PURPOSE: To easily work a weld zone and to form a joint part having excellent weldability and appearance by deforming two side walls including the corner parts at the end of a square pipe toward the inside by using a punch thereby forming the weld zone.
CONSTITUTION: The punch 2 is disposed at the end of the square pipe 1 at the prescribed angle with the axial direction of the pipe. The two side walls 1a, 1b including the corner parts are pressed by the punch 2 and are deformed toward the inside to form the weld zone 3. The weld zone 3 is pressed to the side walls 4a, 4b including the corner parts of the other square pipe 4 and the contact edges are continuously welded 5. Since the weld zone 3 is formed by pressing in the above-mentioned manner,the working is extremely easy. Since the weld zone 3 has the double-layer structure, the difference in the heat quantity is decreased and the weldability is improved. The joint part having the excellent appearance is thus obtd.
ONO MASAHIRO
MATSUO KATSURA
YAMAHA SHATAI KOGYO KK