CLADDING TECHNOLOGY SHANXI CO., LTDMIG Arc Simulation Based on Metal Vapor and External Magnetic Field
Literature Overview
The research by Fu Yu, Han Shaohua, and Xue Dinqi from the School of Mechanical Engineering and Automation at Fuzhou University, published in 2021 in the journal Ordnance Materials Science and Engineering and supported by the Fujian Provincial Natural Science Foundation (2017J05077), presents a computational fluid dynamics (CFD) simulation of gas metal arc welding (MIG) arc behavior incorporating metal vapor transport and external magnetic field effects. This work addresses a critical gap in welding process modeling: the interaction between metal vapor generated during arc melting and externally applied magnetic fields, which significantly influence arc stability, weld geometry, and microstructural outcomes.
Core Technical Framework
The simulation adopted a coupled electromagnetic-thermal-fluid model that accounts for the following physical phenomena:
| Physical Phenomenon | Governing Equation | Numerical Method |
|---|---|---|
| Arc plasma dynamics | Maxwell's equations | Finite volume method |
| Metal vapor transport | Navier-Stokes equations with species diffusion | Eulerian-Lagrangian approach |
| External magnetic field | Lorentz force coupling | Magnetohydrodynamic (MHD) model |
| Heat transfer | Energy equation with radiation and convection | Discrete ordinates method |
| Arc shape prediction | Current density distribution | Magnetic field force balance |
The model treats the arc plasma as an electrically conducting fluid and solves the coupled equations for current density, velocity field, temperature distribution, and species concentration. The external magnetic field is introduced as a boundary condition that modifies the Lorentz force distribution within the arc column, thereby altering the arc shape, heat flux distribution, and metal transfer characteristics.
Metal Vapor Behavior Analysis
Metal vapor generation during MIG welding is a complex process influenced by arc temperature, wire feed rate, shielding gas composition, and travel speed. The simulation results demonstrated that metal vapor concentration is highest in the arc root region near the molten pool surface, with typical concentrations ranging from 10% to 30% by volume in the near-wire region. The vapor transport is governed by a combination of convective flow driven by arc plasma motion and diffusive transport driven by concentration gradients.
The presence of an external magnetic field was shown to significantly modify the metal vapor distribution. Under a transverse magnetic field of 10–50 mT, the arc column experiences a lateral deflection due to the Lorentz force acting on the current-carrying plasma. This deflection redirects the heat flux distribution on the molten pool surface, creating an asymmetric temperature gradient that promotes directional metal flow. The resulting metal vapor plume is also deflected, reducing vapor deposition on the weld surface and potentially minimizing porosity formation.
External Magnetic Field Effects
The external magnetic field introduces several beneficial effects on the welding process:
| Effect | Mechanism | Magnitude (at 30 mT) |
|---|---|---|
| Arc stability improvement | Magnetic field constrains arc oscillation | Arc width reduced by 15–20% |
| Weld width control | Asymmetric heat flux distribution | Weld width reduced by 10–15% |
| Penetration enhancement | Directed plasma jet increases arc pressure | Penetration depth increased by 8–12% |
| Metal vapor reduction | Vapor plume deflected away from pool | Surface vapor concentration reduced by 25% |
| Microsegregation control | Modified solidification front velocity | Grain refinement of 10–20% |
The magnetic field strength was varied from 5 mT to 80 mT in the simulation, with optimal results observed in the 20–40 mT range. Below 20 mT, the Lorentz force was insufficient to produce significant arc modification, while above 40 mT, excessive arc deflection led to unstable metal transfer and potential spatter increase. The optimal magnetic field configuration was identified as a transverse field applied perpendicular to the welding direction, which provided the best balance between arc stabilization and penetration enhancement.
Engineering Practice Implications
For cladding and weld overlay applications, the magnetic field-assisted MIG process offers several advantages. First, the improved arc stability reduces the risk of undercut and lack of fusion defects, which are common concerns in multi-pass overlay welding. Second, the controlled penetration depth is particularly beneficial for cladding applications where the overlay layer thickness must be precisely controlled to avoid excessive dilution with the base metal. Third, the reduced metal vapor deposition minimizes the risk of gas porosity in the overlay layer, which is critical for corrosion-resistant cladding systems such as stainless steel or nickel-based alloy overlays on carbon steel substrates.
The study also provides a theoretical basis for magnetic field-assisted cladding processes, which could be particularly valuable for dissimilar metal welding scenarios. For example, when cladding nickel-based alloys onto carbon steel, the magnetic field could be used to control the dilution rate and promote a more uniform composition gradient at the cladding interface. This approach could complement existing techniques such as low-dilution welding consumable selection and interlayer material placement.
Key Reflections
The simulation study demonstrates that external magnetic field application represents a promising approach for process optimization in MIG welding, particularly for applications demanding high precision and defect-free joints. The coupling between metal vapor transport and magnetic field effects reveals a previously underappreciated mechanism for controlling weld quality. For engineers involved in bimetal product manufacturing, this research opens new avenues for process innovation, though practical implementation requires careful consideration of magnetic field source design, field uniformity, and compatibility with existing welding equipment. The study serves as a valuable theoretical foundation for experimental validation and eventual industrial adoption.