Design and performance evaluation of sheet metal punch tip inserts manufactured by bulk forming for the automotive industry

This Master’s thesis investigates the fatigue resistance and wear behavior of cutting punches used for sheet metal punching of advanced high-strength steels (AHSS) in automotive applications. Due to their high strength, AHSS such as DP1000 impose significantly higher mechanical and tribological loads on cutting tools, leading to accelerated wear and reduced tool life compared to conventional steels. Previous studies on tool wear for conventional steels do not fully capture the stresses and effects on tools when processing AHSS. Although research has explored tool wear through experimental and numerical methods, and improvements via coatings and materials, little work has been done on how tool manufacturing processes affect wear and fatigue resistance in AHSS punching. The study focuses on punches manufactured from tool steel 1.2363, comparing conventionally machined punches with punches produced by cold forging followed by finishing operations. Unlike standard manufacturing routes, the formed punches exploit plastic deformation to modify the internal material structure, with the objective of improving fatigue resistance and wear performance. The sheet material used in the experimental investigation is dual-phase steel DP1000, representative of current automotive AHSS grades. A dedicated punching test series was conducted under high-cycle loading conditions to evaluate tool wear, damage evolution, and fatigue behavior. The punches were subjected to identical cutting conditions to enable a direct comparison between manufacturing routes. Wear mechanisms and surface damage were analyzed, with particular attention to edge degradation and microstructure features. The experimental results show that cold-formed punches exhibit a wear and fatigue behavior comparable to that of conventionally machined punches under the tested conditions. No significant differences in tool life or dominant wear mechanisms were observed between the two manufacturing approaches. These findings indicate that cold forging of 1.2363 tool steel is a viable alternative to conventional machining for punch manufacturing, offering similar performance while providing potential advantages in material utilization and production efficiency.