Welding deformation control in welded structures

In the welding process, due to some high temperature heating and rapid cooling, thermal strain and compressive plastic strain will occur in the weld and near weld area of base metal, resulting in internal stress and deformation of components. The common welding deformation includes longitudinal deformation, tortuous deformation and distorted deformation. In actual production, these welding deformation usually do not appear alone, They come together and influence each other.

Control welding deformation from structural design

1.Select reasonable weld size

The weld size is too large, the welding quantity is large, and the welding deformation is large, but the smaller the weld size is, the better. In the welding process, due to the fast cooling speed, a series of welding defects will occur. Therefore, only on the premise of ensuring the structural bearing capacity and welding quality of the weld, can the smaller weld size be selected.

2.Reasonable weld orientation

In the design of welding structure, the welding seam should be organized in the direction symmetrical to or close to the neutral axis of the section. For symmetrical welding structure, the welding seam should be placed symmetrically with the neutral axis, and two welders should weld symmetrically together, so that the deformation can offset each other and reduce the welding deformation. For asymmetrical welding structure, reasonable welding sequence should be selected, The welding deformation will be significantly reduced.

3.Select reasonable weld groove method

The weld groove form has a great influence on the welding deformation. The larger the angle of view of the weld groove is, the greater the amount of deposited metal is, the more uneven the transverse shortening along the plate thickness direction is, and the greater the welding deformation is. For thick plate, the deposited metal of V-groove is larger than that of x-groove, and the greater the welding deformation is.

4.Minimize unnecessary welds

In the design of welded structure, the rib plate is often used for the stability and stiffness of the structure. However, if the number of rib plates is too large and the welding seam is too dense, the welding deformation will be narrower. Therefore, while ensuring the strength of the component, the unnecessary welding seam should be reduced as far as possible.

Reduce welding deformation in technical way

1.Select reasonable welding methods and standards

The principle of selecting welding method and standard is: on the premise of ensuring welding quality, selecting lower line energy can avoid welding deformation. For example, compared with manual arc welding, active submerged arc welding has higher power, higher heat utilization rate, faster welding speed, smaller weld shortening and welding deformation, and gas welding has larger deformation after welding than arc welding, which is also due to the large heating range of weldment, The welding speed is slow, which increases the heated volume of the metal, resulting in large deformation after welding. Using CO2 gas shielded welding instead of arc welding is not only efficient, but also has small deformation.

2.Select reasonable assembly and welding sequence and direction

The assembly and welding sequence of welded structure will have a great impact on the deformation of the structure. In order to shorten the weld freely, generally, when there are butt welds and fillet welds, butt welds should be welded first. When there are thin plates and thick plates at the same time, thick plates should be welded first. When there are continuous welds and intermittent welds, continuous welds should be welded first. When welding, symmetrical welding should be adopted, For asymmetric welding, the side with less welds should be welded first. For long welds in the structure, segmented welding should be used as far as possible.

3.Rigid fixation method

The essence of the rigid fixation method is to fix the weldment on the basis of meeting the stiffness during welding, so that the weldment can not move during welding, and spread the weldment after the welding is completely cooled. At this time, the deformation of the weldment is less than that in the free state.

4.Reverse deformation method

According to the law of deformation in production, the weldment is artificially made into a deformation in advance, so that the deformation is opposite to the deformation after welding, and the value is equal, so as to avoid the occurrence of residual deformation. This method has been well applied in practical production, for example, selecting external force to press the component on the fixture platform with enough stiffness, so as to produce reverse deformation, Then welding.

5.Heat dissipation method

The heat dissipation method is to dissipate the heat at the weld rapidly, so as to greatly reduce the heating area near the weld metal, so as to reduce the welding deformation. However, it should be noted that the heat dissipation method is not suitable for steel plates with quenching tendency.

Basic knowledge about welded pipe