Abstract
The periodic nanotexture was superposed to the micro-textured grooves on the side surface of the punch. These grooves with nanotextures were shaped to have parallel and vertical orientations to the punch stroke direction, respectively. A stack of five amorphous electrical steel sheets was punched out with these micro-/nano-textured punches. The process affected zone at the vicinity of the punched hole was analyzed by SEM (Scanning Electron Microscopy) and a three-dimensional profilometer. The punch surfaces were also observed by SEM to describe the debris particle adhesion on them. The dimensional change in each layer of the stack before and after perforation was measured to describe the punching behavior with the comparison to the punch diameter.
Highlights
A high-capacity motor core with low iron loss has been strictly demanded by automotive companies with an urgent shift of production to electric vehicles [1]
Each amorphous electrical steel sheet of the pierced stack was analyzed by SEM to measure its affected zones by piercing
When using punch #2, two types of defects were induced to the first sheet in the pierced stack, e.g., a shear droop at the edge of the pierced hole, and a circumferential crack along the hole
Summary
A high-capacity motor core with low iron loss has been strictly demanded by automotive companies with an urgent shift of production to electric vehicles [1] As their essential parts, the motor-core is made from a stack of pierced electrical steel sheets. An amorphous electrical steel sheet is highlighted and selected recently to improve magnetic performance and to reduce the iron losses by 1/10 in comparison to polycrystalline electrical steels [2,3] These amorphous work materials for piercing have no ductility but are high strength enough to induce many defects in them in piercing even by using a cylindrical punch. Microscopic defects and damages are left as an affected zone at the vicinity of the pierced holes even without visible flaws in macroscopic observation They have a risk to deteriorate the quality of magnetic properties and increasing the iron loss in total [4]. As had been studied in [5,6,7], this affected zone increases by piercing, and the shearing tool life was significantly reduced to lower the cost-competitiveness
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