针对激光加工具有海量微孔的金属滤网时基板热变形严重,且所加工微孔锥度大、孔形一致性差等问题,提出了背面水辅助的激光微孔加工法。该方法利用水进入微孔的毛细现象,光在气液界面的反射、折射现象,激光辐照到水中产生的力效应、空泡效应,以及水的冷却作用,实现了提高微孔加工质量的目的。采用皮秒脉冲激光分别在无水和有水辅助情况下对不同厚度的304不锈钢板进行打孔试验,验证了背面水辅助激光加工法的可行性。试验结果表明:在相同的加工参数下,相对于无水激光直接加工法,采用背面水辅助法加工得到的微孔锥度降低了2°~6°,再铸层减少,热影响区减小,所加工滤网的变形量减小,微孔的一致性得到提高。最后采用正交试验优化的工艺参数,在60 μm厚板材上实现了出口孔径为55 μm的具有海量微孔的滤网的加工。

In this study, we propose a water-assisted laser micropore processing method to address the problems of severe deformation of the metal filter screen, the large tapering and poor shape consistency of the micropores when lasers are used to process massive micropores on the metal plate. The micropore processing quality can be improved based on the capillary phenomenon of the water entering the micropores, the reflection and refraction phenomena of light at the gas-liquid interface, the force and cavitation effects generated by the irradiation of laser into the water, and the cooling effect of the water. Herein, perforation experiments were conducted on a 304 stainless steel plate with different thicknesses using a picosecond pulsed laser with and without water assistance; thus, the feasibility of water-assisted laser processing can be confirmed. The experimental results denote that the micropore tapering obtained by the water-assisted method is reduced by approximately 2°--6° and that the recast layer and the heat-affected zone reduce compared with those obtained by direct laser drilling using the same processing parameters. Further, the amount of deformation of the processed filter screen is reduced, and the consistency of the micropores is improved. Finally, a filter screen containing a large number of micropores having an exit pore size of 55 μm is realized on a 60-μm-thick sheet using the process parameters optimized via an orthogonal experiment.