Technological Measures to Reduce Welding Residual Deformation
1. Anti-deformation method
When assembling before welding, the size of the deformation is estimated based on experience, and a deformation opposite to the direction of the welding deformation is given to the component, so as to offset the welding deformation, so that the structure can meet the technical requirements after welding.
There are two methods of anti-deformation: ①malleable anti-deformation; ②elastic anti-deformation. In actual production, elastic reverse deformation is more reliable than malleable reverse deformation. This is because the angular deformation can always be reduced even if the prestrain amount for the malleable counter-deformation is not accurate enough. If malleable anti-deformation is used, the selected malleable pre-bending must be very precise, otherwise good results will not be obtained.
2. Welding under external constraints
Rigidly holds the weldment in a fixture to limit deformation of the workpiece during welding. It has a good effect on reducing the angular deformation of the workpiece, and can reduce the welding deformation, but the welding stress is relatively high.
3. Reasonable selection of welding methods and welding specifications
In order to reduce welding deformation, welding methods with high energy density should be used as much as possible. Such as electron beam welding, laser welding, narrow gap welding, etc. These welding methods have lower welding input energy and minimal welding distortion.
In general production, CO2 gas shielded welding replaces manual welding, which not only has high efficiency, but also can significantly reduce welding deformation. Tungsten pulse argon arc welding or resistance welding can be used to weld thin plates.
If there is not a chance to adopt the low-line energy method in production and the welding specification is not reduced, direct water cooling or water-cooled copper blocks can be used to change the thermal field distribution to achieve the purpose of reducing deformation. However, for metal materials with high hardenability, this method should be used with caution.
4. Choose a reasonable assembly welding sequence and welding direction
The design of the assembly welding sequence mainly considers the influence of the welding stress and deformation generated by the previous weld on the subsequent weld. Practice has proved that correct selection of assembly welding sequence is a powerful measure to prevent welding deformation.
Under normal circumstances, the welding seam with large shrinkage should be welded first, and the welding seam with small shrinkage should be welded later. When there are butt welds and fillet welds at the same time, the butt welds should be welded first, and then the fillet welds; when there are transverse welds and longitudinal welds at the same time, the transverse welds should be welded first, and then the longitudinal welds. When there are thick plate and thin plate welds at the same time, the thick plate welds should be welded first, and the thin plate welds should be welded second; when there are intermittent welds and continuous welds in the structure, the continuous welds should generally be welded first Welds, post-welding intermittent welds.
5. Preheating
Uneven welding heat field is the main cause of welding deformation. Therefore, proper preheating is adopted; making the welding temperature distribution tend to be uniform is also an effective measure to reduce welding residual deformation.