Research On The Polishing Characteristics Of Optical Surface For Ceramic And Metal Materials

With the development of space optical systems,the requirements of the performance of reflective space optical systems are growing,while the machining accuracy of the surface of optical workpieces is increasing as well.The analysis and research of the surface material changes in the optical manufacturing processes have received little attention.In the optical surface manufacturing process,improvement of the accuracy of the ultra-precision polishing process,polishing efficiency,and the achievement of a deterministic and repeatable polishing process are crucial research.In the current study,ultra-precision polishing process was investigated for different surface properties of various materials.Two different types of materials were studied,ceramic and metal.They are representative of silicon carbide and aluminium alloy.Computer-controlled ultra-precision bonnet polishing and deterministic precision lowcompressive polishing were applied for two materials in the study.The Taguchi approach was used in the design of the experiment during the manufacturing process of silicon carbide surface.Multi-scale polishing influencing factors of the polishing process were affected by many parameters,which included polishing angle,polishing speed,polishing pressure and compensation depth,and so on.The study focused on analyzing and calculating the tendency of change of surface profile,surface roughness,optical reflective rate and materials removal characteristic.The relationship between the surface characteristic parameters and materials removal rate was modelled by using Preston's equation and Hertz theory.A Fast Fourier transform method was used to convert the surface shape characteristics of aluminium alloy workpiece,which converted a 2D surface feature curve into a space spectrum expression.The machining errors on the optical surfaces,such as surface roughness,form error,and waviness curve between them,were transformed into three spatial frequency domains,such as higher spatial frequency spectrum,lower spatial frequency spectrum and the middle spatial frequency spectrum.The study introduced a concept of power spectral density,which was analyzed during the spatial frequency spectrum corresponding to the surface roughness.It was also able to judge the corresponding mode of the surface form and spatial frequency spectrum,and the range of spatial frequency spectrum during ultra-precision polishing process accurately.By selecting the optimal process parameters accurately,the relationship between higher frequency error and the reflection efficiency was quantified.An efficient and deterministic polishing process was achieved using the spatial frequency spectrum.According to the difference in material properties,i.e.brittleness and plasticity,the removal mode of two bodies and three bodies was contrastively analyzed.Experimental data and surface measurement data were collected,and the Zeeko ultra-precision polishing system was used to convert 2D profile curve removal characteristics to 3D.The surface removal profile and spatial frequency were analyzed,simulated and compared by using Matlab and Geany software respectively.A contact profilometer measurement system,non-contact laser interference topography instrument,and the Fourier infrared spectrometer were employed to measure the workpiece surface profile and reflectance.The relationship of the influence factors between surface quality and reflectance was confirmed for silicon carbide material.For metal surfaces,based on various depths of cutting and cutting turning mark of the workpiece,the trend of surface roughness and reflectivity during deterministic precision low-compressive polishing process could be determined.It summarized the optical surface characteristics of different materials in the ultra-precision polishing process.