Abstract: Provided is a multipoint stretch forming apparatus enabling individual clamping control for manufacturing a curved panel, wherein a plurality of stretching units are positioned at both sides at a lower position of a supporting frame in forward and backward directions, and each of the stretching units is independently and individually controlled. Further, since the distance between the right and left stretching units is adjustable in accordance with the size of punch modules and the size of a curved panel to be formed, the precision formation of both wide and narrow curved panels/shapes is possible. Through this technical constitution, an atypical curved panel is formed more efficiently and the loss of panel material is remarkably reduced.

Abstract: Provided is a multipoint stretch forming apparatus enabling individual clamping control for manufacturing a curved panel, wherein a plurality of stretching units are positioned at both sides at a lower position of a supporting frame in forward and backward directions, and each of the stretching units is independently and individually controlled. Further, since the distance between the right and left stretching units is adjustable in accordance with the size of punch modules and the size of a curved panel to be formed, the precision formation of both wide and narrow curved panels/shapes is possible. Through this technical constitution, an atypical curved panel is formed more efficiently and the loss of panel material is remarkably reduced.

Abstract: There is provided a combination welding method performed by leading with a tungsten arc welding method and following with a submerged arc welding method by keeping a predetermined separation distance from the tungsten arc weld zone. According to the combination welding method of the present invention, the occurrence of bending of a steel pipe is reduced and a welding time is shortened since the inside welding and the outside welding are simultaneously performed by keeping the predetermined separation distance. In addition, since the outside welding is performed before a fusion area temperature is below an A1 transformation point after the inside welding, the bending of the steel pipe is properly controlled after the welding and therefore straightening time in a post-process is shortened.