CLADDING TECHNOLOGY SHANXI CO., LTDHeat Input Effects on TIG Welding Distortion of Thin Steel Plates
Research Overview
The 2022 study by Guo Wenju and colleagues from Wuhu Polytechnic and Henan University of Science and Technology addresses a persistent challenge in thin-plate welding fabrication: the relationship between heat input and angular distortion in TIG welding of thin steel plates. Thin plates (typically defined as those with thickness below 6 mm) are particularly susceptible to welding distortion because their low bending stiffness cannot resist the thermal stresses generated during welding. This work provides quantitative data that can directly inform process optimization for thin-plate fabrication.
Heat Input and Distortion Relationship
The research systematically varies welding parameters to establish the correlation between heat input and angular distortion. The experimental matrix includes:
| Parameter | Levels Tested | Range |
|---|---|---|
| Welding current | 3 levels | 100, 140, 180 A |
| Travel speed | 3 levels | 200, 300, 400 mm/min |
| Plate thickness | 3 levels | 2, 3, 4 mm |
| Shielding gas flow | 2 levels | 8, 12 L/min |
The fundamental relationship observed is that angular distortion increases approximately linearly with heat input for a given plate thickness, following the general trend:
Angular distortion (degrees) ≈ k × (Q / t²)
where Q is the heat input in kJ/mm, t is the plate thickness in mm, and k is a material-dependent constant approximately equal to 0.3–0.5 for carbon steel.
Distortion Mechanism Analysis
The distortion mechanism in thin-plate TIG welding involves three sequential phases:
- Thermal expansion phase: The weld pool and adjacent heated zone expand longitudinally, compressing the cooler base material laterally.
- Cooling contraction phase: Upon cooling, the weld zone contracts but is constrained by the cooler surrounding material, generating residual tensile stresses in the weld and compressive stresses in the adjacent plate.
- Elastic-plastic bending phase: The asymmetric stress distribution causes the plate to bend away from the weld line, producing angular distortion.
The key finding is that the transition from elastic to plastic deformation in the base metal occurs at a critical heat input threshold, beyond which distortion increases super-linearly. This threshold depends on plate thickness, material yield strength, and constraint conditions.
Process Optimization Recommendations
Based on the research findings, the following optimization strategies are recommended for minimizing distortion in thin-plate TIG welding:
- Reduce heat input by increasing travel speed and decreasing current within the penetration window
- Employ back-plate cooling or copper backing to reduce through-thickness temperature gradient
- Use intermittent welding (skip welding) to distribute thermal input along the weld length
- Apply mechanical clamping fixtures to provide external constraint during welding
- Pre-bend the plate in the opposite direction to the expected distortion (springback method)
For plates thinner than 3 mm, the recommended maximum heat input is below 0.8 kJ/mm to maintain angular distortion under 1 degree per 100 mm of weld length. This constraint significantly limits the practical welding speed range and demands careful parameter optimization for each specific application.