28 Oct 2021
Various problems will inevitably occur when the welding machine is performing welding work, and welding deformation is a relatively serious problem often encountered in welding assembly structures. Because there are many parameters related to the welding process, it makes it difficult to predict the deformation. Welding deformation mainly includes: shrinkage deformation, angular deformation, bending deformation, wave deformation and twisting deformation. If there is a deformation on the workpiece, it takes a lot of time and energy to correct it. For more complex deformations, the workload required for correction may be greater than that of welding. Sometimes the deformation is too large to be corrected, resulting in waste. What are the technological measures taken to prevent deformation in the production of specific structures?
The first method is the anti-deformation method. The most commonly used method in anti-deformation French production. Estimate the size and direction of the structural deformation in advance, and then give an opposite pre-deformation during assembly, which can offset the welding deformation, so that the welded components can meet the design requirements. For example, in order to prevent the angular deformation of the butt joint, it can be Padded the welding groove in advance; when welding beams, columns and other slender components, if the welding seam is asymmetric, the components will tend to undergo greater deflection and deformation after welding. To prevent such deformations, external forces can be used to compress the components. On a fixture or platform with sufficient rigidity, make it produce an anti-deformation, and then perform welding. It is also possible to fix the two components together back to back for welding, so that the reverse deformation can be carried out when there is no rigid platform, and good results can be obtained.
The second method is the rigid fixation method. The method of using external rigid constraints to reduce the post-weld deformation of the weldment is called the rigid fixation method. This method is to fix the component to limit welding deformation without anti-deformation. Using this method to prevent the flexural deformation of the component can only reduce this deformation to a certain extent, and the effect is far less than the anti-deformation method. However, it is better to use the rigid fixing method to prevent angular deformation and wave deformation. When welding thin plates, fix it with clamps on both sides of the weld to prevent wave deformation. The fixed position should be close to the weld, the pressure must be uniform, and its size should increase with the increase of the plate thickness to maintain a higher uniform pressure. On the one hand, it can prevent the movement of the workpiece, and on the other hand, the fixture can conduct heat evenly and reliably, limit the width of the high-temperature zone of the workpiece, thereby reducing post-welding deformation.
The third method is to choose the welding method and specification reasonably. Selecting a welding method with a smaller heat input can effectively prevent welding deformation. For example, carbon dioxide semi-automatic welding is used to replace gas welding and electrode arc welding, which not only has high efficiency, but also reduces the deformation of the thin plate structure. During the welding process, according to the specific conditions of the welding structure, as much as possible the use of smaller welding parameters, that is, a small diameter electrode and a small welding current, can reduce the heat input of the welding arc, and make the heat affected zone smaller, thereby reducing Small welding distortion.
The fourth method is to choose a reasonable assembly welding sequence. Divide the structure into several parts appropriately, assemble and weld them separately, and then weld these parts as a whole, so that those welds with asymmetric or large contraction force can shrink freely without affecting the overall structure, thereby controlling the structure The welding distortion. According to this principle, when assembling and welding a more complex structure, it can be divided into several simple parts, assembled and welded separately, and then assembled and welded. This is not only conducive to the control of welding deformation, but also because of the expansion of the work surface, it also creates good conditions for shortening the production cycle and improving production efficiency.
The fifth method is the reserved margin method. The longitudinal and transverse shrinkage deformation can be compensated by estimating the shrinkage of the weld seam, and leaving a shrinkage margin in advance during the material preparation process. The diameter error caused by the transverse shrinkage of the longitudinal seam of the cylindrical body can be overcome by the method of reserved shrinkage margin.
The sixth method is to appropriately change the welding sequence. A reasonable welding sequence can make the welding seam in a state of free shrinkage, so as to reduce the restraining stress of the welding seam metal deformation, thereby controlling the welding deformation. This method has symmetrical method, jumper welding method and segmented back welding method. Among them, the symmetric method is to formulate the welding sequence symmetrically; the skip welding method is to weld in a jump, and after each section of the weld is cooled, the interval of each section of the weld is welded; the segmented back welding method is to make the weld during welding The temperature gradient decreases uniformly, and the entire weld is equally divided into several sections for welding. The welding direction is opposite to the welding completion direction, and the welding is carried out in the form of backwards.
The last method is hammering. The weld is hammered with a hammer in the red hot state to extend the weld metal and reduce the tensile stress during shrinkage. This method is often used in multi-layer and multi-pass welding and when welding base materials with poor plasticity with welding materials with good plasticity. However, the first weld and surface welds should not be hammered to prevent root cracks and hardening of the surface welds. Hammering is generally to use a flat long round head hammer to hammer in sequence along the weld, the strength should be moderate and even.
Welding deformation not only affects the accurate size and beautiful appearance of welded structural parts, but also may reduce the load-bearing capacity of the structure and cause accidents. Therefore, it is of very important practical significance to grasp the law of welding deformation and the method of controlling welding deformation. In the welding process, whether or not a beautiful weld can be obtained is a test of a welder's welding skills. If you want to become a better welder, you should learn and master more welding technology knowledge, and then apply it to the welding process of the welding machine to present a more perfect weld.
Keywords: welding machine
Originally published 28 Oct 2021, updated 28 Oct 2021.