• 대한기계학회논문집B
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• 제33권2호
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• pp.93-100
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• 2009

Characteristics of micro-sonic/supersonic axi-symmetric jet impinging on a flat plate with a pre-drilled hole were both experimentally and numerically studied, to observe the role of assist-gas jet to eject melted materials from the cut zone in the laser machining. For various Mach numbers of the nozzle and the total pressures of the assist gas, detailed impinging jet flow structures over the plate and the variations of mass flux through the pre-drilled hole were observed. It was found that the present experimental and numerical results show a good agreement, which proves the accountability of the present work. From the present study, it was also observed that the mass flow rate through the hole was closely related with the total pressure loss caused by the Mach disc on the work piece, and that supersonic nozzle could perform more efficient roles as blowing the assist-gas jet in the laser machining, as compared to sonic nozzles.

• Tribology and Lubricants
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• 제39권2호
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• pp.56-60
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• 2023

In this study, we evaluate the anisotropic flow of droplets according to the directionality of asperities. We manufacture a mold with an inclined hole by adjusting the jig angle using a high-power diode laser. Using the manufactured mold, we prepare specimens for wettability studies by the micro molding technique. We fabricate twelve kinds of surfaces with micro-asperities inclined at 0°, 15°, 30°, and 45° for asperity pitches of 100 ㎛, 200 ㎛, and 300 ㎛. We evaluate the static and dynamic behaviors of the droplets as a function of the asperities pitch and inclination angles. The anisotropic effect increases as the pitch increases between asperities, and the anisotropic flow characteristics increase as the inclination angle of the asperities increases. On the surface with hole pitches of 100 ㎛ and 200 ㎛, the contact angle of the droplet shows high hydrophobicity at approximately 160°, but on the surface with the 300-㎛ hole pitch, the contact angle is approximately 110°, indicating that the hydrophobic effect rapidly reduces. Additionally, when the inclination angle of the asperities is approximately 30°, the left and right contact angle deviations of the droplet are the lowest, showing that the roll-off angle is relatively low.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.952-957
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• 2001

The objectives of this investigation were to obtain an excellent spray by cavitation under the low injection pressure. When cavitation occurs in the nozzle hole, the atomization of the liquid jet enhanced considerably. In this experiments, a acrylic nozzle made the gap and installed the bypass in the nozzle hole was used to enhance the atomization of the liquid jet at the low injection pressure. The liquid flow in the nozzle hole was photographed by a transmitted light using a micro flash. The spray angle was measured macroscope images of PMAS and the Sauter mean diameter was measured PDA system. To measure the pressure of the nozzle hole, pressure transducer was used. The results of this study indicated that enhanced atomization of the liquid jet at the low injection pressure was obtained by making the gap and installing the bypass at the single hole nozzle.

• 한국분무공학회지
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• 제7권1호
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• pp.36-42
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• 2002

The objective of this investigation was to obtain an excellent spray at the low injection pressure. When cavitation occurred in the nozzle hole the atomization of the liquid jet enhanced considerably. In this experiments, a acrylic nozzle which was installed the gap and installed the bypass in the nozzle hole was used to enhance the atomization of the liquid jet at the few injection pressure. The liquid flow in the nozzle hole was photographed by a transmitted light using a micro flash. The spray angle was measured by macroscope images of PMAS and the Sauter mean diameter was measured by PDA system. The pressure of the notate hole was measured by pressure transducer. It was found that enhanced atomization of the liquid jet at the low injection pressure was obtained by installing the gap and the bypass at the single hole nozzle.

• 한국재료학회지
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• 제29권3호
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• pp.155-159
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• 2019

Surface plasmon resonance is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity material stimulated by incident light. In particular, when light transmits through the metallic microhole structures, it shows an increased intensity of light. Thus, it is used to increase the efficiency of devices such as LEDs, solar cells, and sensors. There are various methods to make micro-hole structures. In this experiment, micro holes are formed using a wet chemical etching method, which is inexpensive and can be mass processed. The shape of the holes depends on crystal facets, temperature, the concentration of the etchant solution, and etching time. We select a GaAs(100) single crystal wafer in this experiment and satisfactory results are obtained under the ratio of etchant solution with $H_2SO_4:H_2O_2:H_2O=1:5:5$. The morphology of micro holes according to the temperature and time is observed using field emission - scanning electron microscopy (FE-SEM). The etching mechanism at the corners and sidewalls is explained through the configuration of atoms.

• 대한기계학회논문집A
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• 제28권6호
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• pp.867-875
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• 2004

In order to inspect burr geometry and hole quality in micro-drilling processes, a cost-effective method using an image processing and shape from focus (SFF) methods on the machine tool is proposed. A CCD camera with a zoom lens and a novel illumination unit is used in this paper. Since the on-machine vision unit is incorporated with the CNC function of the machine tool, direct measurement and condition monitoring of micro-drilling processes are conducted between drilling processes on the machine tool. Stainless steel and hardened tool steel are used as specimens, as well as twist drills made of carbide are used in experiments. Validity of the developed system is confirmed through experiments.

• 한국공작기계학회논문집
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• 제13권1호
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• pp.55-62
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• 2004

This paper addresses the method for figuring out the hole diameter on the mask containing the information about machining depth. With this mask e micro machining is carried out with a simple 2D movement of the mask. Based on e suggested method excimer laser ablation processes are modeled and determination of the optimal laser ablation conditions such as hole diameter, step size, mask movement velocity, etc. is completed. The excimer laser ablation simulation for creating 3D micro lens is carried out by employing determined ablation conditions to prove verification of the method. The results from simulation illustrated the average error of 140nm and e relative error of 2％.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1195-1198
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• 2003

Micro former has been known as a useful tool for machining micro parts. It makes micro holes automatically with punches, a hole-shape die and material by rotation of crank shaft synchronously. Micro displacement in micro forming affects on the performance of machining because micro forming size is similar with its mechanical displacement. Therefore, the measurement of this micro displacement is essential to be guaranteed to obtain high forming precision in the whole machine as well as its devices. This paper addresses the development of a laser interferometer to measure micro displacement for a micro former. The laser interferometer is able to measure micro displacement during a few micro seconds with non-contact. For the experiment, a laser probe is installed on the optical table with optical devices and a micro displacement generating device. The velocity decoding board is also added to calculate doppler shift frequency directly. Finally simple experiments are conducted to confirm its functional operation.

• 한국정밀공학회지
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• 제22권3호
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• pp.15-20
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• 2005

This paper describes the PCB drilling using an ultra high-speed air bearing spindle system and micro drill. For this research, we have developed the ultra high-speed air bearing spindle of 125,000 rpm and made an experiment for the application possibility in the PCB drilling. In order to estimate the drilling performance, we have investigated the size and damage of drilled hole, and the wear of drill at 90,000rpm. Results are as follows; we have confirmed the possibility in the PCB drilling of air bearing spindle. In case of micro-drilling PCB at $0.1mm\sim0.3mm$, the increase in the number of drilling has resulted in a bigger size of holes and also a bigger size of damage. It has been found that the wear of micro drill tends to concentrate in the main cutting edge.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 하계학술대회 논문집 C
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• pp.1924-1926
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• 2001

A novel wet release process ($\mu$ CARP - Micro Channel Assisted Release Process) for releasing an extreme large-area plate structure without etching hole is proposed and experimented. Etching holes in conventional process reduce a effective area and degrade an optical characteristics by a diffraction. In addition, as the area of a released structure increases, the stietion becomes more serious. The proposed process resolves these problems by the introduction of a micro fluidic channel beneath the structure which will be released. In this paper, a 5 mm${\times}$5mm-single crystal silicon plate structure was released by the proposed $\mu$CARP without etch holes on the structure. The variation in etching time with respect to the of the introduced micro channel is also examined. This process is expected to be beneficial for the actuator of a nano-scale data storage and the scanning mirror.