Abstract
In recent years, the material strength of metals used in automotive manufacturing has steadily increased to meet improved crashworthiness and weight reduction requirements. This increase in material strength has led to several difficulties in traditional press forming methods. Failure of the press-forming die is one such difficulty. To prevent failure, improved die design is necessary, which requires a detailed understanding of the mechanical properties of die materials. This paper identified the work-hardening parameters of a hardened tool steel (SKD11). Due to the brittle behavior of SKD11 in tensile tests, which were fractured at the 1.2 % equivalent strain, a shear punching test was used as the low stress-triaxiality suppresses material fracture. Furthermore, a minute punch-die clearance of 5.0 μm was used to increase the compression stress due to material deformation. SKD11 steel sheets of 1.0 mm thickness were successfully deformed with up to 30% strain, and the punching force and stroke were recorded for inverse analysis using the finite element analysis (FEA). Subsequently, FEA of the shear punching test was repeated to optimize the parameters of Swift’s work-hardening law. Consequently, the Swift parameters were derived to ensure that the measured values of the punching force and stroke correspond with the numerically simulated curve.
