formation by continuous surface shape measurement and finite element analysis (FEA) of the formation process of a skid line during press forming. In this study, the effect of material strength on skid line formation was investigated by conducting experiments on skid line reproduction and measuring the skid line profiles, using 270-440 MPa grade sheet steels, which are used for automobile outer panels. The results suggest that the Yield point (YP) of sheet steel has a major effect on skid line formation as shown by the finding that skid lines became more marked with the decrease in material strength. From the test results, the prediction equation of the estimated Δs of skid lines by the blank holder force and YP was obtained.
