Patent ID: 7562803

Claim:
A method for obtaining a friction spot joint structure in which a first plate member and a second plate member are point joined with each other by plastic flow to form a joined part, said method comprising: providing a rotary tool the rotary tool having a pin portion at a tip end thereof and a shoulder portion having a larger diameter than that of the pin portion at a base end of the pin portion; and a receiving member arranged so as to face the rotary tool in an axial direction of a rotary axis; overlapping the first plate member and the second plate member with each other and interposing them between the rotary tool and the receiving member arranged so as to face each other, pressing the pin portion into the first plate member while rotating the rotary tool, and pressing the shoulder portion against the first plate member thereby forming a concave portion by the pin portion, the concave portion including a continuous interface between the first plate member and the second plate member, forming an annular bulging portion of the second plate member inside the first plate member and protruding into the first plate member around an entire outer periphery of the concave portion, and forming a protruding portion protruding outward in the radial direction from the annular bulging portion to encroach into the first plate member to anchor the first plate member with respect to the second plate member, wherein the first and second plate members are joined with each other by the annular bulging portion and the protruding portion created by plastic flow in a solid phase state.