Process Measures to Reduce Residual Deformation of Welding

1. Anti-deformation method

The size of the deformation is predicted based on experience when assembling before welding, and the member is given a deformation in the opposite direction of the welding deformation, so that the deformation is offset with the welding deformation, so that the structure can meet the technical requirements after welding. There are two methods of counter-deformation: ① plastic counter-deformation; ② elastic counter-deformation. In actual production, elastic counter-deformation is more reliable than plastic counter-deformation. Because even if the pre-strain of elastic counter-deformation is not accurate enough, it is always possible to reduce the angular deformation. If the plastic anti-deformation is used, the selected plastic pre-bending amount must be very accurate, otherwise it will not get good results.

2. Welding under external constraint conditions

The weld is rigidly fixed in a fixture to limit the deformation of the member during welding. It has a good effect on reducing the angular deformation of the welded parts, which can make the welding deformation reduced, but the welding stress is higher.

3. Reasonable choice of welding methods and welding specifications

To reduce welding deformation, high energy density welding methods should be used as much as possible. Such as electron beam welding, laser welding, narrow gap welding, etc.. They have a lower welding line energy, welding deformation is very small. In general production, CO2 gas shielded welding to replace manual arc welding, not only has high efficiency, but also can significantly reduce welding deformation. When welding thin plates, tungsten pulse argon arc welding or resistance welding, and seam welding, all can prevent pressure bending deformation.

If there are no conditions in the production of low line energy methods, and do not reduce the welding specification, direct water cooling or the use of water-cooled copper block to change the distribution of the heat field to reduce the deformation of the purpose. But for hardened metal materials, this method is used with caution.

4. Select a reasonable assembly welding sequence and welding direction

The design of the assembly welding sequence mainly considers the impact of welding stresses and deformations generated by the first weld on the subsequent weld, but also considers how the stresses and deformations generated by the subsequent weld interact with the impact of the first weld. The practice has proved that the correct choice of assembly welding sequence, is a powerful measure to prevent welding deformation.

In the production is usually used to produce a small spell large welding structure, first welded into a number of parts and components, and then assembled and welded into a whole structure. As the assembly and welding sequence of the welded parts are different, the incremental structural rigidity and the impact on the welding deformation during production are also different, so they should be analyzed and compared to choose a reasonable assembly and welding sequence with the least deformation.

In general, should be first welded shrinkage of the weld, after welding shrinkage of the weld is small. When there is a butt weld and fillet weld, generally should be first welded butt weld, then welded fillet weld; when there is a transverse weld and longitudinal weld, should be first welded transverse weld, then welded longitudinal weld; when there is a thick plate weld and thin plate weld, generally should be first welded thick plate weld, then welded thin plate weld; when there is both intermittent and continuous weld in the structure, generally should be first welded continuous weld, then welded intermittent Weld seam.

5. Preheating

Uneven heat field of welding is the main cause of welding deformation. Therefore, the use of appropriate preheating; welding temperature distribution tends to be uniform, is also an effective measure to reduce residual deformation of welding.

6. Stretching method and heating method to reduce the out-of-plane deformation of welded sheet

Mechanical method or preheating method to make the welded wall plate stretch or elongate, while the wall plate is welded to the structure of the frame, after welding, remove the tensile load. At this time, the contraction of the wall plate is constrained by the welded frame, so that only a small amount of out-of-plane deformation in the wall plate is produced. At this time there is residual tensile stress in the wall plate after welding, while in the frame there is residual compressive stress. This method has a good effect on reducing the compression bending deformation of the welded sheet.