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Single-crystal sapphire (α-Al2O3) has a wide range of applications in a variety of extreme environments due to its excellent mechanical and chemical properties as well as its stability under extreme service conditions. In addition, sapphire is a hard and brittle material, which makes it difficult to avoid the introduction of subsurface damage during processing, and the existence of a subsurface damage layer seriously affects the performance of the optical system. Therefore, this study focuses on the mechanism of subsurface damage in sapphire grinding, the suppression of damage depth, and the accurate and fast prediction of damage depth. A subsurface damage model for ultrasonic vibration–assisted grinding of sapphire was established by combining ultrasonic vibration single abrasive grain kinematics and dynamics analysis. The mechanism of ultrasonic vibration–assisted grinding was investigated by combining force and acoustic emission (AE) signals. And the effects of ultrasonic vibration–assisted grinding on the surface quality, subsurface damage form, and depth were analyzed. A comprehensive prediction model of SSD based on surface roughness (Sz) was established by combining indentation fracture mechanics and Gaussian process regression. Finally, by analyzing the influence law of each process parameter on the subsurface damage depth (SSD), the grinding process parameters were optimized, and the subsurface damage suppression strategy was proposed. This study provides theoretical guidance for the high-efficiency and low-damage grinding of sapphire. [ABSTRACT FROM AUTHOR]

High-efficiency precision grinding can shorten the machining cycle of aspheric optical elements by a factor of 2–10. To achieve this objective, ultrasonic vibration (UV)–assisted grinding (UVG) has been increasingly applied to manufacture aspheric optics. However, the mechanisms of material removal and surface formation in UV-assisted aspheric grinding of glass ceramics have rarely been studied. Herein, rotary UV-assisted vertical grinding (RUVG) was used to explore the machining mechanism of coaxial curved surfaces. First, RUV-assisted scratch experiments were conducted on aspheric surface of glass ceramics, which exhibited multiple benefits over conventional scratching. These include a reduction in the scratch force by 37.83–44.55% for tangential component and 3.87–28.15% for normal component, an increase in plastic removal length by 43.75%, and an increase in material removal rate by almost a factor of 2. Moreover, grinding marks on the aspheric surface in RUVG were accurately simulated and optimized by adjusting grinding parameters. RUVG experiments were performed to verify the accuracy of grinding texture simulations and investigate the UV effect. The results demonstrate that UV can improve the surface quality of aspheric grinding when compared with conventional vertical grinding. In particular, the total height of the profile of form accuracy and its root mean square were significantly improved by a factor of 3.38–4.54 and 7.15–10.82, respectively, and the surface roughness reduced by 10.03–12.10%. This study provides deeper insight into material removal and surface generation mechanisms for RUVG of aspheric surfaces, and it is thus envisaged that these results will be useful in engineering applications. [ABSTRACT FROM AUTHOR]

A serious challenge faced by manufacturers of large-aperture aspheric optical components of glass ceramics is the long processing time. Ultrasonic vibration–assisted grinding (UVG) allows one to effectively shorten the subsequent polishing process by several times, which is essential for grinding of aspheric components. However, the surface creation mechanism of UVG-treated glass ceramics is rarely studied. Herein, rotary ultrasonic vibration–assisted vertical grinding (RUVG) and parallel grinding (RUPG) are applied to polish the aspheric glass ceramics. Particular attention is paid to the surface formation mechanism of UVG-processed ceramics. The single-grain kinematic functions are created and the contact characteristics between the grinding wheel and aspheric surface are analyzed for the two UVG methods in terms of contact area, velocity, and trajectory. In addition, aspheric grinding texture is simulated and comparative experiments are conducted correspondingly. According to the results, the rotary ultrasonic vibration mainly influences the microscopic grinding marks. Besides, the aspheric surface form accuracy of Pt and RMS value in RUVG is 2.16 and 3.71 times lower than those in RUPG, respectively, whereas the surface roughness–related parameters (mean deviation Sa and maximum height of profile Sz) in RUVG are 6.36% and 4.56% higher than those in RUPG. This indicates that RUVG is more suitable for high precision and efficiency grinding of the aspheric surface than RUPG due to the fact that the polishing depth is primarily determined by surface form accuracy rather than surface roughness. Thus, the current research enables an in-depth understanding of surface generation mechanism in rotary ultrasonic vibration–assisted grinding, pointing out its benefits in the high-efficiency aspheric surface manufacturing. [ABSTRACT FROM AUTHOR]

Axial ultrasonic vibration–assisted grinding has been widely proved to be effective on the ground quality as well as efficiency for hard and brittle materials. However, the deference of two typical modes, axial ultrasonic vibration–assisted peripheral grinding (AUPG, vibration directions are parallel to the ground surface) and axial ultrasonic vibration–assisted end grinding (AUEG, vibration directions are vertical to the ground surface), exerting on the grinding process has not yet been thoroughly investigated. In this paper, the single grain kinematic functions corresponding to AUPG and AUEG have been created to theoretically analyze the interactional mechanism of peripheral grinding and end grinding respectively. For AUPG and AUEG, their axial ultrasonic vibrations are capable of increasing the dynamic contact length, decreasing the chip thickness, but their different effects on grinding behavior need further investigation. A series of comparative experiments have been conducted subsequently, and the results show that under the identical material removal rate, axial vibration in AUPG and AUEG can decrease the grinding forces, while AUEG is with a lower one than AUPG with a factor of 39.80%. With regard to the ground surface quality and subsurface damage, AUPG shows a positive effect while AUEG shows a negative role. The grinding kinematic, grinding force, ground surface quality, and subsurface damage have been analyzed in terms of the axial ultrasonic vibration effect on the peripheral grinding and end grinding behavior theoretically and experimentally, the conclusion will be meaningful for researchers to choose the appropriate approach in applying axial ultrasonic vibration to grinding optical elements. [ABSTRACT FROM AUTHOR]

Axial ultrasonic vibration-assisted peripheral grinding (AUPG) has the major advantages of simultaneously improving the grinding quality and material removal rate compared with conventional grinding methods. In this study, a grinding force prediction model for the AUPG of Zerodur was developed to investigate the generation mechanism of the grinding force for guidance in practical engineering applications. Taking into consideration the material removal mechanism, material properties and vibration impact, the three primary grinding force components were first separately modelled, namely, the ductile removal force in the ductile removal phase, the brittle removal force in the brittle removal phase and the frictional force of the friction process. The critical uncut chip thickness and maximum uncut chip thickness were subsequently researched to define the two material removal modes in the AUPG of Zerodur, namely, the ductile removal mode and the mixture of brittle and ductile removal mode. The grinding force models of these two material removal modes were developed using effective grinding force component models. The instantaneous variation of the grinding force with time and space was also analysed to derive models of the final time-averaged normal force, tangential force and axial force. Finally, grinding experiments were performed, the results of which showed that the prediction errors of the developed model were only 7.37 and 11.53% for the normal and tangential grinding forces, respectively. The axial ultrasonic vibration was also determined to reduce the surface roughness by 18.0% compared with conventional grinding, while the normal and tangential forces were reduced by 27.31 and 22.52%, respectively. This indicates that AUPG affords a significantly improved grinding surface quality. The developed model enables an understanding of the comprehensive mechanism of AUPG and provides a basis for the development of the grinding force models of the other brittle materials. [ABSTRACT FROM AUTHOR]