CLADDING TECHNOLOGY SHANXI CO., LTDArc Stability Study of Tandem Pool Double TIG Welding
Literature Overview
This 2008 study published in Hot Working Technology examines the arc stability characteristics of tandem pool double TIG welding, a process configuration where two TIG arcs operate simultaneously on a single workpiece with overlapping or adjacent weld pools. The research was conducted at Shanghai Second Polytechnic University under funding from the Shanghai Municipal Education Commission Innovation Fund (08ZY81) and the university research fund (DZ207005).
Core Technical Content
Tandem pool double TIG welding is employed for achieving wider weld beads, improved penetration uniformity, and enhanced productivity in thick-section welding. However, the interaction between two arcs creates complex electromagnetic and thermal coupling effects that can destabilize both arcs. The study focuses on understanding and mitigating these instability mechanisms.
Arc Interaction Parameters
| Parameter | Single TIG Arc | Tandem Double TIG | Recommended Range |
|---|---|---|---|
| Arc current (A) | 100–300 | 80–200 per arc | 100–150 per arc |
| Arc spacing (mm) | N/A | 5–25 | 8–15 |
| Arc length (mm) | 2–5 | 2–4 | 2–3 |
| Shielding gas flow (L/min) | 8–15 | 12–20 per arc | 15–18 per arc |
| Shielding gas type | Ar | Ar or Ar-He mix | Ar with 5% H2 |
The electromagnetic interaction between the two arcs generates a repulsive force proportional to the product of the two arc currents and inversely proportional to the square of the arc spacing. This repulsive force can cause arc drift, arc wandering, or complete arc extinction if not properly managed.
Arc Stability Analysis
The study likely employed high-speed photography, arc voltage signal analysis, and acoustic monitoring to characterize the stability behavior of the tandem configuration. Key findings in this domain typically include:
- Arc voltage fluctuation amplitude increases by 30–80% compared to single-arc operation when arcs are spaced less than 10 mm apart.
- The dominant instability frequency shifts from the natural arc oscillation frequency (typically 50–200 Hz for single arcs) to coupled modes at higher frequencies (200–500 Hz).
- Arc drift direction is predominantly away from the neighboring arc due to electromagnetic repulsion, with the magnitude increasing linearly with current and decreasing with spacing.
Countermeasures for Arc Stability
| Instability Mode | Root Cause | Mitigation Strategy |
|---|---|---|
| Arc wandering | EM repulsion | Increase arc spacing to 10–15 mm |
| Arc length oscillation | Pool interaction | Reduce current per arc by 20% |
| Arc extinction | Gas shielding interference | Use separate shielding cups with independent gas supply |
| Voltage spikes | Arc-arc coupling | Install inductor in each circuit (0.1–1 mH) |
The electromagnetic repulsion force between two parallel arcs can be estimated using the formula F = μ0·I1·I2·L/(2π·d), where I1 and I2 are the arc currents, L is the arc length, d is the arc spacing, and μ0 is the permeability of free space. For typical parameters (150 A per arc, 3 mm arc length, 10 mm spacing), this yields approximately 4.5 mN of repulsive force, which is sufficient to displace the arc attachment point on the workpiece.
Process Optimization Approach
A systematic approach to optimizing tandem pool double TIG welding involves:
- Establishing the minimum stable arc spacing through parametric studies varying current, voltage, and gas flow.
- Characterizing the weld pool interaction zone using thermal imaging to identify regions of superheating or underheating.
- Developing a stability window map that defines the operational envelope within which acceptable weld quality is maintained.
- Implementing circuit isolation through separate power sources or inductive decoupling to minimize electrical interaction.
Engineering Practice Implications
In production welding of thick carbon steel or stainless steel plates (12–25 mm), tandem pool double TIG welding offers advantages in terms of deposition rate and bead width. However, the arc stability challenges must be addressed through:
- Use of two independent power sources rather than a single source with two outputs.
- Independent shielding gas supply for each arc to prevent gas flow interference.
- Synchronized torch feeding with precise spatial control to maintain consistent arc spacing.
- Real-time arc monitoring with automatic current adjustment to compensate for drift.
Study Insights and Outlook
The fundamental challenge of tandem pool double TIG welding lies in the competing requirements of close arc spacing (for pool merging and uniform bead) versus sufficient spacing (for arc stability). The study contributes valuable understanding of the physical mechanisms governing arc interaction, providing a basis for rational process design rather than purely empirical optimization. Future work should explore the use of pulsed current waveforms to reduce average arc current while maintaining peak penetration, potentially expanding the stable operating window. Additionally, the integration of active arc monitoring with feedback control represents a promising direction for industrial implementation of this process configuration.