Multi-Physics Coupled Numerical Simulation of TIG Welding Arc

Literature Overview

This paper by Guo Zhaobo, Cui Lulu, Tao Kai, and Wang Huimin, published in Journal of Henan Institute of Technology (2020, Vol. 28, No. 1, pp. 60–64), presents a two-dimensional axisymmetric numerical model of a free-burning TIG welding arc. The study provides quantitative analysis of temperature field, pressure field, and flow field distributions within the arc plasma. This computational approach is valuable for understanding the fundamental physics of the TIG arc, which directly influences weld pool behavior, penetration depth, and bead geometry in pipe and fitting welding applications.

Numerical Model and Key Results

The authors established a two-dimensional axisymmetric mathematical model for steady-state TIG welding arc simulation. The model solves coupled equations for electromagnetic field, thermal field, momentum field, and mass conservation within the plasma region. The arc geometry is modeled as axisymmetric about the electrode axis, which is a valid assumption for free-burning arcs without external magnetic field distortion.

Physical Quantity	Distribution Pattern	Key Observation
Temperature field	Maximum at cathode (tungsten) tip	Decreases axially and radially with distance from cathode
Pressure field	Highest at arc center	Decreases with radial distance from arc axis
Flow velocity field	Maximum at arc center	Plasma velocity peaks at central axis
Anode surface pressure	Highest at center	Decreases with radial distance from anode center

The temperature field results show that the highest temperature occurs directly below the tungsten electrode tip, which is consistent with the concentrated heat generation at the cathode spot. The temperature decreases both along the arc axis (away from the cathode) and in the radial direction (away from the arc center), creating a thermal gradient that drives plasma convection.

The pressure field analysis reveals that the arc pressure is highest at the arc center and decreases radially outward. On the anode surface, the pressure distribution follows a similar pattern, with maximum pressure at the center of the arc attachment point. This pressure distribution creates a jet-like effect that compresses the weld pool and influences molten metal flow patterns.

Effect of Welding Parameters on Arc Characteristics

The study systematically investigated the effects of welding current and arc length on arc characteristics, providing valuable insights for process optimization.

Parameter Change	Effect on Arc Temperature	Effect on Plasma Velocity	Effect on Arc Pressure
Decrease welding current	Significant decrease	Significant decrease	Significant decrease
Decrease arc length	Moderate decrease	Significant decrease	Significant decrease

The finding that reducing welding current substantially decreases arc temperature, plasma velocity, and arc pressure is consistent with the well-established relationship between current and arc energy density. In pipe welding applications, this means that lower current settings produce shallower penetration and narrower bead profiles, which is useful for root pass welding where controlled penetration is essential.

The arc length effect on plasma velocity and pressure is particularly important for practical welding. In pipe welding, joint fit-up variations directly affect arc length, and the study confirms that even small changes in arc length can significantly alter plasma dynamics. This has direct implications for welding quality consistency, as inconsistent arc length leads to variable penetration and bead geometry.

Engineering Practice and Quality Control Implications

The numerical simulation results provide a theoretical foundation for understanding how process parameters affect weld quality. For pipe welding procedure development, the arc pressure distribution on the anode surface explains why the weld pool is compressed at the center, creating deeper penetration in the center of the weld bead. This understanding helps in predicting weld geometry from process parameters.

For quality control purposes, the simulation results support the use of arc length monitoring systems in automated pipe welding. Maintaining consistent arc length is critical for uniform penetration and bead geometry, and the quantitative data from this study can inform the design of arc length control algorithms.

The temperature field distribution provides insight into heat input distribution, which is critical for predicting distortion and residual stress in pipe welds. In large-diameter pipe welding, understanding the spatial distribution of heat input helps in developing welding sequences and restraint strategies to minimize distortion.

Study Insights and Recommendations

This numerical simulation study provides valuable fundamental understanding of TIG arc physics that complements experimental welding studies. The coupled multi-physics approach captures the complex interactions between electromagnetic, thermal, and fluid dynamics within the arc, which are difficult to measure experimentally.

For engineers developing welding procedures for pipe and fitting applications, the key insight is that arc length control is as important as current control in determining weld quality. The significant effect of arc length on plasma velocity and pressure means that joint fit-up tolerances must be tight, or arc length compensation mechanisms must be employed in automated welding systems.

The simulation methodology can be extended to more complex scenarios including magnetic field effects, forced convection from shielding gas, and transient conditions during start and stop of welding. These extensions would provide even more detailed predictions of weld pool behavior and penetration characteristics for specific pipe welding configurations. The fundamental physics understanding gained from this study should be integrated with experimental data to develop comprehensive welding process models that can predict weld quality from process parameters.