PURPOSE: To form a titled flange part at high working efficiency by piercing a hole on a tube plate with a drill, expanding the upper part of the hole by cutting with a facing rod, and pressing down a punch having small diameter tip to protrude the lower part of the hole to lower face.

CONSTITUTION: A hole 2 is pierced on a tube plate 1 with a drill 3. Then, the hole is cut with a facing rod 4 having an outer diameter larger than the diameter of the hole 2 from above to the part shown by slanting lines leaving necessary thickness L at the lower end of the hole 2. Further, the tube plate 1 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 2) than the diameter L2 of the part expanded by cutting with the facing rod 4. Then, a punch 7 having outer diameter equal to the expanded part 2a of the hole 2, and diameter L1 of the tip part 7a equal to or slightly smaller than the diameter of the hole 2 is pressed down to apply pressure by its slanted face 7b. Thus, a welded flange part 1a of the tube is formed.