| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for forming a thick necking which has a sufficient spring effect and excellent in durability and corrosion resistance, to a cylindrical member. SOLUTION: In a method for forming a necking to a cylindrical member 34, in which a mandrel 30 having a recessed part over a whole peripheral face is arranged inside a cylindrical member 34, while rotating the cylindrical member 34 at least, the part corresponding to the recessed part of a mandrel 30 out of the outer peripheral face of the cylindrical member 34 is pressed by a first peripheral pressing part 36a to produce a necking 10a, further, by pressing with a second peripheral face pressing member 36b, a necking 10b deepened is obtained, a radius of curvature of a tip part of the first peripheral pressing member 36a is made larger than the second peripheral pressing member 36b, in pressing by the second peripheral pressing member 36b, the necking 10b is elongated at a state of abutting to a recessed part of the mandrel 30 and its depth is increased. |
