激光抛光表面形貌的误差复映规律

Error Remapping of Surface Morphology by Laser Polishing

目的探究激光抛光工艺中的表面形貌误差复映规律。方法首先采用纳秒光纤激光对不锈钢表面进行标刻加工制备微结构,再通过纳秒光纤激光对预制微结构的表面进行抛光加工,通过超景深显微镜测量加工后的表面形貌,分析表面形貌随加工参数的变化规律。其中纳秒光纤激光波长为1064 nm,脉宽约200 ns,最大激光功率为20 W。进行标刻时,激光功率设置为18 W,激光脉冲频率为20 kHz,扫描速度500 mm/s,通过多次重复标刻在不锈钢表面标刻出一定深度的凹槽。采用低功率(6、4、2、1、0.2 W)的纳秒激光对预制的局部微结构进行激光抛光处理,抛光过程的扫描线间距设置为10μm,扫描速度设置为200 mm/s,对包含凹槽的2 mm×2 mm的区域进行两次抛光处理。结果经标刻加工的微凹槽周围存在较大的边缘凸起;激光抛光能够有效降低凹槽边缘凸起高度,选择合适的抛光参数可将凹槽边缘凸起高度降低到2μm以下。对于高度大于10μm的边缘凸起,在激光功率大于2 W时,抛光后的边缘凸起高度随激光功率的增大而线性减小;在激光功率小于2 W时,边缘凸起高度随激光功率变化不明显。对于高度小于10μm的边缘凸起,激光抛光存在抛光饱和的现象——凸起高度随激光功率密度变化不明显。结论已有微结构的不锈钢表面经激光抛光会形成残留微结构,从而表现出一定的形状复映规律。经抛光处理后的沟槽边缘凸起的高度随着所使用的激光能量密度的增大而减小,基本服从线性变化规律。

The work aims to explore error remapping of surface morphology during laser polishing.The stainless steel surface was firstly written by nanosecond pulsed fiber laser to fabricate microstructure and then the surface of the prefabricated microstructure was polished by the nanosecond pulsed fiber laser.The surface morphology after processing was measured by an ultra-depth microscope and the variation of the surface morphology with the polishing parameters was investigated.The parameters of the nanosecond pulsed fiber laser were as follows:1064 nm in wavelength,~200 ns in pulse duration and 20 W in laser power.In the direct writing by laser,grooves with different depths were marked several times on the surface of stainless steel by the laser beam with the energy density of 18 W,the pulse frequency of 20 kHz,and the scanning speed of 500 mm/s.The local microstructures were laser-polished by nanosecond laser with low energy density(6 W,4 W,2 W,1 W,0.2 W).The distance between the scanning lines was set as 10 microns,and the scanning speed was set to 200 mm/s.The 2 mm×2 mm area containing grooves and the bulges were polished twice.There were larger edge bulges around the grooves directly written.Laser polishing could effectively reduce the height of the bulge around the groove.The height of the bulge around the groove could be reduced to less than 2 microns through appropriate polishing parameters.For the initial height of the bulge around groove greater than 10μm,the bulge height after polishing decreased linearly with the increase of laser power density when the laser power density was greater than 2 W.Oppositely,the bulge height around the groove did not change significantly with the laser power density when the laser power density was less than 2 W.For the initial height of the bulge around the groove less than 10μm,a polishing saturation occurred for laser polishing at higher laser power,i.e.the change of the bulge height with laser power density was not obvious.After laser polishing,residual microstructure will be formed on the surface of the existing stainless steel,thus showing a certain law of shape duplication.After polishing,the raised height of the groove edge decreases with the increase of the laser energy density,which is basically changed in a manner of linear regularity.