Fine Piercing of Amorphous Electrical Steel Sheet Stack Using Micro-/Nano-Textured Punch

The amorphous electrical steel sheets were expected to be used for motor cores because of their high strength and low iron loss even in high frequency electromagnetic field. However, their high strength without ductility caused various difficulties in piercing them. In addition to reduce the punch and die wear in piercing, their shearing performance must be improved to minimize the affected damages induced at the vicinity of punched out holes. In the present paper, the shearing behavior in piercing the amorphous electrical steel sheet stack was investigated by using the micro-/nano-textured punches. In particular, the effect of nano-texturing orientation and the punch-to-die clearance on this piercing behavior was discussed for improvement of the sheared blank quality. In the piercing experiments, five sheets were stacked into a specimen. The affected damages induced at the vicinity of pierced holes were analyzed by SEM (Scanning Electron Microscopy) and three dimensional profilometer. The punch side surfaces were also observed by SEM to analyze the adhesive behavior of debris particles from the specimen work on them. As a result, it was confirmed that the micro-/nano-textured punch improves the quality of the sheared surface when shearing amorphous electromagnetic steel sheets, resulting in lower shear load, and the tool adhesion was reduced while the hole diameter variation was suppressed. A shearing mechanism by the micro-/nano-textured punch was discussed to develop the piercing process with less affected damages and less iron loss.