Investigation of Optimal Air Driving Fluid Jet Polishing Parameters for the Surface Finish of N BK7 Optical Glass

Abstract

The aim of this study is to investigate optimal airdriving fluid jet polishing (FJP) parameters by using Taguchi's method to improve surface roughness of NBK7 optical glass on a machining center. An orthogonal array and the signaltonoise (S/N) ratio are employed to determinate the optimal polishing parameters, and analysis of variance (ANOVA) is used to identify the main parameters that affect the surface roughness of the NBK7 optical glass. An airdriving FJP tool is newly designed and fabricated to conduct experiments. To determinate the optimal airdriving FJP parameters, six polishing parameters, namely air pressure, impact angle, standoff distance, the abrasive material, abrasive concentration, and polishing time, are selected as the control factors of experiments. Based on the Taguchi's L18 orthogonal array experimental results and the S/N ratio, the optimal parameters for the NBK7 optical glass are found. These optimal parameters are to be as follows: an air pressure of 0.490 MPa, an impact angle of 40 deg, a standoff distance of 12 mm, the abrasive material of Al2O3, an abrasive concentration of 10 wt. %, and a polishing time of 30 min. The surface roughness of specimen is improved from Ra = 0.350 خ¼m–0.032 خ¼m by using the optimal airdriving FJP parameters. In addition, the determined optimal polishing parameters for the plane surface are applied to the surface finish of an NBK7 spherical lens, and the surface roughness of the spherical lens can be improved from Ra = 0.421 خ¼m to 0.202 خ¼m within an area of 283.6 خ¼m أ— 200 خ¼m.