Patent ID: 6892928

Claim:
A method of manufacturing a desired tubular body, comprising a step of forming an aluminum plate into a generally cylindrical body such that opposite end sections of the generally cylindrical body are flattened and butted together along a joint region extending along a joint line parallel to an axis of the generally cylindrical body, and such that each of the opposite flattened end sections has a predetermined width dimension L as measured in a direction perpendicular to said joint line, and a step of joining together said opposite flattened end sections at said joint region, by a friction stir butt welding operation wherein a rotary tool having a circular shoulder surface at a bottom end thereof and a probe coaxial with and extending from said shoulder surface is moved relative to said generally cylindrical body while said shoulder surface is in rubbing contact with outer surfaces of said opposite flattened end sections, with said probe being rotated with said rotary tool and inserted in said joint region, said method further comprising a step of: determining said width dimension L of each of said opposite flattened end sections of said generally cylindrical body, so as to satisfy a first formula, L≧r when 2r/sin θ<R, and a second formula, L≧r+3 when 2r/sin θ≧R, wherein “r”, “θ” and “R” respectively represent a radius (mm) of said rotary tool, an angle (°) of inclination of an axis of rotation of said rotary tool with respect to a normal to said surface of said joint region, and an outside radius (mm) of said desired tubular body.