| 摘要 |
PROBLEM TO BE SOLVED: To provide a hydroform processing method for a metal tube capable of preventing deterioration of wall thickness as much as possible in the case that a bulge portion is formed on a part in the peripheral direction of the tube in the hydroform processing method for the metal tube used for an exhaust duct or the like of the internal combustion engine, for example. SOLUTION: The hydroform processing method is characterized in that a metal stock material tube is provided inside a forming die and the end portion of the stock material tube is pressed and at the same time, when fluid pressure is given into the stock material tube through the hydroform process to manufacture the metal tube having the bulge portion on the part of the tube, a forcing volume into the forming die in the side to form the bulge portion on at least one part end portion of the stock material tube is made higher compared with the other region. Specifically, for example, at least one end portion of the stock material is formed in the inclined surface and is rammed into the inward direction of the forming die, or, at least one end portion of the stock material tube is expanded and simultaneously, a step portion is formed and the step portion is rammed into the inward direction of the forming die by a tubular body.
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