Micro-level clearance punching on NGO electrical steel

Non-grain-oriented electrical steel lamination is a critical component for the magnetic core. Punching such steel sheet with a large shear region, a low burr and small rollover is required to ensure accuracy. Densely packed grain deformation and plastic strain near cut surface are generally accompanied which detrimentally influence magnetic properties. In this study, micro-clearance (CL: 1 and 5 µm) punching of electrical silicon steel was conducted to investigate the influences of punching speed, micro-clearance, and counterforce on dimensional accuracy and microstructural changes. Electron backscatter diffraction analysis was performed to investigate the microstructural characteristics and detailed texture of specimens produced by shear speeds of 100, 260, and 600 mm/s with and without applied counterforce. Rollover height was found to be significantly reduced at a shear speed of 260 mm/s with applied counterforce under 1 µm clearance punching. The applications of counterforce and higher speed both significantly increased grain deformation, although the dimensional accuracy was improved. Grain conditions and the quality of cut surface were compared for different punching conditions to advance the understanding on the correlations between dimensional accuracy, grain deformation, and plastic strain.