Patent ID: 8393522

Claim:
A joining method comprising: preparing a pair of workpieces to be joined together each of which has a non-flat portion and an abutting surface continuous to the non-flat portion; providing an extension portion on each of the workpieces, the extension portion having a surface continuous with the non-flat portion and the abutting surface and projecting outward from the workpiece; holding the workpieces so as to form a joining line between the extension portions of the and between the pair of workpieces by bringing the abutting surfaces thereof into contact with each other; preparing a joining tool having a substantially cylindrical shoulder portion and a projection projecting outward from a tip surface of the shoulder portion and pressing the shoulder portion against the workpieces while rotating the joining tool so that the projection is positioned on the joining line; moving the rotating joining tool along the joining line until the joining tool reaches the extension portions; and separating the extension portions from the workpieces by pressing the joining tool against the extension portions with a force after the joining tool reaches the extension portions.