In metal welding, welding distortion is a critical issue affecting part precision and performance. Whether it's a small precision component or a large structural part, factors such as uneven heat input and differential material shrinkage during metal welding can lead to welding distortion, increasing subsequent correction costs and even causing part scrap. Therefore, mastering scientific methods for controlling welding distortion is crucial for optimizing metal welding processes and improving product quality.

Mechanism of Welding Distortion in Metal Welding

Metal welding uses a high-temperature heat source to melt and then solidify the material in the weld area, forming a weld. During this process, a significant temperature gradient forms between the weld area and the surrounding material. The expansion of the material in the high-temperature area is constrained by the low-temperature area, generating compressive stress; during cooling and contraction, the material is also constrained, generating tensile stress. The uneven distribution of internal stresses caused by thermal expansion and contraction ultimately leads to welding distortion, which commonly occurs in the form of shrinkage, angular deformation, bending deformation, and wave deformation. The type and degree of distortion vary significantly in different metal welding scenarios.

Metal Welding Deformation Control: Scientific Selection of Welding Methods

The welding method directly affects the heat input and heat distribution during metal welding and is a fundamental step in controlling deformation.

• In thin-plate welding, laser welding or plasma arc welding requires less heat input than traditional arc welding, significantly reducing the risk of wave deformation.

• When welding heat-sensitive materials such as aluminum alloys, friction stir welding, as a solid-phase welding method, eliminates the need to melt the material, fundamentally reducing deformation caused by heat input.

• Metal welding for circular welds uses a symmetrical welding method to evenly distribute heat input and avoid shrinkage deformation caused by continuous welding on one side.

Metal Welding Deformation Control: Appropriate Use of Welding Auxiliary Tools

Welding auxiliary tools suppress material deformation through physical restraint or auxiliary support, and are an important means of improving metal welding accuracy.

• Fixtures and fixtures securely hold the welded parts before welding, limiting their free expansion and contraction. In steel structural welding, rigid fixtures clamping the plates on both sides of the weld can reduce shrinkage deformation. 

• When welding thin-walled cylinders, internal support fixtures maintain the roundness of the cylinder wall, preventing collapse or elliptical deformation. 

• When welding thin metal sheets, placing a copper backing plate beneath the weld can accelerate heat dissipation, minimize the heat-affected zone, and thus control deformation.

Metal Welding Deformation Control: Precise Control of Welding Parameters

Welding parameters determine the heat input and weld shape of metal welds. Precise control can reduce deformation at the source.

• Welding current and voltage affect arc power and heat input. While maintaining weld strength, lower values should be selected. When welding thin mild steel sheets, reducing the current from 180A to 140A reduces heat input by approximately 20% and deformation by over 15%.

• Welding speed must be appropriately controlled: Increasing the speed shortens the time the material remains in the high-temperature zone, reducing heat accumulation, but ensuring complete penetration is essential. Slowing the speed can concentrate heat input and increase the risk of deformation.

• Multi-pass welding utilizes layered welding with controlled layer thickness to distribute heat input and avoid deformation caused by localized overheating.

Metal Welding Deformation Control: Optimizing Welding Sequence Design

The welding sequence affects the distribution and release of internal stress during metal welding. A sound design can balance internal stress and reduce deformation.

• For symmetrical structures, a symmetrical welding sequence, alternating from the center to the sides, is used to offset heat input and shrinkage on both sides. For box beam welding, symmetrical welds of the upper and lower cover plates are welded first, followed by the web welds, to reduce bending deformation.

• For large, complex structural components, the principles of "welding welds with large shrinkage first, then welds with small shrinkage," and "welding butt welds first, then fillet welds" are followed. This prioritizes the release of shrinkage stress in primary welds and avoids deformation caused by secondary stress.

Metal Welding Deformation Control: Supplementary Post-Welding Treatment Measures

Even with control measures implemented during welding, some metal welds may still experience slight deformation. Post-weld treatment can further correct this deformation and relieve stress.

• Post-weld aging treatment involves heating the welded parts to a specific temperature, holding them at that temperature, and then slowly cooling them to promote the release of internal stress and reduce deformation caused by residual stress. 

• Small precision components use mechanical correction methods to restore deformed parts by applying external force, but excessive force must be avoided to prevent damage to the parts. Vibration aging technology applies low-frequency vibrations to welded parts, accelerating the relaxation and uniform distribution of internal stresses without affecting weld performance. It is suitable for a wide range of metal welds.

Conclusion

Welding deformation control is a core technical step in the metal welding process, directly impacting product precision, performance, and manufacturing costs. By scientifically selecting welding methods, utilizing welding auxiliary tools, precisely controlling welding parameters, optimizing the welding sequence, and implementing effective post-weld treatment measures, a comprehensive metal welding deformation control system can be established. In actual metal welding production, it is necessary to flexibly combine various control methods based on part materials, structural characteristics, and precision requirements, and continuously optimize the welding process to minimize welding deformation and enhance the quality and competitiveness of metal welded products.

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