| 摘要 |
PROBLEM TO BE SOLVED: To provide a friction stir welding method capable of attaining a lightweight, satisfactory joining. SOLUTION: An end of a side wall 11 of a hollow shape 10 is butt-joined with an end of a side wall 21 of an another hollow shape 20. The end of the side wall 21 overlaps with a protrusion 15. A smaller part 52 in diameter of a rotating tool 50 is inserted into the portion to be butt joined, the smaller part 52 being rotated clockwise seen from the side of a larger part 51 in diameter, and traveled along the portion to be butt joined in a direction from the front side of the Fig. 1 to the depth. On the Fig. 1, the right-hand side of the axis of the rotating tool has a higher pressure in liquidized metal. As concerns wall thickness measured from the tip of the smaller part 51 to hollow parts 10a, 10b, the right-hand side is larger. Thus as the right-hand side where the higher pressure is produced has the larger wall thickness, the liquidized metal will not flow out to the hollow part 10a. A thinner wall formed in the left-hand side contributes to reduce the weight.
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