Friction stir welding method and rotary tool

A friction stir welding method comprising using a rotary tool having a groove formed to the end surface of a large-diameter portion facing a small-diameter portion, said groove extending from the outer periphery of said large-diameter portion and reaching said small-diameter portion side, said rotary tool being rotated while said small-diameter portion and the end surface of said large-diameter portion are inserted in the members to be welded;

• and
• said rotary tool is rotated so that the metal constituting said members is moved toward the axial center of said rotary tool along said groove, wherein
• said rotary tool is inserted to the abutted portion between said members,
• wherein only one of said members comprises a projection that protrudes toward said large-diameter portion at said abutted portion;
• and
• wherein the other member is abutted against the portion of said first member excluding said projection.

A friction stir welding method using a rotary tool comprising a large-diameter portion and a small-diameter portion, wherein friction stir welding is performed by rotating said rotary tool while said small-diameter portion and an end surface of said large-diameter portion is inserted to members to be welded:

• wherein
• said large-diameter portion comprises a first large-diameter portion that is formed as a separate member from said small-diameter portion, and a second large-diameter portion that is formed as the same member as said small-diameter portion;
• said small-diameter portion, said first large-diameter portion, and said second large-diameter portion being arranged in said order along the central axis of the rotary tool;
• said first large-diameter portion being screwed onto the axis portion between said second large-diameter portion and said small-diameter portion;
• the end surface of said first large-diameter portion being in contact with the end surface of said second large-diameter portion;
• and
• said rotary tool being rotated in the same direction as the direction of the screw thread used for screwing said first large-diameter portion.

A rotary tool for friction stir welding, comprising:

• a small-diameter portion;
• a large-diameter portion positioned adjacent to the small-diameter portion;
• and
• a groove formed to the end surface of said large-diameter portion facing said small-diameter portion, the groove extending from the outer periphery of said large-diameter portion and reaching said small-diameter portion side;
• said groove having an arc shape that is curved toward the radial outward direction when viewing said end surface from the small-diameter portion side;
• the width of said groove at the radial outward side of said rotary tool is greater than the width of said groove at the radial inward side, a screw thread being formed to said small-diameter portion;
• a notch formed to the outer periphery of said large-diameter portion in the front of said groove in the direction of said screw;
• and a plural number of said grooves formed thereto.

A rotary tool for friction stir welding comprising:

• a small-diameter portion;
• a first large-diameter portion formed as the same member as said small-diameter portion, positioned at one end of said small-diameter portion;
• and
• a second large-diameter portion formed as a separate member from said small-diameter portion;
• wherein
• said small diameter portion, said second large-diameter portion, and said first large-diameter portion being arranged in said order along the central axis of said rotary tool;
• said second large-diameter portion being screwed onto a screw thread formed to the axial portion between said first large-diameter portion and said small-diameter portion;
• the end surface of said second large-diameter portion being in contact with the end surface of said first large-diameter portion, said small-diameter portion is provided with a screw thread;
• and
• the direction of the screw thread on said small-diameter portion is opposite from the direction of the screw thread used for screwing said second large-diameter portion.