| 摘要 |
PROBLEM TO BE SOLVED: To prevent development of a recessed part of a joined part by inserting the small diameter part of a rotary body having a small diameter part to the tip of a large diameter part into a butted part, rotating the rotary body and moving along the butted part at the state where the boundary of the large diameter part and the small diameter part is positioned between the extended line of a first member face except the butted part and the top face of the butted part. SOLUTION: While rotating two rotary bodies 70, 70 for joining, a small diameter part 72 is inserted into the joining part of hollow shapes 50, 60 and simultaneously/horizontally moved in the longitudinal direction of the joining part. The upper side rotary body 70 is set so that the boundary 73 of a large diameter part 71 and the small diameter 72 is positioned slightly above 73a than the upper face of plates 51, 61 of non butted parts. The lower side rotary body 70 is set so that the boundary 73 of the large diameter part 71 and the small diameter 72 is positioned in the butted parts of thick wall parts 56, 66 slightly below 73a than the rear faces of plates 51, 61 of non butted parts. A recessed part is present on the outer face side of the joined part, because the bottom face of the recessed part is outside more than the outer faces of the plates 51, 61 and is turned to the same face with the plates 51, 61. By removing an excessive part of a joined part upper face, the recessed part can be eliminated.
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