Fine-Piercing of Electrical Steel Sheets by Edge-Sharpened Diamond Punch

Femtosecond laser trimming procedure was optimized to reduce the edge curvature of diamond-coated WC (Co) punch as possible and to decrease the maximum roughness of diamond coatings. Bare diamond-coated WC (Co) punches with normal grain size were prepared to have an original film thickness of 9 μm. Through two laser machining steps, the edge width of diamond coating was reduced down to 2 μm. By using the core die with the clearance of 4%, fine piercing experiments were performed to measure the load–stroke relationship and to describe the affected zone formation by shearing. The affected zone area as well as the fractured surface ratio significantly decreased with a reduction of the edge width down to 2 μm.