激光旋切法加工高质量微小孔工艺与理论研究
Study on Machining of High？？Quality Micro？？Holes by Laser Trepan Drilling

针对激光微小孔加工中微小孔几何形貌和孔壁重铸层这2个影响微小孔加工质量的关键因素,利用大功率Nd:YAG毫秒脉冲激光器,分别在304不锈钢和DZ445定向结晶镍基合金上进行孔加工实验,主要研究了激光旋切法加工微小孔的工艺特点,对旋切法所涉及的3个关键参数(旋切路径、旋切速度、旋切圈数)对孔质量的影响规律进行了深入探讨。结果显示:边缘起点的旋切路径易导致孔缘出现缺口,而圆心起点的旋切路径可以避免这种现象;旋切速度和旋切圈数对孔壁重铸层厚度影响显著,重铸层厚度随着旋切速度的降低和旋切圈数的增加而减小,其机理在于,孔壁重铸层在旋切过程中会因激光的重复照射再次发生熔化,并在气化压力与辅助气压等驱动力的共同作用下克服黏滞力发生质量迁移,进而从孔出口排出,在其他工艺条件不变的情况下,重铸层的厚度与质量迁移的持续时间成反比。
The influences of two key factors, geometrical morphology and recast layer, on hole quality in micro？？hole laser drilling are investigated by using high power Nd:YAG millisecond pulsed laser on two different materials － 304 stainless steel and directionally crystalized nickel？？based alloy DZ445. Trepan drilling technique is specially studied, and three related key factors are analyzed for their influences on hole quality, including trepanning path, trepanning velocity and trepanning times. The results show that the edge？？started laser path will lead to a notch on the hole edge, but this can be avoided when the center？？started laser path is employed; trepanning velocity and orbiting times both have important influences on the thickness of recast layer, and lower velocity and more trepanning times will produce holes with thinner recast layer. The mechanism lies in that the recast layer on the hole wall may remelt under subsequent radiation of laser in the trepanning process, resulting in melt migration by overcoming the viscous force under combined force of the vaporization pressure and the assistant gas pressure, and finally the melt is ejected from the hole exit end. The thickness of recast layer is inversely proportional to the time duration of melt migration when other experimental conditions remain unchanged