Oscillations of keyhole pressure and plasma radiation during cw CO2 laser welding

Z. Szymanski; J. Hoffman; J. Kurzyna; A. Kolasa; J. Jakubowski

doi:10.1117/12.405976

2 November 2000 Oscillations of keyhole pressure and plasma radiation during cw CO₂ laser welding

Z. Szymanski, J. Hoffman, J. Kurzyna, A. Kolasa, J. Jakubowski

Author Affiliations +

Proceedings Volume 4238, Laser Technology VI: Applications; (2000) https://doi.org/10.1117/12.405976
Event: Laser Technology VI, 1999, Szczecin, Poland

Abstract

The analysis of the fluctuations of pressure and plasma radiation observed during welding with a cs CO₂ laser is presented. Welding was done with a continuous wave CO₂ laser. Photon Sources VFA 2500, operating at the power of 1.75-2 kW. The welded materials were mild and stainless steel sheets 0.8-2 mm thick. Shielding gas was argon or helium. Plasma fluctuations were registered in monochromatic radiation with the use of a monochromator and photomultiplier while the pressure variations - with a microphone in the frequency range of 20-2x10⁴ Hz. T he results show that the optical and acoustic signals emitted during the welding process can be used for process monitoring. The most promising method is a frequency analysis based on the Fourier techniques. The Fourier spectra (power spectrum densities - PSD) of pressure waves and plasma emission change with the welding conditions and hence contain information about the process of welding. Power spectra of both signals and their coherence are studied in dependence on the welding conditions. Generally two intrinsic frequency peaks are always present but the relative peak amplitude, exact frequency and width depend on welding conditions. In the case of mild steel 0.8 mm thick when helium is used as the shielding gas these peaks correspond to the frequencies of approximately 1.3 kHz and approximately 3.7 kHz on the PSD of both signals, optical and acoustic. The clear dependence of the measured signals on process parameters shows that they can be used to find the best welding conditions.

Citation Download Citation

Z. Szymanski, J. Hoffman, J. Kurzyna, A. Kolasa, and J. Jakubowski "Oscillations of keyhole pressure and plasma radiation during cw CO₂ laser welding", Proc. SPIE 4238, Laser Technology VI: Applications, (2 November 2000); https://doi.org/10.1117/12.405976

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