Observation of Thermocapillary Effect in Gas -Assisted CO2 Laser Cutting of Steel

Investigations of melt’s dynamics have been performed with pyrometer in the gasjet-assisted CO2 laser cutting. Pyrometer consists of 4 sensors and local luminosity of metal melt has been measured precisely on different depth along front of cutting with long dimension resolution about 0.1 mm and with time resolution as short as 0.06 ms. The results of data processing of brightness temperature are reported for laser cutting of mild-steel plate 3 mm, 6 mm and 10 mm thick, that allows obtaining spectra of melt’s surface deformation for different values of cutting velocity and assisted gas pressure. The generation of capillary-wave turbulence following thermo-capillary effect can be observed in the locations, where intensity of radiation of CO2 laser on melt’s surface exceeds 1 MW/cm2. The R-M-S of temperature fluctuations is greater than 10 K in the range of sub-millimeter capillary waves. Thus, an additional mechanism of the anomalous absorption on the front of cutting can compensate the low absorption of the metal in case of 10.6 μm laser in comparison with the absorption of the metal in the near infrared range

Pyrometric Monitoring of Gas-Assisted Cutting of Steel Using Fiber Laser

Measurements of the temperature in zone of action of laser radiation on the molten metal have been performed. The results are reported for different speed of cutting of mild-steel plate of 3 mm-thick with high-power fiber laser; oxygen was used as an assisted gas. Researches demonstrate that fluctuations of local temperature are related to unequal radiation absorption that associates with local deformations of surface of melt. Thus noise spectrum of those fluctuations reflects turbulent surface deformation caused by gas jet and capillary waves. The standard temperature deviation does not exceed 10 K on the frequency of 7 KHz and above, and power law of spectrum of density of fluctuations of local temperature is about “-2.8” in range of capillary turbulence. Thus we can distinguish radiation pulsation due to laser cutting from other processes of radiation affection to the sample, including unwanted, degrading the quality of technological operations. The results of investigation can be useful for monitoring laser cutting process