55 巻 (2014) 637 号 p. 148-152
A 3-stage stamping process including thickening of the bottom and flange corners of a cup with a flange was developed to improve the fatigue strength of the cup. A circular blank was drawn with conical punches in the 1st and 2nd stages, and the bottom and flange corners were thickened by flattening the conical bottom of the cup with a flange in the 3rd stage. Not only the bottom corner but also the flange corner of the cup was thickened by forming the flange corner in the latter half of the 3rd stage. The amounts of thickening at both corners were improved by the contact of the inclined portion between the two corners with the counter punch in the 3rd stage, i.e., thickening was concentrated around the two corners by preventing thickening of the inclined portion. A wheel disk formed by 6-stage stamping having the following 3 stages exhibited 15% and 10% thickening at the bottom and flange corners, respectively, and the bending rigidity was 1.7 times as large as that without thickening. It was found that the present stamping method is considerably effective in reducing the weight of parts and production cost.