• 한국분무공학회지
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• 제17권1호
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• pp.14-19
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• 2012

The present study conducts experimental investigation on spreading and deposition characteristics of a $4.3{\mu}l$ de-ionized (DI) water droplet impacting upon aluminum (Al 6061) flat and textured surfaces. The micro-textured surface consisted the micro-hole arrays (hole diameter: $125{\mu}m$, hole depth: $125{\mu}m$) fabricated by the conventional micro-computer numerical control (${\mu}$-CNC) milling machine process. We examined the surface effect of texture area fraction ${\varphi}_s$ ranging from 0 to 0.57 and impact velocity of droplet ranging from 0.40 m/s to 1.45 m/s on spreading and deposition characteristics from captured images. We used a high-speed camera to capture sequential images for investigate spreading characteristics and the image sensor to capture image of final equilibrium deposition droplet for analyze spreading diameter and contact angle. We found that the deposition droplet on textured surfaces have different wetting states. When the impact velocity is low, the non-wetting state partially exists, whereas over 0.64 m/s of impact velocity, totally wetting state is more prominent due to the increase kinetic energy of impinging droplet.

• 한국레이저가공학회지
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• 제6권1호
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• pp.9-16
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• 2003

Micromachining using the DPSS 3rd Harmonic Laser (355nm) has outstanding advantages as a UV source in comparison with Excimer lasers in various aspects such as maintenance cost, maskless machining, high repetition rate and so on. It also has the greater absorptivity of many materials in contrast to other IR sources. In this paper, the process for micro-drilling of blind hole in Cu/PI/Cu substrate with the DPSS UV laser and the scanning device is investigated by the experimental methods. It is known that there is a large gap between the ablation threshold of copper and that of PI. We use the Archimedes spiral path for the blind hole with different energy densities to ablate the different material. Finally, the blind via hole of diameter 100$\mu\textrm{m}$ and 50$\mu\textrm{m}$ was drilled.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1997년도 추계학술대회 논문집
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• pp.37-42
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• 1997

This paper describes result of experiment of parameters affecting the micro hole drilling time, kind of assisting gas and it's pressure. The result reveals that parameter value of 0.08J, 20Hz, dwell time of 300 microseconds can be a good machining condition to make micro hole diameter range of 50-70${\mu}{\textrm}{m}$, Assistant gas such air, O2, Ar, N2 was adapted. Assistant gas of air makes heat affected zone enlarge due to burning of material, also it makes hole irregular and damage because of refusion stick to caused by chemical reaction with Al2O3 ceramic material. O2(99.9%) has good characteristic to get good drilling and smooth surface on pressure of 0.2kgf/$\textrm{cm}^2$, but it is expensive. Ar, N2 makes material burn and crack severely and proved to be an appropriate but, Ar was better than N2.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.213-216
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• 2001

A micro hole punching system was developed and micro holes of 100m in diameter were successfully made on brass sheets of loom in thickness. A micro punch made of tungsten carbide was designed to withstand the punch load, considering the buckling and the bending moment due to possible misalignment error. The punch was fabricated by the grinding process with diamond wheel. The die was designed considering the punch load and fabricated by micro electrodischarge machining process. In this system the stripper is designed to guide punch tip to minimize the possible misalignment. The punch was installed on a vertical stepper and the die was mounted on an X-Y translation unit. The precision motion controller controlled all motions of the micro hole punching system. In this study technical difficulties and solutions in the micro hole punching process were also discussed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1052-1058
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• 2003

The possibility of micro/nano machining through electro-chemical process is discussed in this research. Electro-chemical dissolution region is localized within 1 ${\mu}m$ by applying ultra short pulses with tens of nanosecond duration. The effects of voltage, pulse duration, and pulse frequency on the localization distance are investigated. Localization distance can be manipulated by controlling the voltage and pulse duration, and various hole shapes are produced including stepped holes and taper free hole. High quality micro-hole with 8 ${\mu}m$ diameter with 20 ${\mu}m$ depth and micro-groove with 9 ${\mu}m$ width with 10 ${\mu}m$ depth are machined on 304 stainless steel.

• 한국기계가공학회지
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• 제11권5호
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• pp.88-93
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• 2012

This paper describes the machinability of the sintered carbide and tool-die steel(STD-11) by electric discharge drilling with various tubular electrodes which have multi-holes. Various types of electrode which have different diameters and materials are used with the application of continuous direct current and axial electrode feed. Inner part of electrodes are inserted with smaller tubes or Y-channel or bar. In ED-Drilling, the dielectric flushed down the interior of the rotating tube electrode, in order to remove machining debris from the hole. As result of experiments, the bigger the diameter of the electrode is, the lower the material removal rate is. Machinability of copper electrode is higher than that of brass. In machining of sintered carbide, to use oil is better than distilled water as dielectric.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.671-674
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• 2002

Pressure compensating temperature control valve(TCV) is one of the important control devices, which is used to maintain the constant temperature of working fluid in power and chemical plants. The ratio of cylinder hole diameters of inlet and outlet is the main design parameters of TCV. So this needs to be investigated to improve the function of control of temperature and void fraction. In this study, numerical analysis is carried out with various ratios of cylinder hole diameters of the inlet and outlet in the TCV. Especial1y, the distribution of the static pressure Is investigated to calculate the new coefficient($C_{\upsilon}$) and resistance coefficient(K). The governing equations are derived from making using of three-dimensional Naver-Stokes equations with standard $k-{\varepsilon}$ turbulence model and SIMPLE algorithm. Using a commercial code, PHOENICS, pressure and flow fields in TCV are calculated with different inlet and outlet diameters of the cylinder hole for cold and hot water passages.

• Journal of Mechanical Science and Technology
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• 제14권10호
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• pp.1021-1027
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• 2000

In this study, fatigue tests were performed to examine the effects of micro drill hole on fatigue limit of as cast and austempered ductile cast iron (ADI) using the rotary bending fatigue tester. As results, micro drill holes ($diameter{\leq}0.4mm$) did not influence the fatigue limit of ADI, compared to annealed ductile cast iron; the critical defect size of crack initiation, in ADI was larger than as cast. If the ${\sqrt{area}}$ of micro drill hole and graphite nodule in ADI are comparable, crack initiates at the graphite nodule. When the ruggedness developes through austempering treatment process, microstructure on crack initiation at micro drill hole is tougher than that of as cast ductile cast iron.

• 한국기계가공학회지
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• 제16권5호
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• pp.7-12
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• 2017

It is assumed that the buckling and cutting conditions depending on the slenderness ratio will affect the machining quality of the rotary boring tool mounted on a milling machine. In this study, the boring cutter was designed and fabricated to precisely create the Ø30 hole. Through the performance evaluation, the accuracy of the hole according to the slenderness ratio and cutting conditions was analyzed, and the following conclusions were obtained. The higher the RPM, the smaller the change in the working diameter, and the smaller the hole. Next, the smaller the slenderness ratio, the smaller the change in straightness due to the change in cutting conditions. Finally, the slenderness ratio also affects the tendency for changes in the concentricity. The larger the slenderness ratio, the more sensitive the concentricity to changes in cutting conditions.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 가을 학술발표회 논문집
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• pp.431-438
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• 1999

Vertical congressive and horizontal pile load tests were performed to a instrumented large diameter (D : 1,000 mm) drilled shaft. A drilled shaft was penetrated into the weathered soil and weathered rock. PMT was done for evaluation of properties for these strata. It was expected to be difficult to get undisturbed samples of weathered soils and rocks. Thus. PMT was done at the several selected depths. In those strata, to prevent the test bore hole from collapsing, bentonite slurry was used for making the test bore hole. In this study. soil properties was evaluated by means of PMT results and estimating method (direct method, the Memard method) of vertical pile capacity and horizontal pile behaviors were summarized. Also, vertical and horizontal pile capacity were calculated using PMT and pile load test results.