The basic forms of welding deformation include shrinkage deformation, angular deformation, bending deformation, wave deformation, and twisting deformation. Uneven heating and cooling of the welded parts during the welding process is the fundamental cause of welding stress and deformation. The main process measures to reduce welding stress and deformation include:
1、 Reserve shrinkage deformation based on theoretical calculations and practical experience, and consider shrinkage allowance in advance during welding preparation and processing, so that the welded workpiece can achieve the required shape and size.
2、 The anti deformation method estimates the direction and magnitude of structural welding deformation in advance based on theoretical calculations and practical experience, and then provides a pre-set deformation with opposite direction and equal magnitude during welding assembly to offset the deformation generated after welding. 3、 When using the rigid fixation method for welding, the welded parts are rigidly fixed. After welding, the welded parts are cooled to room temperature before removing the rigid fixation, which can effectively prevent angular deformation and wave deformation. This method will increase welding stress and is only suitable for low carbon steel structures with good plasticity.
4、 Choose a reasonable welding sequence to maximize the free shrinkage of the weld seam. When welding structural components with a large number of welds, staggered short welds should be welded first, and then straight through long welds should be welded to prevent cracks from occurring at the junction of the welds. If the weld seam is long, the stepwise retreat welding method and skip welding method can be used to make the temperature distribution more uniform, thereby reducing welding stress and deformation.
5、 During the cooling process of the weld seam, the hammering method uses a round headed small hammer to uniformly and quickly hammer the weld seam, causing plastic extension deformation of the metal and offsetting some of the welding shrinkage deformation, thereby reducing welding stress and deformation.
6、 Before welding using the heating "stress reduction zone" method, heat the area near the welding site (known as the stress reduction zone) to elongate it. When cooling after welding, the heating zone shrinks together with the weld seam, effectively reducing welding stress and deformation.
7、 The purpose of pre weld preheating and post weld slow cooling preheating is to reduce the temperature difference between the weld area and other parts of the weldment, lower the cooling rate of the weld area, and enable the weldment to cool down more evenly, thereby reducing welding stress and deformation.
