Method of and apparatus for friction stir welding

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 corresponding to said abutment portion, said buffer member being deformable and having a shape corresponding to the shape of the first and second cylindrical members;
• and
• performing friction stir welding along said abutment portion by inserting said probe from said one surface of said abutment portion and maintaining a tip of said probe at a position separated from said buffer member while said first cylindrical member and said second cylindrical member are held by said backing jig, and said first cylindrical member and said second cylindrical member are relatively expanded as compared with said backing jig.

A friction stir welding apparatus for 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 apparatus comprising:

• a backing jig which holds another surface of said abutment portion where said first cylindrical member and said second cylindrical member are arranged and which is to be disengaged from said other surface of said abutment portion after performing friction stir welding,
• said backing jig including a recessed section which is provided corresponding to said other surface of said abutment portion,
• wherein a buffer member, which is to be disengaged from said other surface of said abutment portion after performing said friction stir welding, is attached to said recessed section, said buffer member being deformable and having a shape corresponding to the shape of the first and second cylindrical members.