The method of preventing and reducing welding deformation needs to consider the welding process design to overcome the changes in the heat and cold cycle during the welding process. The shrinkage cannot be removed, but it can be controlled. The ways to reduce the shrinkage deformation are as follows.
1. Do not weld too much
The more metal filled in the welding point, the greater the deformation force will be generated. Correctly setting the weld size can not only get smaller welding deformation, but also save the welding material and time. The amount of welding metal in the fill weld should be small, and the weld It should be flat or slightly convex. Excessive welding metal will not increase the strength, but will increase the shrinkage force and welding deformation.
2. Intermittent weld
Another way to reduce the fill of welds is to use more discontinuous welding, such as welding reinforcement plates. Intermittent welding can reduce the fill of welds by 75% and ensure the required strength.
3. Reduce the weld bead
Welding with thick wire and few beads has less deformation than thin wire and multi-bead welding. When there are multiple beads, the cumulative shrinkage caused by each bead increases the total shrinkage of the weld, and the welding process with less bead and thick electrode is more The welding process effect of welding bead and fine welding rod is better. Pay attention to the thick welding wire, less welding or thin welding wire and multi-bead welding process according to the material. Generally speaking, low carbon steel, 16Mn and other materials are suitable for thick welding wire. Weld bead welding, while stainless steel and high carbon steel are suitable for fine wire and multi-bead welding.
4. Anti-deformation technology
Before welding, bend or tilt the part in the opposite direction of welding deformation (except for overhead welding or vertical welding). The preset amount of anti-deformation needs to be determined by experiment. Pre-bending, pre-setting or pre-arch welding parts are a kind of reverse A simple method for mechanical force to offset the welding stress. When the workpiece is preset, the deformation of the workpiece and the welding seam will be opposite to the shrinkage stress. The preset deformation before welding and the deformation after welding cancel each other out, making the welding workpiece an ideal plane.
Another commonly used method to balance the contraction force is to place the same welding workpieces relative to each other and clamp them. This method can also be used for pre-bending. Before clamping, place the wedge in the proper position of the workpiece.
Special heavy welding workpieces can produce the required balance force due to their own rigidity or the mutual position of the parts. If these balance forces are not generated, other methods should be used to balance the shrinkage force of the welding material to achieve the purpose of offsetting each other. The force can be other contraction forces, the mechanical restraint force formed by the tooling, the restraint force formed by the order of assembly and welding of the components, and the restraint force formed by gravity.
5. Welding sequence
According to the structure of the workpiece, determine the reasonable assembly sequence, make the structure of the workpiece shrink at the same position, open the double-sided groove in the workpiece and the shaft, adopt multi-layer welding, and determine the double-sided welding sequence, and the fillet weld is intermittent. Welding, the shrinkage in the first welding is balanced by the shrinkage in the second welding. The fixture can fix the workpiece in the required position, increase the rigidity, and reduce the welding deformation. This method is suitable for welding small workpieces or small parts, but Due to the increase in welding stress, it is only suitable for low-carbon steel structures with good plasticity.
6. Removal of shrinkage force after welding
Percussion is a method to counteract the shrinkage force of the weld. Just like the cooling of the weld, the percussion will make the weld extension and thinner to remove the stress (elastic deformation). However, this method requires attention and cannot be knocked. Strike the root of the weld, which may lead to cracks. Under normal circumstances, knocking cannot be used on the cover weld. The cover layer may have weld cracks, which will affect the weld detection and produce a hardening effect. Therefore, the use of technology is limited. , There are even instances requiring that only in the multi-layer weld bead (except for bottom welding and cover welding) be knocked in the weld bead to solve the problem of deformation or cracks. Heat treatment is also one of the methods to remove the shrinkage force and control the workpiece High temperature and cooling, sometimes the same workpiece is clamped and welded back to back, and the stress is removed by this straightening condition, so that the residual stress of the workpiece is smaller.
7. Reduce welding time
Heating and cooling occurs during welding, and heat transfer takes time, so the time factor also affects deformation. Generally, it is hoped to complete the welding as soon as possible before the large workpiece is heated and expanded. The welding process, such as the type and size of the electrode, welding current, welding speed, etc., affect the welding The degree of shrinkage and deformation of the workpiece, and the use of mechanized welding equipment reduces the welding time and the deformation caused by heating.
Tips: ERW welded pipe is formed by rolling strip and welding the seam, with tighter dimensional tolerances and less weight. The weld seam is heat treated after welding that no untempered martensite remains, and the weld flash can be removed from both inner and outer surfaces.