• Proceedings of the KSME Conference
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• 2001.11b
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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.

• Journal of ILASS-Korea
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• v.7 no.1
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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.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1064-1067
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• 2001

Micro drilling is used in the production of fuel injection nozzle, watch, camera, air bearing and pinted circuit boards(PCB) are demanded for high precision. Recently industries of precision production require more small hole, high aspect ratio and high speed working for micro deep hole drilling. But the undesirable characteristics of micro drilling is the small signal to noise ratios, wandering motion of drill, high aspect ratio and the increase of cutting force as cutting depth increase. So in this paper to obtain the optimization of cutting condition a study on the characteristics of micro deep hole drilling used Tool dynamometer is proposed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.04a
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• pp.275-280
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• 2001

Recently, the trends of industrial products grow more miniaturization, variety and mass production. Micro drilling which take high precision in cutting work is requested more micro hole and high speed working. Especially, Micro deep hole drilling is becoming more important in a wide spectrum of precision production industries, ranging from the production of automotive fuel injection nozzle, watch and camera parts, medical needles, and thick multi-layered Printed Circuit Boards(PCB) that are demanded for very high density electric circuitry. This paper shows the tool monitoring results of micro drill with tool dynamometer. And additionally, microscope with built-in monitor inspection show the relationship between burr in workpiece and chip form of micro drill machining.

• Journal of ILASS-Korea
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• v.20 no.1
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• pp.43-52
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• 2015

Experimental study was conducted to investigate the effects of ultra-high injection pressure and nozzle hole diameter on diesel flow and spray characteristics. Electronically controlled ultra-high pressure fuel injection system was made to supply the fuel of ultra-high pressure consistently. Three injection pressures, 80, 160, and 250MPa were applied. Four type of injectors with identical eight nozzle holes were used. The four injectors have nozzle hole diameters of 115, 105, 95, and $85{\mu}m$ respectively. Injection quantity and rate were measured to investigate flow characteristics according to injection pressures and nozzle hole diameters. Mie-scattering and shadowgraph were performed to visualize liquid and vapor phases of diesel spray in a constant volume combustion chamber (CVCC). Ambient conditions of high pressure and high temperature in a diesel engine were simulated by using CVCC.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1294-1298
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• 2005

In this study, combined micro press and surface finishing process are proposed to fabricate the micro nozzle array on a stainless steel sheet metal. In micro hole punching process the burr occurs inevitably, but the burr must be minimized in order to improve the quality and accuracy of the product. For this reason, subsequent magnetic field-assisted finishing technique is applied to remove the burr which exists around the nozzles for ink-jet printer head and proved to be a feasible for deburring by experiment. The deburring characteristics of sheet metals were investigated changing with polishing time and magnetic abrasive size. After the deburring, the burr size has remarkably reduced and roundness of the hole also has improved.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.285-288
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• 2007

Numerical study of the influence of the boundary layer of micro-supersonic jet impinging on a flat plate with a hole was performed, to investigate the role of gas jet to eject melted materials from the cut zone in the laser machining. The detailed shock structures and the information of the mass flow rate through the hole were compared to the results of the previous study, in which the effects of boundary layer inside nozzle was not accounted. It was found that the boundary layer inside the micro- nozzle introduced stronger Mach disc over the machining zone, and thus that the mass flow rate through the hole decreased.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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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.

• Journal of Sensor Science and Technology
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• v.10 no.4
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• pp.232-238
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• 2001

We fabricated micro-pump using stereolithography technology. The pump was fabricated using PZT for its drive and used non-movable valve of diffuser/nozzle concept. Size of the pump chamber is, $14mm{\psi}$, narrow hole of diffuser/nozzle is $0.5mm{\psi}$ and wide hole $1mm{\psi}$ and chamber depth is 1.2mm, respectively. We confirmed its operation at frequency 100Hz, supply voltage $90{\sim}250Vp-p$. As the result of the pump working measurement, when ethanol is used, the pressure head difference between inlet and outlet of the pump is about 53mm in the frequency of 100Hz, 200V of Vp-p.

• Transactions of Materials Processing
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• v.21 no.5
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• pp.312-318
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• 2012

With an increasing trend toward miniaturization, electrical discharge machining(EDM) has been receiving a lot of attention as a suitable production technology for micro-parts, since it enables the machining of hard conductive materials with a high degree of repeatability and without alteration to the material. When a micro-hole is fabricated by EDM, however, the diameter of the inlet hole is larger than that of the outlet region due to the additional discharge effect caused by the eroded particles. In this paper, a shot blasting surface treatment, in which an abrasive material is accelerated through a pressurized nozzle and directed at the surface of a part, is suggested as an effective method to reduce the tapered shape of EDM micro-hole. In addition, the influence of process parameters such as spark-on time and electrode diameter on the machining performance was investigated. It is shown quantitatively that the difference in diameter between the inlet and outlet holes decreases with the shot blasting treatment and with decreasing spark-on time.