Improvement of Geometric Accuracy in Micro-Slot Punching with Small Pitch

Abstract

Sheet metal parts with many slots are used for filters, and decreases in the pitch between adjacent slots are demanded. However, in punching narrow slots with a small pitch, the bridge portion between slots tends to be twisted, causing functional problems. In this paper, countermeasures for this defect are proposed and demonstrated using a stainless steel sheet of 0.25mm thickness. When the pitch was reduced to the same value as the sheet thickness, in the conventional punching process, the defect could not be prevented by increasing the blank holding force. At the same pitch, the punch with an inclined face was effective for reducing the defect if the proper angle and direction of inclination were selected. From the viewpoint of supporting the side face of the bridge portion, the method of using punched scraps as guide tools was tested. By this method, the defect of the bridge portion at a small pitch of less than the sheet thickness could be prevented although an additional stage was needed for removing the scraps.