Friction stir welding method

Abstract

End portions of members 10, 20 are abutted against each other. A trapezoidal convex portion 22 of the member 20 is inserted into a trapezoidal concave portion 12 of the member 10. A friction stir welding is performed by inserting a rotary tool 50 from the side of raised portions 13, 23. A small-diameter portion 51 b of the rotary tool 50 is tapered and is provided with a screw thread 51 b. A large-diameter portion 53 is of a member different from an axis portion of the rotary tool 50 and is connected thereto by a pin 59. The screw thread of the screw thread portion 51 b could be formed in the vicinity of a concave surface 53 g of an end surface of the large-diameter portion 53, so that stirring near the end surface can be performed sufficiently. Therefore, good friction stir welding can be achieved.

What is claimed is:  
     
         1 . A rotary tool for friction stir welding, wherein: 
 said rotary tool is comprised of a small-diameter portion which is equipped with a screw thread, and a large- diameter portion of a different member provided on an axis end of said small-diameter portion;    a surface of said large-diameter portion on said small-diameter portion side is concave; and    an end portion of said screw exists inside the bounds of said concave surface of said large-diameter portion.    
     
     
         2 . A rotary tool for friction stir welding according to  claim 1 , wherein: 
 an axis end opposite to said axis end provided with said large-diameter portion is provided with a second large-diameter portion of a different member;    a surface of said second large-diameter portion on said small-diameter portion side is concave; and    an end portion of said screw thread exists inside the bounds of said concave surface of said large-diameter portion.