Comparative Study on MIG Welding Arc Simulation with Argon and Helium Shielding

Literature Overview

The paper by Li Ye, Li Zhiyong, Hu Xiaofei, and Zhang Junqiang from North University of China and Shanxi Product Quality Supervision and Inspection Research Institute, published in Hot Working Technology (Vol. 48, No. 9, 2019), presents a two-dimensional axisymmetric numerical simulation of MIG welding arcs using both helium and argon shielding gases. The study was funded by the Shanxi Provincial Key R&D Project (201603D321122) and employs Fluent computational fluid dynamics software to model arc plasma behavior including metal vapor and radiation effects. This work is particularly relevant to engineers who must select shielding gases for high-conductivity materials or when arc stability and penetration characteristics are critical quality parameters.

Core Technical Points

The fundamental premise of this research is that metal vapor inevitably exists within the arc plasma during MIG welding, and its presence significantly influences arc characteristics such as temperature distribution, electrical conductivity, and energy transfer efficiency. The authors established a two-dimensional axisymmetric arc model that accounts for both metal vapor transport and arc radiation energy loss—two factors that are frequently oversimplified in industrial practice.

The key finding is that when radiation is included in the model, the helium arc temperature field contracts noticeably, resulting in a lower peak arc temperature compared to argon. However, the high-temperature region of the helium arc is larger than that of the argon arc. This apparent contradiction is explained by the fundamental differences in thermophysical properties between helium and argon. Helium possesses a thermal conductivity approximately 1.4 times that of argon at arc temperatures, yet its lower atomic mass (4 vs. 40) results in different momentum transfer and ionization characteristics within the plasma column.

Thermophysical Property Comparison

Interpretation of Technical Findings

The contraction of the helium arc temperature field under radiation consideration is a critical insight. In practice, this means that the effective heat input zone of helium-shielded MIG welding is more concentrated axially but broader radially. For pipe welding applications, particularly for thin-walled stainless steel or high-alloy pipe fittings, this characteristic can be advantageous—it promotes lateral heat distribution while maintaining sufficient penetration depth.

From a welding metallurgy perspective, the lower peak temperature of the helium arc (compared to argon under radiation-inclusive conditions) suggests that helium shielding may produce slightly less thermal dilution in the weld metal. This has implications for maintaining alloying element integrity in corrosion-resistant alloy (CRA) pipe welding, where excessive dilution can compromise the corrosion resistance of the weld metal.

The presence of metal vapor in the simulation is particularly important. In industrial MIG welding of carbon steel and low-alloy steel pipes, metal vapor from both the electrode wire and the base metal significantly alters the arc's electrical conductivity and optical properties. The simulation results suggest that neglecting metal vapor in process optimization can lead to inaccurate predictions of heat input and weld geometry.

Engineering Practice Integration

For pipeline and pipe fitting fabrication, the shielding gas selection directly impacts weld quality, productivity, and cost. The following engineering considerations should be drawn from this study:

1. Helium-argon mixtures: In practice, pure helium is rarely used due to cost. Mixtures such as 75% Ar + 25% He or 80% Ar + 20% He are commonly employed. The simulation insights suggest that even moderate helium additions will begin to broaden the high-temperature zone and slightly reduce peak temperature, which can improve weld bead appearance and reduce spatter.
2. Stainless steel pipe welding: For austenitic stainless steel pipes (e.g., 304, 316L per ASTM A312), helium-containing shielding gases promote better wetting and smoother bead profiles. The broader high-temperature zone helps achieve the required dilution control for filler metal selection.
3. Aluminum alloy pipe welding: For 6082-T6 aluminum alloy pipes, helium-rich mixtures (e.g., 70% He + 30% Ar) are standard practice due to aluminum's high thermal conductivity. The simulation confirms the physical basis for this practice—the higher thermal conductivity of helium compensates for aluminum's rapid heat dissipation.
4. Pipe fitting fabrication: For forged butt-weld fittings (per ASTM A403/A234), where the cross-section varies significantly, the broader heat input zone of helium-containing gases can help maintain consistent penetration across varying wall thicknesses within the fitting.

Key Questions and Reflections

Several questions arise from this study that merit further investigation in engineering practice:

• The two-dimensional axisymmetric model simplifies the inherently three-dimensional nature of real welding arcs, particularly in pipe welding where the arc shape changes with travel angle and pipe orientation.
• The radiation model employed may not fully capture the complex spectral radiation characteristics of metal vapor-rich plasmas at industrial current densities.
• The study does not address the effect of gas flow rate and nozzle geometry on the arc characteristics, which are critical parameters in pipe welding where access is often restricted.

For our engineering teams, I would recommend that shielding gas selection decisions incorporate not only the thermophysical property differences highlighted in this study but also practical considerations such as gas cost, supply availability, and the specific joint geometry of the pipe or fitting being welded. The simulation results provide a solid theoretical foundation, but validation through actual weld coupon testing on representative pipe geometries remains essential.

Study Insights and Implications

This literature provides valuable theoretical support for shielding gas selection in MIG welding of pipes and fittings. The key takeaway is that the interaction between metal vapor, radiation, and shielding gas thermophysical properties creates a complex but predictable system. Engineers who understand these interactions can make more informed decisions about gas mixtures for specific pipe welding applications, ultimately improving weld quality and reducing rework rates. The simulation methodology itself—incorporating metal vapor and radiation in axisymmetric arc models—represents a state-of-the-art approach that should be considered for future process development programs involving new pipe materials or welding configurations.