Methods of Controlling Welding Distortion

1. Design measures

(1) Select a reasonable weld size:

As the weld size increases, the deformation increases, but too small weld size will reduce the bearing capacity of the structure, accelerate the cooling rate of the welded joint, increase the hardness of the heat-affected zone, and are prone to cracks and other defects. On the premise of structural bearing capacity and ensuring welding quality, the smallest weld size that may be selected in the process is selected according to the thickness of the plate.

(2) Minimize the number of weld:

Appropriately select the thickness of the plate and reduce the number of ribs, so as to reduce the correction amount of welding seam and deformation after welding, such as thin plate structural parts, the rib plate structure can be replaced by a profiled structure to reduce the number of welding seams and prevent or reduce the deformation after welding.

(3) Reasonable arrangement of welding seam position:

The welding seam is symmetrical to the neutral axis of the weldment section or making the welding seam close to the neutral axis can reduce bending deformation.

(4) Reserved shrinkage margin:

The longitudinal and transverse shrinkage deformation of the weldment after welding can be controlled by estimating the shrinkage of the weld and leaving a shrinkage margin in advance in the design.

(5) Reserve the position of the welding fixture:

There are places on the structure where welding jigs can be installed, so that the jigs can be used to control the technical deformation during the welding process.

2. Anti-deformation method

(1) The unilateral V-groove butt welding of steel plates with a thickness of 8 to 12 mm has almost no angular deformation after the anti-deformation of 1.5° during assembly. 

(2) The angle deformation of the I-beam caused by lateral shrinkage after welding, if the upper and lower cover plates are pre-pressed into reverse deformation (plastic deformation) before welding, and then welded after assembly, the upper and lower cover plates can be eliminated. deformation after welding. However, the magnitude of the reverse deformation of the upper and lower cover plates is mainly related to the thickness and width of the plate, as well as the thickness of the web and heat input. 

(3) The pipe joints of boilers and containers are concentrated in the upper part, which will cause bending deformation after welding. Therefore, a forced anti-deformation clamping device should be used, and the sequence of traces of symmetrical and uniform heating should be used. The alternate jump welding method is used under the action of external force. The elastic anti-deformation is combined with a reasonable heating welding sequence, and the bending deformation can be basically eliminated after welding. 

(4) The two main beams of the bridge crane are box-shaped structures composed of left and right webs and upper and lower cover plates. In order to improve the rigidity of the beam, large and small ribs are designed in the beam, and these ribs are designed. Plate fillet welds are mostly concentrated on the upper part of the beam, which will cause bending deformation of the lower radius after welding. However, the technical requirements for bridge cranes stipulate that the main girder should have a certain degree of upper camber after welding. In order to solve the contradiction between post-weld deformation and technical requirements, the method of prefabricated web camber is often used, that is, when preparing materials, the two The web of the block leaves the upper camber.

3. Rigid fixing method

Before welding, the welded parts are restrained by additional rigidity, and the welded parts cannot be deformed freely during welding.

(1) When welding flanges, fixing the two flanges back to back can effectively reduce the corner deformation.

(2) When the sheets are butted, use a weight around the sides to prevent wave deformation of the sheets after welding.

After welding, when the external restraint is removed, there will still be a little deformation on the weldment, but it is much less than the original. This method will generate a large welding stress in the weldment. Use with caution.

4. Choose a reasonable welding sequence

The welding sequence has a great influence on the welding structure. Improper welding sequence will affect the smooth progress of the entire process. For asymmetric welded structural parts, more attention should be paid to the rational arrangement of the order.

(1) For example, the I-beam can be welded by two people at the same time.

(2) When the restoration arrangement is asymmetrical, the side with less welds should be welded first, because the deformation of the welds is large first, and then the deformation caused by the more welds on the other side is used to offset the deformation caused by the welds first. , which can greatly reduce the deformation of the overall structure.

(3) When welding long welds, the deformation of through welding is the largest, which is the result of long-term heating of continuous welding butt welds. If possible, continuous welding should be changed to intermittent welding, which can reduce the amount of welding seam and mother. The material undergoes plastic deformation due to the increase of the heated surface.

5. Heat dissipation method

During welding, the heat in the welding area is dissipated by forced cooling (water spray cooling method), forcing the heating area to be greatly reduced, so as to achieve the purpose of reducing deformation.

For example, the heat dissipation method can reduce welding deformation, but it is not suitable for welding parts with high hardenability.

6. Self-weight method

If the upper part of the I-beam has more welds than the lower part, the I-beam will bend upwards after welding.

For example, if the I-beam is turned over and the two piers are placed at the two ends, the bending deformation after welding can be gradually offset by the bending tendency of the beam's own weight. , the key is that the distance between the two piers must be properly selected.