CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Plasma-MIG Welding Control System
Literature Overview
Published in 2002 in the Journal of Shenyang University of Technology by Zhang Yishun, Ma Guohong, Shao Chengji, Wang Rui, and Zhou Ye from Shenyang University of Technology and Shenyang High Voltage Switchgear Co., Ltd., this study documents the development of a dedicated control system for plasma-MIG hybrid welding. The research bridges the gap between welding process research and industrial implementation, addressing the practical engineering challenges of integrating plasma arc and MIG welding power sources into a coordinated, controllable system.
Core Technical Content
System Architecture and Control Strategy
The control system developed in this study integrates a plasma arc power supply with a MIG welding power supply through a centralized controller that coordinates arc ignition, current regulation, travel speed synchronization, and wire feed rate control. The system employs a microprocessor-based controller that manages the sequence of operations and maintains stable welding conditions through real-time feedback from current and voltage sensors.
| System Component | Specification | Function |
|---|---|---|
| Plasma Power Supply | 30 to 120 A, DC | Pilot arc and thermal energy |
| MIG Power Supply | 100 to 400 A, DC | Filler metal deposition |
| Travel Speed | 50 to 800 mm/min | Joint traversal control |
| Wire Feed Speed | 2 to 15 m/min | Deposition rate control |
| Controller | Microprocessor-based | Process coordination |
| Feedback Sensors | Current, voltage, position | Real-time monitoring |
Process Stability and Arc Control
The study addresses the challenge of maintaining stable plasma arc characteristics when operating in conjunction with the MIG arc. The electromagnetic interaction between the two arcs can cause arc drift and instability if not properly controlled. The developed system implements arc current feedback control that adjusts the plasma power supply output to maintain a stable arc length and current, compensating for variations in base metal thickness, joint geometry, and environmental conditions.
The control algorithm employs a proportional-integral (PI) controller that monitors the plasma arc voltage as an indicator of arc length. Deviations from the setpoint voltage trigger adjustments to the plasma current or travel speed to restore stable conditions. This feedback control is essential for maintaining consistent weld quality over long production runs.
Industrial Application and Performance
The system was developed in collaboration with Shenyang High Voltage Switchgear Co., Ltd., indicating its application in the manufacturing of high-voltage electrical equipment. These applications typically involve welding of copper, copper alloys, and steel components where the combination of deep penetration from the plasma arc and high deposition rate from the MIG arc provides significant productivity advantages over conventional welding processes.
The study reports that the hybrid plasma-MIG process achieves 30 to 50 percent higher travel speeds compared to conventional MIG welding while maintaining equivalent or superior weld quality. The reduced heat input per unit length compared to conventional MIG also results in reduced distortion, which is critical for the dimensional accuracy requirements of electrical equipment fabrication.
Engineering Practice Integration
Relevance to Cladding and Overlay Welding Automation
The control system architecture described in this study provides a template for developing automated cladding and overlay welding systems. In bimetal pressure vessel fabrication, automated cladding operations require precise control of multiple process parameters simultaneously, including travel speed, wire feed rate, torch angle, and shielding gas flow. The feedback control principles developed in this study can be adapted to maintain stable cladding weld conditions over large surface areas with varying substrate conditions.
For plasma-assisted overlay welding of nickel-based alloys on carbon steel, the same control challenges arise: maintaining stable arc characteristics, controlling dilution rate, and ensuring uniform cladding thickness. The system's ability to coordinate multiple power sources through centralized control is directly transferable to hybrid plasma-MIG cladding operations.
Quality Control Integration
The control system's monitoring capabilities can be extended to include in-process quality monitoring. By analyzing the welding current and voltage waveforms in real-time, the system can detect anomalies such as arc extinction, excessive spatter, or lack of fusion before they result in weld defects. This proactive quality control approach reduces rework costs and improves first-pass yield, which is particularly valuable in high-value applications such as pressure vessel fabrication.
Key Questions and Reflections
The study raises an important question about the long-term reliability and maintenance requirements of the integrated control system in industrial environments. Welding operations expose control systems to electromagnetic interference, temperature extremes, and mechanical vibration. The study does not address the environmental protection and maintenance schedule for the control system, which are critical considerations for industrial deployment.
Additionally, the study focuses on the control system development but does not extensively discuss the economic evaluation of the hybrid process compared to conventional welding. Engineers must evaluate the total cost of ownership, including capital investment in the control system, power supply upgrades, and operator training, against the productivity gains and quality improvements achieved through hybrid welding.
Study Insights and Implications
This research demonstrates that successful implementation of advanced welding processes requires not only process optimization but also robust control system development. The integration of plasma and MIG welding into a coordinated system requires careful attention to power supply compatibility, control algorithm design, and sensor integration.
For engineers involved in cladding and bimetal product manufacturing, the study provides a practical example of how advanced welding processes can be implemented in industrial settings. The collaboration between academia and industry exemplified in this study is a model for technology transfer that engineers should advocate for in their organizations.
The principles of coordinated multi-source control established in this study are applicable to emerging hybrid welding processes such as laser-MIG, laser-plasma, and arc-laser hybrid systems. As the welding industry continues to evolve toward more complex hybrid processes, the control system architecture developed in this research provides a foundation for future developments in automated cladding and overlay welding technology.