To provide a hollow shape allowing frictional connection from one face side by forming the face of one end of a first plate including a projection protruded toward a second plate side along one end of the first plate along the thickness direction of the first plate.
Tips of lower plates 34 are connected by a rotating tool 50. Hollow shapes 31, 32 including the connection sections of the plates 34 are mounted on a bed. The upper face of the bed (backing of connecting beads) of the connection sections is flat (A). A joint 60 is mounted between two hollow shapes 31, 32 (B). The connection section between the joint 60 and the hollow shape 31 is friction-connected by the rotating tool 50 (C). The connection section between the joint 60 and the hollow shape 32 is friction-connected by the rotating tool 50 (D). Connection can be made from one face side, and the inverting work is not required. Since the inverting work is omitted, such merits as the omission of inverting and positioning time, the omission of an inverting device and the improvement of assembling precision can be obtained.
ISHIMARU YASUO
TAKENAKA TAKESHI
