CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Analysis of Dual TIG Welding Arc
Literature Overview
The numerical analysis of dual TIG welding arcs provides fundamental understanding of the complex electromagnetic, thermal, and fluid dynamics phenomena that govern the process. Unlike single-arc TIG welding, the dual-arc configuration introduces additional complexity through arc-arc interaction, coupled electromagnetic fields, and non-linear thermal coupling between the two arcs and the workpiece. This literature presents computational models that simulate the arc plasma behavior, current density distribution, heat flux patterns, and fluid flow dynamics in dual TIG welding, providing quantitative insights that are difficult to obtain through experimental measurement alone.
Mathematical Modeling Framework
The numerical model typically employs a coupled approach solving Maxwell's equations for the electromagnetic field, the Navier-Stokes equations for fluid flow in the molten pool, and the heat conduction equation for the thermal field. The arc plasma is modeled as a conductive fluid with temperature-dependent properties, and the boundary conditions include the cathode and anode current density distributions, the gas flow from the shielding nozzle, and the radiation heat loss from the plasma surface.
| Model Component | Governing Equation | Key Parameters |
|---|---|---|
| Electromagnetic field | ∇×H = J + ∂D/∂t | Current density J, magnetic permeability μ |
| Plasma fluid flow | ρ(∂v/∂t + v·∇v) = -∇p + μ∇²v + J×B | Plasma viscosity μ, density ρ |
| Heat transfer | ρCp(∂T/∂t + v·∇T) = ∇·(k∇T) + Q_arc | Thermal conductivity k, heat source Q |
| Molten pool flow | Same as plasma flow + surface tension gradient | Marangoni coefficient, surface tension σ |
| Phase change | Enthalpy method | Solidus/liquidus temperatures, latent heat |
The arc heat source model is typically represented as a double-ellipsoidal or Gaussian distribution with two centers corresponding to the two electrode positions. The heat flux distribution at the workpiece surface is determined by the arc plasma properties and the electrode configuration.
Arc-Plasma Electromagnetic Analysis
The electromagnetic simulation reveals that the magnetic field distribution in dual TIG welding is significantly different from single TIG. The interaction between the two arcs creates a complex magnetic field pattern with regions of constructive and destructive interference. The Lorentz force (J×B force) generated by the interaction of the current density and magnetic field creates electromagnetic stirring in the plasma, which affects the arc shape, stability, and heat transfer characteristics.
The current density distribution at the cathode tip is non-uniform, with higher concentrations at the electrode apex. In dual TIG, the current density profiles of the two electrodes are influenced by their mutual electromagnetic interaction. When the electrodes are positioned closer together (spacing < 10 mm), the current density at the inner edges of the electrodes increases due to the repulsive magnetic force between the two arcs. This effect becomes more pronounced at higher currents (above 150 A per electrode).
| Electrode Spacing (mm) | Current Density at Inner Edge (A/mm²) | Current Density at Outer Edge (A/mm²) | Arc Stability Index |
|---|---|---|---|
| 6 | 450–520 | 380–420 | 0.65–0.72 |
| 8 | 420–480 | 390–430 | 0.75–0.82 |
| 10 | 400–450 | 395–440 | 0.82–0.88 |
| 12 | 390–440 | 400–445 | 0.85–0.90 |
| 15 | 385–430 | 405–450 | 0.88–0.92 |
The arc stability index, defined as the ratio of steady-state arc voltage to peak voltage fluctuation, increases with electrode spacing up to a point beyond which the arcs become too independent and the combined heat input becomes less uniform. The optimal spacing of 10–12 mm provides the best balance between arc stability and heat input uniformity.
Thermal Field and Heat Flux Distribution
The thermal simulation of dual TIG welding reveals a distinctive heat flux pattern at the workpiece surface. Unlike the single Gaussian peak of single-arc TIG, the dual-arc configuration produces a bimodal heat flux distribution with two peaks corresponding to the electrode positions and a saddle point between them. The peak heat flux at each electrode position is approximately 70–85% of the equivalent single-arc peak at the same total power, while the minimum heat flux at the saddle point is 40–60% of the peak value.
| Heat Input Parameter | Single TIG (150A) | Dual TIG (2×75A) | Dual TIG (2×100A) |
|---|---|---|---|
| Peak heat flux (W/mm²) | 12000–15000 | 9500–11500 | 11000–13500 |
| Saddle heat flux (W/mm²) | N/A | 5000–7000 | 6000–8500 |
| Maximum temperature (°C) | 2400–2600 | 2100–2300 | 2200–2400 |
| Thermal penetration depth (mm) | 3.5–4.5 | 3.0–4.0 | 3.5–4.5 |
| HAZ width (mm) | 8–12 | 12–18 | 15–22 |
The reduced peak temperature in dual TIG compared to single TIG at equivalent total power is a critical finding for cladding applications. Lower peak temperatures reduce dilution, minimize carbide coarsening, and decrease the risk of phase transformation in the heat-affected zone. This makes dual TIG particularly suitable for overlay welding of hardfacing alloys where maintaining the as-deposited microstructure is essential.
Fluid Dynamics and Molten Pool Behavior
The electromagnetic stirring induced by the dual-arc configuration creates a distinctive flow pattern in the molten pool. The Lorentz force drives a convergent flow toward the center of the pool between the two arcs, while the Marangoni convection (driven by surface tension gradients) creates an outward flow at the pool surface. The competition between these two forces determines the final pool geometry and the mixing characteristics of the weld metal.
At the saddle point between the two arcs, the electromagnetic stirring is weakest, creating a region of reduced mixing. This can lead to compositional segregation in the weld metal, particularly in multi-element overlay alloys where element partitioning occurs during solidification. The numerical simulation shows that increasing the travel speed from 100 to 300 mm/min increases the mixing uniformity by 15–25% due to the enhanced Marangoni convection at higher heat input rates per unit length.
Engineering Significance of Numerical Findings
The numerical analysis provides quantitative predictions that guide process parameter selection for dual TIG cladding operations. The thermal simulation results enable the prediction of dilution rates, which is the single most important factor in determining overlay composition and properties. By adjusting the electrode spacing, current distribution, and travel speed, the dilution rate can be controlled within a range of 10–35%, providing significant flexibility for different cladding requirements.
The electromagnetic analysis also predicts the optimal electrode configuration for minimizing arc instability. The critical spacing below which arc merging occurs is approximately 4–6 mm for standard tungsten electrodes (2.5–3.0 mm diameter) at currents of 75–125 A per electrode. Operating above this critical spacing ensures independent arc behavior while maintaining sufficient interaction for uniform heat distribution.
Study Insights and Outlook
The numerical modeling of dual TIG welding arcs provides an indispensable tool for understanding and optimizing this advanced process. The key insight is that the dual-arc interaction creates fundamentally different thermal and electromagnetic conditions compared to two independent single arcs, and these differences must be accounted for in process design. The coupling between the electromagnetic, thermal, and fluid dynamic fields is non-linear, meaning that simple scaling laws do not apply, and each process configuration requires individual simulation. Future modeling efforts should incorporate more sophisticated arc plasma models that account for radiation transfer, plasma turbulence, and the effects of magnetic field on arc shape, as well as multi-physics coupling with the solidification process to predict microstructure evolution in the deposited overlay.