• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.85-85
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• 2003

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1265-1268
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• 2005

Due to the increase of the need for reliable high density information storage devices, the demand for precise machining of the slider in HDD is rapidly growing. The present fabrication process of slider bears some serious problems such as low yield ratio in mass production, which is mainly caused by inefficient machining processes in shaping camber and crown on the slider. In order to increase slider yield ratio in HDD, a new systematic machining process is proposed and developed in this work. This new machining process includes the use of magnetorheological (MR) fluid, a smart polishing material generally used for ultra-fine surface finishing of micro structures. It is shown that the process proposed in this work enables to make camber and crown pattern in the scale of few tens of nanometers. Experiment results shows that the MR polishing can be also used for shaping process of micro structures.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.496-500
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• 2004

A new, commercially available polishing process called magnetorheological finishing is used to polish and figure precision optics. To understand and model this process correctly it is important to determine the mechanical properties of the fluid under the influence of the magnetic field. Magnetorheological (MR) fluids are commonly modeled as Bingham fluids, so one of the essential properties to measure is the yield stress. Since MR fluids are inherently anisotropic, the yield stress will depend on the mutual orientation of the magnetic field and the direction of deformation. The relative orientation of the field and deformation in polishing does not coincide with common rheological setups, so a new rheometer has been designed and tested. This new magnetorheometer design has been shown to give correct stresses during calibration experiments using Newtonian fluids with a known viscosity. The measured stress has also been shown to have a magnitude consistent with published finite element approximations for magnetic fluids. The design of the instrument was complicated because of the requirements imposed upon the magnetic field, and the difficulty in satisfying the no slip boundary condition. Our results show the importance of having a homogeneous field in the test region during measurements. The solutions to these problems and discussion of the measurements on nonmagnetic and magnetic fluids are given.

• The Journal of Korean Academy of Prosthodontics
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• v.58 no.3
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• pp.207-216
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• 2020

Purpose: To compare the polishing characteristics and their influence on Candida albicans adhesion to the recently introduced polyetherketoneketone (PEKK) and the conventional polymethylmethacrylate (PMMA) denture resin material. Materials and methods: Specimens from PEKK (Group E) and PMMA (Group M) were made in dimensions of 8 mm in diameter and 2 mm in thickness. The specimens were further divided into sub-groups according to the extent of polishing (ER, MR: rough; EP, MP: polished, N = 12 each). The specimens were polished using polishing machine and SiC foil. ER and MR group specimens were polished with 600 grit SiC foil only. EP and MP groups were further polished with 800, 1,000, 1,200 grit SiC foils sequentially. To measure the surface roughness values (Sa) of specimens, atomic force microscope (AFM) was used and scanning electron microscope (SEM) observation under 1,000, and 20,000 magnifications was performed to investigate surface topography. The polished specimens were soaked in C. albicans suspension for 2 hours with shaking to promote adhesion. The attached C. albicans were detached from the surface with 10 times of pipetting. The suspension of detached C. albicans was performed by serial dilution to 10³ times, and the diluted suspensions were inoculated on Sabouraud dextrose agar plates using spread plate method. After incubating the plate for 48 hours, colony forming unit (CFU)/plate of C. albicans was counted. Statistical analysis was performed using one-way ANOVA and Tukey HSD test to confirm significant difference between the groups (α=.05). Results: Average Sa value was significantly higher in MR group compared to other groups (P<.05), meaning that additional polishing steps reduced surface roughness effectively only in the PMMA specimens. There was no significant difference in Sa values between MP and EP groups. In SEM images, PEKK specimens showed numerous spikes of abraded material protruding from the surface and this phenomenon was more significant in EP group. The mean CFU/plate value was the highest in EP group and this was significant when it was compared to MP group (P<.05) which was the lowest. Conclusion: Polishing PEKK using serial SiC abrasive foil may result in higher adhesion of C. albicans. In clinic, this should be considered carefully.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.447-448
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.557-560
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• 2003

Magnetorheological finishing(MRF) is a newly developed and recently commercialized for finishing optical components. The magnetorheological fluid consists of a water based suspension of carbonyl iron, nonmagnetic polishing abrasives, and small amounts of stabilizer. This magnetorheological fluid is pumped from conditioner on the rotating wheel and suctioned back to the conditioner, where it cooled to setpoint temperature and evaporative losses are replaced. This method could produce some problems in suction. So newly designed MRF tools is proposed in which MR fluid is not circulated and conditioned by the slurry. The new polishing mechanism is experimented. Measured surface roughness supports the validity of this mechanism.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.439-440
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• 2012

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.263-263
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• 2003

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.05a
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• pp.21-22
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• 2010

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.311-318
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• 2000

Several factors which influence baseline instability (BLI) phenomenon in MR drive were investigated experimentally. In particular, the role of surface topography on BLI was studied in detail. The r esults show that BLI is linearly proportional to the surface waviness with a spatial wavelength of 0.4 to 5.0 min. BLI becomes worse as the surface waviness increases. On the other hand, surface roughness which has a spatial wavelength below 25 $\mu$ m has no effect on BLI. The results further show that the effect of bias current on the BLI is amplified on the disk with worse surface waviness. The disk surface waviness is dependent on the manufacturing process and becomes an inherent surface property of media. The disk surface waviness. therefore, can not be overlooked when evaluating the media for a high-performance hard disk drive. In general, waviness is reduced mainly during grinding and polishing process during manufacturing.