CLADDING TECHNOLOGY SHANXI CO., LTDSimulation of TIG Welding Arc Under Longitudinal Alternating Magnetic Field and Pulsed Current
Literature Overview
This study, published in 2021 in the journal Hot Working Technology, was conducted by researchers from Shenyang Aerospace University and Shenyang University of Technology, supported by the National Natural Science Foundation of China (Grant No. 51475084). The work focuses on the computational simulation of the gas tungsten arc welding (GTAW/TIG) arc behavior when subjected to a longitudinal alternating magnetic field combined with pulsed current. This is a fundamental study in arc physics that has significant implications for understanding how external magnetic fields can be leveraged to improve welding quality, particularly in cladding and overlay applications where arc stability and penetration control are critical.
Core Technical Content
The research investigates the interaction between the welding arc plasma and an externally applied longitudinal alternating magnetic field. In conventional TIG welding, the arc column is influenced primarily by the electromagnetic forces generated by the current itself and the geometry of the workpiece. By introducing a longitudinal alternating magnetic field, the researchers explored how the Lorentz force (J × B) modifies the arc shape, heat distribution, and mass transport within the weld pool. The pulsed current component adds another layer of complexity, as the arc characteristics vary cyclically between peak and background current levels.
Key Simulation Parameters
| Parameter | Typical Range | Description |
|---|---|---|
| Welding current (peak) | 80–200 A | Peak value of pulsed current |
| Background current | 20–50 A | Minimum current during pulse cycle |
| Pulse frequency | 5–50 Hz | Frequency of current modulation |
| Magnetic field strength | 0.1–1.0 T | Longitudinal alternating field |
| Magnetic field frequency | 50–500 Hz | Alternating magnetic field frequency |
| Shielding gas | Ar or Ar/He mix | Arc shielding environment |
| Electrode material | Pure tungsten or thoriated | Arc cathode |
Physical Mechanisms Analyzed
The simulation addresses several coupled physical phenomena:
- Electromagnetic force on plasma: The external magnetic field interacts with the arc current to produce additional Lorentz forces that can compress or elongate the arc column, altering the heat flux density at the workpiece surface.
- MHD (Magnetohydrodynamic) coupling: The arc plasma behaves as an electrically conducting fluid, and the interaction between fluid motion, electromagnetic fields, and thermal transport is governed by coupled Navier-Stokes, energy, and Maxwell equations.
- Arc constriction and penetration: A longitudinal magnetic field aligned with the current direction can produce a magneto-hydrodynamic effect that narrows the arc root, increasing energy density and potentially enhancing penetration depth.
- Pulse-current interaction: The alternating magnetic field superimposed on pulsed current creates time-varying force fields that may suppress arc wandering and improve bead uniformity.
Engineering Relevance to Cladding and Overlay Applications
For cladding and weld overlay operations, particularly in bimetal pressure vessel fabrication, arc stability and penetration control are paramount. The findings from this study have several direct engineering implications:
- Improved dilution control: In cladding applications where low dilution is required (e.g., overlaying Inconel 625 on carbon steel for pressure vessel internals), understanding how magnetic fields affect arc shape can help minimize base metal dilution.
- Enhanced bonding strength: A more concentrated and stable arc can improve the metallurgical bond between the overlay layer and the substrate, which is critical for meeting bond strength requirements per NB/T 47014 and ASME IX.
- Reduction of arc wander: Pulsed current combined with magnetic field stabilization can reduce arc wander, a common defect source in multi-pass overlay welding.
- Penetration tailoring: For applications requiring specific penetration profiles (such as in hydrogenation reactor cladding where deep fusion is needed), the magnetic field parameters provide an additional process variable for optimization.
Study Insights and Reflections
This research represents a significant advancement in understanding the fundamental physics of TIG arc behavior under non-standard conditions. While the study is computational in nature, its practical value lies in providing a theoretical basis for process optimization in challenging overlay scenarios. In my experience with bimetal pressure vessel fabrication, achieving consistent overlay quality often requires fine-tuning of multiple parameters simultaneously. The introduction of external magnetic fields as a process variable offers a potentially powerful tool for achieving this fine-tuning, particularly in automated welding systems where magnetic field application can be precisely controlled.
However, practical implementation faces challenges including the cost and complexity of magnetic field generation equipment, the need for careful calibration to avoid interference with other process parameters, and the requirement for qualified welding procedures that incorporate magnetic field parameters. Future work should focus on experimental validation of the simulation predictions and the development of practical magnetic field application systems suitable for industrial cladding operations.
The study also highlights the importance of multi-physics simulation in welding research. As computational resources become more accessible, such detailed modeling can bridge the gap between fundamental understanding and practical process development, ultimately contributing to improved quality and reduced costs in bimetal manufacturing.