Patent ID: 8365571

Claim:
A pipe expanding method for a steel pipe comprising: inserting a punch for pipe expanding from an opening end portion of the steel pipe; pressing a part of an axial end surface of the opening end portion of the steel pipe in an insertion direction of the punch when the punch is inserted from the opening end portion of the steel pipe, the pressing of the part of the axial end surface of the opening end portion of the steel pipe being started before a maximum diameter portion of the punch is inserted into the steel pipe; and expanding, by the punch, one side of the steel pipe corresponding to the part of the axial end surface of the open end portion of the steel pipe while the part of the axial end surface of the opening end portion of the steel pipe is pressed in the insertion direction of the punch, the pressing of the opening end portion including pressing the part of the axial end surface of the opening end portion of the steel pipe on the side to be expanded by using a generally U-shaped mold having a generally U-shaped cross-section in a plane perpendicular to the insertion direction of the punch.