CLADDING TECHNOLOGY SHANXI CO., LTDKTIG-MIG Composite Welding Arc Droplet Behavior and Temperature Field Analysis
Literature Overview
This 2025 study from Qingdao University of Technology, Harbin University of Science and Technology, Harbin Institute of Technology (Weihai), and Jingdian Heavy Industry Group investigates the synergistic behavior of the KTIG (Keyhole TIG) and MIG composite welding process. Funded by the National Natural Science Foundation of China and Shandong Provincial programs, this research addresses a frontier technique that combines the deep penetration of keyhole TIG with the high deposition rate of MIG welding.
Core Technical Principles
The KTIG-MIG composite process operates by positioning a high-current TIG arc (typically 200-400 A) to create a keyhole cavity, while a MIG torch deposits filler metal into and around the keyhole. This configuration achieves deposition rates of 2-4 kg/h with penetration depths exceeding 8 mm in single-pass welding of medium-thick plates.
Arc-Droplet Interaction Mechanisms
The electromagnetic forces, plasma drag forces, and surface tension forces acting on the MIG droplet are modified by the presence of the TIG arc. The TIG arc creates a strong upward plasma flow that influences droplet detachment frequency and transfer mode. Key observations include:
| Parameter | TIG Arc | MIG Arc | Combined Effect |
|---|---|---|---|
| Current | 250-400 A | 150-250 A | Total 400-600 A |
| Voltage | 12-18 V | 18-25 V | Arc stability enhanced |
| Penetration | 5-12 mm | 1-3 mm | 8-15 mm total |
| Deposition rate | 0 | 2-4 kg/h | 2-4 kg/h |
| Travel speed | 150-400 mm/min | 150-400 mm/min | 200-500 mm/min |
Temperature Field Characteristics
The temperature field in KTIG-MIG composite welding exhibits a bimodal distribution. The TIG arc creates a deep, narrow high-temperature zone (exceeding 3000°C at the arc root), while the MIG arc produces a broader, slightly lower temperature region. The combined thermal profile results in a wider heat-affected zone compared to pure TIG but with significantly deeper penetration than pure MIG.
The peak temperature in the weld pool center can reach 2800-3200°C, while the HAZ extends 15-25 mm from the weld centerline depending on plate thickness and travel speed. The cooling rate at the fusion boundary typically ranges from 10-50°C/s, which is slower than pure MIG but faster than pure TIG.
Droplet Transfer Behavior
The presence of the TIG arc fundamentally alters droplet transfer. In pure MIG, short-circuiting or globular transfer dominates at lower currents, while spray transfer occurs at higher currents. In KTIG-MIG, the strong electromagnetic field of the TIG arc accelerates droplet detachment, promoting a more stable spray transfer mode at lower MIG currents than would normally be required.
The droplet diameter typically ranges from 1.2-1.8 mm, with detachment frequency increasing by 30-50% compared to standalone MIG operation. This enhanced detachment rate contributes to improved weld bead uniformity and reduced spatter.
Engineering Applications and Quality Control
For cladding and overlay applications, the KTIG-MIG process offers several advantages:
- Single-pass deep cladding: Enables deposition of thick overlay layers with good bonding in fewer passes.
- Reduced dilution: The keyhole effect concentrates the heat, potentially reducing substrate dilution in the first layer.
- High productivity: Deposition rates 3-5 times higher than conventional TIG cladding.
- Process flexibility: Suitable for both ferrous and non-ferrous base materials.
Defect Analysis
Common defects in KTIG-MIG composite welding include:
- Undercut: Caused by excessive TIG current or travel speed; mitigated by reducing TIG current by 10-15% or increasing MIG current.
- Porosity: Results from incomplete keyhole collapse or gas entrapment; controlled by proper shielding gas flow and torch angle.
- Washout: Occurs when TIG arc is too close to the MIG wire; prevented by maintaining proper torch-to-wire spacing (3-5 mm).
Key Questions and Reflections
The primary engineering question is how to maintain consistent keyhole stability during production welding. Keyhole collapse can lead to weld defects such as incomplete fusion or excessive spatter. Real-time monitoring of arc voltage fluctuations and acoustic signals can provide early warning of keyhole instability.
Study Insights and Implications
The KTIG-MIG composite welding technology represents a paradigm shift in overlay and cladding operations. For bimetal pressure vessel fabrication, this technology could enable single-pass application of corrosion-resistant alloy cladding layers with thicknesses exceeding 5 mm, significantly reducing fabrication time and cost. However, the complex thermal cycling and the interaction between two arcs demand sophisticated process monitoring and control systems to ensure consistent quality.