What are the effects of welding residual stress on the welded component during the welding of the machine frame?

During the welding of machine frames, residual stress from welding has six impacts on the welded components.

① Impact on Strength: If significant defects exist in the high residual tensile stress area and the welded component operates below the brittle fracture temperature, the welding residual stresses during the welding frame assembly will result in a reduction of static load strength. Under cyclic stress, if residual tensile stresses are present at stress concentration points, the welding residual tensile stresses will decrease the fatigue strength of the welded component. The fatigue strength of the component is not only related to the magnitude of the residual stresses but also to the stress concentration factor, the stress cycle characteristic factor, and the magnitude of the cyclic stresses. Its impact diminishes with the decrease in stress concentration factor and intensifies with the reduction (e.g., the impact on alternating fatigue strength is greater than that on pulse fatigue), and diminishes with the increase. As the yield strength is approached, the influence of residual stresses gradually diminishes.

② Impact on Rigidity: The superposition of welding residual stress and stress caused by external loads may lead to premature yielding and plastic deformation in localized areas of the welded part. Consequently, the rigidity of the weldment may also decrease.

③ Impact on the Stability of Welded Components Under Compression: When the welded rod is under compression, the residual stress from welding combines with the stress caused by the external load, which may lead to local yielding of the rod and subsequently local instability. The overall stability of the rod will thus decrease. The influence of residual stress on stability depends on the geometric shape of the rod and the distribution of internal stress. The impact of residual stress on non-enclosed cross-section rods (such as I-shaped cross-section) is greater than that on enclosed cross-section rods (such as box-shaped cross-section).

④ Impact on Processing Precision: The presence of residual welding stress has varying degrees of influence on the processing precision of weldments. The smaller the stiffness of the weldment, the greater the processing volume, and the greater the impact on precision.

The impact on dimensional stability: Welding residual stress changes accordingly over time, which also affects the size of the welded parts. The stability of the size of the welded parts is further influenced by the stability of the residual stress.

⑥ Impact on Corrosion Resistance: Welding residual stresses and load stresses can also lead to stress corrosion cracking.