CLADDING TECHNOLOGY SHANXI CO., LTDPLC-Based Steel Pipe TIG Welding Machine Control System
Literature Overview
This 2015 publication in the journal Welding (焊接) by researchers from Zhengzhou Tourism College presents a practical engineering application of programmable logic controller (PLC) technology to the control of a TIG welding machine designed for steel pipe applications. While the academic depth of this work is moderate, its practical significance lies in demonstrating how industrial automation technology can be applied to welding equipment to improve process consistency, reduce operator dependency, and enable complex welding sequences.
Core Technical Content
System Architecture
The control system is built around a PLC as the central processing unit, interfacing with various input and output modules to control the TIG welding parameters and auxiliary functions. The system architecture follows a hierarchical control approach:
| Component | Function | Specification |
|---|---|---|
| PLC (main controller) | Logic control, parameter management | Siemens S7-200 or equivalent |
| Power supply control | Arc current regulation | Constant current source, 20–300 A |
| Gas control | Shielding gas flow management | Solenoid valve control, 0–25 L/min |
| Torch positioning | Torch angle and distance control | Servo motor or stepper motor |
| Workpiece rotation | Pipe rotation control | Variable speed motor, 0–30 rpm |
| HMI interface | Parameter input, monitoring | Touch panel display |
| Sensors | Current, voltage, gas flow monitoring | Analog input modules |
Control Logic and Welding Sequences
The PLC program implements a structured welding sequence that includes:
- Pre-gas purge: Shielding gas flow is established for 3–5 seconds before arc striking to purge the joint area of atmospheric gases.
- Arc striking: High-frequency or contact start with controlled current ramp-up over 0.5–2 seconds to avoid excessive spatter.
- Welding phase: Constant current welding with synchronized pipe rotation, maintaining consistent travel speed and arc parameters.
- Post-arc cooling: Gas flow continues for 3–5 seconds after arc extinction to protect the cooling weld pool from oxidation.
- Parameter logging: Recording of all process parameters for quality traceability.
Parameter Control and Adaptation
The system allows operators to preset welding parameters based on pipe diameter, wall thickness, and material grade. The PLC implements a lookup table approach where base parameters are stored for common configurations, and the system can interpolate between values for intermediate conditions. This approach is particularly valuable for production welding where the same joint configuration is repeated many times.
| Pipe Configuration | Current (A) | Speed (mm/min) | Gas Flow (L/min) | Rotation (rpm) |
|---|---|---|---|---|
| DN50, 3 mm, 20# steel | 120–150 | 150–200 | 12–15 | 15–20 |
| DN80, 4 mm, 20# steel | 150–180 | 120–160 | 15–18 | 10–15 |
| DN100, 5 mm, 16Mn | 180–220 | 100–140 | 15–20 | 8–12 |
| DN150, 6 mm, 16Mn | 220–260 | 80–120 | 18–22 | 6–10 |
Engineering Practice Implications
For engineers involved in pressure vessel fabrication, the integration of PLC control into welding equipment is not merely an automation convenience but a quality assurance necessity. ASME and GB/T 150 standards require that welding procedures be qualified and consistently applied, and manual TIG welding introduces variability that can compromise weld quality. The PLC-based system ensures that each weld is produced with the same parameter set, reducing the scatter in weld quality and making qualification data more reliable.
The system also facilitates implementation of weld traceability requirements, where each weld can be linked to specific parameter records, operator identification, and time stamps. This is essential for compliance with regulatory requirements in pressure vessel manufacturing, particularly for nuclear and aerospace applications where full traceability is mandated.
Key Questions and Reflections
While the PLC control system offers significant benefits in terms of consistency and traceability, it does not address the fundamental challenge of adapting to geometric variations in the joint. In practice, pipe joints may have slight misalignments, uneven gaps, or variable wall thickness due to manufacturing tolerances. A more advanced system would incorporate real-time gap sensing and adaptive parameter adjustment, but this significantly increases system complexity and cost.
From a standards perspective, the qualification of a PLC-controlled welding procedure under ASME IX or NB/T 47014 requires careful documentation of all automated parameters and their control ranges. The WPS must specify not only the nominal parameters but also the acceptable variation limits, and the PLC program must be locked or password-protected to prevent unauthorized modification during production.
Study Insights and Outlook
This work represents a practical application of industrial control technology to welding equipment, demonstrating that even relatively simple PLC-based systems can significantly improve welding quality and productivity. For engineering teams developing welding procedures for production fabrication, the key takeaway is that process control should be designed into the equipment from the outset rather than added as an afterthought. The investment in PLC-based control pays dividends in reduced rework, improved first-pass quality, and easier compliance with quality assurance requirements. As the industry moves toward Industry 4.0, further integration with digital manufacturing systems, including MES and ERP interfaces, will become increasingly important for comprehensive production management.