Zhuojin Pipe Fitting Co., LtdPLC-Controlled High-Frequency Contact Arc Striking System for TIG Welding
Literature Overview
The paper by Lin Dechao and Shi Yaowu (1997), published in Mechanical Science and Technology, presents a high-frequency contact arc striking system for TIG welding, controlled by a Programmable Logic Controller (PLC). The system was developed to improve the arc striking success rate for automated TIG welding of motor steel plate shells, addressing the challenges of high-volume production with consistent weld quality. The authors reviewed various TIG arc striking techniques and proposed a hybrid approach combining high-frequency and contact arc striking methods.
Core Technical Content
Arc striking is a critical initial step in TIG welding that directly affects weld quality and production efficiency. In automated welding operations, a failed arc strike can lead to incomplete welds, rework, and production delays. The conventional high-frequency (HF) arc striking method is reliable but requires specialized equipment and can cause electromagnetic interference. The contact arc striking method is simpler but risks tungsten electrode contamination and burn.
Arc Striking Method Comparison
| Method | Success Rate | Tungsten Contamination | Equipment Complexity | EMI Risk |
|---|---|---|---|---|
| Pure HF Arc Striking | 90-95% | None | High | High |
| Contact Arc Striking | 85-90% | Significant | Low | None |
| HF Contact Hybrid | 100% | Minimal | Moderate | Low |
The proposed hybrid method combines the reliability of HF arc striking with the simplicity of contact arc striking. The system uses a PLC to control the sequence of operations: first, the tungsten electrode is brought into contact with the workpiece to establish a conductive path; then, a high-frequency voltage is applied to ionize the gas and initiate the arc; finally, the contact is broken to establish a stable arc.
PLC Control Architecture
The PLC control system provides precise timing and sequencing of the arc striking process. The PLC monitors the welding circuit for arc voltage and current signals, detecting the establishment of the arc within milliseconds. This rapid response capability ensures that the arc is stabilized before the welding current ramps up to the full welding value.
The system design incorporates several key features:
- Contact pressure control to ensure reliable electrical contact without excessive tungsten deformation
- HF voltage and frequency optimization for efficient arc initiation
- Arc detection circuitry for immediate feedback on arc establishment
- Interlock circuits to prevent hazardous conditions during the contact phase
- Parameter memory for storing welding procedures for different materials and thicknesses
Application to Motor Steel Plate Shell Welding
Motor steel plate shells are typically made of low-carbon steel or low-alloy steel, with thicknesses ranging from 2 to 8 mm. The longitudinal weld seams are critical for structural integrity and must be free of defects such as lack of fusion, porosity, and cracks. The high-volume production environment demands consistent arc striking performance to maintain production throughput.
The 100% arc striking success rate achieved with the PLC-controlled system represents a significant improvement over conventional methods. In production environments, even a 1% failure rate can result in substantial rework costs and production delays. The system's reliability enables continuous automated welding without manual intervention for arc striking.
Engineering Practice Implications
In pipeline welding and other automated welding applications, arc striking reliability is a fundamental requirement. The PLC-controlled approach demonstrated in this paper is particularly relevant for robotic welding cells and automated welding stations where consistent performance is essential.
The hybrid HF-contact method offers a practical solution that balances reliability with equipment simplicity. Compared to pure HF arc striking systems, the hybrid approach reduces the risk of tungsten contamination while maintaining high success rates. This is important because tungsten contamination can lead to tungsten inclusions in the weld metal, which are difficult to detect and can compromise weld integrity.
The PLC control system provides a platform for integrating additional process monitoring and control functions. Modern welding systems often incorporate real-time monitoring of arc characteristics, travel speed, and other process parameters. The PLC architecture used in this paper can be extended to support these advanced features, making it a versatile foundation for automated welding systems.
Study Insights and Reflections
This paper represents an important contribution to the field of welding automation, demonstrating that reliable arc striking can be achieved through intelligent control systems. The use of PLC technology reflects the broader trend of applying industrial control systems to welding processes, enabling precise and repeatable operation.
The hybrid HF-contact method is particularly elegant in its simplicity. By combining two established techniques, the authors achieved a performance level that neither method could attain alone. This approach of integrating complementary technologies is a hathe writing systemark of practical engineering innovation.
The 100% arc striking success rate is a remarkable achievement, but it must be placed in context. The system was designed for specific applications (motor steel plate shells) with defined welding parameters. In practice, the success rate may vary with material type, thickness, surface condition, and environmental factors. However, the principles demonstrated are applicable to a wide range of automated TIG welding applications.
From a quality assurance perspective, the PLC-controlled system provides traceability of arc striking events. Each arc initiation can be logged with timestamp, parameters, and outcome data. This traceability supports quality management systems and provides data for process improvement.
The paper's enduring value lies in its demonstration of the power of control systems in welding technology. The integration of PLC control with hybrid arc striking techniques has been widely adopted in modern automated welding systems, and the principles described remain relevant today.