炭素鋼の異形状打抜き加工におけるダイ肩形状がせん断面形成に与える影響

The formation of a sheared surface is an important factor in punching. The fine-blanking method is known as a method for forming a sheared surface by applying compressive stress to a work material during punching. The element used for continuously variable transmission (CVT) has been put into practical use for fine-blanked carbon steel. Since this element has a different shape and a different plate thickness, there is a problem that compressive stress cannot be sufficiently applied, causing cracks occur during punching. In this study, the shoulder part of the punching die was changed in multiple steps from one step to three steps. The fine-blanked work materials were observed by scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The damage value was analyzed by the finite element method (FEM). Through these experiments and verifications, we identified a basic phenomenon in the formation of the sheared surface of the element and devised a design guideline for the die shoulder shape. When the punching die shoulder changed to the optimized three-step shape, the work hardening ability was maintained during punching. Then the sheared surface was formed with low plastic strain conditions in the deformed state of the grains.