Zhuojin Pipe Fitting Co., LtdNumerical Analysis of Dual-TIG Welding Arc Physics
Literature Overview
This paper, published in "Hot Working Technology" (2020, Vol. 49, Issue 7, pp. 133-138) by Wang Xinxin, Luo Yi, Li Chuntian, and Chi Luxin from Chongqing University of Technology, presents a comprehensive numerical model of the dual-TIG welding arc. The research was funded by the National Natural Science Foundation of China (51705054), the Chongqing Education Commission (KJ1600903), and the Chongqing University of Technology Spark Plan (2015XH20). This work provides the theoretical foundation for understanding the arc behavior that underpins the dual-TIG active arc process described in the companion study.
Mathematical Model Formulation
The authors established a mathematical model of the dual-TIG welding arc that includes both tungsten electrodes. The model solves for three coupled fields: temperature field, flow field, and electromagnetic field. The governing equations incorporate the effects of Lorentz force, plasma jet shear force, and arc pressure on the molten pool surface. The numerical solution employs finite element or finite volume methods to resolve the strongly nonlinear coupling between these fields.
The model accounts for the following physical phenomena:
- Electric current density distribution between the two electrodes and the workpiece
- Magnetic field generation and Lorentz force computation
- Plasma gas dynamics including buoyancy and electromagnetic body forces
- Thermal radiation and convection heat transfer
- Arc pressure and plasma jet force acting on the molten pool surface
Key Numerical Findings
The following table compares arc behavior under symmetric and asymmetric current distributions:
| Condition | Temperature Field Distribution | Flow Field Distribution | Arc Pressure Distribution |
|---|---|---|---|
| Equal current distribution (total current constant) | Symmetric about the centerline | Symmetric about the centerline | Symmetric about the centerline |
| Unequal current distribution | High-temperature zone closer to the high-current electrode | Arc as a whole deflects toward the low-current electrode side | Peak arc pressure and plasma jet force shift toward the low-current electrode side |
A particularly important finding is that when the current distribution is equal, both the arc pressure and the plasma jet pulling force on the base metal surface are significantly lower than those of a single-TIG arc under the same total current conditions. This reduction in surface forces explains why dual-TIG welding can achieve different penetration profiles compared to single-TIG welding. When the current distribution is unequal, the peak forces shift toward the low-current electrode side, creating an asymmetric force environment that influences molten pool flow patterns and weld geometry.
Engineering Implications
The numerical results have direct implications for dual-TIG process design. The finding that equal current distribution reduces arc pressure and plasma jet force relative to single-TIG welding suggests that dual-TIG welding may produce less surface distortion and lower risk of undercut. The asymmetric current distribution, where the high-current electrode dominates heat input while the low-current electrode serves an auxiliary role, creates a predictable force gradient that can be exploited for controlling weld pool shape.
For pipe welding applications, the arc deflection toward the low-current electrode side is particularly relevant. In pipe welding, where the weld pool must remain stable on a curved surface, this deflection can be used to control the molten pool position relative to the pipe seam. By adjusting the current distribution, operators can effectively "steer" the arc pressure toward the desired location on the pipe circumference.
Comparison with Single-TIG Arc Characteristics
The reduction in arc pressure and plasma jet force under equal current distribution is quantitatively significant. In single-TIG welding, the arc pressure on the molten pool surface can reach 100-300 Pa depending on current and arc length. The dual-TIG configuration with equal current distribution produces substantially lower peak pressures, which translates to reduced risk of crater formation and improved weld bead profile control. This is especially beneficial for thin-walled pipe applications where excessive arc pressure can cause burn-through.
Study Insights and Reflections
The numerical modeling approach adopted in this study provides a rigorous framework for understanding dual-TIG arc physics. The agreement between simulation results and previously reported experimental data validates the model's predictive capability. One notable aspect is the inclusion of the tungsten electrodes in the model domain, which allows for accurate computation of the arc root behavior and current density distribution at the electrode tips.
From a practical standpoint, the findings suggest that dual-TIG welding offers a fundamentally different arc force environment compared to single-TIG welding. The reduced arc pressure under symmetric current distribution is a key differentiator that enables the process to achieve deep penetration without the surface defects typically associated with high arc pressure. This insight has implications beyond dual-TIG welding itself, as it suggests that multi-arc configurations can be designed to produce favorable force environments for specific welding challenges.
The model also highlights the importance of current distribution as a process control variable. In engineering practice, this means that dual-TIG welding requires careful calibration of both torch currents to achieve the desired arc force profile. Process parameter windows must be established through both numerical simulation and experimental validation to ensure consistent weld quality in production environments.