CLADDING TECHNOLOGY SHANXI CO., LTDThree-Dimensional Surface Evolution of Pulsed TIG Weld Pool Using Structured Laser Reflection
Literature Overview
This 2016 publication from Lanzhou University of Technology, supported by the National Natural Science Foundation of China (Grant 51205179), presents a significant advancement in weld pool monitoring technology. The research, conducted at the State Key Laboratory of Advanced Processing and Recycling of Non-ferrous Metals, addresses the challenge of real-time observation of the weld pool surface topography during pulsed TIG welding. The collaboration with Changsha Zhongtai Automobile Industry Co., Ltd. indicates practical industrial application potential, particularly in automotive manufacturing where welding quality directly impacts structural integrity.
Core Technical Methodology
Structured Laser Reflection Principle
The technique employs a structured laser light sheet projected onto the weld pool surface, with the reflected pattern captured by a high-speed camera. The deformation of the structured pattern on the weld pool surface encodes three-dimensional topographical information. By analyzing the spatial distortion of the laser pattern, the complete three-dimensional surface profile of the weld pool can be reconstructed in real time.
The physical basis relies on the specular reflection characteristics of the molten metal surface. The structured laser pattern, typically consisting of multiple parallel lines or a grid pattern, provides a known reference geometry. When reflected from a curved or deformed weld pool surface, the pattern undergoes measurable distortions that can be mathematically decoded to extract surface coordinates.
Experimental Configuration
The experimental setup typically includes a pulsed TIG welding system, a structured laser projection system, a high-speed camera, and a computational processing system. The laser projection angle and camera viewing angle are carefully optimized to maximize surface coverage while minimizing interference with the welding arc.
| Parameter | Typical Value | Notes |
|---|---|---|
| Laser Wavelength | 632.8-670 nm | He-Ne or diode laser |
| Laser Power | 5-50 mW | Sufficient for reflection imaging |
| Camera Frame Rate | 1000-10000 fps | Captures dynamic surface evolution |
| Spatial Resolution | 0.1-1 mm | Depends on optical system |
| Temporal Resolution | 0.1-1 ms | Synchronized with pulse frequency |
| Welding Current | 100-200 A | Pulsed TIG parameters |
| Pulse Frequency | 1-50 Hz | Controls pulse on/off time |
Key Technical Challenges
The primary challenge in weld pool surface observation is the intense light and electromagnetic interference from the welding arc. The structured laser reflection method addresses this by using optical filtering and synchronization techniques to separate the laser signal from the arc radiation. Additionally, the high temperature of the weld pool surface creates convective flow patterns and splashing that complicate surface reconstruction.
Numerical Simulation Integration
The research connects experimental observations with numerical simulation models of weld pool dynamics. The three-dimensional surface data provides boundary conditions for computational fluid dynamics (CFD) simulations of the weld pool. Key physical phenomena modeled include:
- Electromagnetic force (Lorentz force) acting on the molten metal
- Marangoni convection driven by surface tension gradients
- Buoyancy-driven natural convection
- Surface tension effects at the free surface
- Heat transfer and phase change
The comparison between experimental surface profiles and numerical predictions validates the simulation models and identifies areas for improvement. Discrepancies often arise from uncertain material property data at elevated temperatures, simplified boundary conditions, and the complexity of arc-metal interaction modeling.
Engineering Significance
For cladding and overlay welding applications, understanding weld pool surface evolution is critical for predicting weld geometry, controlling dilution, and ensuring proper bond quality. In bimetal pressure vessel fabrication, where overlay layers must achieve specific thickness and composition uniformity, real-time weld pool monitoring enables process control and quality assurance.
The structured laser reflection technique offers several advantages over alternative methods such as infrared thermography or acoustic emission. It provides true three-dimensional surface information rather than merely temperature distribution, and it operates without physical contact with the weld pool. The technique is particularly valuable for pulsed TIG welding, where the periodic nature of the process creates reproducible surface evolution patterns that can be systematically studied.
Study Insights and Implications
This research represents a meaningful contribution to the field of welding process monitoring and control. The structured laser reflection method provides a practical, non-contact approach to weld pool surface measurement that can be integrated into industrial welding systems. For engineers working in cladding and bimetal fabrication, the ability to monitor weld pool geometry in real time opens possibilities for adaptive process control, automated defect detection, and improved quality assurance. The work demonstrates that advanced optical measurement techniques, once confined to laboratory research, can be adapted for practical industrial applications with appropriate engineering considerations for arc interference and environmental robustness.