Control on Shearing Process of Amorphous Electrical Steel Sheets by Punch-Edge Shaping and Finishing

High efficiency of electric motors is an essential requirement for an electrified society. Amorphous electrical steel sheets are supplied as thin foils with a thickness of approximately 25 µm and exhibit a high tensile strength of about 2.2 GPa, limited elongation of around 1%, and a high hardness exceeding 900 HV. During the shearing process of motor cores, these materials tend to exhibit brittle fracture behavior, and their high hardness often leads to frequent tool damage. To suppress tool damage, introducing a chamfer at the punch edge is an effective approach to avoid excessive stress concentration during shearing. However, the chamfer length in the punch stroke direction induces inward drawing of the work material toward the die center during shearing, resulting in bending deformation and crack formation on the punched hole surface. In this study, a chamfer of 20 µm was introduced in the radial direction at the punch edge, and an additional chamfer of 1–2 µm was provided in the stroke direction. Furthermore, a condition with a nano-texture applied to the punch surface was also prepared. Half-shearing experiments were conducted on amorphous electrical steel sheets to observe crack initiation behavior, and the fracture propagation and fracture mechanisms were discussed.