Several factors affecting the welding deformation of pipe trusses and their countermeasures and controls

Internal stress will be generated when the steel pipe structure is welded. When the welded rods are welded and cooled, uneven temperatures will affect the thermal stress. The internal stress generated by the metallographic structure in the metal structure is constrained by the structure, resulting in constrained stress. If the internal stress is not well controlled during the welding process, it will cause the shape and size of the welding rod to change. Small deformations will affect the accuracy of the structure and cause difficulties in assembly. Excessive deformation can also cause cracks, thereby reducing the load-bearing capacity of the structure. Therefore, welding deformation will not only affect the appearance of the building structure, reduce its applicability, and cause economic losses.

Welding materials
Welding base metal and welding materials are the main factors affecting the welding deformation of pipe trusses. Welding materials are metals, and their unique thermophysical properties and changes in mechanical properties can cause deformation of the electrode during the welding process. The greater the coefficient of the material's heat transfer system, the smaller the temperature gradient, and the smaller the welding deformation during the welding process. Metal materials have thermal expansion and contraction characteristics, and the increase in the linear expansion coefficient of the material will increase the deformation of the welding rod. At the same time, different materials have different chemical compositions and affect mechanical properties. For example, Q345B structural steel has low impact toughness, while G20Mn5 cast steel will inevitably produce shrinkage cavities, component segregation, coarse grains and other defects during the casting process. These factors all affect welding performance to a certain extent.

Welding Technology
The influence of welding technology on the welding deformation of pipe trusses is complex. When processing the pipe truss structure, factors such as the production, positioning and assembly requirements of the welded tire frame, and transportation determine the welding method of the pipe truss fittings, thereby affecting the welding current, welding voltage, structural positioning, fixing method and welding selection sequence. For example, multi-layer welding has a greater impact on welding technical parameters. Research shows that the first layer of welds shrinks the most, and the second and third layers shrink rapidly. The shrinkage of the second layer is 20% of the first layer, and the third layer is about 5% of the first layer. . The more welding layers, the greater the impact of welding deformation; the deformation caused by intermittent welds is smaller than that of continuous welds; the welding sequence has a greater impact on the residual stress and stress distribution of the material. It is generally believed that the cause of excessive welding deformation is usually due to failure to follow reasonable welding procedures or to perform overall splicing without welding sub-components.

structural factors
Welded structure design is also an important aspect that affects the deformation of pipe trusses. Generally, when the constraint degree of the structure increases, the welding deformation decreases relatively. During the welding process, the constraints of the structural members themselves continue to change as the complexity of the structure increases and the welding work develops. In the design of welded structures, using ear plates or stiffening plates to improve the stability and stiffness of structural members can reduce welding deformation, but this method increases the workload of assembly and welding, and increases the difficulty of welding deformation analysis.