CLADDING TECHNOLOGY SHANXI CO., LTDHigh-Frequency Hybrid Dual-Tungsten Electrode TIG Welding Method and Digital Power Source
Literature Overview
The study by Wu Tongli, Wang Kehong, Yang Jiajia, and Zhou Xiaoxiao, published in the Journal of Welding (2018), presents both the welding method and the digital power source development for high-frequency hybrid dual-tungsten electrode TIG welding. This work, funded by the National Defense Basic Scientific Research Program (Grant No. JCKY2016208A001), was conducted at the School of Materials Science and Engineering, Nanjing University of Science and Technology. Unlike the companion study focusing on welding process and metallurgy, this paper emphasizes the power electronics and control system aspects that enable the high-frequency hybrid welding process.
Power Source Architecture and Design Principles
The digital power source for high-frequency hybrid dual-electrode TIG welding represents a significant advancement in welding power electronics. The system employs a full-bridge inverter topology with silicon carbide (SiC) MOSFETs as the main switching devices, enabling switching frequencies up to 100 kHz. The power source provides two independently controlled output channels, each capable of delivering up to 400 A of welding current with high-frequency modulation capability.
The digital control architecture is based on a field-programmable gate array (FPGA) combined with a digital signal processor (DSP) for real-time current and voltage waveform shaping. This architecture enables precise control of the high-frequency current components superimposed on the base welding current, with phase synchronization between the two channels achieved through hardware-level phase locking.
| Power Source Parameter | Specification | Significance |
|---|---|---|
| Maximum Output Power | 80 kW | Supports dual-electrode operation at high currents |
| Switching Frequency | Up to 100 kHz | Enables high-frequency current modulation |
| Current Regulation Accuracy | ±1% | Ensures stable arc and consistent weld quality |
| Phase Synchronization Accuracy | ±1 degree | Controls electromagnetic stirring direction |
| Response Time | < 10 μs | Enables real-time arc feedback control |
| Power Factor | > 0.99 | Minimizes harmonic distortion on the power grid |
| Efficiency | > 92% | Reduces energy consumption and thermal management requirements |
High-Frequency Current Generation Technology
The generation of high-frequency welding currents requires specialized power electronics that go beyond conventional welding inverters. The researchers developed a novel current shaping circuit that uses a combination of series and parallel resonant topologies to achieve the required high-frequency amplitude modulation. The key challenge is maintaining arc stability while superimposing high-frequency components with amplitudes reaching 80% of the base current.
The solution involves a two-stage modulation approach: first, the base current is established using conventional PWM control, and then the high-frequency component is added through a separate resonant circuit that injects the modulated current into the welding circuit. This architecture allows independent control of the base and high-frequency components, providing maximum flexibility in process parameter optimization.
Control Strategy and Arc Feedback
The digital control system implements a multi-loop feedback architecture with the following control loops:
- Outer loop: Welding current regulation based on current sensor feedback
- Middle loop: Arc voltage stabilization using arc voltage sensing
- Inner loop: High-frequency current amplitude and phase control
- Auxiliary loop: Tungsten electrode condition monitoring based on arc voltage waveform analysis
The arc voltage waveform contains rich information about the welding process state, including arc length, electrode condition, and workpiece surface quality. The digital power source continuously analyzes the arc voltage waveform to detect and compensate for process disturbances in real time.
Engineering Application and Performance Validation
The developed power source was validated through extensive welding experiments on stainless steel, carbon steel, and nickel-based alloys. The results demonstrated that the system could maintain stable welding over a wide range of process parameters, with arc stability indices exceeding 0.95 under all tested conditions.
For cladding applications, the power source's ability to precisely control the high-frequency current amplitude and phase difference provides a powerful tool for managing dilution ratios. By adjusting the phase difference between the two electrode currents, engineers can control the direction and intensity of electromagnetic stirring in the weld pool, which directly affects the mixing between the base metal and the cladding material.
The power source also includes a built-in welding procedure specification (WPS) management system that stores and recalls welding parameters for different material combinations and joint configurations. This feature is particularly valuable for production environments where consistency and traceability are critical.
Comparison with Conventional Power Sources
| Feature | Conventional Inverter | High-Frequency Hybrid Digital Source |
|---|---|---|
| Switching Frequency | 20–50 kHz | Up to 100 kHz |
| Current Control Resolution | 1 A | 0.1 A |
| Waveform Shaping Capability | Basic pulse | Arbitrary waveform |
| Phase Control | Not available | Multi-channel phase synchronization |
| Arc Feedback | Open-loop or simple closed-loop | Multi-loop real-time feedback |
| Deposition Rate | 1–2 kg/h (TIG) | 3–5 kg/h (dual-electrode TIG) |
| Cost Index | 1.0 | 3.0–4.0 |
Summary and Outlook
This research bridges the gap between welding process innovation and power electronics development, demonstrating that advanced welding processes require correspondingly advanced power sources. The digital power source developed in this study provides the technical foundation for implementing high-frequency hybrid dual-electrode TIG welding in production environments. For engineers in the cladding and bimetal industry, this work highlights the importance of investing in advanced power source technology as a prerequisite for implementing next-generation welding processes. The modular architecture of the power source also suggests potential for extension to other hybrid welding processes, such as laser-arc hybrid welding, where similar high-frequency current modulation capabilities would be beneficial.