During the forming of low carbon steel welded pipe,the springback is generally not a very prominent problem. With the development of China's welded pipe industry,the application of various new terials in the welded pipe industry,the addition of various metal elements such as low alloy and alloy steel welded pipe,and the development and production of alloy welded pipe,their springback in the forming process has become a more prominent problem.
Forming springback is inly shown as follows:
1.The forming roll is designed according to the pass design method. Due to rebound,the actual final forming is not the required shape,especially the edge forming of strip steel is insufficient.
2.During high-speed production of alloy welded pipe,large rebound will cause cracks at the weld that has not fully solidified when leaving the extrusion roll,and cracks will appear on the inner su ce of the weld of welded pipe.
3.In order to improve the welding speed of alloy welded pipe,the two edges of the pipe blank need to be in close contact. If the rebound is large,the pipe blank will open at the front and rear edges of the extrusion roll, king the welding impossible.
The forming of welded pipe is a plastic defor tion process,which includes part of elastic defor tion,and it is elastic defor tion that causes springback. Metal is not an ideal plastic defor tion terial. The work hardening phenomenon of metal terials and the complexity of defor tion conditions in the forming process of welded pipe ke it difficult to accurately solve the springback problem.
As far as iron and steel terials are concerned,their elastic modulus is not very sensitive to s ll changes in chemical composition and microstructure,and there is little difference in their elastic modulus. Therefore,their resilience inly depends on the yield strength. Therefore,as a low-carbon steel,cold-rolled strip has higher strength and greater resilience than hot-rolled strip,and the strength of low-alloy steel and alloy steel is higher than that of low-carbon steel,Therefore,the rebound is large.
Several methods to overcome rebound:
1.Properly increase the defor tion of forming roll
For some terials with large springback or large welded pipe,when designing the forming roll,the factor of large springback should be considered,and the defor tion of each forming roll should be appropriately increased to ke the shape of the pipe blank after springback reach the required shape,especially the edge part of the metal belt. This method is conducive to preventing the occurrence of peach shaped pipe.
2.Heating forming method is adopted
Because the yield strength and elastic modulus of metal terials will decrease with the increase of temperature,heating forming can reduce the amount of springback in the forming process.
3.Adopt asymmetric forming method
Asymmetric forming method refers to the use of two groups of asymmetric forming rollers before the extrusion roller,so that the pipe blank has two asymmetric defor tion before entering the extrusion roller. As long as the asymmetric roller is reasonably designed,under the action of the two groups of extrusion rollers,the two edges of the pipe blank can intain close contact within a certain distance,so as to meet the welding requirements.