• Tribology and Lubricants
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• v.25 no.4
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• pp.217-224
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• 2009

In this study, friction tests were carried out in order to investigate the friction behavior of textured surface in unlubricated state using ball-on-disk type apparatus. Test specimens were SUJ2 bearing steel ball and SM45C steel disk. Square arrays of circular micro-dimples were created on the surface of disk specimen by Nd:YAG Laser. Friction tests were performed for the disk specimen with various micro-dimple parameters and was also conducted for the variation of normal loads and relative velocities. The results showed that fiction coefficient of textured surface was lower than that of non-textured surface and the deeper depth of micro-dimple was, the lower friction coefficient obtained at the same diameter of micro-dimple in unlubricated state. Area density of micro-dimple had an effect on the friction coefficient. It was also found that friction coefficient generally decreased with the increase of normal load and relative velocity.

• 대한공업교육학회지
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• v.31 no.2
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• pp.350-363
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• 2006

Recently, the micro end-milling processing is demanded the high-precise technique with good surface roughness and rapid time in milli-structure parts, micro machine parts and molding industry. The cutting conditions of micro end-milling has an effect on surface roughness of cutting surface. Therefore this study was carried out to cut stainless steel using high revolution air bearing spindle and micro end-mill and analyze the cutting condition to get the optimum surface roughness by design of experiment. From this study, surface roughness have an much effect according to priority on depth of cut, revolution of spindle and feed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.10a
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• pp.933-934
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.1217-1218
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• 2010

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.39-40
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.83-84
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• 2008

• Journal of the Korean Society for Precision Engineering
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• v.29 no.12
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• pp.1279-1284
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• 2012

Micro structures which are widely used at various fields are commonly fabricated by lithograph, etching and laser methods. Recently, with the emergence of micro tools and ultra-precision machine tools, fabrication of the micro structures obtained using end-milling are studied. However, there are some problems due to the diameter of the micro end-mill getting smaller below $100{\mu}m$. The micro run-out resulted from miniaturization of end-mills have influence seriously on accuracy of micro structures. The error of run-out with a tooling jig showed a decrease of about $9.3{\mu}m$. Furthermore, micro structures with width of $30{\mu}m$ could be applied through experiments of slot machining obtained using 30 and $50{\mu}m$ end-mill. Also, narrow angle structures with $30^{\circ}$ angle could be applied through analysis of machining acute angle structures. Based on basic experiments, micro fluidics channels and spiral patterns for air bearing were machined.

• Tribology and Lubricants
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• v.32 no.5
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• pp.147-153
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• 2016

Friction reduction between machine components is important for improving their efficiency and lifespan. In recent years, surface texturing has received considerable attention as a viable means to enhance the efficiency and tribological performance of highly sliding mechanical components such as parallel thrust bearings, mechanical face seals, and piston rings. In this study, we perform lubrication analysis to investigate the effect of dimple shapes and orientations on the lubrication characteristics of a surface textured parallel thrust bearing. Numerical analysis involves solving the continuity and Navier-Stokes equations using a commercial computational fluid dynamics (CFD) code, FLUENT. We use dimples consisting of hemispherical and different semiellipsoidal orientations for simulation. We compare pressure and streamline distributions, load capacity, friction force, and leakage flowrate for different numbers of dimples and orientations. We find that the dimple shapes, orientations, and their numbers starting from an inlet influence the lubrication characteristics. The results show that partial texturing of the bearing inlet region, and the ellipsoidal dimples with the major axis aligned along the lubricant flow direction exhibit the best lubrication characteristics in terms of higher load capacity and lower friction. The results can be used in the design of optimum dimple characteristics for parallel thrust bearings, for which further research is required.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.3
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• pp.130-136
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• 2021

With the development of the industry, bearings that require higher durability and efficiency are required, and various methods to reduce friction and wear of bearings are being studied. In this study, a wear test was conducted for STB2, a bearing steel material, by machining a micro-line pattern on the race surface of the bearing by machining. The pattern pitch of the specimens was processed to 40㎛, 80㎛, and 150㎛, and the coefficient of friction characteristics were investigated for the unpatterned specimen and the specimen with a DLC thin film deposited on the surface. As a result of the wear test, the pattern pitch showed the smallest coefficient of friction at 40㎛, and it was confirmed that the smaller the pattern pitch, the better the tribology characteristics.

• Proceedings of the KIEE Conference
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• 2008.04c
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• pp.80-82
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• 2008

This paper deals with the design of an 870 krpm class high-speed permanent magnet synchronous generator (PMSG) applied to micro turbine system. Since space where the high-speed PMSG coupled with the micro turbine occupies in the system is strictly limited, the work described in this paper is motivated by the desire to make maximum output power of the generator considering the rotor and stator structures, winding methods and bearing system under restricted space.