Patent ID: 6601427
Filing Date: 2003-08-05
Classification: B21C

Abstract:
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 deforming at least a portion of said lower surface to project outwardly by applying a force and close-fitting said first and second edge portions and deforming said lower surface into a flat condition by applying a force on the projected portion of said lower surface to maintain said spring back force in said third flat surface.