Causes and Control Methods of Welding Deformation

【Summary Description】 Causes and Control Methods of Welding Deformation The welding deformation is harmful, and the deformation control equipment; 1. Causes of deformation To put it simply, it should be caused by the unbalanced shrinkage in the process of cooling and shrinkage of the steel due to thermal expansion and contraction after the steel is heated and melted during the welding process. 2. Influencing factors of welding deformation There are many factors that affect welding deformation, which can be summarized as material, structure and process. 01 1) Material factors Mainly due to the physical characteristics of the material itself, especially the thermal expansion coefficient of the material and the yield limit and the elastic modulus of the material, the greater the expansion coefficient of the material, the greater the welding deformation, the elastic modulus increases, the welding deformation decreases, and the yield limit will cause higher residual stress caused by increased deformation. The expansion coefficient of stainless steel is greater than that of carbon steel, so the welding deformation tendency of stainless steel of two materials of the same thickness is greater than that of carbon steel. 02 2) Structural factors The design of welding structure has the most critical influence on welding deformation. The general principle is that with the increase of restraint degree, the welding residual stress increases and the welding deformation decreases accordingly. 03 3) Process factors The main influencing factors are welding method, welding heat input (current and voltage), positioning or fixing method of components, welding sequence, and the use of welding fixtures. The biggest impact is the welding sequence. 3. Welding deformation control 1) Design measures 1 reasonable choice of welding size and form Under the condition of ensuring the bearing capacity of the structure, the weld size should be as small as possible to reduce the influence of welding heat input on the material performance. 2 Reasonable selection of weld length and quantity As long as allowed, the use of profiles, stamping parts; weld more and dense place can be cast-welded joint structure, can reduce the number of welds. In addition, the appropriate increase in the thickness of the wall plate to reduce the number of ribs, or the use of pressure structure instead of rib structure, can prevent the structural deformation of the thin plate. 3 reasonable arrangement of weld position Arrange the weld as far as possible to use symmetrical to the neutral axis of the section, or make the weld close to the neutral axis, which has a good effect on reducing the flexural deformation of the beam and column. 2) Process measures 1 Anti-deformation method The use of anti-deformation to control welding deformation is the most commonly used welding method. 2 Allowance method During blanking, the actual length or width dimension of the part is appropriately increased compared with the design dimension to compensate for the shrinkage of the weldment. This method is suitable for preventing the shrinkage and deformation of the weldment. 3 Rigid fixation The use of clamps or rigid fixtures to fix the welded parts as much as possible can effectively control the angular deformation and bending deformation of the components to be welded. ① Fix the weldment on a rigid platform (suitable for rigid fixation when splicing thin plates) ② Combine the weldments into a more rigid or symmetrical structure (suitable for the control of T-beams and other structures) The use of welding fixture to increase the rigidity and restraint of the structure ④ Use temporary support to increase the restraint of the structure. 4 Choose a reasonable assembly welding sequence The assembly sequence has a great influence on the deformation of the welded structure. ① Large and complex welding structure, as long as the conditions allow, he is divided into a number of simple structure components, separate welding, and then assembly. ② The weld being welded shall be close to the neutral axis of the structure section. ③ For the structure with asymmetrical arrangement of welds, the side with less welds shall be welded first during assembly and welding. ④ The structure with symmetrical arrangement of welds shall be welded symmetrically by even number of welders. ⑤ When welding a long weld (more than 1m), the direction and sequence shown in Figure 12 can be used for welding to reduce the shrinkage deformation after welding. In view of welding deformation, we should pay attention to the selection of welding methods and welding process parameters, try to choose the method and process parameters with small welding heat input, and avoid the increase of welding deformation caused by large welding parameters and welding methods. We should still experience and summarize more in practice.

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