Simulation of TIG Welding Arc Under Longitudinal Alternating Magnetic Field and Pulsed Current

Literature Overview

This 2021 study by Zhao Lei, Mo Chunli, Liu Chunyu, and Chang Yunlong from Shenyang Aerospace University and Shenyang University of Technology investigates the behavior of the TIG welding arc when subjected to a longitudinal alternating magnetic field combined with pulsed current. The research was supported by the National Natural Science Foundation of China (Grant No. 51475084) and published in the journal "Hot Working Technology." The work addresses a fundamental question in advanced welding process physics: how external electromagnetic fields influence arc stability, plasma morphology, and energy transfer characteristics in gas tungsten arc welding.

Core Technical Content

The study employs computational fluid dynamics (CFD) coupled with electromagnetic field modeling to simulate the TIG arc under two distinct operating conditions: conventional DC pulsing and a hybrid mode incorporating a longitudinal alternating magnetic field. The key physics involved includes Lorentz force generation within the arc plasma, induced current density distributions, and the resulting convective flow patterns in the arc column.

The researchers modeled the arc as a magnetohydrodynamic (MHD) system where the governing equations include Navier-Stokes equations for fluid motion, Maxwell's equations for electromagnetic fields, energy conservation, and species transport equations for argon plasma. The longitudinal alternating magnetic field introduces an additional Lorentz force component that acts perpendicular to both the current density vector and the applied magnetic field direction, thereby inducing azimuthal rotation of the arc plasma.

Key Simulation Parameters

Interpretation of Technical Points

The most significant finding is that the superposition of longitudinal alternating magnetic field with pulsed current produces a synergistic effect on arc energy concentration. The alternating magnetic field causes the arc root to oscillate periodically along the electrode axis, which effectively increases the local heat input intensity at the weld pool surface during peak current phases. This results in deeper penetration without proportionally increasing total energy input, which is highly relevant for cladding applications where controlled dilution and penetration are critical.

From a cladding perspective, this technique could be particularly valuable for overlay welding of nickel-based alloys onto carbon steel substrates. The enhanced arc stability and deeper penetration may allow for better metallurgical bonding between the cladding layer and base metal while maintaining the integrity of the overlay composition. The pulsed mode component provides thermal cycling that can refine the microstructure of the weld overlay, reducing hot cracking susceptibility in high-nickel alloys.

Engineering Implications for Overlay Welding

Process Analysis and Engineering Practice Integration

The simulated results suggest that the optimal combination for cladding applications would involve a peak current of 150–180 A with a background current of 20–30 A, a pulse frequency of 20–40 Hz, and an applied magnetic field of 0.3–0.5 T. These parameters should produce a stable, focused arc with sufficient penetration to ensure metallurgical bonding while the pulse cycling provides thermal management to minimize distortion.

For bimetal pressure vessel fabrication, where cladding thickness typically ranges from 3 to 15 mm, this technique could reduce the number of overlay passes required by 15–20%, directly improving productivity. The improved arc stability also reduces the risk of arc wandering, which is a common defect in multi-pass overlay welding of large-diameter vessels.

However, practical implementation requires careful consideration of the magnetic field source. Permanent magnet arrays or electromagnets must be positioned around the workpiece without interfering with the welding setup. The alternating nature of the field also requires a power supply system capable of generating controlled magnetic fields, adding complexity to the equipment configuration.

Key Questions and Reflections

Several important questions emerge from this research that warrant further investigation. First, how does the longitudinal alternating magnetic field interact with the magnetic fields generated by the welding current itself, and are there resonant conditions that could destabilize the arc? Second, what is the effect of magnetic field intensity on the arc root spread and whether this can be used to control weld width independently of current magnitude? Third, for cladding applications specifically, does the enhanced penetration lead to excessive dilution when overlaying dissimilar materials?

The study provides valuable theoretical groundwork, but practical validation on actual cladding operations is needed. Engineers working in the field should note that while the simulation results are promising, real-world conditions involving base metal geometry, joint configuration, and material properties will introduce additional variables not captured in the idealized model.

Study Insights and Implications

This research represents an important advancement in understanding how electromagnetic field manipulation can enhance TIG welding performance. For the cladding and bimetal fabrication industry, the potential to achieve deeper, more stable penetration with controlled energy input is highly attractive. The technology could enable more efficient production of clad plates and overlay pressure vessels, particularly for applications requiring thick overlay layers of expensive nickel-based or titanium alloys.

The fundamental insight is that the superposition of externally applied electromagnetic fields with welding current creates a controllable energy focusing mechanism that can be tuned to specific process requirements. This opens a new dimension of process control beyond traditional parameter adjustment of current, voltage, and travel speed. Future work should focus on experimental validation, equipment development, and qualification testing for specific cladding applications in pressure vessel manufacturing.