PURPOSE: To form a titled flange part at high working efficiency by piercing a hole in the tube plate with a drill, expanding the upper part of the hole with a facing rod, pushing down a working roll while rotating it, and protruding the lower part of the hole to lower face.

CONSTITUTION: A hole 2 is pierced in a tube plate 1 with a drill 3. The plate 1 is cut from above with a facing rod 4 having outer diameter slightly larger than the hole 2 to the part shown by slanter lines, leaving a specified thickness L at lower end of the hole 2. Then, it is placed on a die 6 provided with a concavity or a hole 5 having inner diameter slightly larger (corresponds to the thickness L of the hole) than the diameter L2 of the part 2a cut and expanded by the facing rod 4. It is then pressed by rotating and pressing a working roll 8 provided with pressing rolls 7 arranged at equal spaces on the outer periphery and incorporated in the frame allowing independent free rotation and the part L of the hole 2 is pressed and bent by the slanted faces 7a of the rolls 7 against the lower face of the tube plate 1. Thus, a welded flange 1a is formed.