Abstract: In a friction stir welding method, a tool is moved being rotated along portions to be joined of a work piece, where the portions include a corner with a smaller curvature that connect two portions with larger curvatures. The method includes the steps of setting the work piece on a supporting member, rotating the tool around a center axis thereof, moving the tool toward the work piece to penetrate a portion of the tool into the work piece at the portions to be joined, and moving and turning the tool along the portions to be joined. A rotation speed of the tool around the center axis thereof is decreased to be smaller at the corner with the smaller curvature than the rotation speed of the tool around the center axis thereof at the portions with the larger curvatures.

Abstract: In a friction stir welding method, a tool is moved being rotated along portions to be joined of a work piece, where the portions include a corner with a smaller curvature that connect two portions with larger curvatures. The method includes the steps of setting the work piece on a supporting member, rotating the tool around a center axis thereof, moving the tool toward the work piece to penetrate a portion of the tool into the work piece at the portions to be joined, and moving and turning the tool along the portions to be joined. A rotation speed of the tool around the center axis thereof is decreased to be smaller at the corner with the smaller curvature than the rotation speed of the tool around the center axis thereof at the portions with the larger curvatures.

Abstract: A heat exchanger includes a pair of header tanks and a plurality of tubes. Each of the header tanks includes an outer member and an inner member, The outer member has insertion holes allowing insertion of the tubes, while the inner member has insertion grooves allowing insertion of respective ends of the tubes. The heat exchanger is provided by brazing the so-inserted tubes to the peripheries of the insertion holes of the outer member. In order to suppress capillary phenomenon of a molten brazing filler metal in a clearance between each insertion groove and the tube, a broad portion is formed in the insertion groove to have an inside width larger than an inside width of the insertion hole. When brazing the tube to the outer member and the inner member, the molten brazing filler metal does not reach the tip surface of the tube but remains in the broad portion while maintaining the brazing strength of the tube.