Study of the dynamics of material removal processes in combined pulse laser drilling of alumina ceramic

Combined pulse laser (CPL), one of the hybrid laser processing technologies, has proven to be a reliable tool for the high-quality and high-efficiency material processing. In CPL drilling, the nanosecond laser has been proven that it can improve the drilling performance of the millisecond laser by increasing the laser absorption or improving the sputtering of the melt. However, the dynamics of material removal processes regarding CPL drilling have not been systematically investigated. In this paper, a numerical model of the CPL drilling of alumina ceramic was built to reveal the dynamic processes of the energy absorption, phase transformation, and microhole deformation process. The millisecond laser absorption enhanced by the ablated keyhole was quantified and considered as saturation (100 %), thus improving the drilling efficiency. In addition, the shock wave generated by the nanosecond laser accelerated the removal of the melt with a sputtering velocity of up to 23.8 mm/ms, which was much higher than the recoil pressure generated by the saturation vapor pressure, ensuring the drilling quality. Also, the experimental results showed that well drilling quality (1.09 degrees taper angle, 0.96 circularity) were obtained for 1 mm thick alumina ceramic with a material removal rate as high as 1.9 x 104 mu m3/mu J. The analysis and summary of the CPL drilling mechanism helps to further improve the drilling performance and provide a new technological route for high-speed processing of ceramic substrates.