Papers by Author: Tsunemoto Kuriyagawa

Abstract: Reaction-bonded silicon carbide (RB-SiC) is a recently developed ceramic material with many merits such as low manufacturing temperature, dense structure, high purity and low cost. In the present paper, the precision machinability of RB-SiC was studied by microindentation and single-point diamond turning (SPDT) tests. The influence of depth of cut and tool feed rate on surface roughness and cutting force was investigated. Results showed that there was no clear ductile-brittle transition in machining behavior. The material removal mechanism involves falling of the SiC grains and intergranular microfractures of the bonding silicon, which prevents from large-scale cleavage fractures. The minimum surface roughness depends on the initial material microstructure in terms of sizes of the SiC grains and micro pores. This work preliminarily indicates that SPDT can be used as a high-efficiency machining process for RB-SiC.

Abstract: The service life of a diamond tool in cutting single-crystal silicon is normally very short because of severe tool wear. Therefore, it is important to use a proper coolant in order to restrain tool wear. In this paper, the performances of oil-based and water-based coolants were compared in silicon machining by investigating cutting forces and tool wear geometries. The water-based coolant was found to restrain flank wear more effectively than the oil-based one. The effective tool life using the water-based one was averagely three times longer than that using the oil-based one. The tool wear mechanism might be related to microplasma generated between silicon and diamond during cutting.

Abstract: The measurement principle where in a high-NA (Numerical Aperture) surface, for which the degree of the angle of surface inclination exceeds π/3 radians, could be evaluated with high precision and high speed is proposed. This is based on the stitching method, where aspherical surface measurement becomes possible by dividing the surface of the sample into a range so that measurements can be made with an interferometer and finally combined. We examine the method of applying an interferometer to the condition in which the sample is rotated on an air spindle at a constant speed. It is not necessary in this method to make the sample static. Therefore, the vibration of the servo motor and any location errors can be eliminated. Moreover, the measurement time does not depend on the number of divided areas which are necessary for the stitching method, allowing for high-speed measurement. The principle behind this technique is expanded first, and an experiment system based on it was constructed. The principle proposed was evaluated, and its effectiveness was confirmed.

Abstract: The use of aspherical optical parts has become common as optical instruments are becoming smaller with and are achieving higher resolution. Nano-order roughness and high-precision shapes are simultaneously required for the surface of aspherical optical parts. At present, form accuracy of the aspherical lens becomes less than 50 nm, and the maximum height roughness becomes less than 20 nm. These values of form accuracy and maximum height roughness satisfy the requirement for most precision optical parts. However, nano-topography, which causes grinding marks and deteriorates accuracy of optical parts, is generated on the ground surface. Conventional evaluation criteria such as form accuracy and surface roughness cannot estimate the nano-topography. In the present paper, the cross sectional profile of the axisymmetric ground surface is calculated in order to estimate the distribution of the nano-topography. As a result, the possibility of control of the nano-topography distribution is confirmed. In addition, controlling the amplitude of nano-topography is easier than controlling the distribution of nano-topography.

Abstract: A Nd:YAG crystal having a special structure achieved laser operation with an extinction ratio of over 20 dB, a CW (continuous wave) average power of 6 W, a pulse width of 50 ns, and repetition rates in the range 1 kHz – 10 kHz for an output wavelength of 1064 nm for effectively cooling the crystal for the case of laser dressing. The birefringence induced by the stress applied to the crystal results in the production of elliptical polarization before the Brewster-window and thus decreases the laser efficiency. In this paper, we analyzed the relationship between the distortion and the birefringence in a Nd:YAG crystal and the resulting effect on the laser power.

Abstract: Aspherical surfaces are an important technology in optical instruments. Until now, only improvements in form accuracy and surface roughness of aspherical surfaces have been investigated. However, when the surface roughness becomes low, the small waviness of the surface becomes marked. This small waviness is termed “Nano-topography.” Nano-topography causes grinding marks and reduces the accuracy of an optical instrument. Nano-topography is caused by the vibration of a grinding wheel during the manufacture of the surface. This paper will reveal how a rubber-bonded grinding wheel has been developed to absorb that vibration. The dressing of the grinding wheel was also investigated. As a result, it is possible to eliminate the generation of nano-topography.

Abstract: A completely new diamond wheel, named the 3R wheel, has been developed. The 3R wheel has three unprecedented functions, reconfiguration, restoration and recyclability, and is molded from a mixture of special thermoplastic resin filler and diamond powder. The concept of the 3R wheel is to control the quantity and the position of abrasive material by actively using heat. In this study, tungsten carbide (WC) was ground using a thermoplastic resin bonded diamond wheels (radius 1.4 mm) with three different concentrations of 1500 grain size abrasive. As a result, a grinding ratio of over 200 and 18 nmRa roughness was achieved without dressing. In addition, a large quantity of abrasives was confirmed on the wheel surface by observation.

Abstract: This paper deals with the mechanism of surface heterogeneity due to crystallographic anisotropy effects in diamond turning of single-crystalline germanium. A microplasticity-based numerical simulation model was proposed, in which the effects of tool geometry and machining conditions can be involved. Two coefficients were introduced to compensate the Schmid factors of two different types of symmetrical slip systems. Simulation of ductile machinability was conducted on two crystallographic planes (100) and (111), and the simulation results were consistent with the experimental results. It was indicated that the simulation model can be used to predict the brittle-ductile boundary change with machining conditions and crystal orientations of germanium.

Abstract: Nanoindentation was used to study the deformation and removal mechanisms of cemented tungsten carbide. It was found that the microstructure of the material has significant influences on its mechanical properties, which determines the critical conditions for damage-free nanogrinding. The results also indicated that when material removal events occur at nanometric scale, such influences should be taken into account for gaining the full potential of nanogrinding.

Abstract: Plane honing machining of aluminum nitride (AlN) was investigated in this study. AlN has advantageous thermal and dielectric characteristics and is in great demand as a semiconductor mounting board or packaging parts material. However, as AlN is a sintered material, the AlN grains readily detach during machining making it difficult to obtain fine surface roughness at high efficiency. In previous studies, we have developed a new plane honing method that makes it possible to grind hard and brittle materials. In this paper, plane honing experiments of AlN were carried out using a resinoid or vitrified bond wheel. Fine surface roughness could be obtained using the resinoid bond wheel but there was low-machining efficiency due to burying and detachment of abrasives. The vitrified bond wheel, however, enabled high efficiency grinding but resulted in traces of detached AlN grains forming at the machined surface. Highly efficient mirror grinding of AlN could be achieved by using a vitrified bond wheel for semi-finishing and a resinoid bond wheel for finishing.