US Patent 7909229 Method for joining material

A method for joining materials in which a second material is overlapped over a first material preliminarily formed with a joining hole so as to cover the joining hole. A joining tool arranged in alignment with the joining hole is pressed, while rotated, onto the second material so as to locally soften and enter the second material in solid phase state into the joining hole of the first material through frictional heat generated between the joining tool and the second material. The joining tool is pulled out after a geometric engaging part is provided by the second material in relation with the first material and the engaging part is allowed to harden to join the first and second materials.