Method for manufacturing eccentrically expanded pipe

Abstract

A method for manufacturing an eccentrically expanded pipe in which the plate thickness of the peripheral surface on the large expanding side that tends to easily produce cracks and necking is suppressed from becoming thin is provided. The problem is solved with a method for manufacturing an eccentrically expanded pipe plastically deforming an end of a pipe to an eccentrically expanded pipe part through an eccentrically expanding step; said eccentrically expanding step includes a first eccentrically expanding step, expanding an peripheral surface of the end of the pipe opposing to a peripheral surface finally expanded to be a final product, and a second eccentrically expanding step, expanding the peripheral surface finally expanded to be the final product.

1 . A method for manufacturing an eccentrically expanded pipe plastically deforming an end of a pipe to an eccentrically expanded pipe part through an eccentrically expanding step;
 said eccentrically expanding step includes a first eccentrically expanding step, expanding an peripheral surface of the end of the pipe opposing to a peripheral surface finally expanded to be a final product, and a second eccentrically expanding step, expanding the peripheral surface finally expanded to be the final product;   in the first eccentrically expanding step, a first eccentric punch whose axis of a cylindrical body is eccentric to a small expanding side with respect to an axis of tapered portion of the first eccentric punch and whose bus on the small expanding side of the tapered portion is longer than a bus on a large expanding side, is fitted with pressure to the end of the pipe to expand the small expanding side; and   in the second eccentrically expanding step, a second eccentric punch whose axis of a cylindrical body is eccentric to the large expanding side with respect to an axis of tapered portion of the second punch and whose bus on the large expanding side of the tapered portion is longer than a bus on the small expanding side, is fitted with pressure to the end of the pipe to expand the large expanding side.   
   
   
       2 . The method for manufacturing the eccentrically expanded pipe according to  claim 1 , wherein
 the first eccentric punch is fitted with pressure to the end of the pipe fixed to a first eccentric die having a space defined by an inner surface on the large expanded side, an inclined inner surface on the large expanding side, an inner surface on the small expanding side, and an inclined inner surface on the small expanding side, the space copying an outer shape of the first eccentric punch; and   the second eccentric punch is fitted with pressure to the end of the pipe fixed to a second eccentric die having an inner surface on the small expanding side one size larger than the outer shape of the expanded pipe part, which is a final product.   
   
   
       3 . The method for manufacturing the eccentrically expanded pipe according to  claim 1 , wherein
 the first eccentric punch is fitted with pressure to the end of the pipe fixed to an eccentric die having a space defined by a inner surface on the large expanding side, a inclined inner surface on the large expanding side, a inner surface on the small expanding side, and a inclined inner surface on the small expanding side, the space being one size larger than an outer shape of the expanded pipe part, which is a final product; and   the second eccentric punch is fitted with pressure to the end of the pipe fixed to said eccentric die right after the first eccentrically expanding step.