Method of manufacturing a metal pipe with an eccentrically expanded open end

Abstract

A method of manufacturing a metal pipe with an eccentrically expanded open end comprises the steps of plastically deforming to a coaxially expanded state M1 so that an axial wall length L2 at a side to be eccentrically expanded is longer than an axial wall length L1 at the opposite side to be expanded without eccentricity. The coaxially expanded open end M1 is then plastically deformed to an eccentrically expanded state M2 by forcibly inserting an eccentrically expanding punch into the coaxially expanded open end M1. The eccentrically expanding punch has a boundary between a conical tip and a cylindrical body inclined with a predetermined angle θ so as to bring the cylindrical body into contact with an inner wall of the coaxially expanded open end M1 at a side to be eccentrically expanded earlier than the opposite side to be expanded without eccentricity. When the coaxially expanded open end M1 is plastically deformed to an eccentrically expanded state M2, metal flow is suppressed at a side to, be eccentrically expanded, but metal flow from the opposite side to be expanded without eccentricity to the former side is promoted. Consequently, the open end is plastically deformed to the eccentrically expanded state M2 without any thickness deviation along a circumferential direction.

Dependencies are inferred from the claim text.