Fang-Jung Shiou

The inconvenience of conventional wool ball polishing is that the surface finishing process should be equipped with a slurry container. The main objective of this research is to develop an ultrasonic-assisted surface finishing process for STAVAX mold steel on a 5-axis CNC machining center, by using new lab-made rubber polishing balls containing the abrasive aluminum oxide instead of the traditional wool ball polishing. In total, five types (type A to type E) of new rubber-matrixed polishing balls with a composite of nitrile butadiene rubber (NBR), an abrasive of aluminum oxide, and an additive of silicon dioxide have been developed. The performance of the composites with different grain sizes (0.05 μm to 3 μm) and concentrations of the abrasive of aluminum oxide have been investigated. The effects of multiple polishing passes on the surface roughness improvement for the lab-made polishing balls have also been investigated in this study. A surface roughness of Ra 0.027 μm on average was achieved by using the multiple polishing process of E-C-B-A. The volumetric wear of the lab-made polishing balls, using ultrasonic vibration-assisted polishing, can be improved from about 12.64% (type A) to 65.48% (type E) compared with the non-vibration-assisted polishing. The suitable combination of the ultrasonic vibration-assisted polishing parameters were an amplitude of 10 μm, a frequency of 23 kHz, a spindle speed of 5000 rpm, a feed rate of 60 mm/min, a stepover of 20 μm, a penetration depth of 180 μm, and a polishing pass of E-C-B-A, based on the experimental results. The surface roughness improvement on a test carrier with a saddle surface has also been presented by using the ultrasonic vibration-assisted polishing with the lab-made polishing balls.

Ultraprecision freeform polishing using a bonnet or a felt ball mounted on a polishing head plays an important role in the mold and lens production industries. The volumetric wear of a bonnet or a felt polishing ball is still a problem to be solved. The objective of this study was to develop an ultrasonic-vibration-assisted ball polishing process on a CNC machining center to improve the surface roughness of a STAVAX mold steel and to reduce the volumetric wear of the polishing ball. The optimal combination of the ultrasonic-vibration-assisted ball polishing parameters for a plane surface was determined by conducting the Taguchi L18 matrix experiments, ANOVA analysis, and verification experiments. The surface roughness of the polished specimens was improved from the burnished surface roughness of Ra 0.122 μm to Ra 0.022 μm. In applying the optimal plane surface ball burnishing and vibration-assisted spherical polishing parameters sequentially to a fine-milled and burnished aspherical lens surface carrier on a five-axis machining center, the surface roughness of Ra 0.014 μm was obtainable. The improvement in the volumetric wear of the polishing ball was about 62% using the vibration-assisted polishing process compared with the nonvibrated polishing process.

Precision surface finishing plays an important role in product quality owing to its direct effects on product appearance. As a result, automated precision surface finishing processes (APSFPs) are key technologies for industrial products and molds for forming and shaping processes. APSFPs can be divided into three main categories, namely, mechanical processes, electrochemical processes, and high energy beam processes. The objective of this special issue is to collect the cutting-edge research works focused on APSFPs. This issue includes 11 papers on APSFPs covering the following topics: ===danraku===- Review of ultraprecision surface finishing processes. ===danraku===- Ultraprecision surface machining and finishing with compensated feeding mechanisms. ===danraku===- Ultrasonic assisted cutting of unidirectional wetting surfaces and polishing of mold steels. ===danraku===- Vibration-assisted polishing of glass lenses. ===danraku===- Magnetic-assisted polishing of mirror surfaces. ===danraku===- Chemical-mechanical polishing of single-crystal SiC and GaN wafers. ===danraku===- Direct transfer of smoothing Au surfaces. ===danraku===- Plasma surface finishing of narrow channel walls of X-ray crystal monochromators. ===danraku===- Analysis and characterization of finished surfaces. It is expected that this issue will be helpful for readers to understand the recent developments in APSFPs and will lead to further research on APSFPs. We deeply appreciate the contributions of all authors and thank the reviewers for their incisive efforts.

As the demand for optical glasses has increased, precision requirements for specific shapes, forms, surface textures, and sizes (miniaturization) have also increased. The standards and surface finishes applied to the reference mirrors used in measuring appliances are crucial. Hence, enhancements in figuring and surface finishing are indispensable to manufacturing industries. In this article, a novel self-propelled multi-jet abrasive fluid polishing technique is proposed for an ultra-precision polishing process in which a blade-less Tesla turbine was used as a prime mover. The turbine was characterized by high swirling velocity at the outlet; therefore, high levels of kinetic energy moving away from the turbine were used as polishing energy. Computational fluid dynamics (CFD) was also used to simulate the flow on the turbine blades. With a newly designed and manufactured polishing tool, the optimal polishing parameters for improving the surface roughness of crown optical glasses (N-BK7) were investigated. Taguchi's experimental approach, an L₁₈ orthogonal array, was employed to obtain the optimal process parameters. An analysis of variance (ANOVA) was also conducted to determine the significant factors. The surface roughness has been improved by approximately 94.44% from (R_a) 0.36 μm to (R_a) 0.02 μm. This study also presents a discussion on the influence of significant factors on improving surface roughness.

The aim of this study is to investigate optimal air-driving fluid jet polishing (FJP) parameters by using Taguchi's method to improve surface roughness of N-BK7 optical glass on a machining center. An orthogonal array and the signal-to-noise (S/N) ratio are employed to determinate the optimal polishing parameters, and analysis of variance (ANOVA) is used to identify the main parameters that affect the surface roughness of the N-BK7 optical glass. An air-driving FJP tool is newly designed and fabricated to conduct experiments. To determinate the optimal air-driving FJP parameters, six polishing parameters, namely air pressure, impact angle, standoff distance, the abrasive material, abrasive concentration, and polishing time, are selected as the control factors of experiments. Based on the Taguchi's L₁₈ orthogonal array experimental results and the S/N ratio, the optimal parameters for the N-BK7 optical glass are found. These optimal parameters are to be as follows: an air pressure of 0.490 MPa, an impact angle of 40 deg, a standoff distance of 12 mm, the abrasive material of Al₂O₃, an abrasive concentration of 10 wt. %, and a polishing time of 30 min. The surface roughness of specimen is improved from R_a = 0.350 μm–0.032 μm by using the optimal air-driving FJP parameters. In addition, the determined optimal polishing parameters for the plane surface are applied to the surface finish of an N-BK7 spherical lens, and the surface roughness of the spherical lens can be improved from Ra = 0.421 μm to 0.202 μm within an area of 283.6 μm × 200 μm.

This work presents the development of a meso-scale 3-axis milling machine with a nanometer resolution. Regarding the Z-axis design of the meso-scale 3-axis milling machine, it mainly includes a pagoda structure, the high speed air bearing spindle, two HR8 ultrasonic motors, a laser diffraction grating interferometer system (LDGI), and a coaxial counter-balance system for the spindle. The optimal geometrical dimensions of the pagoda structure have been determined by ANSYS software. According to the simulation results, the maximum static deformation along the z-axis of the pagoda was about 5.05 nm. The designed meso-scale 3-axis milling machine is equipped with an X-Y coplanar positioning stage with nanometer resolution, including the low-cost components and two ultrasonic motors, in order to reduce the complexity and error resulted from the combination of a long-stroke stage and short-travel stage. The coplanar stage developed by Nation Taiwan University was integrated with two laser diffraction grating interferometer system as displacement feedback sensors, so that a two-axis closed-loop control was possible. The positioning accuracy of the coplanar stage was about 50nm after error compensation using the gate mode, base on the test results. A circular positioning test with the radius of 7 mm using the developed stage was tested, and the overall roundness error was about 0.094 μm based on the preliminary test results. A preliminary cutting tests for the oxygen-free copper using a polycrystalline diamond tool have been investigated with respect to different depth of cut and cutting speed on the developed meso-scale machine tool.