With the continuous development of optics, optical components have been widely used in military and civilian fields such as national defense construction, aviation and aerospace, industrial and agricultural production, and people’s lives. Especially, the large and medium-sized optical components are the core components of astronomical observation systems, laser nuclear fusion devices, precision optical measurement instruments, and other high-tech products. Optical mirrors require strict control of the surface/subsurface quality of the lens to ensure the optical performance of the mirror while achieving low surface roughness, high surface accuracy, and high surface integrity. However, optical materials are difficult to process due to their high hardness and brittleness, and surface/subsurface damage such as scratches, microcracks, breakage, residual stresses, etc., often occur after processing, resulting in a decrease in the material’s strength and refractive index, which directly affects important performance indicators such as the coating quality of the optical element, long-term stability, laser damage resistance threshold, and lifetime, and has a significant impact on the performance of the entire optical system. In the last few decades, high-precision free-form optic components such as high-resolution observation and precision-guided munitions play an important role in national defense. The fundamental goal of high-efficiency, precision, low-damage manufacturing of brittle optical materials is to maximize the material removal rate while maintaining a certain degree of surface integrity and subsurface quality of the material. However, the higher material removal rates usually used to improve machining efficiency are often prone to heavy damage, which affects the surface/subsurface quality of the workpiece. Therefore, a clear understanding of the cutting mechanism of brittle optical materials is necessary for the efficient, high-precision, and low-damage grinding of large and medium-sized optical components. There has been a great deal of research and development in this area, such as material removal mechanism and qualitative and quantitative analysis of surface/subsurface damage in manufacturing process. Currently, the ultraprecision grinding is the main manufacturing process to cut the optical materials. However, it is a challenge work to fabricate the free-form surface with high quality and closed tolerance due to the rapid change in the concavity-convexity and curvature of the surface, the effective cutting zone of the grinding wheel changes frequently in ultraprecision grinding, and the current flat surface-based theoretical model cannot be applied to the prediction of the surface topography generation in the ultraprecision grinding of the curved surface with rapidly varied curvature, which may seriously restrict the machining quality and efficiency of the optical elements. In this chapter, take the silicon carbide (SiC) as an example, which is a typical difficult-to-machine material that has been widely used in the fabrication of optical elements and structural and heat-resistant materials. The parallel grinding has been frequently adopted to produce a high-quality surface finishing. The surface generation is a vital issue for assessing surface quality, and extensive modeling work has been developed. However, most of them were based on the disc wheel with the cylindrical surface, and the surface topography generation based on the arc-shaped tool has paid relatively little attention. In this study, a new theoretical model for surface generation in ultraprecision parallel grinding has been established by considering the arc-shaped effect, synchronous vibration of the wheel, and cutting profile interference at the tool feed direction. Finally, the ground surface generation mechanism and grinding ductility were analyzed in the grinding of SiC ceramics. The results showed that the spiral and straight-line mode vibration patterns were the main feature of the machined surface and its continuity was mainly affected by the phase shift. Furthermore, for the in-phase shift condition, the grinding ductility is more significant than that of out-of-phase shift due to the continuously decreasing relative linear speed between the wheel and workpiece. High-precision optical components with complex shape or microstructure have been extensively used in numerous fields such as biomedicine, energy, and aerospace. In order to accurately achieve the specific functions of the components, the form accuracy and uniform surface quality need to reach an ever-high level. To achieve this, ultraprecision normal grinding is used for machining various types of complex optical surfaces. However, the intricate variation of the workpiece curvature and grinding wheel vibration give rise to great challenges to obtain higher precision and uniform surface condition. Finally, the micro-sinusoidal array with the setting value for scallop height is achieved by controlling the feed speed, which is determined by the local curvature of surface profile.

Manufacturing Processes of Optical Materials

工具书词条
发表日期：

2025年

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Shanshan Chen

摘要

With the continuous development of optics, optical components have been widely used in military and civilian fields such as national defense construction, aviation and aerospace, industrial and agricultural production, and people’s lives. Especially, the large and medium-sized optical components are the core components of astronomical observation systems, laser nuclear fusion devices, precision optical measurement instruments, and other high-tech products. Optical mirrors require strict control of the surface/subsurface quality of the lens to ensure the optical performance of the mirror while achieving low surface roughness, high surface accuracy, and high surface integrity. However, optical materials are difficult to process due to their high hardness and brittleness, and surface/subsurface damage such as scratches, microcracks, breakage, residual stresses, etc., often occur after processing, resulting in a decrease in the material’s strength and refractive index, which directly affects important performance indicators such as the coating quality of the optical element, long-term stability, laser damage resistance threshold, and lifetime, and has a significant impact on the performance of the entire optical system. In the last few decades, high-precision free-form optic components such as high-resolution observation and precision-guided munitions play an important role in national defense. The fundamental goal of high-efficiency, precision, low-damage manufacturing of brittle optical materials is to maximize the material removal rate while maintaining a certain degree of surface integrity and subsurface quality of the material. However, the higher material removal rates usually used to improve machining efficiency are often prone to heavy damage, which affects the surface/subsurface quality of the workpiece. Therefore, a clear understanding of the cutting mechanism of brittle optical materials is necessary for the efficient, high-precision, and low-damage grinding of large and medium-sized optical components. There has been a great deal of research and development in this area, such as material removal mechanism and qualitative and quantitative analysis of surface/subsurface damage in manufacturing process. Currently, the ultraprecision grinding is the main manufacturing process to cut the optical materials. However, it is a challenge work to fabricate the free-form surface with high quality and closed tolerance due to the rapid change in the concavity-convexity and curvature of the surface, the effective cutting zone of the grinding wheel changes frequently in ultraprecision grinding, and the current flat surface-based theoretical model cannot be applied to the prediction of the surface topography generation in the ultraprecision grinding of the curved surface with rapidly varied curvature, which may seriously restrict the machining quality and efficiency of the optical elements. In this chapter, take the silicon carbide (SiC) as an example, which is a typical difficult-to-machine material that has been widely used in the fabrication of optical elements and structural and heat-resistant materials. The parallel grinding has been frequently adopted to produce a high-quality surface finishing. The surface generation is a vital issue for assessing surface quality, and extensive modeling work has been developed. However, most of them were based on the disc wheel with the cylindrical surface, and the surface topography generation based on the arc-shaped tool has paid relatively little attention. In this study, a new theoretical model for surface generation in ultraprecision parallel grinding has been established by considering the arc-shaped effect, synchronous vibration of the wheel, and cutting profile interference at the tool feed direction. Finally, the ground surface generation mechanism and grinding ductility were analyzed in the grinding of SiC ceramics. The results showed that the spiral and straight-line mode vibration patterns were the main feature of the machined surface and its continuity was mainly affected by the phase shift. Furthermore, for the in-phase shift condition, the grinding ductility is more significant than that of out-of-phase shift due to the continuously decreasing relative linear speed between the wheel and workpiece. High-precision optical components with complex shape or microstructure have been extensively used in numerous fields such as biomedicine, energy, and aerospace. In order to accurately achieve the specific functions of the components, the form accuracy and uniform surface quality need to reach an ever-high level. To achieve this, ultraprecision normal grinding is used for machining various types of complex optical surfaces. However, the intricate variation of the workpiece curvature and grinding wheel vibration give rise to great challenges to obtain higher precision and uniform surface condition. Finally, the micro-sinusoidal array with the setting value for scallop height is achieved by controlling the feed speed, which is determined by the local curvature of surface profile.