CLADDING TECHNOLOGY SHANXI CO., LTDMeasurement and Analysis of Arc Pressure in Coupled Arc Tungsten TIG Welding
Literature Overview
This study by Huang Yong, Hao Yanzhao, Qu Huaiyu, and Liu Ruilin from Lanzhou University of Technology (supported by the National Natural Science Foundation of China, Grant 51265029), published in the Journal of Welding (2013), investigates the arc pressure characteristics in coupled arc tungsten TIG welding. The coupled arc configuration, which combines two or more plasma streams or employs dual-electrode arrangements, represents an advanced welding technology with significant potential for enhanced productivity and penetration in thick-section fabrication.
Coupled Arc TIG Configuration
The coupled arc TIG process utilizes two closely spaced arcs that interact to create a modified arc pressure field. This interaction can produce higher arc forces, deeper penetration, and more stable arc characteristics compared to conventional single-arc TIG welding.
Arc Pressure Measurement Methodology
| Measurement Aspect | Method | Instrument |
|---|---|---|
| Arc force magnitude | Static force measurement | Load cell with strain gauge |
| Arc force distribution | Pressure-sensitive film | Fuji Prescale |
| Arc force temporal variation | Dynamic force measurement | High-frequency load cell |
| Arc column shape | High-speed photography | CCD camera |
Key Findings on Arc Pressure Characteristics
Effect of Arc Parameters on Arc Pressure
| Parameter | Variation | Arc Pressure Change | Mechanism |
|---|---|---|---|
| Welding current | 50-200 A | Increases proportionally | Higher current density increases electromagnetic force |
| Arc length | 2-8 mm | Non-monotonic relationship | Short arc: high pressure; long arc: reduced pressure |
| Coupling angle | 0-30° | Increases with angle | Arc interaction creates converging force |
| Electrode spacing | 2-10 mm | Optimal at 4-6 mm | Maximum interaction effect at intermediate spacing |
| Shielding gas flow | 5-20 L/min | Moderate increase | Gas momentum contributes to total force |
Arc Pressure Distribution Analysis
The coupled arc produces a distinctly different pressure distribution compared to single-arc TIG. The interaction zone between the two arcs exhibits peak pressure values that can exceed those of individual arcs by 30-50%. This enhanced pressure field results in:
- Deeper root penetration
- Narrower weld width relative to penetration depth
- Improved wetting of the root face
- Reduced likelihood of lack of fusion in narrow-gap configurations
Application to Pressure Vessel and Cladding Fabrication
The enhanced arc pressure characteristics of coupled arc TIG welding have direct relevance to several critical applications:
- Deep-penetration single-pass welding of thick-section pressure vessel components, reducing the number of weld passes and associated heat cycles
- Narrow-gap welding of clad pipe assemblies where maintaining low heat input while achieving full root penetration is essential
- Overlay welding where controlled arc pressure ensures uniform deposition and proper bond line formation
Comparison with Conventional TIG for Cladding Applications
| Performance Metric | Conventional TIG | Coupled Arc TIG |
|---|---|---|
| Penetration depth | 1-3 mm per pass | 3-6 mm per pass |
| Deposition rate | 0.5-1.5 kg/h | 1.5-3.0 kg/h |
| HAZ width | 2-4 mm | 3-5 mm |
| Arc stability | Good | Excellent |
| Equipment complexity | Low | Moderate |
| Process cost | Low | Moderate |
Critical Analysis and Engineering Considerations
While the enhanced arc pressure offers significant productivity advantages, several engineering concerns must be addressed:
- Heat input management — The increased arc force comes with higher energy delivery, which must be carefully controlled for cladding applications where thermal damage to the substrate is unacceptable
- Process repeatability — The coupled arc configuration requires precise alignment and synchronization, adding complexity to automated welding systems
- Qualification requirements — Under NB/T 47014 and ASME IX, coupled arc TIG would require separate qualification as a distinct welding process variant
The study demonstrates that fundamental understanding of arc physics remains essential for developing advanced welding processes that can address the demanding requirements of modern pressure vessel and cladding fabrication.