There are UOE forming method, CFE forming method and CE forming method for manufacturing large diameter steel saw pipe. For most forming processes, the final step is to expand the whole length of welded pipe to improve the shape and quality of welded pipe. It is an important process to expand into large-caliber vertical production to ensure the quality of finished pipe.


Expansion is a pressure forming process in which hydraulic or mechanical devices are used to push the pipe radially outward from the pipe wall. Machinery is simpler and more efficient than hydraulic mode. It adopts the world's most advanced pipeline system technology of enlarging longitudinally several large diameter. The technological process is as follows: the split side of enlarged diameter is used in mechanical expansion, because the pipe expands along the radial direction, so the whole length plastic deformation process of the pipe section is gradually realized along the longitudinal direction. It is divided into five stages.
1. Initial phase full circle. The section opens until all sections are exposed to the tube wall. At this time, the steps of each point in the radius of the steel tube are almost the same, and the steel is ready to be rounded.
2. The nominal inner diameter of the stage. The speed is reduced from the front position until the desired position is reached, which is within the quality requirement of the circumferential position of the finished pipeline.
3. Rebound compensation stage. The position at the beginning of the second stage is further low until the desired position is reached, which is the circumference of the pipeline before the complex process design requirements of the missile.