| 摘要 |
PROBLEM TO BE SOLVED: To reduce die manufacturing costs and to shorten a time required for replacing and attaching a die by fitting a plurality of replaceable combination split dies into a groove frame space provided in a die holder. SOLUTION: A die holder is attached to the slide and bolster of a press machine, and a die is held on a lower die holder without being fixed. When the central part of a pipe is stepwise expanded, the central part of the metal pipe is expanded at three stages of 30%, 60% and 100%. The die holder itself is used as the die 24 of expansion ratio of 100%. An interpolation die 23 of expansion ratio of 30% is held by the die part having the expansive dimension of 100%, and hydroforming is executed. Then, hydroforming is executed by the replaced interpolation die 23 of expansion ratio of 60%. The interpolation die 23 is removed and hydroforming is executed by the die holder 24 used in common with the die having the expansive dimension of 100%.
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