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Hard and brittle materials are widely used in many frontier fields because of their better properties, and their efficient precision polishing methods are attracting much attention. The research on surface quality of optical lenses with surface finishing requirement not only involves surface roughness, but also surface form accuracy. The generated surface profile is a key factor affecting the surface form accuracy and overall smoothness. From experience, both processing mechanism of adopted method and toolpath have effects on the generated surface profile. For this, the paper presents a theoretical and experimental study of the generated surface profile of spiral toolpath in axial ultrasonic vibration-assisted polishing (UVAP). Based on classical Preston equation, Hertzian contact theory and the axial vibration-assisted processing principle, a prediction calculation model for generated surface profile of spiral toolpath is proposed. The model can specifically analyze the dwell-time distribution characteristics of periodically varying contact pressure and sliding velocity in the areas near/far-from the curvature center of curve toolpath, accurately predict the surface profile shape and material removal rate (MRR), and scientifically reveal the assisted processing principle. Accordingly, a series of experiments are conducted to verify the rationality of the proposed model and the polishing performance of axial UVAP. Compared to conventional methods, the predictions can more reasonably and accurately present the real surface profile characteristics, both high MRR and superior surface quality are obtained. This study would aid in achieving a deterministic processing technology of higher efficiency and better surface quality, laying a crucial theoretical basis for the global polishing of optical lens. [ABSTRACT FROM AUTHOR]

K9 optical glass is one of the typical components in optical systems. However, because of its poor fracture resistance, it is difficult to polish it with ultra-precision and high-efficiency and without any surface damage simultaneously. The emergence of the obliquely axial ultrasonic vibration-assisted polishing (UVAP) method can solve this problem which encounters in polishing efficiency and shape accuracy. However, due to the unclear material removal profile (MRP) mechanism, obliquely axial UVAP is not widely used in the processing field. This paper introduces the obliquely axial UVAP method in research processes, mainly focusing on the fixed point MRP analysis of the obliquely axial UVAP. Based on Hertz's contact theory, polishing pressure, the length of the semi-long axis (LLA) and the length of the semi-short axis (LSA) of the contact area are calculated under ultrasonic vibration conditions. Meanwhile, the relative linear velocity distribution of the oblique polishing tool in the instantaneous contact area is modeled by mathematical geometry method. A novel model of the MRP distribution for obliquely axial UVAP is proposed following the Preston equation. Subsequently, a series of polishing experiments were carried out to verify this model. The results show that the numerical model has good agreement with the experimental results on MRP, LLA, LSA, material removal depth and material removal rate (MRR). In addition, the material removal capability can be significantly improved by larger ultrasonic amplitude and larger oblique angle. This model not only more clearly elucidates the processing mechanism of obliquely axial UVAP, but also provides theoretical support for the polishing of free-form optical lenses. [ABSTRACT FROM AUTHOR]

Optical glass BK7 is widely used in optical lenses. It is a kind of hard and brittle material and thus difficult to machine. To solve the problems it has encountered in terms of polishing efficiency and quality, the axial ultrasonic vibration assisted polishing (UVAP) method is adopted in this study. A mathematical-prediction-model, firstly considering the effects of periodically changing pressure caused by ultrasonic vibration, is developed to predict the generated surface-profile. And for the first time, the concept of "Preston-coefficient distribution-function" is proposed to describe the effect of the abrasive-particle distribution on material-removal distribution-function. A series UVAP experiments on optical glass BK7 at different polishing parameters are conducted to validate the polishing efficiency and feasibility of the developed prediction model and proposed concept. The results confirm that UVAP method can realize a higher material removal rate (MRR) and a better surface quality. Compared to conventional method, the predictions are in good agreement with the experiments. The comparison of the obtained surface profiles proves the benefits of ultrasonic vibration as well. Moreover, the research results can be used to guide the adjustment of polishing parameters for deterministic material removal in straight feeding process of UVAP, and provide a valuable basis for trajectory planning of the global polishing of workpiece surfaces. [ABSTRACT FROM AUTHOR]

• Preston coefficient is affected by ultrasonic amplitude • Contact pressure is affected by ultrasonic amplitude • Large ultrasonic amplitude helps to improve the polishing ability • Local surface profile can be well predicted by the proposed calculation model • Prediction of surface profile is a basis for free-form surface polishing of UVAP With the rapid progress of science and technology, many applications of hard and brittle materials require advanced and suitable machining-techniques. One technique in particular, ultrasonic vibration-assisted polishing (UVAP), has been studied intensively by researchers worldwide. These studies indicate that UVAP has the capability to improve the surface quality as well as the machining efficiency. However, few studies focus on the deterministic material-removal of UVAP. The difference between generated and theoretical surface profiles determines the surface accuracy. Therefore, this paper focuses on predicting the generated local surface profile and providing a theoretical basis to reduce this error by controlling the polishing parameters. In addition to the axial ultrasonic vibration of polishing tool, ultrasonic atomization was adopted to provide uniformly distributed polishing slurry. To ensure sufficient surface-accuracy, it is necessary to predict the generated surface profile for a fixed spot as a basis research. This means, to enable accurate predictions the following improvements are realized: (i) A novel model for the elastic spherical contact-deformation of the polishing tool is used to calculate both the polishing force and contact radius. It takes into account the nonlinear elasticity of the polishing tool and the lateral extension of the contact area, which makes it more consistent with the actual deformation. (ii) A novel model for the material-removal distribution function for UVAP is proposed, based on the Preston equation. It considers the periodic changes of polishing force and contact radius caused by ultrasonic vibration. (iii) A series of fixed-spot polishing experiments on BK7 glass are carried out to verify the proposed models. The results show that the Preston coefficient is affected by axial ultrasonic amplitude, and large ultrasonic amplitude improves the polishing ability. In addition, the generated local surface profile, the maximum contact radius, as well as the material-removal depth and material-removal rate (MRR) can be predicted well. The new models not only provide a possibility to realize deterministic material removal but also enables in-depth-understanding of UVAP. It also represents a basic theoretical foundation for future, flat or free-form surface-polishing. [ABSTRACT FROM AUTHOR]