Excellent! Thin plate welding deformation is an extremely common and troublesome problem. It is primarily caused by uneven thermal expansion and contraction during welding. The weld area expands due to heat, but is constrained by the surrounding cold metal, resulting in compressive plastic deformation. Contraction upon cooling can cause distortion, angular distortion, and wave-like deformation throughout the plate.

The core approach to addressing thin plate welding deformation is "prevention is better than cure," prioritizing measures to control deformation rather than correcting it afterward.

The following is a systematic solution, encompassing design, process, and operational controls:

1. Pre-welding Precautions (Most Important!)

This is the most effective and cost-effective stage for controlling deformation.

1. Optimize Structural Design

Reduce the number and length of welds: While meeting strength requirements, use bending, profiling, and other processes instead of welding whenever possible.

Avoid excessive concentration of welds: Arrange welds symmetrically to distribute heat input. Choose the right groove shape: In thin plate welding, an I-groove (no groove) or a shallow V-groove can reduce the amount of deposited metal, thereby reducing heat input, more effectively than a steeper groove.

2. Choose the right base metal and welding consumables

While meeting performance requirements, choose materials with low thermal conductivity and a low coefficient of linear expansion.

Using low-hydrogen welding consumables or high-efficiency welding consumables can reduce welding energy.

3. Pre-weld preparation

Reverse deformation method (very effective): Before welding, the workpiece is artificially deformed in the direction opposite to the intended deformation. After welding, the shrinkage offsets the pre-deformation, restoring the workpiece to a straight line. This requires experience to estimate the amount of deformation.

For example, when welding a T-joint, tilt the vertical plate (rib) slightly (1°-3°) to the opposite side before welding. This will create a vertical position after welding.

Rigid fixation method: Secure the workpiece to a solid work platform or jig using a clamp, pressure plate, or spot welding to prevent deformation. Note: This method generates significant internal stress. For some critical structural components, post-weld stress relief annealing may be required.

Allow shrinkage allowance: When cutting material, allow for shrinkage in the dimensions based on experience.

II. Control Measures During Welding

1. Select the Correct Welding Method and Parameters

Low-heat-input welding methods: TIG (argon arc welding), pulsed MIG/MAG welding, laser welding, plasma welding, and other methods with high energy density and a small heat-affected zone are more suitable for thin plates than traditional manual arc welding.

Use Low Current and Fast Welding Speed: While ensuring full penetration, use the lowest possible welding current and fastest possible welding speed to reduce heat input.

Use Fine-diameter Welding Wire/Rod: At the same current, fine wire concentrates more energy than thicker wire.

2. Adopt a Proper Welding Process

Segmented Back-Welding Method: Divide a long weld into several sections, welding each section from the back to the front (toward the previously welded section). This ensures more even heat distribution and reduces cumulative deformation. Skip welding: Instead of welding sequentially, skip welding sections, also to distribute heat.

Symmetrical welding: For symmetrical workpieces, it's best to have two welders weld simultaneously, symmetrically, to offset shrinkage stresses on both sides.

Reducing deposited metal: For fillet welds, avoid excessively large leg sizes; simply meet design requirements.

3. Using jigs and backing plates

Copper backing plates: Place a copper plate (or a water-cooled copper backing plate) on the back of the weld. Copper's excellent thermal conductivity quickly dissipates heat from the weld, minimizing the heat-affected zone and effectively preventing deformation.

Heat dissipation method: Use a metal block with high thermal conductivity (such as copper) near the weld to help dissipate heat.

III. Post-weld Corrective Measures

If deformation has already occurred, the following methods can be used to correct it, but these are remedial measures and may affect appearance and performance.

1. Mechanical Correction Method: Use a jack, press, hammer (with wooden blocks to prevent damage), or other tools to apply opposing force to the deformed area to restore it to a straight line. Suitable for materials with good plasticity and minor deformation.

2. Thermal Correction (Flame Correction)

Use an oxyacetylene flame to heat specific points or bands within the deformed area (do not directly heat the weld seam), followed by rapid cooling (usually with air, but water can be used for mild steel). This method utilizes the new thermal expansion and contraction stresses to correct the deformation. This method requires advanced skill and experience, and has strict requirements for heating temperature, position, and speed. Improper operation may lead to deterioration of material properties or even more severe deformation.

Summary and Practical Recommendations

For thin plate welding, the most effective strategy is "prevention first, comprehensive treatment."

A typical thin plate welding process should be:

1. Design Phase: Minimize weld seams.

2. Pre-welding:

Clean the area to be welded.

Apply a counter-deformation according to the estimated deformation.

Use a clamp and pressure plate to securely and rigidly secure the workpiece to the platform.

Place a copper backing plate on the back of the weld seam. 

3. During welding:

Select TIG welding or low-current MIG welding.

Use low current and fast welding speed.

For long welds, use the step-by-step back-welding method.

4. After welding:

Wait until the workpiece has completely cooled before releasing the clamps to prevent stress release and deformation.

If minor deformation persists, consider mechanical correction or professional flame correction.

Remember, controlling heat input is the golden rule throughout. For particularly delicate or complex parts, process trials are required before formal welding to determine the optimal parameters and amount of deformation relief.