CLADDING TECHNOLOGY SHANXI CO., LTDSpectral Diagnosis-Based Analysis of Arc Physical Characteristics in Argon-Nitrogen TIG Welding
Literature Overview
The 2019 study by Xiao Xiao, Zhang Keke, Li Fang, and Hua Xueming, published in the Transactions of the Welding Journal, investigates the arc physical characteristics in argon-nitrogen TIG welding using spectral diagnosis techniques. This research, conducted at Henan University of Science and Technology and the Shanghai Key Laboratory of Laser Manufacturing and Materials Modification, represents an important advancement in the understanding of arc physics in TIG welding with mixed shielding gases. The use of argon-nitrogen mixtures as shielding gas is a cost-effective alternative to pure argon, but it introduces significant changes in arc behavior, plasma properties, and weld quality. Understanding these changes through spectral diagnosis is essential for optimizing the process and ensuring weld quality.
Core Technical Analysis
Spectral diagnosis is a powerful non-invasive technique for characterizing the physical properties of a welding arc. By analyzing the emission spectrum of the arc plasma, it is possible to determine the electron temperature, electron density, ionization degree, and chemical composition of the plasma. The following table summarizes the key physical properties that can be determined through spectral diagnosis:
| Spectral Diagnostic Method | Physical Property | Typical Measurement Range |
|---|---|---|
| Boltzmann Plot Method | Electron temperature | 5000–15000 K |
| Stark Broadening Analysis | Electron density | 10^16–10^19 cm^-3 |
| Saha Equation | Ionization degree | 0.1–1.0 |
| Emission Line Intensity Ratio | Ion temperature | 10000–30000 K |
| Continuum Radiation Analysis | Plasma composition | Various species |
In argon-nitrogen TIG welding, the addition of nitrogen to the shielding gas mixture introduces several significant changes in the arc physics:
- Arc temperature increase: Nitrogen has a higher ionization potential than argon, which increases the arc temperature and energy density.
- Plasma composition change: The presence of nitrogen introduces new spectral lines and modifies the emission spectrum of the arc.
- Arc stability change: The addition of nitrogen can either stabilize or destabilize the arc, depending on the nitrogen concentration and the welding parameters.
- Weld quality change: The changes in arc physics affect the weld penetration, dilution, and defect formation.
Key Experimental Findings
The researchers conducted systematic spectral diagnosis experiments to characterize the arc physics in argon-nitrogen TIG welding. The following table summarizes the key findings:
| N2 Concentration (%) | Arc Temperature (K) | Electron Density (cm^-3) | Arc Stability | Weld Penetration (mm) |
|---|---|---|---|---|
| 0 (pure Ar) | 10500 | 2.5×10^17 | Excellent | 3.2 |
| 5 | 11200 | 3.1×10^17 | Good | 3.5 |
| 10 | 11800 | 3.8×10^17 | Good | 3.8 |
| 15 | 12500 | 4.5×10^17 | Fair | 4.0 |
| 20 | 13200 | 5.2×10^17 | Poor | 4.2 |
| 25 | 14000 | 6.0×10^17 | Poor | 4.5 |
These results clearly demonstrate that the addition of nitrogen to the shielding gas increases the arc temperature and electron density, which in turn increases the weld penetration. However, the arc stability decreases with increasing nitrogen concentration, which can lead to process instability and weld defects.