Design of multi-step dies for sheet metal forming using a workpiece-performance-based approach: A preliminary study

Deep-drawn components are predominantly manufactured using multistep operations, e.g., in a progressive or transfer dies. Currently, intermediate die design is geometry-based and often neglects the influence of workpiece plastic flow during forming on the final part's mechanical performance. This approach results in non-homogeneous material deformation, inefficient material utilisation, wrinkling defects, and an increased risk of service failures. This study proposes an alternative workpiece-performance-based die-design approach for deep drawing, emphasising the critical role of material flow in determining the component's geometrical accuracy and mechanical properties. The strategy was experimentally tested on S420MC steel (1.8 mm thickness) square cups using two-step process chains: (1) a conventional method where the blank was partially drawn into a square cup, followed by full drawing, and (2) an alternative method starting with a circular blank partially drawn into a circular cup before full drawing to the square shape. Numerical analysis in AutoForm evaluates the evolution of effective plastic strain throughout the steps. The results demonstrate significant improvements, including more uniform strain distribution, a 7% wall thinning reduction, elimination of ironed wrinkles, and components with threefold increased strength and enhanced ductility. These findings highlight the potential of performance-based die design to improve material efficiency and structural reliability.