CLADDING TECHNOLOGY SHANXI CO., LTDDevelopment of Plasma-MIG Composite Arc Welding Technology
Literature Overview
This paper by Wang Xueyuan, Yang Xueqin, Yang Tao, and Gao Hongming, published in Welding in 2012, provides a comprehensive review and analysis of the development of plasma-MIG composite arc welding technology. The research was conducted at the Shanghai Academy of Spaceflight Technology's Precision Machinery Research Institute and the State Key Laboratory of Modern Welding at Harbin Institute of Technology. This work represents a significant contribution to the field of hybrid welding technology, addressing the limitations of individual plasma arc welding (PAW) and gas metal arc welding (GMAW) processes and demonstrating how their combination can achieve superior welding performance.
Core Technical Content
Individual Process Characteristics
| Parameter | Plasma Arc Welding (PAW) | GMAW (MIG) |
|---|---|---|
| Arc power density | 1000–10000 W/mm² | 100–500 W/mm² |
| Penetration depth | Deep, narrow | Moderate, wider |
| Deposition rate | Low (0.5–2 kg/h) | High (5–20 kg/h) |
| Heat input | Concentrated, low total | Higher total, more diffuse |
| Bead width | Narrow | Wider |
| Spatter | Very low | Moderate to high |
| Arc stability | Excellent | Good |
| Equipment cost | High | Moderate |
| Flexibility | Limited | High |
| Travel speed | High | Moderate |
Plasma-MIG Composite Arc Welding Configuration
The plasma-MIG composite arc welding process combines a plasma arc and a GMAW arc in a coordinated configuration. The most common configurations include:
- Coaxial configuration: The plasma arc is positioned at the center, with the MIG torch surrounding it. This provides maximum arc interaction and synergy.
- Offset configuration: The plasma torch and MIG torch are positioned at an angle to each other, allowing independent control of the two arcs.
- Sequential configuration: The plasma arc leads the MIG arc, preheating the workpiece and creating a keyhole that the MIG arc fills with molten metal.
Synergistic Effects of Plasma-MIG Combination
The plasma-MIG composite arc welding process exhibits several synergistic effects that are not achievable with either process alone:
- Enhanced penetration: The plasma arc creates a deep, narrow keyhole, while the MIG arc provides additional molten metal to fill the keyhole, resulting in deeper penetration than either process alone.
- Improved arc stability: The plasma arc stabilizes the overall arc column, reducing arc wandering and improving weld bead consistency.
- Reduced spatter: The plasma arc's concentrated heat input reduces the overall arc length and minimizes spatter formation.
- Higher productivity: The combined process achieves deposition rates comparable to MIG while maintaining the penetration characteristics of plasma welding.
- Reduced distortion: The concentrated heat input from the plasma arc reduces the overall heat input, minimizing thermal distortion.
- Wider parameter window: The combination of the two processes provides a wider range of achievable welding conditions than either process alone.
Key Process Parameters
| Parameter | Typical Range | Effect on Weld Quality |
|---|---|---|
| Plasma current | 20–80 A | Controls penetration depth and keyhole formation |
| MIG current | 150–400 A | Controls deposition rate and bead width |
| MIG voltage | 20–30 V | Controls arc length and droplet transfer |
| Plasma gas flow | 10–30 L/min | Controls arc stability and shielding |
| Shielding gas flow | 15–30 L/min | Controls atmospheric contamination |
| Travel speed | 200–800 mm/min | Controls heat input and bead geometry |
| Torch offset angle | 0°–15° | Controls arc interaction and penetration |
| Plasma gas type | Ar, Ar+H₂, Ar+He | Controls arc characteristics and heat input |
| MIG shielding gas | Ar, Ar+CO₂, Ar+O₂ | Controls arc stability and penetration |
Microstructural and Mechanical Property Analysis
The plasma-MIG composite arc welding process produces weld joints with distinct microstructural characteristics compared to conventional welding processes:
- Narrower HAZ: The concentrated heat input from the plasma arc results in a narrower HAZ with less microstructural alteration.
- Refined grain structure: The rapid solidification rates associated with the plasma arc promote fine grain structures in the weld metal.
- Reduced dilution: The keyhole welding mode of the plasma arc reduces the amount of base metal melted, resulting in lower dilution rates.
- Improved mechanical properties: The refined microstructure and reduced HAZ width contribute to improved mechanical properties in the weld joint.
Process Analysis and Engineering Implications
Comparison with Conventional Welding Processes
| Aspect | Conventional MIG | Conventional PAW | Plasma-MIG Composite |
|---|---|---|---|
| Penetration | Moderate | Deep | Deep to very deep |
| Deposition rate | High | Low | High |
| Bead width | Wide | Narrow | Moderate |
| HAZ width | Wide | Narrow | Narrow |
| Spatter | High | Very low | Low |
| Productivity | High | Low | High |
| Equipment complexity | Low | Moderate | High |
| Parameter flexibility | High | Low | Moderate |
| Cost per unit weld length | Low | High | Moderate |
Application Relevance to Cladding and Bimetal Fabrication
The plasma-MIG composite arc welding technology has significant potential for cladding and bimetal product manufacturing:
- High-dilution cladding: For applications where high dilution is acceptable or even desired, the plasma-MIG process can provide faster deposition rates while maintaining good penetration and bonding.
- Low-dilution cladding: For applications requiring low dilution, the plasma arc's keyhole welding mode can be used to deposit thin, uniform layers with minimal base metal melting.
- Thick overlay layers: The combination of high deposition rate and deep penetration makes the plasma-MIG process suitable for building up thick overlay layers in a single pass or few passes.
- Repair welding: The precise heat input control and reduced distortion make the plasma-MIG process ideal for repair welding of pressure vessel components and heat exchanger tubes.
Standards and Qualification Considerations
| Standard | Relevance to Plasma-MIG | Key Requirements |
|---|---|---|
| ASME IX | Procedure qualification | Must document both plasma and MIG parameters |
| NB/T 47014 | Chinese welding procedure qualification | Similar to ASME IX with Chinese-specific requirements |
| AWS D1.1 | Structural steel welding | Plasma-MIG may require additional qualification |
| ISO 15614 | Welding procedure qualification | International standard for procedure qualification |
| API 934 | Welding procedure qualification | Specific to pressure equipment |
The qualification of plasma-MIG composite arc welding procedures requires careful documentation of both the plasma and MIG parameters, as well as demonstration of the interaction between the two processes. The procedure qualification test must demonstrate that the resulting weld metal properties meet the required specifications and that the process is repeatable.
Key Questions and Reflections
- Process control and monitoring: The plasma-MIG composite arc welding process involves multiple parameters that interact in complex ways. Real-time monitoring and control systems are essential to maintain consistent weld quality. What are the most effective sensors and control algorithms for this purpose?
- Scalability: Laboratory-scale demonstrations of plasma-MIG welding