Numerical Simulation of Arc-Pool Interaction Coupling in Stationary TIG Welding

Literature Overview

This study by Lu Fenggui, Tang Xinhua, Li Shaoqing, Yao Shun, and Lou Songnian from Shanghai Jiao Tong University, published in the Journal of Welding in 2005, addresses a fundamental challenge in welding metallurgy and process design: the coupled interaction between the electric arc and the molten pool in stationary (non-traveling) TIG welding. Stationary TIG welding is commonly employed in localized repair, cladding applications, and overlay welding on pressure vessel components where travel speed is zero or near-zero. Understanding the arc-pool coupling is critical for predicting weld geometry, dilution, and microstructural evolution in such scenarios.

Core Technical Points

The study focuses on the coupled numerical model that simultaneously solves for the electric field, magnetic field, fluid flow in the molten pool, and heat transfer. The key coupling mechanisms include:

• Electromagnetic force (Lorentz force) acting on the molten pool due to current density and magnetic field interaction
• Convective heat transfer within the molten pool driven by electromagnetic stirring and natural convection
• Arc pressure distribution on the pool surface, which deforms the free surface and alters heat flux input
• Surface tension gradient (Marangoni effect) driven by temperature-dependent surface tension and surfactant concentration

The numerical approach typically employs a finite element or finite volume method to solve the coupled Navier-Stokes equations with electromagnetic source terms. The arc is modeled using either a homogenized model or a magnetohydrodynamic (MHD) model, depending on the level of detail required.

Process Parameters and Simulation Results

The simulation results demonstrate that the electromagnetic stirring significantly enhances pool fluidity and promotes a wider, shallower weld profile compared to purely conductive heat transfer models. The arc pressure creates a depression on the pool surface, which in turn modifies the heat flux distribution. The coupled model predicts pool dimensions and solidification patterns that agree reasonably well with experimental measurements, validating the necessity of including arc-pool interaction in process simulation.

Relevance to Cladding and Bimetal Applications

In the context of weld overlay and cladding, the arc-pool interaction governs the dilution rate between the overlay material and the base metal. A deeper pool implies higher dilution, which may compromise the corrosion resistance of the overlay layer. For nickel-based alloy cladding on carbon steel pressure vessels, controlling dilution below 5–10% is often required to maintain the alloy's resistance to sulfide stress corrosion (SSC). The numerical insights from this study provide a theoretical basis for optimizing current, electrode configuration, and filler wire feed to minimize dilution while maintaining adequate bond strength.

Study Insights and Reflections

The work represents an early but significant contribution to the coupled simulation of welding processes. It highlights the importance of considering the arc as an active source of heat, force, and mass transport rather than a simple heat flux boundary condition. For engineers involved in cladding design, this study underscores the value of computational modeling in predicting process outcomes before physical trials. However, the model's accuracy depends heavily on the constitutive relationships used for the arc and the pool, which remain areas of ongoing research. The findings also suggest that in stationary TIG overlay, the steady-state pool geometry may differ substantially from traveling-weld predictions, which has implications for multi-pass cladding build-up strategies.

This research provides a foundational understanding that continues to inform modern welding process simulation, particularly in the design of overlay processes for pressure vessel components where dilution control and metallurgical compatibility are paramount.