| 摘要 |
PROBLEM TO BE SOLVED: To provide a forming method of the cup with an inside boss, which prevents shrinkage generated to a bottom part, when forming the cup with the inside boss by backward extrusion and has a projecting shape, at the bottom part, forming the inside boss into a prescribed height. SOLUTION: A stock 10 is formed, in a first process, to a cup outer wall wall 13A and a inside boss 14A by backward extrusion, at the same time, a projecting shape part 15 is formed by forward extrusion so as to prevent generation of shrinkage to a bottom part 16A center part, further, an inside boss is made to a prescribed height, in a second process, the cup outer wall 13A is subjected to ironing and then the bottom part is subjected to sizing, the cup outer wall 13 is finished to a height H (t) from the bottom, an outer diameter of A and a hole diameter of B, further, the inside boss is finished to an outer diameter C and a height H and a bottom thickness (t) of the bottom part 16 is finished. By adjusting a height (h) of the projecting shape part 15, the inside boss 13 is formed to a prescribed height.
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