Ultrasonic Assisted Chemical-mechanical Polishing Of Superhard Micro-structured Optical Surface

Microstructured optical functional surfaces have many advantages and featuresover conventional optical surfaces, which contributes those microstructured elementswidely used in aerospace, electronics, optical digital communications, micro-roboticsand bio-medical industries. With the continuously high requirements for opticalelements, silicon carbide and tungsten carbide etc. hard and brittle materials aregradually replacing the traditional mold steel materials, widely used in the production ofmold. These hard and brittle materials have many excellent characteristics, such as hightemperature resistance, corrosion resistance, high hardness, and excellent properties oflightweight. Glass molding is the most economical means to manufacture these complexglass components with high quantities, which can save lots of time and cost comparedwith grinding and polishing. The accuracy of optical components depends on moldprocessing quality which is decided by chemical and mechanical polishing. This paperstudies the polishing of microstructured mold made of silicon carbide, aiming atimproving the polishing efficiency as well as quality.First, an integration of experimental platform is built, which is used for dressingdiamond grinding wheel, grinding micro-cylindrical array, dressing polishing wheel,(ultrasonic assists) chemical mechanical polishing. The appropriate type of polishingwheel and slurry are selected through single factor experiments. Error sources derivedfrom the experimental system are analyzed, and the effective countermeasures areproposed to reduce these errors simultaneouslyThen, the polishing experiments of silicon carbide micro-cylindrical array are doneby using conventional methods. The effects of factors (moving speed of the workpiece,polishing pressure, polishing time, grit size, grit concentration, PH value) on surfaceroughness, surface accuracy and the material removal rate are analyzed throughorthogonal experiments. Meanwhile, the optimum polishing parameters are obtained.Then the effects of wheel rotational speed, polishing pressure, workpiece moving speedand polishing time on surface roughness, surface accuracy and the material removal rateare studied through single factor experiments.At last, the experiments of ultrasonic assisted polishing are conducted, byorthogonal design, the effects of factors (ultrasonic amplitude, moving speed of theworkpiece, polishing pressure, polishing time, grit size, grit concentration) on surfaceroughness, surface accuracy and the material removal rate are analyzed and theoptimum polishing parameters are obtained. After that, the affecting rules of ultrasonicamplitude and ultrasonic frequency on surface roughness, surface accuracy and thematerial removal rate are studied. In comparison with polishing without ultrasonic, it isfound that the surface roughness, surface accuracy and the material removal rate are improved greatly. At last, the material removal rate equation with and without ultrasonicis regressed using Matlab software.By the contrast of conventional polishing, the results show that the impacts ofvarious factors on the order of indexes are changed. Furthermore, ultrasonic vibrationcan improve the efficiency of microstructure polishing as well as the surface roughnessand surface accuracy.