This paper presents a roll-to-plate hot embossing process (R2PHEP) for precision manufacturing of optical microstructures on polymethylmethacrylate (PMMA) surface. The viscoelasticity of PMMA at embossing temperature is described by the General Maxwell model. The finite element numerical simulations of R2PHEP are carried out to optimize the process parameters, including mold temperature, roller radial displacement, and mold feed rate. The optimized parameters are used in the R2PHEP to fabricate the desired optical microstructures. The results show that R2PHEP is capable of precision manufacturing of complex and high precision optical microstructures on PMMA surfaces, making it a promising technology for efficient preparation of optical microstructure components.
The use of freeform surfaces is increasing greatly in many fields, such as imaging, aerospace, illumination, biological engineering, and green energy, etc. And the polishing process of these surfaces are usually needed to obtain nanometer scale surface roughness, aiming to implement special functionalities and acquire high added value. This paper introduced the development of the two processes for the polishing of freeform surfaces, one is the serial-parallel hybrid machine based polishing using a self-developed ball-end flexible polishing tool, the other is the multi-jet polishing process. The design was presented in detail, and polishing experiments on plane and freeform surface were successfully implemented. As for multi-jet polishing, the process principle was presented at first. Material removal characteristics were demonstrated through a series of experiments, following with the discussion of application. And the experimental results prove that multi-jet polishing is effective to largely boost the polishing efficiency as compared to normal fluid jet polishing without degrading the surface quality, and also has the potential to extend the application field of fluid jet polishing to medium-large size freeform surfaces.
To suppress the medium-high spatial frequency, error on optical surfaces is still a challenging work to date, and the tool path ripple (TPR) error is the main reason for these errors. With this in view, the effect of the tool influence function (TIF) shape of the semirigid (SR) bonnet to the TPR error is analyzed. The SR bonnet is a recently developed bonnet tool for high efficiency polishing. This tool can generate three kinds of TIF including Gaussian-like shape, trapezoidal shape, and “M” shape. Experimental studies have been conducted to analyze their effect to the root mean square/peak-to-valley value of the TPR error, and discussions have been made on those results. It is found that different shapes of TIF can be implemented through controlling its inflated pressure. The Gaussian-like shape has the highest probability to generate lower TPR error than the trapezoidal shape and “M” shape TIFs, which have been proven by the verification experiments.
This paper presents a semirigid (SR) bonnet tool which has the advantages of high efficiency and determinacy for material removal on optical elements and also has the potential to be used on aspheric optics. It consists of three layers: a metal sheet, a rubber membrane, and a polishing pad, from inside to outside. It inherits the flexibility of a normal bonnet but has a higher stiffness. Finite element analysis was performed to determine that the stainless steel is the best-suited material for use as the metal sheet. An SR bonnet with a stainless-steel metal sheet was fabricated and tested. Its tool influence function (TIF) is Gaussian-like, and the TIF stability is more than 90%. The peak-to-valley of its uniform removal area is less than 0.1λ. Tool ripples are highly depressed and the surface profile is well preserved in the prepolishing test. In 12 min, ∼36 mm3 of material is removed.
The purpose of this paper is to study the effect of the inner pressure to the tool influence function (TIF) for polishing using a semi-rigid (SR) bonnet tool. The simulation model of a Semi-rigid (SR) bonnet polishing tool polishing BK7 is demonstrated and the pressure distribution data under different inflated-pressures in the contact area has been extracted. It’s observed that the inflated-pressure has few effects to the polishing pressure, and their shapes are also Gaussian-like. Hence, we made a hypothesis that the effect of inflated-pressure to the TIF is rather small. To verify this hypothesis, a group of experiments to generate TIFs under different inflated-pressure are conducted, and the hypothesis has been proved to be correct through comparing these TIFs.
For extremely high accuracy optical elements, the residual error induced by the superposition of the tool influence function cannot be ignored and leads to medium-high frequency errors. Even though the continuous computer-controlled optical surfacing process is better than the discrete one, which can decrease this error to a certain degree, the error still exists in scanning directions when adopting the raster path. The purpose of this paper is to optimize the parameters used in bonnet polishing to restrain this error. The formation of this error was theoretically demonstrated and will also be further experimentally presented using our newly designed prototype. Orthogonal simulation experiments were designed for the following five major operating parameters (some of them are normalized) at four levels: inner pressure, z offset, raster distance, H-axis speed, and precession angle. The minimum residual error method was used to evaluate the simulations. The results showed the impact of the evaluated parameters on the residual error. The parameters in descending order of impact are as follows: raster distance, z offset, inner pressure, H-axis speed, and precession angle. An optimal combination of these five parameters among the four levels considered, based on the minimum residual error method, was determined.
An on-line condition monitoring and monitoring point position visual system for grinding machine is developed for
monitoring the grinding condition in a grinding operation. This system can set and observe the monitoring point position
in computer, measure the vibration and temperature of the grinding machine to judge the operation state. The
experiments indicate that the visual system described in this paper is more adequate than conventional on-line
monitoring techniques.
Bonnet polishing system is mostly used in rough polishing and fine polishing because of its own features. Due to
different aims of polishing stages, optimal ranges of key parameters are different in various polishing stages. Simulations
in ANSYS are present in order to get optimal ranges of key parameters including inner pressure P and compression of
bonnet H in different polishing stages, firstly, the reliability of simulation of bonnet polishing using ANSYS is verified
through a series of simulation about fine polishing stage, on the condition of using ranges of key parameters got by
former researchers from polishing experiment; secondly, simulations about rough polishing were carried out, and optimal
ranges of key parameters were found, which have reference value in future work.
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