Method of manufacturing pipe body and pipe body manufactured by the method

A method for producing a metal pipe rectangular in section by bending a metal plate having first and second edge portions parallel to each other along a plurality of bending lines parallel to said first and second edge portions and abutting said first and second edge portions, said pipe having a first flat surface including abutting portions of said first and second edge portions, a second flat surface perpendicular at a first corner to said first flat surface, a third flat surface perpendicular at a second corner to said second flat surface and opposite to said first flat surface, and a fourth flat surface perpendicular at a third corner to said third flat surface and at a fourth corner to said first flat surface and opposite to said second flat surface, said method comprising the steps of:

• a first processing step for forming a processed product by bending said metal plate along said bending lines, said processed product having a first upper surface for partially constituting said first flat surface and including said first edge portion, a second upper surface for constituting said first flat surface together with said first upper surface and including said second edge portion, a first side surface for constituting said second flat surface, a lower surface for constituting said third flat surface, and a second side surface for constituting said fourth flat surface, said first and second edge portions being spaced apart;
• and
• a second processing step for generating and maintaining a spring back force which maintains a close-fitting of said first and second edge portions in at least one of said second, third and fourth flat surfaces,
• wherein said second processing step includes close-fitting said first and second edge portions by applying a force on said first and second side surfaces and maintaining said spring back force in said third flat surface by restraining deformation of said lower surface which tends to project outwardly and holding said lower surface in a flat condition.

A method for producing a metal pipe rectangular in section by bending a metal plate having first and second edge portions parallel to each other along a plurality of bending lines parallel to said first and second edge portions and abutting said first and second edge portions, said pipe having a first flat surface including abutting portions of said first and second edge portions, a second flat surface perpendicular at a first corner to said first flat surface, a third flat surface perpendicular at a second corner to said second flat surface and opposite to said first flat surface, and a fourth flat surface perpendicular at a third corner to said third flat surface and at a fourth corner to said first flat surface and opposite to said second flat surface, said method comprising the steps of:

• a first processing step for forming a processed product by bending said metal plate along said bending lines, said processed product having a first upper surface for partially constituting said first flat surface and including said first edge portion, a second upper surface for constituting said first flat surface together with said first upper surface and including said second edge portion, a first side surface for constituting said second flat surface, a lower surface for constituting said third flat surface, and a second side surface for constituting said fourth flat surface, said first and second edge portions being spaced apart;
• and
• a second processing step for generating and maintaining a spring back force which maintains a close-fitting of said first and second edge portions in at least one of said second, third and fourth flat surfaces,
• wherein said second processing step includes close-fitting said first and second edge portions by applying a force on said first and second side surfaces and deforming at least one of said first and second side surfaces and lower surface to project inwardly to maintain said spring back force in at least one of said second, third and fourth flat surfaces.

A metal pipe comprising:

• a first flat surface including first and second edge portions which are parallel to and abutted to each other,
• a second flat surface perpendicular at a first corner to said first flat surface,
• a third flat surface perpendicular at a second corner to said second flat surface and opposite to said first flat surface;
• and
• a fourth flat surface perpendicular at a third corner to said third flat surface and at a fourth corner to said first flat surface and opposite to said second flat surface,
• wherein a portion for generation of spring back force for abutting said first and second edge portions is formed on said third flat surface opposite to said first and second edge portions.

Apparatus for producing a metal pipe rectangular in section formed by bending a metal plate having first and second edge portions parallel to each other along a plurality of bending lines parallel to said first and second edge portions and adapted to abut said and second edge portions, said pipe having a first flat surface including abutting portions of said first and second edge portions, a second flat surface perpendicular at a first corner to said first flat surface, a third flat surface perpendicular at a second corner to said second flat surface and opposite to said first flat surface, and a fourth flat surface perpendicular at a third corner to said third flat surface and at a fourth corner to said first flat surface and opposite to said second flat surface, said apparatus comprising:

• a fixed plate for supporting a processed product which is formed by bending said metal plate along said bending lines and which has a first upper surface for partially constituting said first flat surface and including said first edge portion, a second upper surface for constituting said first flat surface together with said first upper surface and including said second edge portion, a first side surface for constituting said second flat surface, a lower surface constructing said third flat surface, and a second side surface for constituting said fourth flat surface, said first and second edge portions being spaced apart, wherein said processed product is disposed on said fixed plate to position downwardly said lower surface;
• a pair of press punch members for pressing said first and second side surfaces of said processed product on said fixed plate to approach to each other and for abutting said first and second edge portions;
• a drive member for driving said pair of press punch members;
• and
• a press punch member for pressing from above said first flat surface formed by said first and second upper surfaces to close-fit said first and second edge portions.