Steel pipe bending forming and manufacturing

As a method of forming a thick-walled steel pipe, a press forming method of a top and bottom mold (hereinafter also referred to as a bending press) is generally employed.

In the molding method, when a steel sheet having a predetermined width and length is formed into a steel pipe having a longitudinal direction of a tube axis direction, the width end portion of the steel sheet is bent (hereinafter referred to as edge crimping). Next, a method of forming a cylinder by performing a plurality of bending processes in the width direction of the steel sheet. In the main molding step after the curling of the steel sheet, the end portion of the steel sheet in the width direction is formed in the center portion in the width direction of the steel sheet (first half), and is formed in the front portion of the center portion in the width direction of the steel sheet. The end portion on the side opposite to the width direction of the steel sheet faces the center portion in the width direction of the steel sheet (sequentially formed (second half), and finally pressed (final) to the center portion in the width direction of the steel sheet. A tubular body in a state in which the end portions of the plates which are cylindrical and face each other are not welded, that is, a slitted pipe.

The slitted pipe is conveyed along the longitudinal direction of the steel pipe (the vertical direction of the paper) and sent to the next process. In this state, the butt joint edges are welded by a welding machine to form a straight welded steel pipe. It should be noted that the cylindrical shape is corrected by applying an expanded diameter or a reduced diameter process to the welded steel pipe as needed.