Method to Eliminate Welding Residual Stress

Welding stress refers to the stress produced by welding, the internal stress produced in the welding process, and the change of shape and size of weldment caused by welding heat process.

The uneven temperature field and the local plastic deformation and specific capacity caused by it are the fundamental reasons for welding stress and deformation. When the uneven temperature field caused by welding has not disappeared, the stress and deformation in the weldment are called transient welding stress and deformation. The stress and deformation after the welding temperature field disappears are called welding residual stress and deformation. In the welding process, the stress and deformation after the welding temperature field disappears are called welding residual stress and deformation Without external force, the welding stress is balanced inside the weldment, and the welding stress and deformation will affect the function and appearance of the weldment under certain conditions.

Elimination of welding stress

preheat

In the manufacturing of building steel structure, tailor welding process is usually used, that is, the whole welding parts are heat aged first, and then combined with other components on site. It has the triple functions of weld dehydrogenation, recovery molding and stress relief. Generally speaking, the effect of heat aging on stress relief is more than 40%.

remelting

Weld toe defect is a small, sharp and continuous defect in weld fusion line, which is difficult to avoid. It often becomes the crack source of structural fatigue damage. TIG remelting process is often used to repair the weld toe to reconstruct the state before crack, reduce the stress concentration caused by weld toe defect, and prolong fatigue life. At the same time, TIG remelting can also improve the transverse residual stress in weld area, and reduce the fatigue life The results show that the improvement of longitudinal residual stress is not obvious, and the absolute value of residual stress decreases little, but it has an impact on the uniform distribution of longitudinal residual stress, and can significantly improve the transverse residual stress, and the absolute value of residual stress decreases significantly, and the distribution tends to be uniform.

Vibratory stress relief

Vibration aging is to apply alternating stress to the component, and superimpose with the residual stress on the member to achieve the yield stress of the material, and produce local macro and micro plastic deformation. This plastic deformation often occurs at the maximum residual stress and the stress concentration point of the component, so that the residual stress can be released, the residual stress can be reduced and homogenized. Although the vibration aging equipment does not have the hydrogen removal and plastic recovery The function of shape, but from the comparison of dimensional stability, has reached the level of thermal aging. Vibration aging is a kind of technology to eliminate stress and increase the dimensional stability.

Vibration welding

Vibration welding is also known as vibration modulated welding and welding vibration. In the appendix of VSR standard, it has been confirmed as one of the processes that can be combined with VSR. The original welding process is not changed. In the welding process, the vibration with controllable frequency and amplitude is injected into the component through the vibration exciter to form vibration welding. This vibration of amplitude will have an effect on the welding pool and heat affected zone.

When the weld metal is in molten state, bubbles and impurities are easily floated and eliminated due to vibration. The vibration of grains in the recrystallization process is conducive to grain refinement. In the region with temperature higher than 600 ℃, the thermoplastic deformation accompanied by vibration will reduce and homogenize the welding residual stress during the process of strength recovery and cooling, so as to reduce welding deformation and welding crack The formation of striae.