Patent ID: 7051768

Claim:
A hydroform process of advancing expansion of an original tube member, with a predetermined portion approaching an outer peripheral surface of the original tube member, by pressuring the original tube member from inside, using a die assembly having molding surfaces and the predetermined portion, the predetermined portion being included in the molding surfaces and approaching the outer peripheral surface of the original tube member during hydroforming, comprising: attaching an assisting member, made of an incompressible material softer than the original tube member, at least to an area included in the outer peripheral surface of the original tube member and corresponding to the predetermined portion of the die assembly; setting, into the die assembly, the original tube member with the assisting member attached thereto; and pressuring the original tube member from inside, thereby forming the original tube member into a shape corresponding to the molding surfaces, wherein the assisting member covers the outer peripheral surface of the original tube member for a distance greater than one half the peripheral surface in the axial direction of the original tube but less than the total outer peripheral surface of the original tube member before setting into the dye assembly.