The term “thin plate component” typically refers to parts manufactured by welding steel plates less than 4 mm thick, including stainless steel, galvanized sheet metal and tin. Examples of such components produced by our factory include roller hangars, drive chambers and excavator drive chambers.
Controlling and preventing welding distortions in thin sheet composites requires advanced technical skills. The following discussions are based on our consensus and are intended for reference purposes only.
Causes of Welding Distortion
Arc welding is a process that involves rapid heating and cooling, which can result in uneven distortion during or after welding.
The main factors that affect welding distortion are thermal distortion and stiffness of the welded component. Thermal distortion during welding is controlled by the stiffness of the component, leading to compressive plastic distortion and residual welding distortion.
1) Factors affecting welding thermal distortion.
- Welding method.
Different welding methods produce varying temperature fields, resulting in different thermal distortions.
Generally speaking, automatic welding is more focused compared to manual welding, producing a narrower, less distorted result. When using thin welding wire and high current density with CO2 gas shielding, the resulting heat concentration in CO2 gas shielded welding causes less distortion.
- Welding parameters
Factors that influence welding distortion include welding current, arc voltage and welding speed.
The amount of welding distortion increases with increasing line power. Higher welding current and arc voltage result in greater welding distortion, while increasing welding speed reduces welding distortion.
Of the three parameters, arc voltage has a significant impact on welding distortion. Therefore, the use of low voltage, high speed and high current density in automatic welding results in less welding distortion.
- Welding seam quantity and cross section size.
The greater the number of welding seams and the larger the cross-section size, the greater the welding distortion.
- Operation method.
Continuous welding and intermittent welding result in different temperature fields, leading to different thermal distortions.
Typically, continuous welding results in greater distortions, while discontinuous welding produces minimal distortions.
- Thermal physical properties of materials.
Different materials have varying thermal conductivity, specific heat and expansion coefficients, which result in different thermal and welding distortions.
2) Factors affecting the stiffness coefficient of welded components
The size and shape of the components
As the stiffness of a component increases, its welding distortion decreases.
Application of tire clamps
Tire clamps can be used to increase the rigidity of a component, resulting in reduced welding distortion.
Assembly Welding Procedure
The assembly welding process can change the stiffness and center of gravity position of components during different stages of assembly, which significantly impacts the welding distortion of control components.
In general, components tend to experience greater welding distortion under relaxed conditions and less welding distortion under tight conditions.
Types of Structural Steel Sheet Welding Distortion
The welding distortion of any steel structure can be classified into two types: general distortion and partial distortion.
General distortion refers to changes in the size or shape of a component after welding, including longitudinal and transverse shrinkage, which results in a reduction in overall size, bending distortion (such as sagging and sagging), and other types of distortion.
Partial distortion refers to the distortion that occurs in specific areas after welding, including angular distortion and wave distortion.
Principles and Methods for Controlling Welding Distortion in Structural Steel Plates
The two main factors that affect welding residual distortion are thermal distortion and component stiffness during the welding process. As a result, it is not possible to completely eliminate welding distortion.
To control residual welding distortion, both the design of thin-plate components and construction techniques must be considered. The design of thin plate components must not only meet strength and performance requirements, but also minimize welding distortion and labor hours.
Optimizing the layout of slab joints is crucial to reducing welding distortion. The technical properties of joints must also be taken into account during design, as ignoring these properties can easily lead to welding distortion.
The welding process is a significant aspect of steel structure construction, and a well-planned welding process can effectively reduce welding distortion and stress concentration.
To control welding distortion, the following measures must be taken:
- Dividing components into smaller sections can distribute welding distortion and make it easier to control and correct.
- Symmetrical or nearly neutral axis layout of welding seams can reduce distortion and excessive bending distortion after welding.
- Using a small welding foot and short welds for each main welding seam can help control distortion.
- Avoiding excessive concentration and cross layout of welding seams can reduce distortion.
- Using wide and long steel plates as much as possible or reducing the number of welding seams can also help control welding distortion.
Methods for controlling welding distortion of thin plate components are:
- Assembly of components without assembly effort.
- Using automatic welding and other gas shielded welding technologies such as advanced MAG shield welding with Ar + CO2 gas mixture.
- Selecting appropriate welding specification parameters and assembly welding sequence, reducing welding wire supply and adjusting current, voltage and polarity (generally using DC reverse polarity or DC positive polarity). Weld the short seams first, then the long seams, using step-by-step welding from the inside out.
- Implementation of appropriate rigid fixation methods and anti-distortion methods to reduce distortion.
Rectification of welding distortions of thin structural parts
In the fabrication of steel structures, even with measures taken to control welding distortion through component design and construction techniques, welding distortion is still inevitable. Any welding distortion exceeding design requirements must be corrected.
Correction is limited to correcting specific distortions such as angular distortion, bending distortion, and wave distortion. General distortions, such as longitudinal and transverse shrinkage, can only be compensated through blanks or assembly tolerances.
Mechanical correction of steel structures can cause metal hardening and consume material reserves, so it is only suitable for materials with good plasticity. In practice, large-scale hydraulic and friction presses can be used for mechanical correction.
Flame correction can correct the overall distortion of the component, causing irreversible compression and plastic distortion in the cooled welded metal part. However, this method also consumes plasticity, so it should be used with caution for brittle or plastic materials.
The flame heating temperature must be properly controlled. Too high a temperature will reduce the mechanical properties of the material, while too low a temperature will decrease the correction efficiency.
The cooling speed does not affect the correction efficiency, therefore, water can be sprayed during heating to improve the working efficiency and increase the correction effect.
In conclusion, welding distortion is inevitable in the manufacture of steel structures and can only be controlled through effective methods and measures and corrected if it exceeds tolerance requirements. This guarantees the quality of the steel structure and economic efficiency.
