Pipe body and forming method of the same

A method for processing a rectangular metal pipe in section by bending a metal plate having mutually parallel first and second edge sections and a third edge section perpendicular to said first and second edge sections and by opposing said first and second edge sections, comprising:

• a processing step for forming, on said third edge section, a first piece portion having a male engagement section and a second piece portion having a female engagement section;
• a processing step for forming a processed article in which said first and second edge sections and said first and second piece portions are opposed by bending said metal plate parallel to said first and second edge sections and by bending said first and second piece portions along said third edge section;
• and
• a processing step for generating and maintaining a spring back force acting in a direction for urging said first and second edge sections to approach each other in one of four flat surfaces of said metal pipe, for opposing said first and second edge sections and for deforming at least one of said male and female engagement sections in a space occurring within said female engagement section when said male engagement section is inserted into said female engagement section to engage said male and female engagement sections.

A method for producing a metal pipe by bending a metal plate having mutually parallel first and second edge sections and by opposing said first and second edge sections, comprising:

• a step for forming on said first edge section a male portion having a pair of divided pieces to be subjected to deformation and for forming on said second edge section a female portion having a space with a back portion and broadened toward the back portion from an open end of said space for inserting said pair of divided pieces, a projection projecting toward said open end from the center of the back portion for deforming said pair of divided pieces in a mutually spaced direction by said projection being inserted between said divided pieces, and a pair of engaging walls formed on said open end for engaging said pair of divided pieces when the divided pieces are subjected to deformation;
• a step for disposing said first and second edge sections in an opposed relation to each other by bending said metal plate;
• and
• a step for engaging said first and second edge sections with clearances, between said pair of divided pieces and projection by deforming said divided pieces with said projection when said pair of divided pieces are inserted into said space upon bending of said metal plate.

A method for producing a metal pipe by bending a metal plate having mutually parallel first and second edge sections and by opposing said first and second edge sections, comprising:

• a step for forming on said first edge section a male portion having male engagement sections to be subjected to deformation and for forming on said second edge section a female portion having a space with a back portion and broadened toward the back portion from an open end of said space for inserting said male engagement sections, and a pair of engaging walls formed on said open end for engaging said male engagement sections;
• a step for disposing said first and second edge sections in an opposed relation to each other by bending said metal plate;
• and
• a step for engaging said first and second edge sections with clearances between said male engagement sections and female portion when said male engagement sections are inserted into said space, convex engagement sections projecting from said second edge section being pre-provided on said pair of engaging walls, and concave engagement sections opposing to said convex engagement sections being pre-provided on said male portion, said pair of engaging walls being deformed to pinch said male engagement sections from the both sides thereof by engagement of said concave and convex engagement sections.

A method for producing a metal pipe by bending a metal plate having mutually parallel first and second edge sections and by opposing mutually said first and second edge sections, comprising:

• a first processing step for forming a male portion on said first edge section and a female portion on said second edge section;
• a second processing step for bending said metal plate to oppose mutually said first and second edge sections;
• and
• a third and final processing step for engaging said male and female portions to caulk them while maintaining partial lateral clearance between said male and female portions at the end of the said third and final processing step.