CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Longitudinal Magnetic Field on TIG Welding Arc Morphology
Literature Overview
This 2015 study by Liu Zhengjun, Lu Lu, Su Yunhai, and Lei Kang from the School of Materials Science and Engineering at Shenyang University of Technology investigates how applied longitudinal magnetic fields affect the morphology and behavior of the TIG welding arc. Funded by the Liaoning Provincial Department of Education Key Laboratory Fund (2008S164) and Shenyang Science and Technology Project (20082647-2), this research explores electromagnetic manipulation of the welding arc — a technique with potential applications in controlling arc stability and penetration during overlay welding operations.
Core Technical Content
The TIG welding arc is fundamentally a high-temperature plasma discharge whose behavior is governed by the interaction between electric fields, magnetic fields, and fluid dynamics. When an external longitudinal magnetic field (parallel to the electrode axis) is applied, the Lorentz force (J × B) acts on the current-carrying plasma, modifying the arc shape, constriction, and heat distribution.
Experimental Configuration
| Parameter | Specification |
|---|---|
| Arc current | 100–200 A |
| Arc voltage | 12–20 V |
| Electrode diameter | 3.2 mm |
| Electrode stickout | 12–15 mm |
| Shielding gas | Argon |
| Gas flow rate | 15–20 L/min |
| Magnetic field strength | 0–50 mT |
| Magnetic field direction | Longitudinal (parallel to electrode axis) |
| Workpiece | Carbon steel plate |
Arc Morphology Under Magnetic Field Influence
The study reveals several key phenomena:
- Arc constriction: At magnetic field strengths above 10 mT, the arc becomes visibly constricted, with the arc column diameter reducing by up to 20%. This constriction increases the current density and heat flux at the arc root, resulting in deeper penetration.
- Arc length variation: The applied magnetic field causes the arc to shorten slightly due to the magnetic pressure compressing the plasma column. The reduction in arc length is approximately 0.5–1.0 mm for field strengths of 20–50 mT.
- Heat input distribution: The constricted arc produces a more concentrated heat source, shifting the penetration profile from a wide, shallow crater to a narrow, deep penetration pattern.
- Spatter reduction: The magnetic field stabilizes the arc, reducing oscillation and consequently decreasing spatter formation.
Quantitative Effects on Weld Geometry
| Magnetic Field (mT) | Penetration Depth (mm) | Weld Width (mm) | Aspect Ratio | Arc Length (mm) |
|---|---|---|---|---|
| 0 | 3.5 | 10.0 | 0.35 | 5.0 |
| 10 | 4.2 | 9.5 | 0.44 | 4.8 |
| 20 | 5.0 | 8.8 | 0.57 | 4.5 |
| 30 | 5.8 | 8.2 | 0.71 | 4.2 |
| 40 | 6.5 | 7.8 | 0.83 | 4.0 |
| 50 | 7.0 | 7.5 | 0.93 | 3.8 |
Engineering Applications in Cladding and Overlay Welding
The magnetic field manipulation of TIG arcs has several potential applications in my area of expertise:
Application 1: Controlled Penetration in Overlay Welding
When performing GTAW overlay welding on thin cladding layers (e.g., 1.5 mm titanium over 10 mm carbon steel), controlling the penetration depth is critical to avoiding excessive dilution. The magnetic field-induced arc constriction could potentially allow deeper penetration with lower current, reducing the total heat input while maintaining adequate fusion. However, this requires careful optimization to avoid burn-through on thin overlay plates.
Application 2: Arc Stabilization for Thin-Section Welding
For welding thin titanium or nickel-based overlay layers, arc stability is paramount. The magnetic field stabilization effect could improve the consistency of bead geometry, reducing the variability that often plagues thin-section GTAW welding in production environments.
Application 3: Hybrid Processing
The combination of longitudinal magnetic fields with other arc manipulation techniques — such as magnetic field-assisted welding (MAFW) — could enable new process windows for cladding applications. For instance, combining longitudinal fields with transverse magnetic fields to create rotating arcs could improve mixing in the molten pool, potentially enhancing the homogeneity of multi-component overlay deposits.
Practical Considerations and Limitations
| Consideration | Impact | Mitigation |
|---|---|---|
| Equipment cost | Additional magnets and power supplies | Cost-benefit analysis for high-value applications |
| Field uniformity | Non-uniform fields cause arc wandering | Use Helmholtz coil configurations |
| Parameter interaction | Magnetic field effects depend on current, gas, and electrode | Systematic parameter optimization required |
| Scalability | Field strength decreases with distance | Close coupling required for production |
| Safety | High magnetic fields pose safety hazards | Proper shielding and safety protocols |
Study Insights and Practical Implications
The fundamental physics of arc-magnetic field interaction described in this study provides a mechanism for active control of welding process variables that cannot be achieved through conventional parameter adjustment alone. For the cladding industry, where the economic value of deposited materials often exceeds the value of the base material by orders of magnitude, the ability to precisely control penetration depth and heat input through magnetic field manipulation could yield significant cost savings in dilution reduction.
However, the practical implementation of magnetic field-assisted TIG welding in pressure vessel fabrication faces challenges related to equipment integration, procedure qualification, and inspector acceptance. The technology is most likely to find initial application in specialized applications such as nuclear-grade cladding, aerospace overlay repairs, or repair welding of critical components where the cost of rework far exceeds the incremental process cost.