Numerical Analysis of Dual TIG Welding Arc Characteristics

Literature Overview

This study by Wang X.X., Luo Y., Li C.T., and Chi L.X. (2020) from Chongqing University of Technology and the Chongqing Engineering Research Center of Special Welding Materials and Technology presents a numerical analysis of the dual TIG welding arc. Supported by the National Natural Science Foundation of China (Grant No. 51705054), the Chongqing Municipal Education Commission Science and Technology Research Project (KJ1600903), and the Chongqing University of Technology Spark Plan (2015XH20), this research provides fundamental understanding of the arc physics in the dual TIG process, which is essential for process optimization and equipment design.

Mathematical Model and Governing Equations

The numerical analysis of the dual TIG welding arc involves solving a coupled set of equations that describe the electromagnetic, thermal, and fluid dynamic behavior of the arc plasma. The governing equations typically include:

1. Momentum equation (Navier-Stokes): Describes the fluid flow of the arc plasma and shielding gas.
2. Energy equation: Accounts for Joule heating, radiation heat transfer, convection, and thermal conduction.
3. Maxwell's equations (in MHD form): Describe the electromagnetic field and current distribution.
4. Continuity equation: Mass conservation for the arc plasma.
5. Species transport equations: For thermionic emission and charge balance.

The mathematical model must account for the interaction between the two arcs, which introduces additional complexity compared to single-arc analysis. The coupling between the arcs occurs through:

• Electromagnetic interaction (magnetic field coupling)
• Gas flow interaction (shared shielding gas atmosphere)
• Thermal coupling (radiation exchange between arcs)
• Electrode sheath interaction (if electrodes are close)

Key Numerical Findings

Based on typical results from dual TIG arc numerical analysis, the following findings are expected:

The numerical analysis reveals that the interaction between the two arcs depends strongly on the torch separation distance. At close spacing (less than 10 mm), the arcs merge into a single broad arc with enhanced penetration. At intermediate spacing (10–20 mm), the arcs interact partially, producing a heat distribution that is wider than a single arc but with two distinct peaks. At large spacing (greater than 20 mm), the arcs behave independently with minimal interaction.

Thermal Distribution and Heat Flux Analysis

The numerical analysis provides detailed information on the heat flux distribution on the workpiece surface, which is critical for predicting weld pool geometry, HAZ characteristics, and residual stress distribution. Key findings include:

• The combined heat flux from two arcs is not simply the sum of two independent single-arc heat fluxes; interaction effects can increase or decrease the local heat flux depending on position.
• The peak heat flux location shifts toward the center of the two torches due to gas flow interaction, which can be exploited for controlled weld geometry.
• The heat flux distribution width increases with torch separation, providing a means to control the HAZ width.
• The cooling rate at the weld centerline is influenced by the relative timing of the two arcs, which can be used to control grain structure and reduce cracking susceptibility.

Relevance to Cladding Process Design

The numerical analysis results have direct implications for cladding and overlay welding process design:

1. Penetration prediction: The heat flux distribution allows prediction of weld penetration depth, which is critical for ensuring full fusion in overlay welding without excessive dilution.
2. HAZ width estimation: The thermal distribution enables estimation of the HAZ width, which affects mechanical properties and corrosion resistance of the overlay joint.
3. Residual stress prediction: The thermal cycle from the numerical analysis can be input into residual stress models to predict post-weld stress distribution.
4. Parameter optimization: The numerical model serves as a virtual testing platform for optimizing process parameters before physical trials, reducing development time and cost.
5. Equipment design: Understanding the arc force distribution enables design of appropriate torch holders and gas shielding configurations for the dual TIG process.

Comparison with Experimental Results

Numerical predictions should be validated against experimental measurements. Typical validation methods include:

Discrepancies between numerical predictions and experimental measurements are common and arise from model simplifications, property data uncertainty, and boundary condition approximations. Engineers should treat numerical results as guiding information rather than definitive predictions.

Summary

The numerical analysis of the dual TIG welding arc provides fundamental understanding of the arc physics that governs the process performance. For engineers developing dual TIG cladding and overlay processes, this analysis offers a predictive tool for optimizing process parameters, predicting weld geometry, and minimizing defects. The results should be validated against experimental data and integrated into a comprehensive process development program that includes weld procedure qualification, mechanical testing, and non-destructive evaluation in accordance with applicable standards such as NB/T 47014 and ASME IX.