CLADDING TECHNOLOGY SHANXI CO., LTDWeld Seam Tracking Control Using External Magnetic Field Swing TIG Arc
Literature Overview
This 2025 publication by Yue Jian-feng, Chen Hao-jie, Xing En-cheng, Zhou Hao, and Huang Jun-fen from Tianjin Polytechnic University and Beijing Institute of Petrochemical Technology investigates a novel approach to weld seam tracking using an externally applied magnetic field to swing the TIG arc. The research is supported by the National Natural Science Foundation of China (U1733125) and the Beijing Key Laboratory of Optoelectromechanical Equipment Technology Open Project (BIPT-OMET-2022-01). The work addresses a long-standing challenge in automated welding: maintaining accurate torch-to-seam alignment without expensive sensor systems.
Core Technical Content
The fundamental principle of this technique relies on the Lorentz force effect: when an external magnetic field is applied perpendicular to the arc axis, the plasma column experiences a lateral force that deflects the arc away from the electrode. By monitoring the arc voltage and current signals during magnetic field-induced arc swing, the system can determine the relative position of the torch to the weld seam without optical or mechanical sensors.
Arc Swing Mechanism and Signal Analysis
The external magnetic field (typically 0.05-0.2 T) is applied using a permanent magnet or electromagnet positioned adjacent to the welding zone. The arc deflection angle (theta) is proportional to the magnetic field strength and inversely proportional to the arc length. The key measurement is the change in arc voltage when the arc is deflected: a larger voltage change indicates a greater arc length increase, which correlates to the torch being farther from the seam center.
| Magnetic Field Strength (T) | Arc Deflection Angle (°) | Voltage Change (%) | Tracking Accuracy (mm) |
|---|---|---|---|
| 0.05 | 5-10 | 2-4 | 0.5-1.0 |
| 0.10 | 10-15 | 4-8 | 0.3-0.6 |
| 0.15 | 15-20 | 6-12 | 0.2-0.4 |
| 0.20 | 20-25 | 8-16 | 0.1-0.3 |
The tracking algorithm processes the arc voltage signal in real time, comparing the deflected voltage to a reference value to compute the lateral offset. The control system then adjusts the torch position to minimize this offset, achieving closed-loop seam tracking.
Comparison with Conventional Tracking Methods
| Method | Cost | Sensitivity to Fume | Setup Complexity | Accuracy (mm) |
|---|---|---|---|---|
| Visual sensor | High | Low | Medium | 0.1-0.3 |
| Capacitive sensor | Medium | Medium | Medium | 0.2-0.5 |
| Magnetic arc swing | Low | Low | Low | 0.2-0.6 |
| Contact sensor | Low | Low | High | 0.3-0.8 |
The magnetic arc swing method offers a compelling cost-performance balance, particularly for applications where visual sensors are impractical due to intense arc light, heavy fume, or spatter. The technique is especially suitable for thick-section welding where arc stability is less critical and the larger heat input provides inherent seam-following capability.
Engineering Practice Integration
In practical implementation, the system requires careful calibration to establish the relationship between arc voltage change and lateral offset for specific welding conditions. The calibration curve is dependent on arc current, arc length, shielding gas type, and material thickness. A typical calibration procedure involves welding a series of test beads with known lateral offsets and recording the corresponding voltage signals.
For production welding, the system can be integrated with existing CNC welding equipment by adding a magnetic field generator and signal processing unit. The total additional cost is typically 20-30% of a visual sensor system, making it an attractive option for cost-sensitive applications such as pipeline welding, shipbuilding, and structural fabrication.
The technique has particular advantages in underwater welding and welding in confined spaces where visual sensors cannot function. It is also robust against surface contamination, paint, rust, and other variables that can interfere with optical tracking systems.
Key Questions and Reflections
A critical question is the stability of the magnetic field swing method under varying welding conditions. Changes in arc current, travel speed, or joint geometry can alter the arc deflection response, requiring recalibration. The study demonstrates that adaptive algorithms can compensate for these variations, but the practical implementation requires careful validation under production conditions.
Another consideration is the effect of the external magnetic field on weld pool dynamics. The Lorentz force not only deflects the arc but also influences the weld pool flow pattern, potentially affecting penetration profile and bead shape. The study reports that the magnetic field-induced arc swing produces slightly wider, shallower welds compared to unmodified TIG welding, which may be acceptable for many applications but requires procedure qualification for critical components.
The technique also raises interesting questions about its extension to other welding processes. The same principle could potentially be applied to plasma arc welding, where the more confined arc may respond more sensitively to magnetic field deflection, potentially improving tracking accuracy.
In conclusion, this study presents a practical and economical solution to the weld seam tracking problem that leverages fundamental electromagnetic physics to achieve reliable sensorless tracking, with particular promise for industrial applications where cost and robustness are primary concerns.