Bulge forming method and bulge forming apparatus

摘要

A bulge forming method includes arranging a raw material tube inside a die having an inner surface shape, in which plural crest portions and root portions are alternately formed, and providing a rod inside the raw material tube in the axial direction of the raw material tube, and the rod has a pressurized liquid supply opening. The bulge forming method further includes providing a pair of sealing portion having the pressurized liquid supply opening therebetween, and the sealing portions seal a space between the raw material tube and the rod. The bulge forming method further includes 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.