Influence of Stress Distribution on Chipping of Blanking-Punch Made of Tool Steels

Abstract

The present study was undertaken to find the cause of chipping frequently found on blanking-punch, since little had been known about the relation between wear, stress, chipping and materials on the punch. The stress on the operating punch was measured and the stress distribution in the punch was calculated by computer simulation using the measured values.
The results were summarized as follows: When SUS 304 type stainless steel sheet of 2 mm thickness was stamped out by 15 mm punching with a 5% clearance, the peak pressure stress in the axial direction of about 170 kg/mm² appeared on the side surface near the edge of the punch. In this case, owing to this pressure stress, it is unknown whather fatigue took place or not. When a SPCC steel sheet of 2 mm thickness was stamped out by 15 mmφ punching with a 5% clearance, the peak pressure stress of about 55 kg/mm² in the axial direction appeared on the side surface near the edge of the punch. The value was below the fatigue limit of the tool steel. Therefore, in this case, chipping was likely to occur not in the pulling-up process. In the pulling-up process, if the side surface of punch had no adhesion and no wear-pits, the peak stress value was below the fatigue limit of the tool steel. If wear-pits or adhesion, appear in the side surface of the punch, the stress increase above the fatigue limit of the tool steel, and chipping was likely to occur.