Patent ID: 7080438

Claim:
A junction method for joining a workpiece made of a plurality of plate materials superimposed in their thickness directions at points, said method utilizing a junction tool which is configured by first and second tools placed on a junction axis substantially perpendicular to superimposed surfaces of the workpiece while nipping the workpiece therebetween and which has a pin protruding from a distal end surface of the first tool along the junction axis, a recess depressed at a distal end surface of the second tool along the junction axis, and an annular convex portion formed at the distal end surface of the second tool so as to surround the recess, said method comprising: a first step of nipping the workpiece with the junction tool in the direction of the junction axis and pressing the same while rotating one or both of the first and second tools about the junction axis so as to sink the pin of the first tool and the convex portion of the second tool into the workpiece; a second step of caulking, in the direction of the junction axis, the superimposed surfaces of the workpiece softened by a friction heat generated by a rotation of the junction tool between the pin of the first tool and the recess of the second tool; a third step of generating plastic flow within the workpiece by the rotation of the junction tool thereby agitating the vicinity of the superimposed surfaces of the workpiece; and a fourth step of pulling the junction tool from the workpiece.