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Traditionally, high-strength low-alloy (HSLA) steel is used for automotive vehicle weight reduction in the North American automotive industry. Dual phase (DP) high strength steel has gained great attention because it provides a combination of high strength and good formability. The main advantage of DP steel is the high ratio of tensile strength to yield strength, which provides more flexibility in stamping and higher energy absorption in a component crush event. This study compares the performances of DP and HSLA steel grades in stamping processes and component crush events, as shown in a typical automotive unibody inner rail. Simulation results show that DP steel offers more uniform strain distribution, improved formability, and better crush performance than conventional HSLA steel.

A three-dimensional surface profilometer has been used to examine the surface morphology in various regions of stamped automotive steel parts. This analysis provides insight into the nature of the surface morphology development during stamping. For this work, four stamped zinc-coated sheet steel sections were considered. Each of the sections was examined with the 3-D surface profilometer in a variety of regions suspected to show different surface morphology due to differences in forming. Upon analysis of the surface height frequency histograms, different modes of deformation on the part surface were identified and categorized. Three modes of surface deformation were observed - “simple pressing”, “pressing with small scale sliding and bending” and “pressing with gross sliding, stretching and bending”. Each mode had a distinctive set of characteristics in the frequency height histograms. These modes were observed in both galvannealed steel sheet and hot-dipped galvanized steel sheet.

In recent years, strict weight reduction targets have pushed auto manufacturers to use lighter gauge sheet steels in all areas of the vehicle including exterior body panels. As sheet metal thicknesses are reduced, dentability of body panels becomes of increasing concern. Thus, the goal becomes one of reducing sheet metal thickness while maintaining acceptable dent resistance. Most prior work in this area has focused on quasi-static loading conditions. In this study, both quasi-static and dynamic dent tests are evaluated. Fully assembled doors made from mild, medium strength bake hardenable and non-bake hardenable steels are examined. The quasi-static dent test is run at a test speed of 0.1 m/minute while the dynamic dent test is run at a test speed of 26.8 m/minute. Dynamic dent testing is of interest because it more closely approximates real life denting conditions such as in-plant handling and transit damage, and parking lot damage from car door and shopping cart impact.