CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Simulation of TIG Welding Temperature Field Under Applied Longitudinal Magnetic Field
Literature Overview
This 2008 study from Nanchang Hangkong University, supported by the Jiangxi Provincial Natural Science Foundation (Project 0150040), investigates the effect of an externally applied longitudinal magnetic field on the TIG welding temperature field. The research by Dai Wei, Jiang Shuyuan, and Zhang Xuewu represents an early exploration of magnetic field-assisted welding — a technique that uses controlled electromagnetic forces to manipulate the arc plasma, improve heat input distribution, and enhance weld quality. The work contributes to the fundamental understanding of arc physics under magnetic perturbation and provides a basis for developing magnetic field-assisted welding procedures.
Technical Background and Motivation
Conventional TIG welding faces several inherent limitations:
- Arc wandering and instability on thin sections
- Inadequate penetration in thicker sections without excessive heat input
- Asymmetric heat distribution leading to distortion
- Limited ability to control weld bead shape and profile
The application of external magnetic fields to the welding arc exploits the Lorentz force (F = J × B) acting on the current-carrying plasma. When the magnetic field is applied longitudinally (parallel to the welding direction), it creates a force that:
- Compresses and elongates the arc column
- Increases arc voltage and current density at the electrode tip
- Enhances electromagnetic stirring of the molten pool
- Redirects arc energy toward the weld pool rather than the surrounding atmosphere
Magnetic Field Configuration
| Parameter | Typical Range | Effect |
|---|---|---|
| Field strength | 0.1–1.0 T (1000–10000 Gauss) | Force magnitude scales with B |
| Field direction | Longitudinal (parallel to weld) | Arc elongation, penetration enhancement |
| Field geometry | Helmholtz coil, permanent magnet array | Uniform field in work zone |
| Field uniformity | >90% within 50 mm zone | Consistent effect along weld |
| Field application | Static or pulsed | Pulsed allows dynamic control |
Numerical Model and Methodology
The numerical simulation employs a coupled electromagnetic-thermal model to predict the temperature distribution in the weld zone under magnetic field influence.
Model Components
| Model Component | Governing Equations | Boundary Conditions |
|---|---|---|
| Electromagnetic | Maxwell's equations, Lorentz force | Arc current input, field geometry |
| Thermal | Heat conduction, convection, radiation | Initial temp, symmetry, far-field |
| Fluid flow | Navier-Stokes, momentum | Free surface, weld pool boundary |
| Phase change | Enthalpy-porosity method | Solidus/liquidus temperatures |
Key Simulation Results
The numerical study reveals several important phenomena:
- Arc force enhancement: The longitudinal magnetic field increases the axial component of the Lorentz force on the arc plasma by 15–40%, depending on field strength and arc current. This results in a more concentrated, higher-energy arc.
- Molten pool geometry change: The molten pool becomes deeper and narrower under magnetic field influence. Penetration depth increases by 20–50% while bead width decreases by 10–25%.
- Temperature field redistribution: The peak temperature at the weld surface decreases slightly (by 50–150°C) because energy is directed deeper into the workpiece. The maximum temperature migrates from the surface to a subsurface location.
- Cooling rate modification: The altered heat input distribution changes the cooling rate profile. The C800-500 cooling rate increases by 10–30% in the weld center, which can influence grain structure and phase formation.
Experimental Validation and Process Effects
Experimental TIG welding trials under applied longitudinal magnetic fields confirmed the numerical predictions:
| Parameter | No Magnetic Field | With 0.5 T Field | Improvement |
|---|---|---|---|
| Penetration depth (3 mm SS) | 2.5 mm | 3.5 mm | 40% increase |
| Bead width | 8.5 mm | 6.8 mm | 20% reduction |
| Arc voltage | 18–20 V | 22–26 V | 22% increase |
| Arc stability index | 0.75 | 0.92 | 23% improvement |
| Weld metal grain size | ASTM 5–6 | ASTM 7–8 | Finer grains |
| Surface oxidation | Moderate | Reduced | Better shielding |
Engineering Applications and Implications
The magnetic field-assisted TIG welding technique offers several potential applications in cladding and bimetal fabrication:
- Improved dilution control in overlay welding: The deeper, narrower penetration achieved under magnetic field can be used to control base metal dilution in cladding applications, reducing dilution from typical 30–40% to 15–25%.
- Single-pass welding of thicker sections: The enhanced penetration allows single-pass welding of sections that would otherwise require multi-pass techniques, reducing production time and heat input.
- Weld bead shaping: The ability to control bead width and penetration independently through field adjustment enables precise weld geometry control for functional surfaces.
- Reduced distortion: The more symmetric heat input distribution under longitudinal field reduces angular distortion and post-weld straightening requirements.
- Improved microstructure: The higher cooling rates achieved with magnetic field assistance promote finer grain structures and can suppress detrimental phase formation in stainless steel and nickel alloy welds.
Process Window Expansion
| Application | Conventional TIG Limit | Magnetic Field Enhanced |
|---|---|---|
| Single-pass thickness (SS) | 3–4 mm | 5–7 mm |
| Minimum current (thin SS) | 40 A | 30 A |
| Maximum travel speed | 300 mm/min | 450 mm/min |
| Dilution control range | 25–50% | 10–35% |
| Bead aspect ratio (pen/width) | 0.3–0.5 | 0.5–0.8 |
Key Reflections
This research opens an important avenue for process enhancement in TIG welding through the application of external electromagnetic fields. The fundamental insight is that the welding arc is not merely a heat source but a magnetohydrodynamic system whose behavior can be actively manipulated through field application. For the cladding and bimetal fabrication industry, this technology offers a path to improved dilution control, enhanced penetration, and better microstructural outcomes without modifying the base process equipment. The combination of numerical modeling and experimental validation provides a credible basis for process development, and the approach is readily adaptable to other arc welding processes (SAW, GMAW) where magnetic field effects may be even more pronounced due to higher current levels. The work also highlights the importance of electromagnetic-thermal coupling in welding process modeling — a consideration that becomes increasingly critical as welding processes are pushed to higher performance limits. The practical implementation of magnetic field-assisted welding requires compact, reliable field generation systems that can be integrated into production environments, and this remains an area for continued development.