Patent ID: 7082805
Filing Date: 2006-08-01
Classification: B21D,Y10T

Abstract:
1. A manufacturing method for a cylindrical part, having a heavy-walled portion and a thin-walled portion at least at one of longitudinal ends so that an inner-side step portion is formed at an inner boundary between the heavy-walled and thin-walled portions, comprising: a first step of forming a cup-shaped base metal by a pressing process so that the cup-shaped base metal has a cylindrical wall, a closed end and an open end at both longitudinal sides of the cylindrical wall; a second step of forming a thin-walled portion at a portion of the cylindrical wall adjacent to the closed end by an ironing process at an outer peripheral portion of the cylindrical wall, so that an outer-side step portion is formed between the thin-walled portion and a heavy-walled portion which is the remaining portion of the cylindrical wall which is not processed by the ironing process; a third step of punching out the closed end from the thin-walled portion, so that the base metal has the heavy-walled portion and the thin-walled portion; and a fourth step of enlarging the thin-walled portion radially and outwardly so that an inner-side step portion is formed at the boundary between the heavy-walled portion and the thin-walled portion.