| 摘要 |
PROBLEM TO BE SOLVED: To form a complicated shape without generating any lantern-like buckling or cracks by using a tube whose cross-sectional wall thickness is increased in a range including a swollen portion. SOLUTION: A metal pipe P is set inside a die 2, a hydraulic pressure is applied to the inside of the metal pipe P, and an end face of the metal pipe P is pressed by shafts while gradually increasing the hydraulic pressure to form swollen portions 110, 111 in the middle of the metal pipe P. Thick wall regions 120, 121 have a larger wall thickness than a regular thickness region 13. The swollen portion 110 corresponds to the thick wall region 120, while the swollen portion 111 corresponds to the thick wall region 121. The thick wall regions 120, 121 of the metal pipe P are swollen along with the working, and their thickness is reduced. As the wall thickness at the thick wall regions 120, 121 becomes larger, the wall thickness is more uniformly reduced in the whole cross section of the metal pipe P. As a result, the degree of the local concentration of the wall thickness reduction becomes less pronounced, and the radio of crack generation is decreased.
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