Velocity-dependent shear band formation in blanking processes

High-speed blanking processes are of major interest for manufacturing sheet components from high-strength materials, as not only high-quality surfaces but further excellent properties are enabled. Reason for this are adiabatic shear bands (ASB) formed in the shear zone during the process. However, up to now it is not fully understood how ASBs evolve depending on the process conditions. For the first time, surface geometry and ASB formation are investigated for an identical macroscopic stress state using different blanking speeds. A press-hardened 22MnB5 steel is blanked with punch velocities ranging from 0.12 to 17 m/s using different machine drive concepts (mechanical, hydraulic and electromagnetic), resulting in nominal shear strain rates of up to nearly 100,000,000 s⁻¹. The velocity significantly influences ASB length and width as well as the microstructure and hardness of the blanked surfaces. For 17 m/s blanking speed, an ASB covering the full-length of the blanked surface, i.e. the complete sheet thickness, is realized. Further, for high velocities, ASBs not only dominate the appearance of the blanked surface but also lead to significantly lower roughness, when compared to conventionally blanked surfaces. This study lays the foundation for future work on tailoring functional surfaces using high-speed blanking.