CLADDING TECHNOLOGY SHANXI CO., LTDNumerical Simulation and Experimental Verification of Temperature Field in GTAW Flat Plate Cladding with External Longitudinal Magnetic Field
Literature Overview
This 2010 study published in Hot Working Technology by researchers from Chongqing University's State Key Laboratory of Mechanical Transmission and School of Materials Science and Engineering investigates the effects of an external longitudinal magnetic field on the temperature distribution during gas tungsten arc welding (GTAW) cladding on flat plates. Funded by the Ministry of Education Doctoral Point Fund and Chongqing Natural Science Foundation, this research explores electromagnetic field-assisted welding as a means to control weld geometry, dilution, and microstructure in cladding operations. The work combines finite element numerical simulation with experimental thermocouple verification, providing a rigorous methodology for understanding complex thermal phenomena in electromagnetic field-assisted welding.
Technical Principle
The application of an external longitudinal magnetic field (parallel to the welding direction) to the GTAW arc produces Lorentz force effects on the arc plasma. The magnetic field interacts with the electric current flowing through the arc, generating a force that can:
- Compress the arc: Increasing current density and heat concentration at the weld pool center
- Stabilize the arc: Reducing arc wandering and improving energy transfer efficiency
- Modify convection patterns: Altering the fluid flow within the molten weld pool, affecting heat distribution and dilution
The governing equations for the coupled electromagnetic-thermal-fluid problem include Maxwell's equations for the magnetic field, the Navier-Stokes equations for fluid flow, and the heat conduction equation with source terms.
Numerical Simulation Approach
The study employed a three-dimensional finite element model to simulate the temperature field during GTAW cladding with longitudinal magnetic field. The model incorporated:
- Heat source model: A modified double-ellipsoidal Goldak heat source model accounting for the magnetic field's effect on arc energy distribution
- Boundary conditions: Convective and radiative heat loss at the surface, adiabatic conditions at the back face
- Material properties: Temperature-dependent thermal conductivity, specific heat, and density for both base metal and cladding material
- Moving heat source: Gaussian distribution with velocity-dependent parameters
| Simulation Parameter | Value | Description |
|---|---|---|
| Welding current | 120-180 A | GTAW cladding range |
| Welding voltage | 18-22 V | Arc voltage |
| Travel speed | 5-10 cm/min | Cladding travel rate |
| Magnetic field strength | 0-0.5 T | Longitudinal field |
| Shielding gas | Argon 99.99% | Inert atmosphere |
| Base metal | Q235 carbon steel | 12 mm thickness |
| Cladding material | 304 stainless steel | Filler wire |
Experimental Verification
Temperature measurements were conducted using embedded thermocouples (K-type, 0.5 mm diameter) positioned at multiple locations relative to the weld centerline. The experimental setup included a permanent magnet system generating a controllable longitudinal field, a water-cooled welding table, and a multi-channel data acquisition system for real-time temperature recording.
The comparison between simulated and measured temperature profiles showed good agreement:
| Verification Point | Simulated Peak Temp (°C) | Measured Peak Temp (°C) | Deviation |
|---|---|---|---|
| Weld center, 0 mm offset | 1520 | 1480-1560 | <3% |
| 2 mm from centerline | 1180 | 1150-1210 | <3% |
| 5 mm from centerline | 850 | 820-880 | <4% |
| 10 mm from centerline | 450 | 430-470 | <5% |
| Cooling rate at 800°C | 35 °C/s | 30-40 °C/s | <15% |
Effects of Magnetic Field on Cladding Process
The study demonstrated several significant effects of the longitudinal magnetic field:
- Narrower weld width: At 0.3 T field strength, weld width decreased by 15-20% compared to no field, resulting in reduced base metal dilution.
- Deeper penetration: The concentrated arc energy increased penetration depth by 20-30%, improving bond strength between cladding layer and base metal.
- Modified cooling rate: The altered heat distribution produced cooling rates 10-15% higher at the fusion boundary, promoting finer grain structures in the heat-affected zone.
- Reduced porosity: The stabilized arc and modified pool convection reduced gas porosity by 40-60% in the cladding deposit.
Engineering Application Prospects
The magnetic field-assisted GTAW cladding technique offers particular advantages for:
- Low-dilution cladding: Where maintaining high alloy content in the deposit is critical (e.g., nickel-based alloy cladding on carbon steel)
- Thick-section cladding: Where deep penetration improves bond integrity
- Automation: The improved arc stability enables more reliable robotic cladding operations
- Heterogeneous material joining: Where precise thermal control prevents unwanted intermetallic formation
Study Reflections
This research represents a mature application of computational modeling to welding process development. The combination of numerical simulation with experimental verification establishes confidence in the predictive capability of the model, enabling virtual optimization of process parameters before physical trials. The magnetic field approach offers a non-contact, adjustable method for process control that does not require modification of the welding equipment itself—only the addition of a permanent magnet or electromagnet system. However, practical implementation faces challenges including the cost of magnetic field generation systems, the need for precise field uniformity over the weld area, and the potential interaction of external magnetic fields with nearby magnetic materials or instrumentation. For pressure vessel cladding applications governed by ASME or NB/T standards, the qualification of magnetic field-assisted processes would require demonstration of equivalent mechanical properties and acceptable defect levels, which the improved process characteristics shown in this study suggest are achievable. The methodology established here—rigorous simulation validated by comprehensive experimental measurement—sets a benchmark for future process development research in electromagnetic field-assisted welding.