Experimental study on the scanning mode of backwater-assisted laser secondary hole repairing

The method of backwater-assisted picosecond laser secondary hole repairing(LSHR) is proposed to achieve high quality processing of the micro-holes. LSHR helps to reduce the difference in polarized light reflectivity and improve the roundness of the micro-hole outlet. The improvement of the discharge capacity of plasma and steam plays a key role in the improvement of the material removal rate and the improvement of periodic stripes. The mechanism of the two scanning modes was briefly discussed, and the processing effect of LSHR under different combinations of scanning modes was determined, so as to obtain the best combination of high-quality micro holes. Under the best combination, the micro-hole taper is 1.476 degrees, and the micro-hole outlet roundness is 0.924 %. The backwater-assisted method can further increase the material removal rate, reduce the micro-hole taper, and improve the quality of the hole wall. Compared with the air, the micro-hole taper is reduced by 0.636 degrees. However, the micro-hole outlet is more elliptical due to the refractive index of water. The experimental results provide a new reference for optimizing the picosecond laser drilling process.