| 摘要 |
PURPOSE: A metal pipe with an eccentrically expanded open end free from cracks and necking, by formation of a coaxially expanded open end, which is elongated along an axial direction of the metal pipe at a side to be eccentrically expanded longer than the opposite side to be expanded without eccentricity is provided. CONSTITUTION: The method of manufacturing a metal pipe with an eccentrically expanded open end comprises the steps of forcibly inserting a coaxially expanding punch(10) into an open end of an original metal pipe(M), so as to plastically deform said open end to such the coaxially expanded state that a side to be eccentrically expanded is longer than the opposite side to be expanded without eccentricity along an axial direction of said original metal pipe(M); withdrawing said coaxially expanding punch(10) from said original metal pipe; and then forcibly inserting an eccentrically expanding punch, which has a boundary(13) between a conical tip(11) and a cylindrical body(12) inclined with a predetermined angle(α) with respect to a radial direction of said original metal pipe so that said cylindrical body(12) comes in contact with an inner wall of the coaxially expanded open end at the side to be eccentrically expanded earlier than the opposite side to be expanded without eccentricity, into the coaxially expanded open end of said original metal pipe so as to plastically deform said open end to an eccentrically expanded state.
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