MANUFACTURE OF CYLINDRICAL TUBE

摘要

PURPOSE:To facilitate automatization of manufacturing processes for cylindrical tubes by prebending both edges in the axial direction of a flat plate-shaped work into the same direction and forming a positioning notch for welding at an edge in the longitudinal direction. CONSTITUTION:A nip bending die 24 having a recessed part 24a and a cutting die 25 having a die hole 25a are installed on a die holder 22; a flat plate-shaped work 1 is put on the dies 24 and 25 and is held by two couples of movable nets 27. A root bending punch 35 and a cutting punch 36 are moved down by a punch holder 23 to prebend both edges in the axile direction of the work 1 upward and to concurrently form a notch on at least either edge in the longitudinal direction of the work 1. The prebent parts are bent inside to form a U-shape in the width direction of the work 1 and are finish formed into a cylindrical shape. Then, the cylindrical work is positioned against a welding torch, making the notch a reference point. Butted parts of the work 1 are automatically welded by the welding torch to form a cylindrical tube.