Numerical Simulation of TIG Welding Arc Under Argon and Helium Shielding

Literature Overview

The study by Guo Zhaobo et al., published in Journal of Henan Institute of Technology (2026, Vol. 34, No. 1, pp. 26-29), presents a two-dimensional axisymmetric numerical simulation of TIG welding arcs under argon and helium shielding gases. Funded by Henan Institute of Technology innovation education programs, this research provides fundamental insights into the physical mechanisms governing arc behavior under different shielding gas conditions, with direct implications for process selection in welding applications.

Physical Basis of Shielding Gas Selection

The choice of shielding gas in TIG welding profoundly affects arc characteristics, weld quality, and process efficiency. Argon and helium are the two primary shielding gases used, each with distinct physical properties:

Property	Argon (Ar)	Helium (He)
Atomic mass (g/mol)	39.95	4.00
Thermal conductivity (W/m·K at 6000K)	~1.5	~6.0
Ionization energy (eV)	15.76	24.59
Atomic radius (Å)	1.88	1.40
Cost (relative)	1.0	3.0-5.0

These property differences lead to fundamentally different arc behaviors, which the numerical simulation aims to quantify and explain.

Numerical Model and Governing Equations

The study established a two-dimensional axisymmetric mathematical model by solving the following coupled control equations:

Equation	Physical Phenomenon	Key Variables
Continuity equation	Mass conservation	Velocity field, density
Momentum equation	Momentum transport	Velocity field, pressure, electromagnetic force
Energy equation	Heat transfer	Temperature field, thermal conductivity, radiation
Maxwell's equations	Electromagnetic field	Current density, magnetic field, electric field
Species transport equation	Species diffusion	Electron density, ion density

The model incorporates radiation heat transfer, electromagnetic force effects, and plasma fluid dynamics, providing a comprehensive representation of arc physics.

Arc Characteristic Comparison

The numerical simulation reveals significant differences between argon and helium arcs:

Arc Characteristic	Argon Arc	Helium Arc	Engineering Implication
Arc shape	Bell-shaped (钟罩型)	Spherical (圆球形)	Helium arc concentrates energy more uniformly
Maximum arc temperature	Slightly higher	Slightly lower	Argon arc has slightly higher peak energy
Anode region contraction	Moderate	Significant	Helium arc has better anode focusing
Electromagnetic force	Lower	Higher	Helium arc experiences stronger magnetic compression
Maximum plasma velocity	Lower	Higher	Helium arc has faster plasma flow
Anode-region plasma velocity	Moderate	Lower	Helium arc has reduced anode erosion
Arc pressure	Higher	Lower	Helium arc is gentler on workpiece surface

Physical Mechanisms Explained

The study attributes the observed differences to fundamental atomic properties:

Atomic mass effect: Helium's low atomic mass (4.00 vs. 39.95 g/mol) results in higher plasma velocity and more dynamic arc behavior. The lighter atoms accelerate more readily under electromagnetic forces, creating a more energetic plasma flow.
Thermal conductivity effect: Helium's high thermal conductivity (~4x that of argon at welding temperatures) enables more efficient heat transfer from the arc core to the workpiece surface, resulting in a wider, more uniform heat distribution despite the lower arc pressure.
Ionization energy effect: Helium's high ionization energy (24.59 eV vs. 15.76 eV) means that helium plasma requires more energy to maintain ionization. This results in a more compact arc core with higher energy density but lower overall arc pressure, as the plasma is less expanded.
Arc pressure mechanism: Despite higher electromagnetic forces and plasma velocities, helium arcs produce lower arc pressure because the lower atomic mass reduces the momentum transfer to the workpiece surface. This lower pressure is beneficial for precision welding applications where excessive arc pressure can cause surface disturbance and spatter.

Process Selection Guidelines

Based on the simulation results, the following process selection guidelines emerge:

Application	Recommended Gas	Rationale
Thick plate welding (steel)	Argon	Higher arc pressure provides deeper penetration
Thin sheet welding	Helium	Lower arc pressure reduces surface disturbance and spatter
Aluminum welding	Helium	Higher thermal conductivity improves wetting of aluminum
Copper welding	Helium	High thermal conductivity compensates for copper's high heat conductivity
Titanium welding	Argon	Lower cost and adequate performance for titanium
Precision welding	Helium	Compact arc with low pressure enables fine bead control
High production welding	Argon	Lower cost and reliable performance

Engineering Practice Implications

For pipeline and pressure vessel welding, the following considerations apply:

Steel pipe welding: Argon shielding is preferred for most steel pipe applications due to its adequate penetration capability and lower cost. The bell-shaped arc provides good coverage for circumferential welds.
Stainless steel welding: Helium-argon mixtures (typically 70-80% He + 20-30% Ar) can be used to improve wetting while maintaining adequate penetration. The simulation results support the use of helium for applications requiring precise bead control.
Titanium alloy welding: Argon is the standard shielding gas for titanium welding due to its inertness and adequate performance. The lower cost of argon is significant for large-scale titanium fabrication.
Aluminum welding: Helium or helium-rich mixtures are essential for aluminum welding due to the metal's high thermal conductivity. The simulation confirms that helium's higher thermal conductivity provides the additional heat transfer needed for aluminum welding.

Critical Reflections

This numerical study provides valuable fundamental understanding of arc physics under different shielding gases. However, several limitations should be acknowledged:

The two-dimensional axisymmetric model cannot capture three-dimensional effects such as arc wandering, which is significant in practice
The model assumes ideal gas behavior, which may not be accurate at the extreme temperatures present in the arc core
Experimental validation of the simulation predictions would strengthen confidence in the model's accuracy for process optimization

The finding that helium arcs have lower pressure despite higher electromagnetic forces and plasma velocities is particularly insightful. This counterintuitive result is explained by the lower atomic mass of helium, which reduces momentum transfer to the workpiece. This understanding enables rational selection of shielding gases based on the specific requirements of each welding application.

This numerical study provides a solid theoretical foundation for shielding gas selection in TIG welding. The clear correlation between gas properties and arc characteristics enables engineers to make informed decisions about gas selection based on material type, joint geometry, and quality requirements. For pipeline and pressure vessel fabrication, where weld quality is paramount, this fundamental understanding supports the development of optimized welding procedures that balance penetration, bead quality, and production efficiency.