Finite Element Analysis of Three-Dimensional Temperature Field in TIG Welding of Stainless Steel Thin Plate Using SYSWELD

Literature Overview

The research by Li Ruiying et al. (2007), published in Hot Working Technology, presents a finite element analysis (FEA) of the three-dimensional temperature field during TIG welding of stainless steel thin plate using the SYSWELD software platform. The study employs a double-ellipsoid heat source distribution model to simulate the thermal process from arc ignition to quasi-steady state, predicting the dynamic evolution of the temperature field and molten pool morphology. The results are validated against experimental measurements, demonstrating reasonable agreement between the calculated and measured molten pool dimensions at quasi-steady state.

Core Technical Findings

The key findings of this numerical study include:

• The double-ellipsoid heat source model provides an adequate representation of the TIG arc heat input for stainless steel thin plate welding.
• The FEA model successfully predicts the dynamic evolution of the temperature field from arc start to quasi-steady state.
• At quasi-steady state, the calculated molten pool length and width are in reasonable agreement with experimental measurements.
• The model captures the transient thermal behavior that is critical for understanding solidification patterns and HAZ microstructure evolution.

Heat Source Model and Numerical Methodology

The double-ellipsoid heat source model, originally proposed by Goldak, Akerson, and Murray, distributes the heat input between two overlapping ellipsoids—one representing the front portion of the arc (where most energy is deposited) and one representing the rear portion. This model is widely used in welding FEA because it provides a realistic representation of the asymmetric heat deposition characteristic of a moving arc.

The numerical simulation in SYSWELD involves solving the three-dimensional transient heat conduction equation with a moving heat source, accounting for:

• Temperature-dependent thermal properties (thermal conductivity, specific heat, density)
• Phase change (latent heat of fusion)
• Convective and radiative heat loss from the workpiece surface
• Convection at the molten pool surface

Engineering Practice Implications

Finite element analysis of welding temperature fields has significant practical value for engineers in pipe and fitting fabrication:

1. Welding procedure optimization: FEA can be used to predict the HAZ width, maximum temperature, and cooling rates for different welding parameters before conducting physical trials. This reduces the number of trial welds required for procedure qualification and accelerates the WPS development process.
2. Residual stress prediction: The temperature field calculated in this study serves as the input for subsequent elastic-plastic thermal-mechanical FEA, which predicts welding residual stresses. Understanding and controlling residual stresses is critical for preventing distortion in thin-wall pipe assemblies and ensuring long-term structural integrity.
3. Microstructure prediction: The cooling rates predicted by the thermal FEA can be correlated with expected microstructures in the weld and HAZ. For stainless steel, cooling rates in the range of 10–50 °C/s typically produce fine-grained austenite with minimal δ-ferrite, while slower cooling rates may promote carbide precipitation and sensitization.
4. Distortion control: For thin stainless steel plates and pipe sections, the asymmetric thermal input can cause significant angular and longitudinal distortion. FEA can predict these distortions and guide the design of clamping fixtures and welding sequences to minimize deformation.

Validation and Model Limitations

The study validates the model by comparing calculated molten pool dimensions with experimental measurements at quasi-steady state, reporting reasonable agreement. However, several limitations should be acknowledged:

• The double-ellipsoid model does not account for the complex fluid dynamics within the molten pool, which can affect the actual heat distribution.
• Temperature-dependent material properties must be accurately characterized; errors in these properties propagate through the entire simulation.
• The model assumes a constant heat input, whereas in practice, the arc power can fluctuate due to torch movement, filler wire interaction, and atmospheric conditions.
• The simulation does not include the effects of filler wire heat input and dilution, which can significantly affect the thermal cycle.

Key Questions and Reflections

• How does the accuracy of the double-ellipsoid model compare with more advanced heat source models (e.g., conical, Gaussian, or coupled electromagnetic-thermal models) for TIG welding?
• Can the FEA model be extended to predict microstructure evolution (e.g., using phase field or cellular automaton methods) coupled with the thermal analysis?
• What is the effect of welding position (flat, vertical, overhead) on the temperature field distribution and predicted HAZ characteristics?
• How can the FEA results be integrated with digital twin frameworks to enable real-time process monitoring and adaptive control in automated welding systems?

The study provides a solid foundation for thermal FEA of TIG welding, but engineers should be aware that the predictive accuracy depends heavily on the quality of input material properties and the appropriateness of the heat source model for the specific welding configuration.

Summary

This study demonstrates the effectiveness of finite element analysis using the SYSWELD platform for predicting the three-dimensional temperature field during TIG welding of stainless steel thin plate. The double-ellipsoid heat source model, validated against experimental molten pool measurements, provides a reliable tool for welding procedure optimization, residual stress prediction, and distortion control. Engineers in pipe and fitting manufacturing should leverage such numerical methods to reduce trial-and-error in WPS development, improve weld quality, and minimize production costs. The thermal FEA results serve as a critical input for subsequent mechanical and microstructural analyses, forming an integral part of a comprehensive welding process simulation framework.