Sided friction stir welding method of a metal plate with a gap butting portion

In both friction stir welding, even if the gap in the butted portion of the two metal plates is more than 0.5 mm, the bonding strength increased by suppressing bonding defects, enhancing the economics of suppressing an increase in equipment cost, and the production efficiency is high. First and second rotating tool 3 and 4 respectively shoulder 3c, the tool body 3a formed of 4c on the tip portion has a 4a, first rotary tool 3 to further protrude from the tip portion of the tool body It has formed protrusions 3d, a second rotating tool 4 is formed further on the tip portion of the tool body, recess 4d for accommodating the tip portion of the protruding portion 3d at the time of bonding of the two metal plates 1 and 2 the a, in a state where a gap having a diameter of less than occurs in the projections to the butted portion B which butt the end faces of the metal plates 1 and 2, gripping the metal plates 1 and 2 by the gripping devices 5, the projections of the rotating tool insert the tip parts 3d in the recessed portion 4d of the rotary tool, for joining the plate thickness direction entire area of ​​the butt portion friction stir to. .FIELD 4