Patent ID: 8091200
Filing Date: 2012-01-10
Classification: B21D,Y10T

Abstract:
1. A bulge forming method comprising: arranging a raw material tube inside a die having an inner surface shape in which plural crest portions and root portions are alternately formed; providing a rod inside the raw material tube in the axial direction of the raw material tube, the rod having a pressurized liquid supply opening; providing a pair of sealing portions so as to have the pressurized liquid supply opening therebetween, the sealing portions sealing a space between the raw material tube and the rod; and moving the rod in the axial direction while applying compressive stress to the raw material tube in the axial direction and supplying a pressurized liquid from the pressurized liquid supply opening into the raw material tube, whereby the raw material tube is formed into the shape of the inner surface of the die, wherein a sealing portion is in an anterior side of a forming direction and is applied with liquid pressure of the pressurized liquid in a direction from the rod toward the raw material tube so as to be followable to bulging of the raw material tube, and wherein the distance between the sealing portions is set to have a length of at least two crest portions of the inner surface shape of the die, and a length in the axial direction of a sealing portion in a posterior side of the forming direction is set to have a length of at least one crest portion of the inner surface shape of the die.