Numerical Simulation of TIG Arc Characteristics under Argon and Helium Shielding

Literature Overview

This paper, published in the Journal of Henan Institute of Technology (2026, Vol. 34, No. 1), presents a two-dimensional axisymmetric numerical simulation of TIG welding arcs under argon and helium shielding gas conditions. The study solves the governing equations for the temperature field, plasma flow field, arc morphology, and arc pressure to compare the fundamental differences between argon and helium arc characteristics. This work contributes to the ongoing effort to optimize shielding gas selection for different welding applications, particularly where high energy density and fine welding are required.

Mathematical Model and Simulation Approach

The researchers established a two-dimensional axisymmetric mathematical model for the TIG arc. The governing equations include the continuity equation, momentum equation, energy equation, and species transport equation, along with appropriate boundary conditions representing the electrode, workpiece, and shielding gas environment. The model accounts for the physical properties of both argon and helium, including atomic mass, thermal conductivity, and ionization energy.

Key Simulation Results

The simulation results reveal several important differences between argon and helium arcs. The argon arc exhibits a bell-shaped morphology, while the helium arc is more spherical. This difference in shape is attributed to the distinct electromagnetic force distributions and plasma flow characteristics in each case.

The maximum arc temperature is slightly lower in helium compared to argon, despite helium's higher thermal conductivity. This counterintuitive result can be explained by the higher ionization energy of helium, which requires more energy to maintain ionization and thus results in a different temperature distribution. The electromagnetic force in helium arc is larger, and the maximum plasma velocity is higher, but the plasma velocity near the anode region is lower.

The most significant finding for practical welding applications is the arc pressure comparison. Helium's low atomic mass, high thermal conductivity, and high ionization energy result in lower arc pressure compared to argon. This lower arc pressure is advantageous for high energy density precision welding, as it reduces mechanical disturbance of the weld pool and minimizes spatter.

Engineering Applications and Process Selection

The numerical simulation results provide valuable guidance for shielding gas selection in different welding scenarios. For applications requiring high energy density and fine welding, such as thin-gauge sheet metal welding or micro-welding, helium or helium-argon mixtures may be preferred due to the lower arc pressure and higher plasma velocity. For general-purpose welding where arc stability and penetration are important, argon remains the standard choice due to its lower ionization energy and more stable arc characteristics.

In practice, pure helium is rarely used due to cost considerations. Helium-argon mixtures, typically in the range of 50/50 to 75/25 (helium/argon), are commonly employed to balance arc stability, penetration, and cost. The simulation results from this paper provide a theoretical foundation for understanding how different gas compositions affect arc behavior, which can guide the optimization of mixed gas welding processes.

Study Insights and Limitations

The numerical simulation approach offers several advantages over experimental investigation: it provides detailed spatial distributions of temperature, velocity, and pressure that are difficult to measure experimentally, and it allows systematic variation of parameters without the constraints of physical experiments. However, the two-dimensional axisymmetric assumption simplifies the actual three-dimensional arc structure, and certain phenomena such as arc oscillation and turbulence are not captured. Future work should consider three-dimensional simulations with turbulence modeling to provide a more complete picture of arc behavior.

For welding engineers, the key takeaway is that shielding gas selection is not merely a matter of cost or availability but has profound effects on arc characteristics and weld quality. The lower arc pressure of helium makes it particularly suitable for applications where weld pool stability is critical, such as welding thin materials or achieving precise weld bead geometry. Understanding the fundamental differences between argon and helium arcs enables more informed process optimization and troubleshooting in production welding operations.