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Ultra-precision machining for large-sagittal aspheric optical elements has become one of the research hotspots in the world's processing and manufacturing field in recent years. This paper mainly studies the processing of large-sagittal MgF2 aspheric optical components, analyzes the grinding tracks of two different grinding methods, and seeks the best grinding method. Experimental research was carried out on three milling modes in the rigid grinding process. In the processing method of pressed milling, the rotational speed of the workpiece has the most significant effect on the surface roughness. The surface roughness Ra can be reduced by reducing the grain size of the grinding wheel and adjusting the processing parameters. Through the cylindrical milling method, the surface roughness Ra measured with the D46 grinding wheel in the direction of rotation can reach the minimum, which is 0.7–0.8 μm. In the fine grinding stage, the circumferential grinding and endface grinding models are established, and the simulation analysis and experimental verification of the trajectory of the abrasive particles in the two grinding methods are carried out. The comparison shows that with endface grinding, the surface of the component is removed evenly in both directions. When the grain size is 28 μm, the surface roughness Ra∥ and Ra⊥ of face grinding are the smallest. Among them, Ra∥ is 0.0458 μm, and Ra⊥ is 0.0369 μm. This study is of great significance in improving the machining efficiency and accuracy of large-sagittal aspheric optical elements. [ABSTRACT FROM AUTHOR]

To solve the problem of processing quality degradation due to vibration in the robot bonnet polishing system (RBPS), the vibration generation mechanism of the polishing system is revealed based on the modal analysis and dynamic modeling of the RBPS. The modal analysis results showed that the operating frequency of the system is near the natural frequency, which makes the system susceptible to resonance. On the other hand, the forced vibration caused by the polishing force leads to high vibration at the end of the robot during the polishing process. In order to suppress the vibration generated by the polishing system and optimize the dynamic characteristics of the polishing system, a vibration suppression method to increase the damping ratio of the system was proposed. The experiments of SiC fixed point polishing were performed using both vibration suppression bonnet and original bonnet. The surfaces RMS and PV of the parts polished by the vibration suppression bonnet were generally better than those of the original bonnet. The vibration suppression bonnet has improved the convergence ratio of RMS and PV by 42.59% and 19.56% respectively over the original bonnet in the whole surface polishing experiments. The PSD analysis illustrated that the vibration suppression bonnet can better suppress the intermediate frequency errors. The effectiveness of the method in suppressing vibration and improving machining quality is demonstrated. [ABSTRACT FROM AUTHOR]

The development of high-reliability, high-precision large-scale CNC ultra-precision grinding machines is essential for the efficient processing and manufacturing of large-diameter optical components. In this paper, we studied the reliability and the precision-maintenance of the ultra-precision grinding machine tool experimentally. First, the subsystems with poor performance were identified based on former operating data, which turned out to be the hydrostatic spindle subsystem and the feed subsystem. Then, we set up specific experimental platforms for these two subsystems to study the thermal deformation and thermal characteristics. The temperature difference between the inflow and outflow oils of the hydrostatic systems is used as the key parameter to model the accuracy evolution. Our results may provide a method to reveal the relationship between the thermal characteristics and the operating parameters of the subsystems, and therefore compensate the thermal error of the whole ultra-precision grinding machine. [ABSTRACT FROM AUTHOR]

Small-scale aspheric optical elements have an urgent market demand and a wide range of applications. With the development of science and technology and the increasing requirements on product quality, the polishing technology of small size aspheric optical elements is becoming much more important in the field of ultra-precision machining. This paper first gave a brief introduction of the commonly used material for small size aspherical optical lenses and molds. Then, the applicable polishing technologies and their development status were introduced in detail, which included the computer controlled optical surface (CCOS), abrasive jet polishing (AJP), magnetorheological finishing (MF), ion beam polishing (IBP), bonnet polishing (BP), chemical mechanical polishing (CMP), shear-thickening polishing (STP), laser polishing (LP), and several kinds of compound polishing technologies. Finally, the development of polishing technology for small size aspheric optical components was summarized and prospected. [ABSTRACT FROM AUTHOR]

In order to better understand the material removal mechanism during bonnet polishing process, an experimental study on revealing how the key parameters affect the material removal of workpiece from the view of force and friction is presented. Firstly, we propose a setup for the measurement of the polishing forces and the calculation method for the friction coefficient. Subsequently, based on series of experiments, the correlation of key parameters, polishing forces/friction coefficient, and material removal of the workpiece is investigated. It indicates that the variation of the spot size rarely affects the friction coefficient but has evident effect on the normal force, which results in the change of the tangential force (i.e., frictional force) and the material removal. The increase of tool rotational speed slightly affects the normal force, but greatly reduces the friction coefficient due to the friction state, therefore decreases the tangential force, but the material removal still grows because the removal frequency of the polishing tool increases with a larger magnate. The tool inner pressure has little effect on the polishing forces, friction coefficient, and the material removal. The tool surface condition is demonstrated to have great impact on both the polishing forces and the friction coefficient, therefore affects the material removal. Moreover, it is found that conditioning of the tool surface is an effective way to improve the tool removal characteristic. Finally, based on the above results, some suggestions for the optimization of the polishing process are proposed. All the findings in this study are important bases to our future study. [ABSTRACT FROM AUTHOR]

To obtain removal functions with high removal rate and stability in the polishing of hard and brittle material, an optical fabrication technology based on fixed abrasive diamond pellet (FADP) elasticity tool (ET) is designed. In this paper, we focus on the removal characteristics of ET, including removal profile, removal rate, stability of removal functions (RFs), and surface roughness. ET is analyzed theoretically about removal rate, stability, and fine surface adaptability. Modeling of the static influence function of ET based on finite element analysis (FEA) is proposed and fitted. A series of experiments are conducted to verify the effectiveness of the model. Within 640 min, the pellets could provide highly stable RFs with removal rate 1.71 mm/min. In addition, the surface roughness about 43 nm is obtained. [ABSTRACT FROM AUTHOR]

High-efficiency polishing tool is urgently needed to meet the increasing demand of high accuracy optics, especially large aspheric optics. The purpose of this paper is to present an improved semirigid bonnet tool which can deliver high-efficiency polishing on aspheric optics together with the ability to diminish the grinding feature. Its structure is optimized from the former one to solve the defects. The tool influence function is also modeled here based on finite element analysis method. Testing experiments which prove that the improved semirigid bonnet could be used in the pre-polishing stage for plane or aspheric optics to dramatically shorten the process cycle, especially for large size optics, are also conducted. Besides, it also can be used at the early stage of the corrective polishing. [ABSTRACT FROM AUTHOR]

The dynamic performance of ultra-precision cutting machine tools is an important factor for its machining accuracy. To improve the precision of the machine tool, a surface topography model is built in this paper and the tool path during the cutting process is achieved by dynamic finite element analysis (DFEA) of the air spindle in ANSYS, surface topography is obtained using MATLAB simulation by combing the model with the tool path, and an experiment is carried out for validation. Results show the simulation surface is highly consistent with the experimental result. Dynamic performance of the spindle is the main factor for texture generation, and optimization of spindle is investigated, DFEA of the optimized spindle shows better performance, and the connection mode between diamond tool and cutter head should be further studied. [ABSTRACT FROM AUTHOR]

With the aim to achieve the dwell time calculation and the optimization of tool path planning in optical figuring, an improved algorithm is proposed and experimentally validated. Firstly, the principle of the algorithm is introduced, of which tool path planning is added. After that, a two-part simulation is conducted. In the first part, the high convergence accuracy of the proposed algorithm is verified. And it also reveals that although the convergence accuracy of the algorithm without tool path planning is higher, the surface grid size changes with the tool path spacing (TPS) would affect the initial surface error and make the algorithm unpractical. In the second part, the optimization of tool path planning using the proposed algorithm is investigated, in terms of RMS, polishing time, and polishing track. The result reveals that the proposed algorithm can be used to find out the optimal TPS. Finally, polishing experiment is carried out, by using the optimal TPS obtained from the optimization process. Considering the instability of the removal functions in the polishing process and the gradient of the initial surface, the experimental result has shown an acceptable convergence ratio. Therefore, the accuracy and practicality of the presented algorithm are proven. [ABSTRACT FROM AUTHOR]

In order to realize deterministic material removal as well as achieving the prediction of the material removal in dynamic bonnet polishing process, a theoretical model between material removal and feeding speed of bonnet tool is proposed and experimentally validated. This paper starts with the derivation of the theoretical model, based on the analysis of the dynamic removal process and the differential theory, followed by a two-part verification, in which the simulated results obtained based on the proposed model were compared with those of experiments; it is indicated that, in the dynamic deterministic polishing of one single track (the first part), both the contours and removal depths of simulated results are very close to the experimental, with a maximum error of removal depth to be ∼8.66 %; on the other hand, the outcomes of the dynamic deterministic polishing of whole workpiece surface (the second part) revealed that the contours of three sectional views of simulated and experimental polished areas are similar, and the errors of removal depths on XZ and YZ sectional between the two polished areas are ∼12.5 and ∼12.9 %, respectively. Consequently, in consideration of the dynamic polishing process that is affected by many uncontrolled factors, the differences between the results of the simulations and experiments are reasonable, which validated the engineering application value of the proposed model. [ABSTRACT FROM AUTHOR]

Parallel grinding method has been widely used for advanced optics machining, especially f-θ optics. In order to reduce the dependence on high-precision machine tool with many degrees of freedom (DOF) and obtain high machining accuracy, in this paper, we propose a simultaneous 2-axis method to replace the conventional simultaneous 3-axis method in parallel grinding. Firstly, the algorithm of the simultaneous 2-axis method is explained. Then, the motion control errors and machining errors under simultaneous 3-axis and 2-axis methods are comparably analyzed, respectively. Finally, through grinding experiments, the feasibility of the simultaneous 2-axis method is verified. [ABSTRACT FROM AUTHOR]

Ultraprecision optical elements have found an increasing utilization in various fields for their superior performance so do the manufacturing technologies for optics. With the aim to optimize the conformal polishing (CP) process using continuous precession (Con-P), a theoretical and experimental investigation is presented. Firstly, this study introduced the merits of Con-P and the encountered problem when it is used in CP. By analyzing the removal function and dynamic polishing process, it was shown that the bad performance on CP of Con-P is coursed by the incompatibility of rotation speed of A-axis (RSA) and feeding speed (FS) of bonnet tool. Then, in order to obtain the optimal ranges of RSA and FS to improve the performance on CP, comparative simulations of Con-P were implemented and analyzed. It is shown that the ability for CP is changing with a newly proposed conformal factor f, f = n (RSA)/ vfx (FS), in addition, only when f reaches a certain threshold ( f > 20), Con-P has good performance on CP. On the other hand, it was also indicated that the material removal is only affected by the FS of bonnet tool. Finally, polishing experiments were conducted to validate the simulated optimization. It is revealed that the experimental results are basically consistent with the simulations, which proves the reliability of the optimization process by using conformal factor f. [ABSTRACT FROM AUTHOR]

Tool path ripple error (TPR_error) is one of the main reasons due to the medium-high spatial frequency error on the surface of aspheric optics. The purpose of this paper is to analyze the effect of the tool step size to the TPR_error in sub-aperture deterministic polishing (SDP) and study a method which can optimize the tool step size to restrain this error. Three groups of simulation experiments were conducted using three different tool influence functions to simulate the uniform removal of the material. As the TPR_error is influenced by three factors, which are full width at half maximum (FWHM) of tool influence function (TIF), tool step size, and depth of material removed, each group of the experiments was conducted under the fixed TIF and depth of material removed. It turns out that both peak-to-valley (PV) and root-mean-square (RMS) values of the TPR_error become larger with the increase of the tool step size, and the variation tendency likes a reversed 'L' shape curve. And, the method adopted in the simulation was further validated by the experiment. Therefore, the tool step size at the inflection point would be optimal to restrain the TPR_error together with saving the polishing time to a certain extent. This method could be used to determine the best-suited tool step size in SDP whose typical TIF is a Gaussian or Gaussian-like shape. [ABSTRACT FROM AUTHOR]