Patent ID: 7654435

Claim:
A rotary tool for friction stir spot welding comprising: a rod-like probe to be inserted into one side of stacked planar portions of a plurality of metal members to be joined while being rotated; a cylindrical shoulder member which is disposed outwardly of the probe so as to be located coaxially with the probe and which has a shoulder surface to be abutted against a surface of the one side of the stacked portions while being rotated; and a cylindrical pressing member disposed coaxially outwardly of the shoulder member, with a tip surface of the pressing member being pressed against the surface of the one side of the stacked portions by a biasing force applied in an axial direction of the pressing member; wherein the probe and the shoulder member are individual components respectively and are disposed so as to have a double-acting structure which enable the probe and the shoulder member to move independently in their axial direction; wherein a first gap between an inner peripheral surface of the shoulder member and an outer peripheral surface of the probe is formed to have a first small gap on a tip side of the rotary tool and is formed to have a first enlarged gap having larger clearance than the first small gap on a base portion side thereof; wherein a second gap between an inner peripheral surface of the pressing member and an outer peripheral surface of the shoulder member is formed to have a second small gap on the tip side of the rotary tool and is formed to have a second enlarged gap having larger clearance than the small gap on the base portion side thereof.