External Magnetic Field Oscillating TIG Arc for Weld Seam Tracking Control

Literature Overview

This study published in the Journal of Tianjin Polytechnic University (Vol. 44, Issue 5, 2025, pp. 93-99) by Yue Jianfeng, Chen Haojie, Xing Encheng, Zhou Hao, and Huang Junfen addresses the challenge of weld seam tracking control in TIG welding processes. The research is supported by the National Natural Science Foundation of China (Project U1733125) and the Opto-Electro-Mechanical Equipment Technology Beijing Key Laboratory Open Project (BIPT-OMET-2022-01). The work is conducted at the Tianjin Key Laboratory of Modern Electromechanical Equipment Technology, Tianjin Polytechnic University, and the School of Mechanical Engineering, Beijing Institute of Petrochemical Technology.

Core Technical Approach

The study addresses a specific problem in TIG welding: when the tungsten electrode is close to the workpiece, oscillating welding can cause interference and collision between the tungsten tip and the workpiece, leading to tungsten damage. To overcome this limitation, the researchers propose applying an external transverse alternating magnetic field to the TIG arc, causing the arc to oscillate flexibly without mechanical movement of the torch. This approach enables extraction of torch center deviation signals for seam tracking.

Magnetic Field Arc Oscillation Principle

The external transverse alternating magnetic field interacts with the current-carrying TIG arc, producing a Lorentz force that deflects the arc from its original position. By varying the magnetic field frequency and amplitude, the arc oscillation characteristics can be controlled. The key advantages of this approach include:

1. No mechanical oscillation of the torch, eliminating the risk of tungsten-workpiece contact
2. Flexible arc deflection that can be precisely controlled through magnetic field parameters
3. Maintained short electrode-workpiece distance, which is beneficial for arc stability and penetration
4. Continuous arc oscillation that provides rich signal information for seam tracking

Signal Processing and Control Algorithm

The arc voltage signal is processed through an Extended Kalman Filter (EKF) algorithm to achieve effective denoising. The denoised arc voltage signal contains position characteristic information of the weld groove. A mathematical model of torch position deviation is established using the left-right interval integration difference method on the arc voltage signal. A fuzzy self-tuning PID control algorithm is then employed to achieve stable deviation correction and anti-interference capability during TIG welding.

Performance Results

The method demonstrates accurate identification and compensation of weld seam deviation. The TIG welding efficiency and seam tracking accuracy are significantly improved, with the maximum error controlled within 0.25 mm. This level of accuracy is comparable to or better than many conventional optical seam tracking systems, while offering the advantage of no additional hardware sensors.

Engineering Practice Implications

For welding engineers working with automated or semi-automated TIG welding systems, this approach offers several practical benefits:

1. Reduced equipment complexity: No additional optical sensors or mechanical oscillators are required
2. Improved reliability: Elimination of mechanical oscillation reduces wear and failure points
3. Enhanced process flexibility: The magnetic field parameters can be adjusted in real-time to accommodate varying seam conditions
4. Maintained process stability: The short electrode-workpiece distance is preserved, which is critical for consistent arc characteristics

Comparison with Conventional Seam Tracking Methods

The magnetic field arc oscillation method offers a favorable balance between accuracy, complexity, cost, and robustness. The maximum error of 0.25 mm is sufficient for most TIG welding applications, including pipe welding, sheet metal fabrication, and precision component manufacturing.

Key Questions and Reflections

The success of this approach depends on several factors that warrant further investigation:

1. The influence of magnetic field parameters (frequency, amplitude, waveform) on arc oscillation characteristics and tracking accuracy
2. The robustness of the method under varying welding conditions, including different materials, thicknesses, and groove geometries
3. The potential interference of the external magnetic field on other welding processes or nearby equipment
4. The scalability of the method to different torch configurations and welding positions

The Extended Kalman Filter algorithm is a sophisticated signal processing technique that may require careful tuning for different welding conditions. The fuzzy self-tuning PID control algorithm adds another layer of complexity but provides adaptive capability that can accommodate process variations. For industrial implementation, the robustness of these algorithms under real-world conditions with varying signal quality and process disturbances should be thoroughly validated.

Study Insights and Implications

This work demonstrates a novel approach to weld seam tracking control that leverages the inherent properties of the TIG arc rather than relying on external sensors. The combination of magnetic field arc oscillation, advanced signal processing, and adaptive control algorithms provides a robust and cost-effective solution for automated TIG welding. For welding engineers, this approach offers a practical alternative to conventional optical or contact-based tracking systems, particularly in applications where sensor reliability or maintenance is a concern. The maximum tracking error of 0.25 mm is competitive with state-of-the-art systems, while the elimination of mechanical oscillation reduces equipment complexity and failure modes. This work contributes to the advancement of intelligent welding systems and provides a foundation for further development of sensorless or minimally-sensored welding control technologies.