Ultrasonic Vibration Assisted Polishing On Hard And Brittle Microstructured Optical Surfaces

Micro-structured optical functional components have many advantages of a high level of integration, small size, simplifying optical systems. Therefore, micro-structured optical functional components are widely used in micro electronic and communication products, biomedical, automotive lighting, etc. Currently the effective way for mass production of micro-structured optical functional elements is precision replication technology. In replication technology, the precision grinding of superhard molds with the micro-structured surface is the key technology to ensure surface form accuracy of the micro-structured surface. However, some damages at the top intersection and subsurface damage in the mold micro-structured surface may be generated after grinding which may reducing the life of the mold. Consequently the precion polishing of superhard molds with the micro-structured surface is the essential process to improve the surface quality and removal the subsurface damages of the molds micro-structured surface.In this paper, the research object is the superhard mold materials such as silicon carbide, tungsten carbide and silicon nitride. The ultrasonic vibration assisted polishing system of micro-structured surface was established; the size and profile of the polishing wheel’s cross section were corrected. Moreover, the interaction mechanism between abrasives and workpiece surface of ultrasonic vibration assisted polishing for micro-structured surface was revealed; the influence of polishing process parameters on the surface integrity of micro-structures was studied. Finally, several typical micro-structured arrays were polished. In order to realize the high precision, high efficiency machining of superhard material micro-structured optical functional surfaces, the main research work is as follows:In order to avoid the influence of installation deviation and repeat positioning deviation to the micro-structured surface form accuracy, the ultrasonic vibration integrated system used for micro-structured surface grinding and polishing was developed. Then, the influence of the structure characteristics and ultrasonic vibration on the surface material removal uniformity was analysed according to the relative motion relationship between micro-structure surface and abrasive grains. The analysis results show that ultrasonic vibration could improve the effect of structural characteristics on material removal uniformity. Furthermore, for different shape of micro-structured surface, the finite element simulation and Matlab calculation are used to correct the size and profile of the polishing wheel’s section to ensure the surface form accuracy of the micro-structured surface. Meanwhile, the efficient method to truing polishing wheel’s micro-structured section was proposed based on the optimazed size and profile of the polishing wheel’s section. Moreover, in order to enhance the truing accuracy, the impact of polishing wheel position deviatonon the truing profile accuracy and the corresponding solution were provided.The friction force acquisition method was presented to collect the complete ultrasonic vibration polishing friction force data. The effect of ultrasonic vibration on the friction behavior, lubrication state and material removal form of the micro-structured surface was studied based on the measured friction force. The experimental results showed that compared with the traditional abrasive polishing, the friction force between polishing wheel and micro-structured surface was reduced when ultrasonic vibration was introduced, and the lubrication state was closer to thin film lubrication but which was still boundary lubrication. Moreover, in the case of low moving speed and polishing force, high vibration frequency and vibration amplitude, the micro-structured surface material is removed by three body abrasive abrasion.The micro-structured surface quality, surface form accuracy and material removal rate were studied by means of single factor experiment, and then the process parameters were optimizated by means of orthogonal experiment. The subsurface damages of the micro-structured surface through grinding, traditional polishing and ultrasonic vibration assisted polishing were compared with scanning electron microscope. The results showed that a better surface, higer material removal rate as well as more sharp top and bottom of the micro-structured surface could be obtained by introduced ultrasonic vibration. Meanwhile, compard with traditional abrasive polishing, the subsurface damages of the micro-structured surface were removed faster through ultrasonic vibration assisted polishing under identical processing parameters.Based on the above research results, the ultrasonic vibration assised polishing of several typical micro-structured surfaces, including clylindrical array, grating and pyramid array, were performed on the surperhard mold materials such as pressureless sintering silicon carbide, binderless tungsten carbide and silicon nitride. These research works established the technical foundation for precision maching of the surperhard mold material with micro-structured surface using for glass molding optical functional elements.