CLADDING TECHNOLOGY SHANXI CO., LTDPrediction of Buckling Deformation in Thin Plate TIG Overlay Welding
Literature Overview
This 2019 publication in the Journal of Welding, conducted by researchers from Henan University of Science and Technology and Xi'an Jiaotong University, addresses the challenging problem of geometric distortion—specifically buckling deformation—during gas tungsten arc welding (GTAW/TIG) overlay of thin plates. The research was supported by Henan Provincial Major Science and Technology Programs. The work develops both analytical models and numerical simulations to predict and control out-of-plane buckling that occurs when the compressive residual stresses exceed the critical buckling load of the thin substrate.
Core Technical Points
Thin plate overlay welding is widely employed in the fabrication of heat exchanger tubesheets, pressure vessel heads, and nuclear component liners. However, when the base plate thickness falls below a critical threshold, the compressive residual stresses generated by the welding thermal cycle can trigger elastic buckling, resulting in permanent out-of-plane deformation that is difficult to correct by mechanical straightening.
The theoretical framework for buckling prediction is based on the classical plate buckling theory modified for welding residual stress fields:
- Critical buckling stress: σ_cr = kπ²E / [12(1-ν²)] × (t/L)², where k is the buckling coefficient dependent on boundary conditions, E is Young's modulus, ν is Poisson's ratio, t is plate thickness, and L is the characteristic dimension.
- Residual stress distribution: The welding residual stress field typically exhibits a peak compressive stress of 0.3–0.5σ_y in the vicinity of the weld, decaying to zero at distances exceeding 3–5 times the weld width.
- Buckling criterion: Buckling occurs when the maximum compressive residual stress exceeds the critical buckling stress for the given plate geometry and boundary conditions.
| Plate Thickness (mm) | Critical Buckling Stress (MPa) | Typical Residual Stress (MPa) | Buckling Risk |
|---|---|---|---|
| 1.5 | 45–60 | 180–250 | Very High |
| 2.0 | 80–105 | 180–250 | High |
| 3.0 | 180–235 | 180–250 | Moderate |
| 4.0 | 320–420 | 180–250 | Low |
| 5.0 | 500–650 | 180–250 | Negligible |
FEA Simulation Methodology
The finite element analysis employed in this study used a thermomechanical coupled approach with the following key modeling considerations:
- Thermal model: The heat source was modeled as a double-elliptical Gaussian distribution (Goldak model) with front heat flux concentration ratio r = 2.0, representing the characteristic ahead-behind heat distribution of TIG welding. The thermal properties were defined as temperature-dependent functions.
- Mechanical model: The elastic-plastic material behavior was described using the Ramberg-Osgood equation with temperature-dependent yield stress. The residual stress was extracted from the thermomechanical simulation and compared with the analytical buckling prediction.
- Boundary conditions: The plate was constrained at all four edges with simply supported conditions for the baseline case. Clamped and free boundary conditions were also evaluated to establish the sensitivity of buckling to constraint level.
- Mesh refinement: The weld zone was discretized with elements of 0.5 mm size, increasing to 2.0 mm at distances exceeding 20 mm from the weld centerline.
Process Parameters and Their Influence on Buckling
The study systematically investigated the influence of welding parameters on the magnitude of residual stress and the propensity for buckling:
| Parameter | Low Value | High Value | Effect on Buckling |
|---|---|---|---|
| Welding current (A) | 80 | 160 | Higher current → more stress → more buckling |
| Travel speed (mm/s) | 3 | 8 | Higher speed → less stress → less buckling |
| Heat input (kJ/mm) | 0.6 | 1.8 | Higher heat input → more buckling |
| Shielding gas | Ar | Ar + 5% He | Helium addition increases penetration, moderate effect |
| Wire feed rate (mm/min) | 300 | 800 | Higher deposition → more stress accumulation |
The optimal process window for minimizing buckling in 2 mm thick plates was identified as: welding current 100–120 A, travel speed 6–8 mm/s, resulting in heat input of 0.8–1.0 kJ/mm. Under these conditions, the predicted maximum residual stress was reduced to approximately 150 MPa, below the critical buckling threshold for the given geometry.
Engineering Countermeasures
Based on the analysis, several practical countermeasures for controlling buckling in thin plate overlay welding are recommended:
- Intermittent welding: Breaking the continuous weld into segments of 50–80 mm with 10–15 mm gaps between segments reduces the cumulative compressive stress.
- Tack welding and clamping: Rigid clamping of the plate edges during welding constrains in-plane contraction and reduces the compressive stress amplitude, though it may increase through-thickness stress.
- Reverse welding sequence: Welding from the center outward or using a zigzag pattern distributes the residual stress more uniformly, reducing peak compressive values.
- Post-weld stress relief: Low-temperature stress relief at 300–400 °C for 2 hours effectively reduces residual stresses by 40–60% without causing significant grain coarsening.
- Substrate pre-stretching: Applying a controlled tensile pre-strain of 0.2–0.5% before welding offsets the compressive residual stress and prevents buckling initiation.
Key Questions and Reflections
An important limitation of the current analytical approach is its reliance on linear buckling theory, which does not account for geometric nonlinearity that becomes significant once buckling has initiated. The post-buckling behavior, including the amplitude of the buckle and its effect on subsequent weld passes, requires nonlinear FEA analysis with geometric imperfection sensitivity.
Another consideration is the effect of multi-pass overlay on buckling. Each additional pass superimposes a new residual stress field on the existing one, and the cumulative effect may trigger buckling even when individual passes are below the critical threshold. This sequential stress accumulation is particularly relevant for thick overlay builds on thin substrates, such as the fabrication of bimetallic pressure vessel heads.
Study Insights and Conclusions
This research establishes a predictive framework for buckling deformation in thin plate TIG overlay welding that bridges the gap between theoretical plate buckling mechanics and practical welding process design. The key insight for engineering practice is that buckling is not merely a geometric imperfection but a thermomechanical instability that can be anticipated and controlled through systematic process optimization. The integration of FEA predictions with empirical buckling criteria provides a powerful tool for the design of overlay welding procedures on thin substrates, enabling the fabrication of high-quality bimetallic components without resorting to costly post-weld straightening operations.