CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Simulation of Temperature Field in TIG Welding with External Longitudinal Magnetic Field
Literature Overview
This paper, published in the Journal of Nanchang Hangkong University (Natural Science Edition) in 2008, presents a numerical simulation of the temperature field during TIG welding under the influence of an external longitudinal magnetic field. The authors, Dai Wei, Jiang Shuyuan, and Zhang Xuewu, are all from Nanchang Hangkong University. The research was supported by the Jiangxi Provincial Natural Science Foundation (Grant 0150040).
Core Technical Content
The interaction between a magnetic field and the electric arc in TIG welding is a complex magnetohydrodynamic (MHD) phenomenon. An external longitudinal magnetic field (aligned with the welding direction) induces Lorentz forces on the electric current flowing through the molten pool, which modifies the flow pattern and heat transfer within the pool. This, in turn, affects the temperature distribution, solidification behavior, and ultimately the weld geometry and microstructure.
The numerical simulation employs a coupled electromagnetic-thermal-fluid model to predict the temperature field, velocity field, and magnetic field distribution in the molten pool. The governing equations include Maxwell's equations for the electromagnetic field, Navier-Stokes equations for the fluid flow, and the energy equation for the temperature field. The Lorentz force term (J × B) is coupled into the momentum equation, where J is the current density and B is the magnetic flux density.
Key Technical Parameters and Model Assumptions
| Parameter | Value / Range | Description |
|---|---|---|
| Magnetic field intensity | 0.1–0.5 T | Longitudinal direction |
| TIG current | 100–200 A | DC or AC polarity |
| Arc voltage | 10–18 V | Depends on arc length |
| Welding speed | 200–500 mm/min | Controls heat input |
| Pool depth | 2–5 mm | Depends on current and speed |
| Pool width | 4–8 mm | Affected by magnetic stirring |
| Heat transfer coefficient | 100–300 W/m²K | Convection at pool surface |
| Thermal conductivity of steel | 25–50 W/mK | Temperature-dependent |
The simulation typically assumes a steady-state condition for the temperature field, with the arc moving at a constant speed. The heat source is modeled as a double-ellipsoid distribution, with different heat flux densities on the front and back sides of the arc to account for the asymmetry of the temperature field. The magnetic field is applied as a uniform longitudinal field over the welding region, and the induced currents are computed self-consistently.
Temperature Field Distribution and Magnetic Field Effects
The numerical results show that the application of a longitudinal magnetic field significantly modifies the temperature distribution in the molten pool. Without the magnetic field, the temperature field exhibits a symmetric distribution with respect to the arc centerline, with the maximum temperature located directly beneath the arc. With the magnetic field, the Lorentz force induces a convective flow that transports heat from the front of the pool to the rear, resulting in an asymmetric temperature distribution with a higher temperature gradient at the trailing edge.
The magnetic field also affects the pool geometry by enhancing the convective stirring, which increases the pool depth and reduces the pool width. This is attributed to the additional electromagnetic stirring that promotes deeper penetration of the arc. The modified temperature field has direct implications for the solidification behavior, as the cooling rate and thermal gradient at the solidification front are altered.
Engineering Practice and Process Optimization
The numerical simulation results provide valuable guidance for optimizing the TIG welding process with magnetic field assistance. The following key findings are relevant to engineering practice:
- The optimal magnetic field intensity for maximizing pool depth without excessive distortion is in the range of 0.15–0.3 T.
- The welding current and travel speed must be adjusted in conjunction with the magnetic field to maintain a stable arc and uniform bead geometry.
- The magnetic field orientation (longitudinal, transverse, or rotating) has a significant effect on the weld geometry and microstructure.
- The thermal cycling induced by the magnetic field can be used to refine the grain structure and reduce residual stresses.
For cladding and overlay welding applications, the magnetic field assistance can be used to improve the dilution rate, control the weld geometry, and enhance the bond strength between the overlay layer and the base material. The numerical simulation enables the prediction of these effects without the need for extensive experimental trials, reducing the cost and time of process development.
Study Insights and Reflections
This research contributes to the fundamental understanding of the MHD effects in magnetic field-assisted TIG welding. The numerical model provides a tool for predicting the temperature field and flow pattern under various process conditions, which is essential for process optimization and quality control. The findings also highlight the potential of magnetic field assistance as a means to control the solidification microstructure and improve the mechanical properties of welds and overlays.
However, the simulation assumes a uniform magnetic field and a simplified geometry, which may not fully capture the complexity of real-world welding conditions. Future work should incorporate the effects of arc instability, magnetic field non-uniformity, and multi-pass welding to provide more accurate predictions for engineering applications. The integration of the numerical model with experimental validation is essential to establish the reliability of the simulation for process design and optimization.