1, Cause of deformation

To put it simply, during the welding process, after the material is heated and melted, the material shrinks without balance during the cooling and contraction process due to thermal expansion and contraction.

2. Influencing factors of welding deformation

There are many factors impacting welding deformation. To sum up, there are mainly three aspects – material, structure and process.

1). Material factor

It is mainly due to the physical properties of the material, especially the thermal expansion coefficient, yield limit, and elastic modulus of the material. The larger the expansion coefficient, the greater the welding deformation and the greater the elastic modulus would be.

The welding deformation is reduced accordingly, and the large yield limit would cause higher residual stress and increase the deformation. The expansion coefficient of stainless steel is greater than that of carbon steel, so the welding deformation of the two materials of the same thickness, stainless steel, tends to be greater than that of carbon steel.

2). Structural factor

The design of the welding structure has the most critical influence on the welding deformation. The general principle is that as the degree of restraint increases, the welding residual stress increases and the welding deformation decreases accordingly.

3). Process factor

The main influencing factors are welding method, welding heat input (current and voltage), component positioning or fixing method, welding sequence, and the use of welding fixtures. The most influential is the welding sequence.

3. Control of welding distortion

1).Design measures

3.1.1.Reasonable selection of welding size and form

In the case of ensuring the structural bearing capacity, the weld size should be as small as possible to reduce the influence of welding heat input on material properties.

3.1.2. Reasonable selection of weld length and quantity

As long as it is allowed, profiles and stampings are used; where there are many and dense welds, a cast-welded joint structure can be used to reduce the number of welds.

In addition, by appropriately increasing the thickness of the wall plate to reduce the number of ribs, or replacing the rib structure with a profiled structure, you can prevent the structural deformation of the thin plate.

3.1.3 Reasonable arrangement of the position of welding seam

Arrange the welds to be symmetrical to the neutral axis of the section as much as possible, or make the welds close to the neutral axis, which has a good effect on reducing the deflection deformation of beams and columns.

2). Measures of process

3.2.1. Anti-deformation

It is the most commonly used welding method to control welding deformation by anti-deformation.

3.2.2 Remaining margin

When blanking, the actual length or width of the part is appropriately increased compared with the design size to compensate for the shrinkage of the weldment. This method is suitable for preventing shrinkage deformation of the weldment.

3.2.3. Rigid fixation

Using fixtures or rigid tires to fix the welded parts as much as possible can effectively control the angular deformation and bending deformation of the components to be welded. Fix the weldment on the rigid platform (suitable for rigid fixing when splicing thin plates) Combine weldments into a more rigid or symmetrical structure (suitable for the control of structures such as T-beams) Utilize welded fixtures to add rigidity and restraint to the structure Use temporary supportto increase structural restraint

4). Coose a reasonable assembly welding sequence

The assembly sequence has a great influence on the deformation of the welded structure.

For large and complex welding structures, as long as the conditions allow, divide it into several parts with simple structures, weld them separately, then carry out final assembly.

For structures with asymmetrically arranged welds, the side with fewer welds should be welded first during assembly welding.

For structures with symmetrically arranged weld seams, welders should be welded symmetrically by an even number of welders.

When welding long welds (more than 1m), the direction and sequence shown in figure 12 can be used for welding to reduce shrinkage or deformation after welding.

For welding deformation, pay attention to the selection of welding methods and welding process parameters, try to choose methods and process parameters with small welding heat input, and avoid large welding parameters and welding methods to increase welding deformation.