How to prevent welding deformation and stress?
Basic forms of welding deformation include shrinkage deformation, angular distortion, bending deformation, wave deformation and twist deformation, etc. During the welding process, welding pieces of uneven heating and cooling, is the root cause of the welding stress and deformation. Some technological measures to reduce the welding stress and deformation are mainly included:
Preserve shrinkage deformation
According to theoretical calculation and practical experience, considering shrinkage allowance in advance when weld preparation and processing, so as to achieve the required shape and size after welding work piece.
According to theoretical calculation and practical experience, prior estimate direction and size of welding deformation structure, and then give a opposite direction when welding assembly, equal to the size of the preset deformation, to offset the deformation after welding.
Rigid fixation method
Work piece would be fixed rigidity when welding, remove fix parts after cooling to room temperature, which can effectively prevent angular distortion and wave deformation. This method will increase the welding stress, only suitable for low carbon steel structure.
Choose a reasonable welding sequence
Try to make the weld seam shrink freely. When welding structure with many seams, to prevent cracks in weld junction, first weld short weld seam stagger and then welding long seam. If the weld seam is longer, can use back stepping and skip welding method; the temperature distribution is uniform, thereby reducing the welding stress and deformation.
Hammer welding method
In the cooling process of weld seam, hammering weld seams quickly and evenly, make metal extend deformation, offset parts of welding shrinkage deformation, so as to decrease the welding stress and deformation.
Heating area “stress relieving area” method
Before welding, preheat welding position area to make it elongation, cooling after welding, the heating area and welding seam together contraction, which can effectively decrease the welding stress and deformation.
Preheat before welding and slow cooling after welding
Purpose of preheat is to reduce temperature difference of welding area and the rest parts, reduce cooling rate of the weld area to make the welding parts cooled down evenly, thus reducing the welding stress and deformation.