Small Polishing Tool Research Articles

Subsurface damages of fused silica developed during deterministic small tool polishing

The subsurface damages (SSD) of fused silica developed during deterministic small tool polishing are experimentally investigated in this study. A leather pad (i.e., poromeric) is validated to be nearly SSD-free and superior to pitch and polyurethane. Rough abrasives are found to obviously increase SSD depth, and a leather pad can efficiently suppress the adverse effect of rough abrasives. The SSD depth induced by pitch and polyurethane pads (with rough abrasive) ranges from 0.77 to 1.49μm (~1/7-1/5 of abrasive size). High pressure, low velocity and slurry concentration can slightly increase SSD depth. Material removal rate of leather pad is also validated to be comparable with polyurethane and much higher than pitch tool; surface roughness polished by leather pad is Ra = 1.13nm, which is close to that of pitch but much better than polyurethane.

Research on the Residual Error Evaluation Method for Deterministic Polishing of Aspheric Optics

Residual error evaluation method for deterministic polishing of aspheric optics is studied. Two residual error evaluation methods, which are axis-direction error method and normal error method respectively, are researched theoretically. It's inferred that the residual error of aspheric surface should be evaluated by normal error method. A new approach is proposed to calculate normal direction residual error on the basis of the axis-direction residual error of the aspheric surface. There exists difference between these two kinds of error which increases from the center of the aspheric optic to the edge through the comparison of them. Taking bonnet polishing and numerical controlled small tool polishing as examples, experiments are made to quantitatively prove that using axis-direction error method to evaluate residual error in deterministic polishing would introduce different degrees of processing error. It's found that the processing error is positively correlated with the relative aperture of aspheric optics, which is the ratio of the optic's aperture and vertex's curvature radius. Therefore, it is recommended to use axis-direction error method instead of normal error method as the evaluation method of the residual error during deterministic polishing aspheric optics with relatively small relative aperture; the opposite is the other way around.

Small Pitch Tool for Removing Middle Spatial Frequency Errors

More and more optical elements are needed in modern industry, which is reflected by both the bigger amount of requirement, and more complicated designed surface such as asphere and even free form surface. As a result, optical polishing using small tools on CNC machines is applied widely in the whole world, which has a lot of advantages such as fast speed, high accuracy, high flexibility and so on. But the small tool polishing can also cause in some problems. For example, the middle spatial frequency errors (MSFE) may be increased during the polishing. The reasons may consist of the following aspects: 1) the positional error of the workpiece; 2) the mistake of error data input; 3) the unexpected stop of the polishing process; 4) the stabilization of the slurry density during the process; 5) the temperature change of the contact area between the tool and the workpiece and so on. As is known, pitch is usually used in traditional optical manufacture, and it can reduce the middle and high spatial frequency errors in a large extent because of the different removal rate between the high points and low points on the optical surface. Therefore, the application of the combination of pitch and small tool is described in this paper in order to solve the MSFE problem, and we have got good polishing results of reducing the error from 2.155nm to 0.267nm by using the new pitch tool on the CNC machine after two runs.

光学元件中高频PSD2误差的实验研究

Mid-spatial frequency wavefront error of optics is characterized with the power spectrum density (PSD) specification, and is divided into two parts: PSD1 (wavelength 2.5-33 mm) and PSD2 (wavelength 0.12-2.5 mm). Rather than the PSD1 error which has been researched in the literature, the present work focuses on the PSD2 range. Potential factors affecting PSD2 error are firstly analyzed. Polishing experiments reveal that computer controlled small-tool polishing process does not worsen PSD2 error compared to the full-aperture process, while the lap has a decisive effect. The optics polished by pitch laps shows a fair PSD2 error of 0.7 nm (RMS), which is much lower than the specified 1.1 nm. The polyurethane pad commonly results in a much higher PSD2 error of more than 1.5 nm (RMS). For this problem, we adopt diamond conditioner to dress the pad and decrease pad surface roughness. The validation of restraining PSD2 error by diamond dressing has been confirmed.

Development of micro polishing system using a magnetostrictive vibrating polisher

Abstract Recently, micro-optical lenses are highly required in new fields such as Fresnel lenses for solar panels and Wafer Level Cameras (WLC). The lenses are generally molded by micro ceramic molds. In this paper, a novel vibration-assisted polishing (VAP) method by using a magnetostrictive vibrating polisher is proposed to improve the efficiency and stability of micro-optical mold polishing. The magnetostrictive vibrating polisher is composed of a vibrator and a small polishing tool. The small polishing tool is screwed into the head of the vibrator. The vibrating polisher is fixed on a 5-axis ( X , Y , Z , B , C ) controlled table via a balancing adjustment mechanism. The vibration characteristics are evaluated and the polisher vibrates in a lateral motion at frequency of 9.2 kHz with amplitude of 30 μm. The polishing force is controllable within a range of 2–200 mN with a resolution of 2 mN by the balancing adjustment mechanism. Some fundamental polishing experiments are conducted by using molds made of binderless tungsten carbide; the shape of removal function is acquired and surface roughness is improved from 30 nm Rz (4 nm Ra) to 10 nm Rz (2 nm Ra).

Micro Polishing of Tungsten Carbide Using Magnetostrictive Vibrating Polisher

Micro structured glass lenses are highly required in new fields such as Micro channels, Fresnel lenses for solar panels and Wafer Level Cameras (WLC). The glass lenses are moulded bypress moulding with micro ceramics moulds made of tungsten carbides (WC). In this paper, a new Vibration Assisted Polishing (VAP) method is proposed and developed by using circular vibration of the magnetostrictive vibrating polisher. The polisher is composed of a magnetostrictive vibrator and a small polishing tool, and the small polishing tool is mounted on the head of the magnetostrictive vibrator. The concrete design of the magnetostrictive vibrating polisher is assisted by the finite element method (FEM) and through vibration mode analysis, the 4th mode is selected. It generates a circular vibration trace at a frequency of 9.2 kHz with a radius of 30 μm. The polisher is fixed in a 5-axis (X, Y, Z, B and C) controlled polishing system. Through some fundamental polishing experiments, the shapes of the removal function is acquired and surface roughness is reduced to 9 nm Rz (1 nm Ra).

Study on Unicursal Pseudo-Random Tool Path for Computer Controlled Polishing

The application of ‘small tool’ based on computer controlled is a breakthrough in modern optical machining technology. The unicursal pseudo-random tool path, called “random path” for short, was schemed to reduce the high-frequency errors left by small polishing tool. The clipping algorithm has been developed to optimize random path, thereby it can be used in polishing workpiece surface of any boundary shape efficiently. The power spectral density (PSD) of surface before and after polishing with random path was analyzed and the result indicated that the high frequency error can be reduced by the application of random path.

Fabrication of Small Polishing Tool by Using Electrophoresis Phenomenon

In this study, a method is proposed to fabricate the polishing tool with an elastic membrane in thickness of 10 to 120μm, by using the electrophoresis phenomenon. The controllability of the membrane thickness with the applied voltage, processing time and the solution concentration are investigated experimentally. It is found that the thickness can be controlled by the applied voltage and processing time. Moreover, the polishing characteristics with the fabricated tool is examined and compared with the conventional tool. It is found that the polishing tool fabricated with the proposed method achieves the same characteristics as the conventional tool and the tool life is long enough for the practical use.

역회전 편심 운동 방식에 의한 비구면 유리렌즈 금형의 공구마크 제거 방법에 관한 연구

In this paper, new aspherical surface polishing mechanism is suggested to polish aspherical glass lens mold by both airbag polishing tool and reverse-rotational eccentric motion. Up to now, conventional aspherical lens polishing method by the small tool polishing uses the aspherical surface profile and the trajectory of the polishing tool is also controlled. However, full contact concept by airbag polishing tool and no position control make the easy polishing setup and does not need aspherical design profile. An aspherical lens polishing machine was made for this study and a tool mark removal experiment fur the fine-grounded lens mold was successfully performed.

A novel ballonet polishing tool and its robot control system for polishing the curved surface of mould

The curvature of polishing tool is not often accordant with the polished surface in polishing the curved surface of mould so that usually the smaller polishing tools are used for adapting the curvature change of the workpiece. A small polishing tool has often low polishing efficiency because of small contact area with the surface of workpiece. A larger rigid polishing tool often cannot have a good contact state with variable curved surface. In order to improve the efficiency and quality for the polishing curved surface of mould, a novel type of ballonet polishing tool is developed. The tool has a flexible ballonet covered polishing cloth in its head, which is of nicer flexibility so that it can accord with the variable curvature of curved surface of mould by controlling the air pressure of the ballonet. The advantage of the tool is that it has larger and submissive contact area with the polished surface in polishing so that it has higher polishing efficiency and also better polishing surface roughness and...

Prediction of subsurface damage depth of ground brittle materials by surface profiling

In the manufacturing of infrared optics, grinding is usually used as a premachining process for generating aspherical lens figures on brittle materials such as germanium and silicon before diamond turning or polishing. However, microcracks will be generated in workpiece materials by the grinding process. The subsurface crack depth determines the depth of material removal of the finishing processes and affects the total manufacturing time. In order to minimise the depth of finishing removal, it is important to know the grinding-induced crack depth accurately. In this paper, we attempt to predict the subsurface damage depth by surface profiling techniques. The surface roughness of ground silicon and germanium was measured by a stylus-type profilometer with different stylus geometries and the subsurface crack depth was evaluated using two different methods, namely, small-tool polishing method and slanted-polishing method. The relationship between the surface roughness and the subsurface crack depth was experimentally investigated.

Development of Ultrasonic Vibration Assisted Polishing Machine for Micro Aspheric Die and Mold

Demands are increasing for micro axis-symmetric aspherical lenses to be installed in various optical devices. The micro glass lenses are generally molded by glass press process with micro aspheric ceramic molding dies or molds made of tungsten carbide or silicon carbide. These dies and molds are mostly ground with micro diamond wheels, but require additional finishing process as the size of the dies and molds become smaller and the required accuracy becomes higher. In order to finish micro aspheric dies and molds with diameter less than 3mm, an ultrasonic vibration assisted polishing machine is developed. A small polishing tool is mounted on a 3-axis controlled table, and vibrated at an ultrasonic frequency with piezo-electric actuators. The polishing pressure can be controlled with a resolution of 2 mN. Some micro aspheric molding dies made of binder-less tungsten carbide were polished, and the form accuracy below 70 nmP-V and surface roughness of 7 nmRy were obtained with the developed machine.

Polishing Characteristics of ELID-Ground Surface of Nano Precision Optical Elements

This paper describes an ultra precision polishing method of aspherical mirrors, and the fundamental research on polishing characteristics. The aspherical mirrors with a diameter of about 30mm made by fused silica glass and CVD-SiC were ELID (electrolytic in-process dressing)-ground to high form accuracy with #4000 cast iron bonded diamond wheel, and then polished with a small polishing tool. As the result, final surface roughness of 1.4nmRa and form accuracy of 1.2 μm was obtained.

427 極座標型ロボットによる非球面研磨の基礎検討(OS12 研削・砥粒加工)

The polishing operation of a large aspheric optics surface with a small polishing tool takes a very long time. Then, a polishing head with a number of small polishing tools has been manufactured in order to shorten the processing time. The polishing head scanned on the work surface by a r-θ coordinates robot. A basic research of a plane polishing surface has been carried out using a brass workpiece of 80mm diameter. Simulation has been carried out to search the scanning locus of polishing head, which agrees with the experimental result.

406 大型 X 線ミラーの超精密ポリシング

This paper describes an ultraprecision polishing method of larger scale X-ray mirrors which made of fused silica, and the polishing characteristics. The X-ray mirrors which ground high form accuracy with ELID-grinding used #4000 cast iron bonded diamond wheel, it was took polishing with NC control polishing machine using a small polishing tool and Ce_2O_3 slurry. In the results, very good ground surface of Ra < 1nm mirror can be achieved.