Nobuhito Yoshihara

Fabrication of micro end mills by wire EDM and some micro cutting tests

Extremely fine end mills with noncircular cross-sectional profiles have been fabricated utilizing wire electro discharge machining. By using suitable electro discharging conditions, the geometrical error of the end mill and the roundness of the cutting edge were both controlled below 1 µm. Micro grooving tests were performed on electroless nickel plating using these end mills, and the machining behavior was investigated. Nearly burr-free precision machining was realized. Until a total cutting distance of 1000 mm, no remarkable change was found in the cutting force and chip formation, demonstrating the high anti-wear ability of the tools. It can be presumed that the electro discharge-induced micro asperities on the tool surface play an important role in machining by improving the tribological properties of the tool–workpiece interface.

Study on shaping spherical Poly Crystalline Diamond tool by Micro-electro-Discharge Machining and micro-grinding with the tool

Micro-electro-Discharge Machining (Micro-EDM) for shaping of a spherical tool made of Poly Crystalline Diamond (PCD) has been developed for the purpose of enabling a grinding process of a micro-free form surface on hard and brittle materials. Using this spherical PCD tool as a grinding tool, the surface roughness of a minute flat plane (90 × 70 µm), which was ground into tungsten carbide, has 28 nm Rz and 5 nm Ra. This paper describes the capabilities of spherical PCD tool grinding with the following results.

Fabrication of High-Aspect Ratio Micro Holes on Hard Brittle Materials -Study on Electrorheological Fluid-Assisted Micro Ultrasonic Machining-

Ultrasonic machining (USM) is an effective method for machining of hard brittle materials. In this process, the slurry is supplied to the gap between the workpiece and the ultrasonic vibrating tool, and the materials are removed by the impacts of the abrasive grains that are pressurized by an ultrasonic vibrating tool. The purpose of this research is to achieve precise and efficient microfabrication on hard brittle materials by USM. However, in the case of microfabrication, chipping which is generally observed around the edges of machined micro holes and grooves, deteriorates the machining accuracy. In addition, there is another problem in that the machining efficiency decreases with the progress of the machining. Electrorheological fluid-assisted USM has been proposed as a countermeasure to these problems. In the present study, the problems and countermeasures associated with the machining of high-aspect ratio micro holes in hard brittle materials by electrorheological fluid-assisted USM are investigated. By positioning an auxiliary electrode under the workpiece, it becomes possible to keep the electric field high even when the machining depth becomes large. As a result, high-precision and high-aspect ratio micro holes can be machined on hard brittle materials.

Nano-Topography Characterization of Axisymmetrical Aspherical Ground Surfaces

There is nano-topography on axisymmetric aspherical ground surfaces. Usually, the axisymmetric aspherical lens or molding dies are finished by poli shing after they are machined by grinding. However, nano-topography cannot be removed by polishing. Nano-topography caus es grinding marks, which lowers the accuracy of optical instruments such a s lenses. In this research, the formation mechanism of nano-topography on axisymmetric ground surfaces a nd rel tionship between the topography and grinding conditions is analyzed theoretically. The res ults show that the vibration of the grinding wheel causes nano-topography. In addition, grinding marks chang es with the variation in the grinding wheel revolution speed and the workpiece revolution speed. Introduction Axisymmetric aspherical lenses or molding dies are m achined by grinding and finished by polishing. The surface roughness is smoothed with polishing. H owever, polishing cannot eliminate the surface waviness— that is, the nano-topography—that is gene rated by the grinding process. Nano-topography causes the grinding marks, which lowers the accurac y of optical instruments such as lenses. In additio n, the nano-topography measures approximately 30 nm. Be caus the form accuracy of an axisymmetric aspherical surface is approximately 100 nm, nano-top graphy size can adversely affect form accuracy. If the pattern of the nano-topography is controllab le, i.e., removable, it can be controlled by polishing. There fore, to attain the goal of increased accuracy, nano-topogra hy should be controllable. In our research, we apply theory a nd simulation to analyze the relationship between the grinding conditions and grinding marks caused by nano-topogr aphy. Generation Mechanism of Grinding Marks Figure 1 is a photograph of the grinding marks on an axisymmetric aspherical ground surface. The grinding marks, which consist of concentric circle patterns and whirling patterns, are apparent. We found that the cause of the grinding marks in high-speed reciprocation grinding is the vibration of the grinding wheel [1]. Therefore, we believe that the cause of grinding marks in axisymmetric aspherical grinding is also the vibration of the grinding wheel. Figure 2 shows a grinding mark formation model in axisymmetric grinding. In this model, the workpiece rotates at a constant frequency fw and is Fig. 1 Photograph of grinding marks Fig. 2 Formation model of grinding marks Key Engineering Materials Online: 2003-04-15 ISSN: 1662-9795, Vols. 238-239, pp 125-130 doi:10.4028/www.scientific.net/KEM.238-239.125

Optimal strategies for corrective assembly approach applied to a high-quality relay production system

Abstract In the assembly of high-quality products in a corrective assembly approach, measurement and reprocessing errors occur in the measuring and reprocessing stages, and these unexpected errors can lead to the erroneous selection of the reprocessing machine, and produce unsatisfactory products. In this paper, we consider the part flow in a high-quality relay production system applying the corrective assembly approach by incorporating machining, measurement and reprocessing errors simultaneously, and formulate the production rate of high-quality products satisfying the predetermined assembly tolerance. Optimization is used to yield the maximum production rate by using reprocessing machine selection and design strategies. The results indicate the following: (1) the proposed optimization methodology effectively yields the maximum production rate and presents the optimal selection range and the optimal adjustment size of the reprocessing machine, and (2) the reprocessing accuracy affects the maximum production rate but has little effect on the optimal selection range and the optimal adjustment size.

Development of a New Laser Conditioning Method for Ultra-Fine Grit Diamond Wheels

This paper reports a new laser conditioning method for micro-wheels with ultra-fine grit diamond, which are used for the micro grinding of micro-aspherical optics. Resinoid-bonded micro-wheels with ultra-fine grit diamonds are used for micro grinding. Such small wheels have the problem of poor ground surface roughness due to their few effective cutting edges and low peripheral speeds. In the present work, new truing and dressing methods are proposed to produce many effective cutting edges. The new method uses the third harmonic of a Nd:YAG laser, which is suitable for processing resinoid bond material. It was found that a SD1500B wheel treated using the new method had a higher cutting edge density than one treated using a conventional method, the cup truer method. A good surface roughness was obtained using the new method.

Effect of Electrorheological Fluid Assistance on Micro Ultrasonic Machining

Ultrasonic machining (USM) is an effective machining method for hard brittle materials. In the USM process, the slurry is supplied to the gap between the ultrasonic vibrating tool and the workpiece. Materials are removed by the accumulation of small brittle fractures made by the impacts of abrasive grains. In a previous study, we proposed electrorheological fluid (ER fluid) assisted-USM, and the effect of ER fluid-assisted USM was confirmed practically by machining precise micro-holes and micro-grooves on hard brittle materials. In the present paper, in order to confirm the effect of ER fluid assistance for micro USM in more detail, the behavior of abrasive grains in the machining area is observed. The effect of dielectrophoretic force acts on the abrasive grains and the effect of using ER fluid assistance are investigated. As a result, the abrasive grains can closely approach the micro tool by the effect of dielectrophoretic force and be fixed around the micro tool by the effect of ER fluid assistance. Under these conditions, the workpiece is removed primarily by the accumulation of small brittle fractures, and the chipping can be reduced.

Nano-topography on axisymmetric aspherical ground surfaces

Recently, axisymmetric aspherical lenses are being increasingly installed in optical devices such as digital cameras. As the pixel number of digital image sensors increases, both high form accuracy and fine surface roughness are required, compared with conventional products. However, distortion in an optical image occurs even if an axisymmetric aspherical lens, which has high form accuracy and fine surface roughness, is used. The distortion of the optical image is caused by the surface nano-topography, which is generated in the grinding process. In this paper, the relationship between grinding conditions and the distribution of the nano-topography is investigated. In addition, a fluctuation-free grinding machine was developed to control the nano-topography.

Electrorheological fluid-assisted polishing of WC micro aspherical glass moulding dies

Electrorheological fluid (ER fluid) is one of the functional fluids in which viscosity increases with electric field intensity. Tungsten carbide (WC) aspherical glass moulding dies are usually manufactured by the grinding process. However, the number of effective cutting edges decreases in micro-grinding, and so the surface roughness becomes worse. Therefore, the polishing process must be performed after the grinding process. In this paper, ER fluid-assisted polishing, in which the workpiece and the micro-tool are used as the electrode, is proposed to gather the abrasive grain around the micro-tool. A micro polishing pad is created by electrorheological effect. The ground surface roughness is improved.

Study on electrorheological fluid-assisted microultrasonic machining

Ultrasonic Machining (USM) is an effective machining method for machining hard and brittle materials. In this method, materials are removed by the impacts of abrasive grains that are pressurised by an ultrasonic vibrating tool. The purpose of this research is to make precise microholes on hard and brittle materials by using USM. However, chippings which are generally observed around the edge of machined microholes decrease the machining precision. In this paper, generation mechanism of chippings is investigated and Electrorheological fluid (ER fluid)-assisted USM is proposed as a method for restraining chippings. As a result effectiveness of the ER fluid-assisted USM is confirmed practically by machining precise microholes on some hard and brittle materials.