Patent ID: 7093745

Claim:
A friction stir welding method of joining an abutment portion by moving a rotating probe relatively along said abutment portion while pressing said probe against one surface of said abutment portion at which an end of a first cylindrical member and an end of a second cylindrical member are butted together, said friction stir welding method comprising the steps of: attaching a buffer member to a backing jig which holds another surface of said abutment portion so that an opening of said backing jig formed corresponding to said abutment portion is covered therewith, said buffer member being deformable and having a shape corresponding to the shape of the first and second cylindrical members; arranging said first cylindrical member and said second cylindrical member on said backing jig while said first cylindrical member and said second cylindrical member are relatively expanded as compared with said backing jig; performing friction stir welding along said abutment portion by inserting said probe from said one surface of said abutment portion and deforming said buffer member and a part of said abutment portion to protrude toward said opening, while said first cylindrical member and said second cylindrical member are held by said backing jig; and removing a portion protruding from said abutment portion toward said opening after performing said friction stir welding.