CLADDING TECHNOLOGY SHANXI CO., LTDANSYS Simulation of TIG Welding with External Magnetic Field
Literature Overview
This study, authored by Jiang Shuyuan of Nanchang Hangkong University and Zheng Xiaofang of East China Jiaotong University, was published in the Journal of Shanghai Jiao Tong University in 2008 under the funding of the Jiangxi Provincial Department of Education Science and Technology Project (2006-169). The work addresses a critical challenge in gas tungsten arc welding: the inherent limitation of arc stability and weld bead geometry under conventional TIG parameters. The authors employ ANSYS finite element analysis to simulate the electromagnetic field distribution when an external magnetic field is superimposed on the TIG arc, providing a computational framework to predict and optimize magnetic arc welding (MAG) configurations.
Core Technical Approach
The fundamental physics of the TIG arc involve the interaction between the electric current flowing through the arc plasma and the ambient magnetic field, which generates a Lorentz force that deflects the arc column. In conventional TIG welding, the arc tends to be symmetric and vertically aligned, limiting the welder's ability to control heat input distribution across the weld pool. By introducing an external magnetic field—typically generated by permanent magnets or electromagnets positioned near the welding zone—the arc can be tilted, oscillated, or rotated to achieve broader heat distribution, deeper penetration, or improved wetting.
The ANSYS simulation approach involves solving the coupled magnetohydrodynamic (MHD) equations governing the arc plasma behavior. Key physical phenomena modeled include:
| Parameter | Description | Typical Range |
|---|---|---|
| Arc current | Welding current intensity | 50–250 A |
| Arc voltage | Arc column potential drop | 12–25 V |
| Magnetic field strength | External field intensity | 5–50 mT |
| Arc radius | Plasma column diameter | 2–5 mm |
| Travel speed | Welding traverse rate | 50–200 mm/min |
| Heat input | Energy deposited per unit length | 0.5–3.0 kJ/mm |
The simulation domain typically includes the arc plasma, the workpiece surface, and the surrounding gas atmosphere. Boundary conditions account for the cathode and anode sheaths, the external magnetic field sources, and the convective-radiative heat transfer at the workpiece surface. The authors likely utilized ANSYS CFX or ANSYS Fluent for the MHD coupling, with the electromagnetic module handling the magnetic field interactions.
Key Findings and Engineering Implications
The study demonstrates that the external magnetic field can effectively control the arc force distribution and heat input profile without modifying the base welding parameters. Several important observations emerge from the simulation results:
- The Lorentz force generated by the interaction of the arc current and the external magnetic field can be calculated as F = B × I × L, where B is the magnetic flux density, I is the arc current, and L is the effective arc length. Even modest field strengths of 10–20 mT can produce significant arc deflection forces.
- Arc oscillation induced by alternating or rotating magnetic fields broadens the weld bead width and reduces the tendency for centerline cracking in thick-section welds.
- The simulation reveals that the magnetic field configuration—whether axial, transverse, or rotational—has a profound effect on the weld pool geometry and solidification pattern.
For engineering practice in cladding and bimetal welding, this research is particularly relevant to the following scenarios:
- Overlay weld quality improvement: In single-pass TIG overlay welding of corrosion-resistant alloys (such as Inconel 625 or Hastelloy C-276), the external magnetic field can be used to control the dilution rate by adjusting the heat input distribution at the cladding/base metal interface.
- Weld pool stabilization: In vertical or overhead TIG welding positions, magnetic arc manipulation can counteract gravity-induced weld pool sagging, improving bead shape and reducing porosity formation.
- Multi-pass welding optimization: By oscillating the arc laterally, the magnetic field can ensure uniform heat distribution across the previous weld pass, promoting better fusion and reducing residual stress concentration.
Reflections and Limitations
While the ANSYS simulation provides valuable insights into the electromagnetic behavior of the TIG arc, several limitations must be acknowledged. The computational model relies on simplifying assumptions regarding the arc plasma properties—such as constant electrical conductivity and uniform temperature distribution within the arc column—which may not fully capture the complex thermodynamic behavior of the real arc. Additionally, the simulation does not account for the dynamic effects of gas flow, spatter, or the influence of the welding torch geometry on the magnetic field distribution.
Nevertheless, the study establishes a rigorous computational methodology that can be extended to more complex welding scenarios. For practitioners involved in TIG overlay welding of bimetallic components, the key takeaway is that magnetic arc manipulation represents a powerful, non-invasive means of controlling weld quality. The approach avoids the need for mechanical arc oscillators or torch manipulators, which can introduce mechanical vibration and complicate the welding setup. Future work should focus on experimental validation of the simulation predictions, particularly regarding the quantitative relationship between magnetic field strength and weld geometry parameters.
In conclusion, this literature provides a solid theoretical foundation for understanding the interaction between external magnetic fields and TIG arc behavior, and offers practical guidance for engineers seeking to improve TIG welding quality in overlay and bimetal applications through magnetic arc control techniques.