A method of forming a tubular member.

摘要

A method of forming a tubular member of polygonal cross-section from a tubular blank (36) of substantially round cross-section includes the steps of providing a lower die (40) member having a cavity portion submerged substantially below the top surface (46) of the lower die and having a cavity width equal to the width of the desired tubular member and less than the diameter of the tubular blank. The lower die has an entry opening (50) which opens to the top surface of the lower die and is defined by angularly disposed funnel walls (52,54) which converge to intersect with the cavity portion. The tubular blank is placed onto the lower die so that the blank rests on the angularly disposed funnel walls above the cavity portion. An upper die (42) is lowered onto the lower die. The upper die has a lid wall (82) which forces the tubular blank downwardly into the cavity portion while the angularly disposed funnel walls guide the tubular blank to collapse it in a manner preventing pinching of the tubular blank between the upper and lower dies. The application of internal hydraulic pressure then expands the collapsed tubular blank outwardly to the shape defined by the cavity portion of the lower die and the lid wall of the upper die. <IMAGE>