Patent ID: 7857192

Claim:
A friction stir welding method comprising the steps of: providing a friction stir welding tool which includes a rotor to be attached to a rotation-drive section and a probe concentrically provided on a distal end surface of the rotor and which is used in such a manner that the probe is plunged into a joint interface between two workpieces while being rotated, and the two workpieces and the probe are moved relative to each other to thereby friction-stir-weld the two workpieces along the joint interface, wherein a projection for provisional joining is concentrically provided on a distal end surface of the probe, and a relation 0.3 D≦d≦0.8 D is satisfied, where D represents a diameter (mm) of the distal end surface of the probe, and d represents a diameter (mm) of the contour of a transverse cross section of the projection for provisional joining performing provisional friction stir welding in such a manner that, while the rotor of the friction stir welding tool is rotated only, the projection for provisional joining is plunged into a joint interface between two workpieces such that the projection engages the two workpieces, and the two workpieces and the friction stir welding tool are moved relative to each other so as to intermittently weld the two workpieces along the joint interface by use of the projection for provisional joining; and subsequently performing main friction stir welding in such a manner that, while the rotor of the friction stir welding tool is rotated, the probe is plunged into the joint interface such that the probe engages the two workpieces, and the two workpieces and the friction stir welding tool are moved relative to each other so as to continuously weld the two workpieces along the entire joint interface by use of the probe.