CLADDING TECHNOLOGY SHANXI CO., LTDDetermination of TIG Heat Source Model Under Combined Magnetic Field and Activator Action
Literature Overview
This paper published in the Journal of Shenyang University of Technology in 2015 by Liu Zhengjun, Wang Xiaohui, and Su Yunhai from the School of Materials Science and Engineering at Shenyang University of Technology addresses a fundamental yet practically critical issue in TIG (GTAW) welding: the accurate determination of heat source models when external magnetic fields and welding activators are applied simultaneously. The research was supported by the Liaoning Provincial Department of Education Fund Project (201124125) and the Liaoning Provincial Doctoral Startup Fund Project (20131079). The study is particularly significant because magnetic field-assisted TIG welding and activator-enhanced TIG welding are increasingly employed in cladding and overlay applications where penetration control, dilution management, and deposition geometry are paramount.
Core Technical Content
The central challenge addressed in this work is that conventional heat source models used in TIG welding numerical simulations — such as the double-elliptical model or the Gaussian distribution model — do not adequately account for the complex arc behavior modifications introduced by external magnetic fields and flux activators. When a magnetic field is applied, the arc column experiences Lorentz force deflection, which alters the heat flux distribution on the workpiece surface. Simultaneously, welding activators (such as sodium silicate-based fluxes or thoria-containing consumables) modify the arc voltage, arc stability, and the cathode spot distribution, further complicating the thermal input profile.
Heat Source Model Development
The researchers developed a modified heat source model that incorporates both magnetic field parameters and activator characteristics. The key innovation lies in coupling the arc force model with the thermal model to predict the actual heat flux distribution rather than assuming a symmetric distribution. The model accounts for:
- Arc deflection angle as a function of magnetic field strength and direction
- Changes in arc voltage and current density distribution due to activator composition
- Non-uniform heat flux distribution resulting from the combined effects
- Dynamic evolution of the heat source during travel welding
Numerical Simulation Parameters
| Parameter | Typical Range | Description |
|---|---|---|
| Welding current | 100–300 A | Depends on material thickness |
| Arc voltage | 15–25 V | Modified by activator |
| Travel speed | 200–600 mm/min | Process-dependent |
| Magnetic field strength | 0.5–5.0 T | External applied field |
| Arc force | 10–100 N | Calculated from electromagnetic model |
| Heat input | 0.5–5.0 kJ/mm | Combined effect result |
Interpretation of Technical Points
The study demonstrates that the combined action of magnetic field and activator creates a non-axisymmetric heat input that cannot be captured by conventional symmetric heat source models. The researchers validated their model through comparison of predicted weld bead geometry, penetration depth, and temperature field distribution with experimental results. The deviation between simulation and experiment was reduced to within acceptable engineering limits when the modified model was used.
The practical significance of this work for cladding and overlay applications is substantial. In weld overlay processes, precise control of the heat input distribution directly determines the dilution rate between the base metal and the overlay material. For bimetallic cladding, excessive dilution can compromise the corrosion resistance or wear resistance properties of the overlay layer, while insufficient dilution can lead to poor metallurgical bonding and interfacial cracking. The ability to predict and control heat source distribution under modified welding conditions is therefore essential for optimizing cladding process parameters.
Engineering Practice Integration
In practical cladding operations, particularly for overlay welding of nickel-based alloys (such as Inconel 625 or Hastelloy C276) onto carbon steel or low-alloy steel substrates, the dilution rate must typically be maintained below 30% to ensure adequate corrosion resistance. The modified heat source model developed in this study provides a theoretical framework for predicting dilution under magnetic field-assisted conditions, which can be used to optimize process parameters before physical trials.
For engineers working with bimetallic pressure vessels, this research offers a pathway to improve the quality of weld overlay layers on hydrogenation reactors and other high-pressure equipment where both mechanical integrity and corrosion resistance are critical. The model can be integrated into process planning software to pre-calculate optimal parameter combinations for specific cladding configurations.
Key Reflections and Insights
The most valuable contribution of this research is the methodological approach of coupling electromagnetic arc force calculations with thermal modeling rather than treating them as independent phenomena. This coupled approach is essential for any welding process where arc behavior is deliberately modified from its natural state. Engineers should recognize that whenever external influences are applied to the welding arc — whether through magnetic fields, activators, or other means — the heat source model must be correspondingly modified to maintain predictive accuracy.
The study also highlights an important gap in current engineering practice: many cladding process procedures are still developed through trial-and-error methods rather than through physics-based simulation. The development of accurate heat source models represents a step toward rational process design, which is particularly important for high-value overlay applications where material costs and quality requirements are demanding.
Study Value and Outlook
This research provides a solid theoretical foundation for the rational design of magnetic field-assisted and activator-enhanced TIG welding processes in cladding applications. Future work should extend the model to multi-pass cladding scenarios, incorporate the effects of preheat and interpass temperature, and validate the predictions against a broader range of material combinations including titanium alloys and zirconium-clad systems. The model should also be extended to three-dimensional transient analysis to capture the full complexity of real welding conditions.