PURPOSE: To eliminate repair owing to deviation from a central hole and to reduce wasteful man-hour and material cost by punching a semicircular hole to the central titanium material at the end on the groove side of an aluminum clad steel, welding repsectively the upper and lower grooves and forming the central hole.

CONSTITUTION: A semicircular hole 7a is punched to the central titanium material part T at the end of a groove side and the ends 4 of both groove sides are butted to each other in butt welding of the aluminum clad steel consisting of aluminum A and carbon steel S interposed with the titanium material T. Both parts are subjected in this state to aluminum welding 5 and steel welding 6. A plastic packing material is fed into the formed central hole 7 to prevent thoroughly leakage from the weld zone. The usual punching after welding is thus eliminated and the deviation of the punched hole from the center thereof is eliminated by which the need for the man-hour and material cost for repair is completely eliminated. An equally good result is obtd. by pressing a round stainless steel bar 8 or tab piece 9 to the hole 7 and both end faces.