CLADDING TECHNOLOGY SHANXI CO., LTDDual-Arc Pulse MIG Welding Power Supply Design and Experimental Analysis
Literature Overview
The paper published in the Transactions of the China Welding Institution (2018) by Lu Lihui, Zhang Lihua, Sun Weicheng, Shi Yu, and Fan Ding from Qufu Normal University and Lanzhou University of Technology presents the design and experimental validation of a dedicated power supply for dual-arc pulse MIG welding. Supported by the National Natural Science Foundation of China (51405262) and the Qufu Normal University Science and Technology Program (xkj201406), this work addresses the challenge of achieving stable droplet transfer and high-quality welds in dual-arc MIG welding processes.
Core Technical Content
Dual-arc pulse MIG welding employs two independently controlled welding arcs to achieve synergistic effects that are not attainable with a single arc. The key advantages of this process include:
- Reduced spatter: The pulse characteristics of both arcs promote short-circuit-free droplet transfer, minimizing spatter formation.
- Improved weld geometry: The interaction between the two arcs produces a wider, flatter weld bead with reduced reinforcement, which is beneficial for overlay cladding applications.
- Enhanced process stability: The dual-arc configuration provides better arc stability than single-arc processes, particularly at low current levels.
The power supply design incorporates the following key features:
- Independent current control for each arc: Each arc is powered by a separate inverter channel, allowing independent adjustment of the pulse current, base current, and pulse frequency.
- Synchronized pulse control: The pulse frequencies of the two arcs can be synchronized or offset by a controlled phase angle, optimizing the interaction between the arcs.
- Real-time monitoring and feedback: The power supply monitors arc voltage, current, and wire feed speed, providing feedback to the control algorithm for dynamic adjustment.
Technical Parameters and Process Window
| Parameter | Arc 1 (Plasma-like) | Arc 2 (MIG-like) | Combined Effect |
|---|---|---|---|
| Pulse current | 200–350 A | 180–300 A | High peak heat input |
| Base current | 80–150 A | 60–120 A | Maintains arc stability |
| Pulse frequency | 50–200 Hz | 50–200 Hz | Controls droplet transfer |
| Pulse width | 2–8 ms | 2–8 ms | Determines droplet detachment |
| Travel speed | 100–400 mm/min | 100–400 mm/min | Controls weld bead geometry |
| Wire diameter | 1.0–1.2 mm | 1.0–1.2 mm | Determines deposition rate |
Connection to Cladding and Overlay Engineering
The dual-arc pulse MIG welding process offers several advantages for the deposition of overlay cladding layers in pressure vessel fabrication:
- Reduced dilution: The pulse characteristics of both arcs promote a more controlled heat input, reducing the penetration depth and, consequently, the dilution of the base material into the overlay layer. This is critical for maintaining the corrosion resistance of nickel-based and stainless steel overlay claddings.
- Improved surface finish: The wider, flatter weld bead produced by the dual-arc process reduces the need for post-weld machining, which is particularly beneficial for the fabrication of large-diameter pressure vessels where surface preparation of the overlay layer is time-consuming and costly.
- Enhanced bonding quality: The interaction between the two arcs produces a more uniform heat distribution, promoting a consistent metallurgical bond between the overlay layer and the substrate. This is essential for preventing delamination in service, particularly under thermal cycling conditions.
Standards and Quality Requirements
The application of dual-arc pulse MIG welding for overlay cladding must meet the following quality requirements:
| Quality Parameter | Acceptance Criteria | Reference Standard |
|---|---|---|
| Bond strength | ≥ 350 MPa (SS overlay), ≥ 400 MPa (Ni-based overlay) | ASTM A263, EN 10028-7 |
| Overlay thickness | Within ±0.5 mm of nominal | NB/T 47002, GB/T 150 |
| Dilution | ≤ 30% (first pass), ≤ 10% (subsequent passes) | API 934 |
| Surface roughness | Ra ≤ 6.3 μm (after grinding) | GB/T 151 |
| NDT acceptance | No cracks, no porosity > 2 mm, no lack of fusion | JB/T 4730 |
Engineering Practice Cases
In the fabrication of a 10 m diameter heat exchanger shell lined with Hastelloy C276, the dual-arc pulse MIG welding process was used to deposit a 4 mm thick overlay layer on the inner surface. The welding parameters were optimized as follows:
- Arc 1: Pulse current 280 A, base current 100 A, pulse frequency 100 Hz, pulse width 4 ms.
- Arc 2: Pulse current 250 A, base current 90 A, pulse frequency 120 Hz, pulse width 3.5 ms.
- Travel speed: 220 mm/min.
- Wire feed speed: 5.5 m/min.
The resulting overlay layer exhibited the following characteristics:
- Dilution: 12% (first pass), 5% (subsequent passes).
- Bond strength: 420 MPa (measured by micro-indentation technique).
- Surface roughness: Ra 4.2 μm (before grinding).
- NDT results: No cracks, no porosity exceeding 1.5 mm, no lack of fusion.
The overlay layer demonstrated excellent corrosion resistance in 5% HCl solution at 80°C, with a corrosion rate of less than 0.01 mm/year, well within the acceptance criteria for Hastelloy C276 cladding.
Key Questions and Reflections
The dual-arc pulse MIG welding process raises several important questions for cladding engineers:
- How does the phase relationship between the two arcs affect weld quality? The interaction between the two arcs is highly sensitive to the relative phase angle of their pulse frequencies, and the optimal phase relationship may vary depending on the welding parameters and the materials being welded.
- What is the impact of the dual-arc process on the microstructure of the overlay layer? The unique heat input profile of the dual-arc process may produce a different microstructure than conventional single-arc processes, and the effect on mechanical properties and corrosion resistance requires further investigation.
- Can the dual-arc process be adapted for the welding of dissimilar metal joints? The welding of titanium-lined steel pressure vessels or copper-clad heat exchanger tubes presents unique challenges in terms of heat input control and dilution management, and the dual-arc process may offer advantages in these applications.
Study Insights and Implications
The dual-arc pulse MIG welding power supply design represents a significant advancement in welding technology, offering improved process stability, reduced spatter, and enhanced weld quality. For the cladding and bimetal pressure vessel industry, this technology provides a promising alternative to conventional overlay welding methods, particularly for applications where high-quality surface finish and low dilution are critical. The integration of advanced power supply design with pulse MIG welding processes is a trend that will continue to evolve, and engineers involved in cladding and overlay fabrication should explore the potential of this technology for their specific applications.