Patent ID: 6953144

Claim:
A friction stir welding method, comprising the steps of: preparing a first member and a second member, each of said first member and said second member having a first plate, a second plate which is arranged substantially in parallel to said first plate, and a third plate connecting a midway of an end part of said first plate to an end part of said second plate; wherein said end part of said first plate of said first member projects beyond said end part of said second plate of said first member, and said end part of said first plate of said second member projects beyond said end part of said second plate of said second member, thereby forming a space between said end part of said second plate of said first member and said end part of said second plate of said second member when said first and second members abut each other; abutting said end part of said first plate of said first member and said end part of said first plate of said second member, thereby providing an abutting portion, wherein at said abutting portion said end part of said first plate of said first member abuts said end part of said first plate of said second member; inserting a rotary tool from said space formed between said end part of said second plate of said first member and said end part of said second plate of said second member to said abutting portion from an outer side of said second plate of said first member and an outer side of said second plate of said second member; carrying out friction stir welding of said abutting portion, to form substantially flat a face of said abutting portion formed between said end part of said first plate of said first member and said end part of said first plate of said second member; pulling out said rotary tool to an outer side of said second plate of said first member and to an outer side of said second plate of said second member, from said space formed between said end part of said second plate of said first member and said end part of said second plate of said second member; arranging a fourth plate between said end part of said second plate of said first member and said end part said second plate of said second member, at said space formed between said end part of said second plate of said first member and said end part of said second plate of said second member; and carrying out friction stir welding, using said rotary tool, of said fourth plate to said end part of said second plate of said first member and said end part of said second plate of said second member from said outer side of said second plate of said first member and said outer side of said second plate of said second member, one end part of said fourth plate and said end part of said second plate of said first member, and another end part of said fourth plate and said end part of said second plate of said second member, being welded by the friction stir welding.