Patent ID: 6921010

Claim:
A method of joining together two planar members, by butting together the two planar members so as to form a joint region therebetween, and performing a friction stir welding operation wherein a rotary tool having a shoulder surface at a bottom end thereof and a probe coaxially provided on the shoulder surface is moved relative to said two planar members such that said probe is rotated with said rotary tool and inserted in said joint region, said method comprising the steps of: preparing a tab plate having a cutout formed in an end face thereof, such that said cutout has a width which is not smaller than a radius of a peripheral circle to be described by a periphery of said shoulder surface of said rotary tool during rotation of the rotary tool, and a depth which is not smaller than a minimum radius of said probe and not larger than the radius of said peripheral circle of said shoulder surface, said width being measured in a direction parallel to said end face and a direction in which said two planar members are butted together, while said depth being measured in a direction perpendicular to the direction of said width; positioning said tab plate relative to said two planar members such that said end face is held in abutting contact with end faces of said two planar members which correspond to a terminal portion of said joint region at which said friction stir welding operation is to be terminated, and such that one of opposite ends of said width is located on one side of said joint region which corresponds to an upstream side as seen in a rotating direction of said rotary tool, as viewed at a leading end of said rotary tool in its direction of movement, and further such that a distance between a terminal end of said terminal end portion of said joint region and said one end of said width is not smaller than zero and not larger than a maximum radius of said probe, while a distance between said terminal end and the other of said opposite ends of said width is not smaller than the radius of said peripheral circle; and initiating said friction stir welding operation after said tab plate is positioned relative to said two planar members, and terminating said friction stir welding operation after said rotary tool which has been moved to said terminal end of said joint region is further moved across said cutout to a position within an area of said tab plate.