Abstract: Provided is a friction stir spot welded joint having high cross tensile strength even in the case where a steel sheet having a soft surface layer is used as a material to be welded. An annular groove is formed on an upper surface of an upper sheet out of overlapping steel sheets, and a shape and hardness of a welded portion are appropriately controlled simultaneously.

Abstract: A friction stir joining device includes a tool, a rotary driver, a linear-movement driver, and a control device. The control device is adapted to (A) dispose so that a first member opposes to the tool, and the first member, a second member and a third member are located in this order, (B) control the linear-movement driver and the rotary driver so that a tip-end part of the tool presses a joined part of a to-be-joined object while the tool is rotated, (C) control the linear-movement driver and the rotary driver so that the third member softened extends above an upper surface of the second member, and the tip-end part of the tool reaches a first position, and (D) control the linear-movement driver and the rotary driver so that the tool is drawn out from the joined part while the tool is rotated.

Abstract: A chattering vibration preventing jig is made of metal, and is L-shaped as viewed from the side. A horizontal plate portion has a pair of cuts extending in the short-side direction from an end of the horizontal plate portion. A vertical plate portion has a plurality of screw holes arranged in a line in the long-side direction. Screws slightly longer than lengths of the screw holes are screwed into the corresponding screw holes to abut onto a workpiece. Adhesive is applied to abutment surfaces of the screws that abut onto the workpiece.

Abstract: A chattering vibration preventing jig is made of metal, and is L-shaped as viewed from the side. A horizontal plate portion has a pair of cuts extending in the short-side direction from an end of the horizontal plate portion. A vertical plate portion has a plurality of screw holes arranged in a line in the long-side direction. Screws slightly longer than lengths of the screw holes are screwed into the corresponding screw holes to abut onto a workpiece. Adhesive is applied to abutment surfaces of the screws that abut onto the workpiece.