CLADDING TECHNOLOGY SHANXI CO., LTDSeam Tracking Control Based on Externally Applied Magnetic Field Deflected TIG Arc
Literature Overview
This 2025 publication from the Journal of Tianjin Polytechnic University, authored by YUE Jian-feng and colleagues from Tianjin Polytechnic University and Beijing Institute of Petrochemical Technology, presents an innovative approach to weld seam tracking using an externally applied magnetic field to deflect the TIG arc. The research is supported by the National Natural Science Foundation of China (U1733125) and the Beijing Key Laboratory of Opto-Mechatronic Equipment Technology (BIPT-OMET-2022-01), reflecting its significance in advanced manufacturing and intelligent welding technologies.
Core Technical Content and Interpretation
Weld seam tracking is a fundamental challenge in automated welding, particularly for curved seams, complex geometries, and applications where visual sensors may be unreliable due to arc glare, spatter, or restricted access. The proposed method leverages the interaction between an externally applied magnetic field and the electrically conducting TIG arc plasma to achieve both sensing and correction functions in a single integrated system.
Physical Principles of Magnetic Arc Deflection
The TIG arc is an electrically conducting plasma column carrying current from the cathode (tungsten electrode) to the anode (workpiece). When subjected to an external magnetic field perpendicular to the current flow direction, the Lorentz force (F = J × B) acts on the plasma, causing it to deflect. The magnitude of deflection depends on:
| Parameter | Symbol | Typical Range | Effect on Deflection |
|---|---|---|---|
| Arc current | I | 50-300 A | Higher current increases deflection |
| Magnetic field strength | B | 0.1-5 T | Proportional to deflection |
| Arc length | L | 2-8 mm | Longer arc increases deflection |
| Plasma density | n_e | 10^17-10^19 m^-3 | Higher density increases deflection |
| Arc radius | r | 1-3 mm | Smaller radius increases deflection |
Tracking Control Mechanism
The proposed system operates on the following principle:
- A reference magnetic field is applied to the welding zone, creating a known baseline deflection of the arc.
- When the welding torch deviates from the centerline of the seam, the arc impingement point shifts relative to the magnetic field source.
- The asymmetry in arc deflection is detected through changes in the magnetic field distribution or through optical monitoring of the arc position.
- A feedback controller adjusts the torch position or the magnetic field orientation to restore the arc to the desired position on the seam.
This approach offers several advantages over conventional seam tracking methods:
- No optical window or camera required, making it suitable for confined spaces
- Immunity to arc glare and spatter interference
- Potential for real-time control without complex image processing
- Applicability to a wide range of materials and welding positions
Process and Standards Analysis
For integration into industrial welding systems, particularly for cladding and overlay applications, the following process considerations must be addressed:
Parameter Optimization
The magnetic field strength must be carefully calibrated for each welding configuration. Excessive deflection can lead to:
- Poor weld bead uniformity due to asymmetric heat input
- Increased spatter and arc instability
- Reduced penetration depth in the desired direction
- Potential for undercut formation at the weld toe
A systematic parameter study should be conducted for each application, varying the magnetic field strength, orientation, and position relative to the torch axis. The optimal field strength is typically in the range of 0.5-2.0 T for standard TIG welding parameters.
Integration with Existing Standards
The method must be qualified according to relevant welding procedure qualification standards:
| Standard | Application | Requirement |
|---|---|---|
| NB/T 47014 | Pressure vessel welding qualification | Full qualification with magnetic field parameters documented |
| ASME IX | Pressure vessel welding qualification | QW-401 through QW-424 procedures applicable |
| ISO 9606 | Welder qualification | Additional procedures for magnetic field-assisted welding |
| AWS D10.9 | Welding procedure specification | Documentation of magnetic field parameters |
Engineering Practice Integration
For cladding and overlay applications, the magnetic field tracking method can be particularly beneficial in the following scenarios:
- Large-diameter cylindrical cladding: Where the seam is curved and conventional optical tracking may lose the seam during weaving operations.
- Confined space welding: Where access for optical sensors is limited, such as internal cladding of pressure vessels or heat exchanger tubes.
- High-production-rate overlay: Where the speed of magnetic field-based correction exceeds the response time of camera-based systems.
- Multi-pass cladding: Where precise tracking of each subsequent pass is critical for achieving uniform overlay thickness and bond strength.
The method also has implications for the quality of the cladding layer itself. Precise seam tracking ensures that the overlay material is deposited uniformly, minimizing the risk of:
- Incomplete coverage of the base metal surface
- Excessive dilution at the cladding-base metal interface
- Non-uniform hardness and corrosion resistance across the overlay
- Bond strength variations that could lead to delamination under service conditions
Key Questions and Reflections
Several important questions arise from this research that warrant further investigation:
- How does the magnetic field interact with the welding consumable (e.g., gas shield composition, filler wire feeding) and can this interaction be leveraged for additional process control?
- What is the minimum feature size (seam width) that can be reliably tracked using this method, and how does this compare to conventional optical tracking?
- Can the method be adapted for other welding processes (GMAW, FCAW, plasma arc) and what modifications would be required?
- How does the magnetic field affect the solidification microstructure of the weld metal, and are there any beneficial or detrimental effects on mechanical properties?
The most significant reflection from this study is that the integration of magnetic field control with welding process sensing represents a paradigm shift from passive tracking to active process manipulation. Rather than simply detecting the seam and correcting the torch position, the magnetic field itself becomes an integral part of the welding process, potentially enabling new welding capabilities that are not achievable with conventional methods.
Study Insights and Implications
This research demonstrates a novel approach to weld seam tracking that has significant potential for industrial application in cladding, overlay, and pressure vessel fabrication. The method's immunity to optical interference and its potential for real-time control make it particularly attractive for automated welding systems operating in challenging environments. For the bimetallic pressure vessel industry, where precise control of cladding weld geometry is essential for achieving reliable bond strength and corrosion resistance, this technology could represent a meaningful advancement in manufacturing capability. Future work should focus on scaling the technology to industrial welding speeds and demonstrating its reliability in production environments.