• Journal of the Korean Society for Precision Engineering
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• v.27 no.7
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• pp.117-122
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• 2010

Recently, aspheric glass lens molding core is fabricated with tungsten carbide(WC). If molding core is fabricated with silicon carbide(SiC), SiC coating process, which must be carried out before the Diamond-Like Carbon(DLC) coating can be eliminated and thus, manufacturing time and cost can be reduced. Diamond Like Carbon(DLC) is being researched in various fields because of its high hardness, high elasticity, high durability, and chemical stability and is used extensively in several industrial fields. Especially, the DLC coating of the molding core surface used in the fabrication of a glass lens is an important technical field, which affects the improvement of the demolding performance between the lens and molding core during the molding process and the molding core lifetime. Because SiC is a material of high hardness and high brittleness, it can crack or chip during grinding. It is, however, widely used in many fields because of its superior mechanical properties. In this paper, the grinding condition for silicon carbide(SiC) was developed under the grinding condition of tungsten carbide. A silicon carbide molding core was fabricated under this grinding condition. The measurement results of the SiC molding core were as follows: PV of 0.155 ${\mu}m$(apheric surface) and 0.094 ${\mu}m$(plane surface), Ra of 5.3 nm(aspheric surface) and 5.5 nm(plane surface).

• International Journal of Precision Engineering and Manufacturing
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• v.6 no.1
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• pp.59-64
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• 2005

This paper describes an investigation about the fluid delivering method that minimizes the generation of hydrodynamic pressure and improves the grinding accuracy. Traditionally, grinding fluid is delivered for the purpose of cooling, chip flushing and lubrication. Hence, a number of conventional investigations are focused on the delivering method to maximize fluid flux into the contact arc between the grinding wheel and the work piece. It is already known that hydrodynamic pressure generates due to this fluid flux, and that it affects the overall grinding resistance and machining accuracy. Especially in the ultra-precision mirror grinding process that requires extremely small amount of cut per pass, its influence on the machining accuracy becomes more significant. Therefore, in this paper, a new delivering method of grinding fluid is proposed with focus on minimizing the hydrodynamic pressure effect. Experimental data indicates that the proposed method is effective not only to minimize the hydrodynamic pressure but also to improve the machining accuracy.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2514-2522
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• 1994

The mirror surface grinding of carbon fiber reinforced plastics(CFRP) was realized by using the metal bonded super-abrasive micro grain wheel with electrolytic in-process dressing(ELID). The maximum surface roughness $R_{max}$ of CFRP which was obtained with #6,000 wheel, was 0.65 $\mu{m}$, which was rougher surface finish compared to those of hard and brittle materials with the same mesh number wheel with ELID. The grinding performance was much dependent on the grinding direction and the best surface roughness was obtained at $90^{\circ}C$ grinding with fiber direction. The spark-out effect on the surface improvement was significant when smaller mesh number grinding wheels were used. From the surface observations of CFRP with scanning electron microscope(SEM) and Auger electron spectroscopy(AES), it was found that the mirror surface grinding of CFRP was generated by the homogenization due to carbonization of the ground surface and smearing of chips composed of the carbon fiber and carbonized epoxy resin into the ground surface.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.2
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• pp.26-32
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• 2010

This paper reports some experimental result in grinding and polishing of silicon cathodes used in semiconductor manufacturing process. Cup shape diamond core wheels were used in experiments and the radial and tangential grinding forces were measured with surface roughness. In polishing experiments, flat type and donut type wool polishing tools were tested. The experimental results indicate that the grinding forces are proportional to the material removal rates and the surface roughness are inversely proportional to the spindle speed. The surface roughness of polished Si decreases with polishing time and higher spindle speed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.561-562
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• 2006

To enhance the precision and productivity of ultra precision aspheric surface micro lens, the development of ultra-precision grinding system and process for the aspheric surface micro lens are described. In the work reported in this paper, an ultra-precision grinding system for manufacturing the aspheric surface micro lens was developed by considering the factors affecting the grinding surface roughness and profile accuracy. This paper deals with mirror grinding of an aspheric surface micro lens by resin bonded diamond wheel and spherical lens of BK7. The optimization of grinding conditions on ground surface roughness and profiles accuracy is investigated using the design of experiments.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.155-159
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• 2002

This paper has studied to obtain the grinding characteristics and optimal grinding conditions of ceramics in the grinding with diamond wheel by Taguchi method. Feed rate was most important factor to the surface roughness. In the case of 4{Si_3}{N_4}$ and ${A1_2}{O_3}$, surface roughness value were small at 3m/min of feed rate. In the case of $ZrO_2$. surface roughness value was small at 4m/min of feed rate. Surface roughness have much influenced by major load for the :ii3N4 and $ZrO_2$. On the other hand, ${A1_2}{O_3}$ have more influenced by grain shedding of brittle fracture phenomenon. The major factors affecting the surface roughness and the optimum grinding conditions were obtained with minimum experiment using Taguchi method.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.12 no.6
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• pp.317-322
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• 2002

We have studied the sawing sach as the round brilliant cut, cushion barion cut and marquise cut. Through this study, we could examined the rate of waste from the grinding work, and find a solution for many problems which could be derived from the grinding work. We could reduce the rate of waste by this study about sawing technique; 2.5 % for round brilliant cut, 2.5 % for cushion barion cut and 5.5 % for marquise cut.

• Journal of the Korean Ceramic Society
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• v.48 no.2
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• pp.152-159
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• 2011

The green and hard machining characteristics of dental ceramics are of great interest to dental industry. The green bodies of TZP/$Al_2O_3$ composites were prepared by the cold isostatic pressing, and machined on the CNC lathe using PCD (polycrystalline diamond) insert under various machining conditions. With increasing nose radius of PCD insert, surface roughness initially increased due to increased cutting resistance, but decreased by the onset of sliding fracture. The lowest surface roughness was obtained at spindle speed of 1,300 rpm and lowest feed rate. Hard bodies were prepared by pressureless sintering the machined green bodies at several temperatures. The grinding test for sintered hard body was conducted using electroplated diamond bur with different grit sizes. During grinding, grain pull out in the composite was occurred due to thermal expansion mismatch between the alumina and zirconia. The strength of the composite decreased with alumina contents, due to increased surface roughness and high monoclinic phase transformed during grinding process. The final polished samples represented high strength by the elimination of a phase transformation layer.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.1011-1017
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• 1999

Electrolytic in-process dressing grinding technique which enables application of metal bond wheels with fine superabrasives in mirror surface grinding operations has developed. It is possible to make efficient precision machining of hard and brittle material such as ceramic and hard metal by the employment of this technique. However, in order to ensure the success of performances such as efficient machining, surface finish, and surface quality, it is important to sustain the insulating layer that has sharply exposed abrasives in wheel surface. Using AE(Acoustic Emission) sensor, this paper will show whether the insulating layer sustains stably or not in real grinding time. And by comparing AErms value and surface roughness their thresholds for stable electrolytic in-process dressing grinding will be determined.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.108-113
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• 2005

In this study, rotary type diamond dressing system for ultra-precision centerless grinding for ferrule was developed at the first time and experiments were conducted with AE sensor and hall sensor system to verify the optimum dressing condition for ultra-precision centerless grinding for ferrule. The correlations with the condition of dressing are evaluated by AE signal analysis with root mean square (RMS) and frequency analysis. And current signals from hall sensor are also studied as a factor of dressing optimum condition selection. Dressing process was conducted to investigate the effects of depth of cut, rotating speed, and the number of overlap to select the optimum condition of rotary dressing system of ultra-precision centerless grinding machine for ferrule fabrication. In order to verify the optimum condition of dressing, AE and current signals were compared with the surface quality of dressing wheel and grinding wheel for ultra-precision ferrule grinding. All of these experiments were completed by Taguchi Methodology to reduce experimental time. Hence, the optimum condition of rotary dressing system for ultra-precision centerless grinding for ferrule fabrication can be selected following to the experiment result from signals of AE and hall sensor.