Laser Cutting; Experimental Measurement of Fluctuations in Cut Front Temperature and Morphology

Simulations of laser cutting need experimental measurements of the cutting front geometry and its temperature for validation purposes. A combined polarization goniometer and quotient pyrometer was used to measure these values for a cut in 10 mm stainless steel using a framerate of 75 kHz and a spatial resolution of 36 μm. For the first time, synchronized geometric and temperature measurements are given for a laser cutting front. These measurements show that, for 1 μm wavelength laser cutting of stainless steel, one of the main mechanisms of thermal and material flow involves the movement of hot ‘humps’ of liquid down the cutting front. These mobile humps experience an enhanced absorption of laser radiation on their upper surface and a reduced absorbed power density on their lower part, and may even cast a shadow on the cut front immediately below them. In this work, these phenomena resulted in local temperature fluctuations of 800 K, including temperature drops to 200 K below the melting temperature for durations of up to approximately 200 µs.