Optimal Production Trimming Process for AHSS Sheared Edge Stretchability Improvement

Edge fracture is one of the major issues for stamping Advanced High Strength Steel (AHSS). Recent studies have showed this type of fracture is greatly affected by an improper trimming process. The current production trimming process used for the conventional mild steels has not been modified for AHSS trimming. In addition to the high-energy requirement, the current mechanical trimming process would generate a rough edge (burr) with microcracks in trimmed edges for AHSS trimming, which could serve as the crack initiation during forming. The purpose of this study is to develop a proper production trimming process for AHSS and elucidate the effect of the trimmed edge conditions on edge fracture. A straight edge shearing device with the capability of adjusting the shearing variables is used in this study. Two different AHSS grades, DP600 and DP980, with similar thicknesses are selected to assess the edge stretchability of the material for edge conditions created using various shearing variables. For comparison purposes, both water jet cutting and laser cutting processes are also included in this study. The edge stretchability of the sheared specimen is evaluated using a sheared edge tension test and a half dome test. Microhardness measurements on the sheared edge are also conducted to evaluate the shear edge damage resulting from various shearing methods. Results have revealed that the traditional zero degree trimming process would result in the worst edge stretchability, while the optimized mechanical shearing process can greatly improve the edge stretchability and delay edge fracture in the forming process. The optimized mechanical shearing process can achieve a comparable performance to the high-energy laser cutting and water jet cutting processes.