What are the factors that affect the welding deformation of steel structural parts?

The main factors affecting the welding deformation of the steel structure platform are as follows:

1. Arrangement of welds.

If the weld is asymmetrically distributed along the cross-section of the component, it will cause the bending deformation of the component when welding.

2. Structural rigidity.

After welding, the weld generally produces longitudinal and transverse contraction, and this contraction is limited by the entire structure and produces a "shrinkage force". For welded structures with large rigidity, the deformation produced under the action of this force is relatively small; The welded structure with low rigidity will produce large deformation under the action of this force.

3. Assembly and welding sequence.

With a reasonable assembly sequence, it is also necessary to have a reasonable welding sequence to control the deformation.

4. Material preparation and assembly quality.

Material preparation and assembly quality also have an impact on welding distortion. For example, the assembly gap is large, and the lateral shrinkage of the weld is also large.

5. Welding parameters.

Among the many welding parameters, the welding line energy is directly proportional to the welding deformation.

The larger the energy of the welding line, the larger the area of the plastic deformation zone generated during welding, the greater the welding deformation after welding, and the smaller it is vice versa.

6. Welding method.

For the same weldment, the same weld, different welding methods, the welding deformation is also different.

In the welding process of steel structure platform, different influencing factors are mutually influencing and do not appear simply. Therefore, a comprehensive analysis of various factors affecting welding deformation and mastering its influence law can take reasonable measures to control welding deformation.

There are two factors affecting the welding deformation of steel structural parts: design and process. The design aspect refers to the rationality of the structural design, the position of the weld, the form of the weld groove, etc. The process refers to the reasonable welding process regulations, the assembly and welding sequence, the adoption of various anti-deformation and anti-deformation methods, and the stress relief measures taken.

1.Reserve shrinkage margin; 2.anti-deformation method; 3.Reasonable assembly and welding sequence; 4.Rigid fixation method.

To put it simply, it should be fixed with a fixture!

Fixture There is also the problem of the welding machine

The basic forms of welding deformation include shrinkage deformation, angular deformation, bending deformation, wave deformation and twisting deformation. During the welding process, uneven heating and cooling of the weldment is the root cause of welding stress and deformation. The process measures to reduce welding stress and deformation mainly include:

1. Reserve shrinkage deformation According to theoretical calculation and practical experience, the shrinkage margin is considered in advance when preparing and processing weldments, so that the workpiece can reach the required shape and size after welding.

2. Anti-deformation method According to theoretical calculation and practical experience, the direction and size of the structural welding deformation are estimated in advance, and then a preset deformation with the opposite direction and equal size is given during welding and assembly to offset the deformation generated after welding.

3. Rigid fixing method The weldment is rigidly fixed during welding, and the rigid fixing is removed after the weldment cools to room temperature after welding, which can effectively prevent angular deformation and wave deformation. This method will increase the welding stress, and is only suitable for low-carbon steel structures with good plasticity.

Fourth, choose a reasonable welding sequence and try to make the weld shrink freely. When welding structural parts with many welds, the staggered short welds should be welded first, and then the straight through long welds should be welded to prevent cracks at the weld junction. If the weld is long, the step-by-step desoldering method and skip welding method can be used to make the temperature distribution more uniform, thereby reducing the welding stress and deformation.

5. Hammer weld method In the cooling process of the weld, the weld is hammered evenly and quickly with a round-headed hammer to produce plastic extension deformation of the metal and offset a part of the welding shrinkage deformation, thereby reducing the welding stress and deformation.

6. Heating "subtraction zone" method Before welding, the area near the welding part (called the subtraction zone) is heated to make it elongate, and when it is cooled after welding, the heating zone shrinks together with the weld, which can effectively reduce the welding stress and deformation.

7. Preheating before welding and slow cooling after welding The purpose of preheating is to reduce the temperature difference between the weld area and other parts of the weldment, reduce the cooling rate of the weld area, and make the weldment cool down more uniformly, thereby reducing the welding stress and deformation.

Generation and prevention of welding stress.

The internal stresses generated in the weldment during the welding process and the change in the shape and size of the weldment caused by the thermal process of welding. The uneven temperature field of the welding process and the local plastic deformation and the different specific volume of the structure caused by it are the root causes of welding stress and deformation. When the uneven temperature field caused by welding has not disappeared, this stress and deformation in the weldment is called transient welding stress and deformation; The stress and deformation after the disappearance of the welding temperature field is called residual welding stress and deformation.

In the absence of external forces, the welding stress is balanced inside the weldment. Welding stress and deformation can affect the function and appearance of weldments under certain conditions, so they are issues that must be considered in design and manufacturing. Welding Residual Stress The main research content of welding residual stress includes the distribution of stress, its influence, and the methods of elimination and adjustment.

Distribution of welding residual stress In weldments with small thickness, the welding residual stress is basically a plane stress, and the stress in the thickness direction is very small. For a flat plate welded in the free state, the longitudinal residual stress x along the direction of the weld is generally tensile stress at and near the weld, and compressive stress at the distance from the weld. For low-carbon steels and low-alloy structural steels with low strength (yield strength less than 400 MPa), the residual stress x on the weld can reach the yield strength s of the material (Figure 1 [Longitudinal Residual Stress Distribution in the Weld])." class=image>）。

The distribution of transverse residual stresses perpendicular to the direction of the weld is related to the welding sequence and direction, and the section of the post-weld is generally tensile stress, but the two ends of the weld are often compressive stresses in flat butt welding (Fig. 2 [Transverse Residual Stress in Welds])."class=image>[cloth]). The residual stress in the thickness direction of the thick plate weld is related to the welding method. In electroslag welds, it is tensile stress.

Multi-layer welds are lower. The distribution in thickness is highest in the center, gradually transitioning to zero to the surface. x and the distribution on the thickness of the weld is also uneven.

The value of x sum of the scattered posture center in the electroslag weld is greater than that of the surface layer. In contrast to multilayer welds, the surface stress is greater than the center (Fig. 3 [Distribution of residual stresses over thickness] in thick plate multilayer welds). When welding in a restrained state (e.g., a closed weld), higher tensile stresses may occur in a much larger range than in the free state, and the internal stress is more dangerous.

Because the residual stress of welding is affected by many factors, it is often necessary to determine the size and distribution of residual stress through experiments in practical work. Effect of Welding Residual Stress Welding residual stress has 6 aspects of influence on weldments. Effect on Intensity:

If there are severe defects in the region of high residual tensile stress, and the weldment is operating at a temperature below the brittle transition, the weld residual stress will reduce the static load strength. Under the action of cyclic stress, if there is residual tensile stress at the stress concentration, the residual tensile stress of welding will reduce the fatigue strength of the weldment. In addition to the size of the residual stress, the fatigue strength of the weldment is also related to the stress concentration coefficient of the weldment, the stress cyclic characteristic coefficient [min] [max] and the maximum value of the cyclic stress [m].

Hello, the main deformation of welding of slender structural parts is: longitudinal bending deformation of components caused by longitudinal shrinkage. This deformation mostly occurs in the welding of slender parts, and is caused by the asymmetrical longitudinal contraction of the weld along the axial length, and its curved concave surface is located on the side of the weld.

Typical thin-walled coil welded cylinders with small diameters sometimes have longitudinal bending deformation. The longitudinal bending deformation of the component caused by the transverse and longitudinal shrinkage is on the slender member, if there are more welds on one side along the length direction, and the transverse and longitudinal stool shrinkage of these welds is along the length of the component, then the contraction of many welds is comprehensive, and the whole component is often produced by obvious longitudinal bending deformation.

Answer]: a, c, with d, e

2020 Textbook P63 2019 Textbook P53

The hazards of welding finger resistance deformation are mainly manifested in: reducing assembly quality, affecting appearance quality, reducing bearing capacity, increasing correction processes, and increasing manufacturing costs.

Summary. second: use assembly and welding sequences to control deformation;

Adopting reasonable assembly and welding procedures to reduce distortion is a good way to be effective in production practice.

There are many structural cross-sections with symmetrical shapes and symmetrical weld layouts, but after welding, bending or twisting deformation occurs, which is mainly caused by unreasonable assembly and welding sequences, that is, the deformation caused by each weld fails to cancel each other, so deformation occurs.

How to prevent welding deformation of steel structure?

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Hello, I am glad to answer for you, there are two main ways to prevent the welding deformation of steel structures:

The first type: anti-deformation method When assembling before welding, the deformation amount of Lushen preset in the opposite direction is to offset (compensate) the welding deformation, which is called the counter-deformation method of the field. When the V-shaped groove of the steel plate with a thickness of 12mm is welded on one side for 8 - with a loss of 12mm, the angular deformation is basically eliminated after the reverse deformation method is adopted.

second: use assembly and welding sequences to control deformation; Adopting reasonable assembly and welding procedures to reduce distortion is a good way to be effective in production practice. There are many structural cross-sectional shapes symmetrical, weld layout is also symmetrical, but after welding, bending or twisting deformation, which is mainly caused by the unreasonable operation of the assembly and welding filial piety and filial piety side finger sequence, that is, the deformation caused by each weld, failed to cancel each other, so deformation occurred.

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When assembling before welding, the amount of deformation in the opposite direction of the preset is to offset (compensate) the deformation of the weld.