Dual TIG Active Arc Welding Process Development

Literature Overview

This study by Zhang J., Guo C., Shao P.Z., Wang X.X., and Fan D. (2022) from Chongqing University of Technology and the Chongqing Engineering Research Center of Special Welding Materials and Technology investigates a novel dual TIG active arc welding process. The research was supported by the National Natural Science Foundation of China (Grant No. 51705054) and the Chongqing Municipal Education Commission Science and Technology Research Project (KJQN202101135). The dual TIG process represents an advanced welding technology that combines two independent GTAW arcs to achieve enhanced welding capabilities, including increased deposition rate, improved weld quality, and reduced distortion compared to conventional single-arc TIG welding.

Process Configuration and Working Principle

The dual TIG process employs two independently controlled GTAW torches operating simultaneously or in a staggered configuration. The two torches may be arranged in several configurations:

Configuration	Description	Application
Parallel dual torch	Two torches side by side, welding simultaneously	Thick section welding, high deposition rate
Leading-trailing	One torch leads, one trails, both depositing weld metal	Multi-pass welding with reduced interpass time
Oscillating dual torch	Two torches with synchronized oscillation	Wide bead deposition, fill welding
Alternating	Torch 1 welds, then torch 2 welds in sequence	Controlled heat input, reduced distortion

The "active arc" designation likely refers to the use of an active gas (such as CO₂ or a CO₂/Ar mixture) or active flux to modify the arc characteristics, improve penetration, or enhance the welding process. In the context of Chinese welding research, "active arc" may also refer to the use of special electrode coatings or arc conditioning techniques to stabilize and intensify the arc.

Advantages Over Conventional Single-Arc TIG

The dual TIG process offers several advantages that are directly relevant to cladding and overlay applications:

Increased deposition rate: Two arcs depositing simultaneously can double the metal deposition rate, reducing welding time for thick overlay layers.
Reduced heat input per pass: Each arc operates at lower current than a single arc would need for the same total heat input, resulting in narrower HAZ and reduced distortion.
Improved weld quality: The interaction between the two arcs can produce more uniform heat distribution, reducing the risk of solidification cracking and improving grain refinement.
Flexibility in parameter control: Independent control of each arc allows optimization of both penetration and deposition characteristics.
Reduced interpass temperature management: With two arcs operating in close proximity, the interpass temperature is naturally managed, reducing the risk of excessive interpass heating.

Process Parameters and Optimization

The dual TIG process introduces additional parameters compared to conventional TIG welding:

Parameter	Typical Range	Influence
Torch separation distance	5–30 mm	Affects arc interaction and heat distribution
Torch angle	5°–25° from normal	Controls penetration profile and bead shape
Current balance ratio	0.5:1 to 1:1	Determines relative contribution of each arc
Travel speed	100–400 mm/min	Controls heat input and weld geometry
Arc voltage	14–22 V per torch	Controls arc length and penetration
Shielding gas flow	8–20 L/min per torch	Adequate protection of both arcs

The interaction between the two arcs is governed by electromagnetic forces, gas flow patterns, and thermal coupling. When the torches are closely spaced, the arcs may interact through electromagnetic forces (arc force interaction) and shared gas flow patterns, potentially producing a combined arc with enhanced penetration or a wider heat distribution.

Applications in Cladding and Bimetal Fabrication

The dual TIG process has several promising applications in the cladding and bimetal fabrication domain:

Thick overlay deposition: For nickel-alloy overlay on carbon steel base plates, the dual TIG process can deposit thick overlay layers (3–6 mm) in fewer passes, reducing total welding time and thermal cycles.
Reduced dilution control: By operating each arc at lower current, the dilution rate per pass can be controlled more precisely, which is critical for maintaining the corrosion resistance of nickel-alloy overlays.
Multi-material overlay: The two torches can be equipped with different filler materials, enabling graded or multi-layer overlay with tailored properties.
Large-area cladding: For large surface area cladding (heat exchanger tubes, pressure vessel heads), the dual TIG process can cover larger areas per unit time.
Repair welding: For repair of damaged cladding, the dual TIG process provides enhanced penetration and deposition in a single operation.

Defect Analysis and Countermeasures

Defect	Cause in Dual TIG	Countermeasure
Incomplete fusion between arcs	Excessive torch separation	Reduce separation distance
Excessive dilution	High combined heat input	Reduce individual arc currents
Porosity	Inadequate gas shielding of second arc	Increase gas flow, use trailing shield
Cracking	Rapid solidification of combined weld	Add heat input, use appropriate filler
Bead irregularity	Arc interaction instability	Optimize torch angle and separation

Summary

The dual TIG active arc welding process represents a significant advancement in GTAW technology, offering enhanced deposition rates, improved weld quality, and reduced distortion compared to conventional single-arc TIG welding. For engineers involved in cladding and overlay fabrication, this technology provides new opportunities for efficient deposition of thick corrosion-resistant layers while maintaining tight control over dilution and weld quality. The process requires careful optimization of torch separation, current balance, and travel speed to achieve optimal results, and qualification procedures must be developed to ensure regulatory compliance for pressure vessel applications.