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The risk of skid lines for Class A panels has to be assessed before releasing the die development for hard tooling. Criteria are needed to predict skid lines in the formability evaluation stage to avoid expensive changes to tooling and process for resolving skid line issue in production. In this study, criteria using three different measured parameters were developed and validated. A draw-stretch-draw (DSD) test procedure was developed to generate skid lines on lab samples for the physical evaluation. This was done using tooling with various die entry radii and different draw beads. The skid line severity of lab samples was rated by specialists in the inspection of automotive outer panel surface quality. The skid line rating was correlated with geometric measurements of the lab samples after the DSD test. The sensitivity of the appearance of skid lines to tooling and process parameter variations was identified.

Hot stamping or so-called continuous press hardening is a process to make sheet metal parts with yield-tensile strength up to 1150Mpa-1550Mpa. Due to the high specific ratio of quenched Boron steels, which is higher than those of aluminum alloys and magnesium alloys, the components with low mass can be made from hot stamped Boron steels. In current industrial practice, direct hot stamping process, which forms a part directly from a flat sheet blank, is normally used to make geometries with relatively mild deformation, such as B-pillars, A-pillars etc. In this study, indirect hot stamping is introduced to develop geometries with a deep cavity and complex form features. Since the indirect hot stamping develops the part cavity depth in cold drawing and then forms detail features in hot stamping, part with complex geometry can thus be formed. A rocker component is chosen to demonstrate the technology.