Effect of Tungsten Electrode Spacing on Dual-Tungsten Electrode TIG Welding Arc Characteristics

Literature Overview

This study published in Ordnance Materials and Engineering (Vol. 48, Issue 1, 2025, pp. 58-63) by Guo Chaobo, Cui Lulu, Tao Kai, Li Xingxia, Ma Tianfeng, and Wu Zhe investigates the influence of tungsten electrode spacing on the arc characteristics of dual-tungsten electrode TIG (D-TIG) welding. The research is supported by the Henan Provincial Natural Science Foundation (232300420365) and the Key Research Project of Higher Education Institutions Basic Research Special Plan (20B430003). The work is conducted at the School of Materials Science and Engineering, Henan Institute of Engineering, and the Henan Provincial Engineering Technology Research Center for Metal Materials Modification Technology.

Core Technical Content

The study establishes a three-dimensional steady-state mathematical model for the dual-tungsten electrode TIG welding arc. The control equation set is solved iteratively through assumptions and boundary conditions to analyze the arc characteristics under different tungsten electrode spacings. The results are compared with single-tungsten electrode TIG welding arcs to explore differences in arc temperature, plasma velocity, and arc pressure.

Dual-Tungsten Electrode TIG Arc Characteristics

The coupled arc morphology of dual-tungsten electrode TIG welding exhibits a non-axisymmetric distribution, which is fundamentally different from the axisymmetric arc of conventional single-electrode TIG welding. This non-axisymmetry is caused by the electromagnetic interaction between the two arcs and the complex plasma flow patterns that develop in the space between the electrodes.

Parameter	Single-Tungsten TIG	Dual-Tungsten TIG	Effect
Arc Temperature	Higher	Significantly reduced	Lower peak temperature
Plasma Velocity	Higher	Significantly reduced	Slower plasma flow
Arc Pressure	Higher	Significantly reduced	Reduced mechanical stress
Pressure Distribution	Axisymmetric	Non-axisymmetric	Complex pressure field
Arc Morphology	Axisymmetric	Coupled, non-axisymmetric	Merged or interacting arcs

Effect of Tungsten Electrode Spacing

The tungsten electrode spacing is a critical parameter that governs the interaction between the two arcs. As the spacing increases, the following trends are observed:

The interaction force between the arcs weakens, and the coupled arc gradually separates into two independent arcs
The electromagnetic force direction gradually shifts from the arc center toward both sides, and the electromagnetic force magnitude gradually decreases
The arc pressure gradually transitions from a single-peak distribution to a double-peak distribution
The maximum arc pressure first decreases and then increases with increasing spacing

The transition from single-peak to double-peak pressure distribution is a critical phenomenon that indicates the point at which the two arcs cease to interact significantly and behave as independent entities. This transition point is important for process design because it determines the minimum spacing required to achieve independent arc behavior.

Numerical Simulation Approach

The three-dimensional steady-state mathematical model includes the following governing equations:

Mass conservation equation (continuity equation)
Momentum conservation equation (Navier-Stokes equations)
Energy conservation equation (enthalpy equation)
Species conservation equations (for plasma composition)
Maxwell's equations for electromagnetic field
Ohm's law for current density

The boundary conditions include electrode surface conditions (temperature, current density, heat flux), workpiece surface conditions (temperature, heat flux), and domain boundaries (inflow, outflow, symmetry). The iterative solution approach ensures convergence of the coupled system of equations, which is essential for accurate prediction of arc characteristics.

Engineering Practice Implications

Dual-tungsten electrode TIG welding offers several advantages over conventional single-electrode TIG welding, particularly for thick-section welding and applications requiring high deposition rates:

Higher deposition rates due to two simultaneous arcs
Lower arc temperature, which reduces dilution and thermal distortion
Reduced arc pressure, which minimizes mechanical stress on the weld pool
Potential for wider weld beads with improved wetting
Enhanced penetration through electromagnetic stirring effects

The reduced arc temperature and pressure in dual-tungsten TIG welding are particularly beneficial for welding thin materials or materials sensitive to thermal input, such as austenitic stainless steels, titanium alloys, and aluminum alloys. The lower thermal input reduces the risk of distortion, residual stress, and microstructural degradation in the heat-affected zone.

Process Parameter Optimization

For practical implementation of dual-tungsten electrode TIG welding, the following parameters require optimization:

Parameter	Influence	Optimization Consideration
Electrode spacing	Arc interaction, pressure distribution	Balance between interaction and independence
Current per electrode	Arc stability, penetration	Total current vs. individual electrode current
Travel speed	Weld bead geometry, heat input	Deposition rate vs. penetration
Shielding gas flow	Arc stability, contamination prevention	Adequate coverage of both arcs
Electrode configuration	Arc morphology, force distribution	Symmetric vs. asymmetric arrangements

The non-axisymmetric arc morphology requires careful consideration of torch orientation and travel direction to ensure uniform weld quality. The electromagnetic force distribution, which shifts from the center toward the sides with increasing spacing, affects the weld pool dynamics and must be accounted for in process design.

Key Questions and Reflections

The numerical simulation approach provides valuable insights into arc characteristics, but experimental validation is essential for practical application. The steady-state assumption may not fully capture the dynamic behavior of the dual-arc system, particularly during transient conditions such as start, stop, or direction changes. The interaction between the two arcs introduces complex phenomena that may not be fully represented in the mathematical model, including arc flutter, electromagnetic interference, and plasma instability.

The transition from single-peak to double-peak pressure distribution is a critical phenomenon that warrants further investigation. The point at which this transition occurs determines the minimum spacing for independent arc behavior, which is essential for process design. The initial decrease and subsequent increase of maximum arc pressure with spacing suggests a complex relationship that may have implications for weld pool stability and penetration characteristics.

Study Insights and Implications

This work provides a comprehensive understanding of the arc characteristics of dual-tungsten electrode TIG welding as a function of electrode spacing. The numerical simulation results offer valuable guidance for process parameter optimization and equipment design. For welding engineers, the key finding is that dual-tungsten TIG welding offers significantly lower arc temperature and pressure compared to single-electrode TIG, which can be exploited for improved weld quality and reduced thermal distortion. The electrode spacing is a critical parameter that governs arc interaction and pressure distribution, and its optimization is essential for achieving desired weld characteristics. The transition from coupled to independent arc behavior provides a clear design criterion for electrode spacing selection. This work contributes to the advancement of advanced TIG welding technologies and provides a foundation for the development of multi-electrode welding processes for specialized applications.