• 기계와재료
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• v.11 no.4 s.42
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• pp.62-79
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• 1999

• Journal of the Korean Society for Precision Engineering
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• v.33 no.11
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• pp.893-898
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• 2016

Plastic array lens are cheap to manufacture; however, plastic is not resistant to high temperatures and moisture. Optical glass represents a better solution but is a more-expensive alternative. Glass array lens can be produced using lithography or precision-molding techniques. The lithography process is commonly used, for instance, in the semiconductor industry; however, the manufacturing costs are high, the processing time is quite long, and spherical aberration is a problem. To obtain high-order aspherical shapes, mold-core manufacturing is conducted through ultra-precision grinding machining. In this paper, a $4{\times}1$ mold core was manufactured using an ultra-precision machine with a jig for the injection molding of an aspherical array lens. The machined mold core was measured using the Form TalySurf PGI 2+ contact-stylus profilometer. The measurement data of the mold core are suitable for the design criterion of below 0.5 um.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.9
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• pp.58-63
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• 2009

Silicon carbide (SiC) has been used for many engineering applications because of their high strength at high temperatures and high resistances to chemical degradation. SiC is very useful especially for a glass lens mold whose components demanded to the machining with good surface finish and low surface damage. The performance and reliability of optical components are strongly influenced by the surface damage of SiC during grinding process. Therefore, the severe process condition optimization shall be necessary for the highly qualified SiC glass lens mold. Usually the major form of damage in grinding of SiC is a crack occurs at surface and subsurface. The energy introduced in the layers close to the surface leads to the formation of these cracks. The experimental studies have been carried out to get optimum conditions for grinding of silicon carbide. To get the required qualified surface finish in grinding of SiC, the selection of type of the wheel is also important. Grinding processes of sintered SiC work-pieces is carried out with varying wheel type, depth of cut and feed using diamond wheel. The machining result of the surface roughness and the number of flaws, have been analyzed by use of surface profilers and SEM.

• Journal of the Korean Society for Precision Engineering
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• v.33 no.7
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• pp.595-600
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• 2016

An orbital grinding system uses a special motion to machine crankshafts in ships. When a crankshaft is operated, eccentric pins rotate and a grinding wheel moves in order to grind the pins. Thermal error caused by heat generated in the grinding process decreases the quality of the final product. In this study, the thermal error of an orbital grinding system caused by heat generation was investigated in order to predict the extent of thermal error that can occur during the grinding process. Since the machine position changes during orbital grinding, the pin part is divided into 30 degree intervals and heat is generated. Total thermal error was measured by summing the thermal errors associated with the pin and the grinding wheel. Total thermal error was found to reach a maximum at 60 degrees and a minimum at 210 degrees because of the shape of the crankshaft.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.1 s.94
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• pp.108-115
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• 1999

Since grinding is a more complicated process than any other machining process, it is hard for operators to setup a grinding machine properly and to find out correctly abnormal grinding states resulting in damages to products. Abnormalities would be caused by improper setup, improper dressing/grinding conditions which are likely to be occurred without skilled operators' attention. In this study, an AE monitoring unit is developed to help operators conduct with ease setup, and set properly dressing/grinding conditions. AErms(root-mean-square) signal being monitored, on-going process states during grinding and dressing is visualized for machine operators to judge whether the processes are in good condition. Evaluation tests are carried out on centerless grinding machines-both cylindrical and internal. The developed AE monitoring system is verified to be useful to check grinding/dressing states in process even in the centerless grinding of which process is most unknown among various grinding methods because of the complex structure.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.4
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• pp.100-110
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• 1995

This paper aims at reviewing the possibility of application over normal or abnormal, detection used by AE, and the characteristics of grinding processes. In this study, when WA-vitri-fied ' resinoid bond grinding wheels:36 kinds of grinding wheel and grinding depth were tuned at the surface grinding, the zone of AE signal generation is theoretically modelled and reviewed by grinding processes. The variation of grinding resistance( F$n^{9}$ $F_{t}$) and AE signal is detected in-process by the use of AE measuring system. The tests are carried out in accordance with grain size and grade of grinding wheels, and work-pieces-STD11 and STD61. According to the experiment's results, the following can be expected;as grinding time passes by, the relation of grinding depth and quantity of AE signal, observing on AE signal and grinding burn suggest the characteristics of grinding processes and evalution on the possibility of control of grinding machine, and monitoring abnormal conditions.e, and monitoring abnormal conditions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.793-797
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• 2000

The environmental problems by using coolant demanded the new cooling methods. As one of them the studies on the dry grinding with compressed cold air have been done. The cooling method using compressed cold air was effdve thmugh going down the temperature of compressed air supplied below $-25^{\circ}C$ and inneasing the amount of mmpresd cold air, but had not enough cooling effect due to the low performance of lubrication. Therefore, the cooling methods using MQL(Minimum Quantity Lubrication) or mist newly were suggested. These two methods can satisfy both cooling effect and lubrication with only small amount of coolant, also has the benefit in the point of decreasing the envimnmental pollution. This paper focused on analyzing the grindmg characteristics of the cooling method using mid. The generated heat and grinding force of the cooling method using mist were compared with them of coolant and compressed cold air. And them grinding test according to the temperature of compressed cold air, mist spray amount and mist supply direction were done.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.05a
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• pp.870-873
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• 2000

This investigation reports the grinding characteristics of quartz. Grinding experiments were performed at various grinding conditions including wheel mesh, table speed and depth of cut. The grinding forces and specific grinding energies were measured to compare the grindability of quartz with those of structural ceramics such as A1$_2$O$_3$, SiC, Si$_3$N$_4$ and ZrO$_2$. Surface roughness was also measured with tracer and the ground surfaces were observed with SEM. The chip formation energy of quartz was about 6J/㎣, which is quite smaller than those of structural ceramics. Although plastic flows are occured in Si$_3$N$_4$ and ZrO$_2$, micro/macro cracks are occured in ground surface of quartz like in A1$_2$O$_3$ and SiC.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.12 s.255
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• pp.1634-1641
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• 2006

High-precision centerless grinding machines are emerging as a means of finishing the outer diameter grinding process required for ferrules, which are widely used as fiber optic connectors. In this study, a sensitivity analysis for structural and thermal characteristics was carried out using a virtual prototype of a centerless grinding machine to realize systematic design technology and performance improvements required to manufacture ferrules. The prototype consisted of a concrete-filled bed, hydrostatic grinding wheel (GW) and regulating wheel (RW) spindle systems, a hydrostatic RW table feed mechanism, a RW swivel mechanism, and on-machine GW and RW dressers. The results of the structural sensitivity analysis illustrated that the vertical stiffness of hydrostatic guideway for the RW table feed system greatly influenced the horizontal loop stiffness, and the results of the thermal sensitivity analysis illustrated that the heat generation rates at hydrostatic bearings and belt pulley greatly influenced the temperature rise of hydrostatic bearings and the deviation of thermal displacement between GW and RW.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.555-556
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• 2006

In recent years, the higher flatness level in wafer shape has been strictly demanded with a high integration of the semiconductor devices. It has become difficult for a conventional wafer preparing process to satisfy those demands. In order to meet those demands, surface grinding with in-feed grinder is adopted. In an in-feed grinding method, a chuck table fur fixing a semiconductor wafrr rotates on its rotation axis with a slight tilt angle to the rotation axis of a cup shaped grinding wheel and the grinding wheel in rotation moves down to grind the wafer. So, stability of the grinder structure is very important to aquire a wafer of good quality. This paper describes the features of the in-feed grinder and some FEM analysis results of the grinder structure.