Influence factors of precision of femtosecond laser ablating 0Cr18Ni9 stainless steel

The 0Cr18Ni9 stainless steel sheet was cut and drilled by a femtosecond laser, and the influence factors of machining accuracy of femtosecond laser ablation were studied. The morphology of stainless steel ablation zone and metallographic structure of cutting seam were examined by means of Nikon SMZ800 optical microscope and 4XC optical metallographic microscope. Based on the laser speckle on the surface of stainless steel observed by a coaxial CCD in the process of stainless steel ablation, the laser beam divergent propagation behavior was simulated using COMSOL Multiphysic numerical simulation software, and the beam divergence angle was calculated. Experimental and simulation results demonstrate that when the laser repetition rate is 5 kHz, the edge of cutting seam and hole are obviously blackened; metallographic phase shows that grain size significantly gets larger at cutting seam and heat affected zone cant be avoided in the femtosecond laser ablation process; metal-air hybrid plasma induced by ultra-high power density femtosecond laser makes the laser beam scatter along the direction of propagation in the process of machining, the divergence angle is between 6 to 10. The existence of heat affected zone and the behavior of the metal-air hybrid plasma are the main factors influencing the precision of femtosecond laser ablation.