• 한국레이저가공학회지
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• 제14권2호
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• pp.8-12
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• 2011

As the aged population grows around the world, many medical instruments and devices have been developed recently. Among the devices, a drug delivery stent is a medical device which requires precision machining. Conventional drug delivery stent has problems of residual polymer and decoating because the drug is coated on the surface of stent with the polymer. If the drug is impregnated in micro hole array on the surface of the stent, the problem can be solved. Micro sized holes are generally fabricated by laser machining; however, the fabricated holes do not have an enough aspect ratio to contain the drug or a good surface finish to deliver it to blood vessel tissue. To overcome these problems, we propose a vibration-assisted machining mechanism with PZT (Piezoelectric Transducers) for the fabrication of micro sized holes. If the mechanism vibrates the eyepiece of the laser machining head, the laser spot on the workpiece will vibrate vertically because objective lens in the eyepiece shakes by the mechanism's vibration. According to the former researches, the vibrating frequency over 20kHz and amplitude over 500nm are preferable. The vibration mechanism has cylindrical guide, hollowed PZT and supports. In the cylinder, the eyepiece is mounted. The cylindrical guide has upper and low plates and side wall. The shape of plates and side wall are designed to have high resonating frequency and large amplitude of motion. The PZT also is selected to have high actuating force and high speed of motion. The support has symmetrical and rigid characteristics.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2009년도 춘계학술대회 논문집
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• pp.877-878
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• 2009

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.620-623
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• 2003

The material processing by using ultrashort pulse laser, in recently, is actively applying into the micro machining and nano-machining technology since ultrashort pulse has so faster than the time which the electrons energy absorbing photon energy is transmitted to surrounding lattice-phonon that it has many advantages in point of machining. The micro machining of metallic thin film on the plain glass is widely used in the fields such as mask repairing for semiconductor, fabrication of photonic crystal, MEMS devices and data storage devices. Therefore, it is important to secure the machining technology of the sub-micron size. In this research, we set up the machining system by using ultrashort pulse laser and conduct on the Cr 200nm thin film ablation experiments of spot and line with the variables such as energy, pulse number, speed, and so on. And we observed the characteristics of surrounding heat-affected zone and by-products appeared in critical energy density and higher energy density through SEM, and also examined the machining features between in He gas atmosphere which make pulse change minimized by nonlinear effect and in the air. Finally, the pit size of 0.8${\mu}{\textrm}{m}$ diameter and the line width of 1${\mu}{\textrm}{m}$ could be obtained.

• 한국생산제조학회지
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• 제25권6호
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• pp.421-425
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• 2016

Micro-EDM is one of the recent fine-machining technologies. Micro-EDM is widely used in precision processes because products manufactured via EDM are free from workpiece hardness. However, the debris produced during the process cause many problems such as reduced precision of the process. The first solution of this problem involves using the milling hole process. Micro-EDM hole process involves an electrode moving rapidly in the vertical direction via a servo system to disperse debris. However, this process can cause reduced work efficiency owing to contact between the electrode and workpiece. In this study, ultrasonic vibration is added to micro-EDM channel machining. Ultrasonic vibration removes the debris during machining and enables precision machining. Consequently, a clean work environment for the subsequent processes is maintained.

• 한국정밀공학회지
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• 제27권11호
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• pp.24-29
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• 2010

The shape of combustion nozzles varies from large diameter to small diameter ones. In the case of small nozzle, nozzle exit can be easily winkled or damaged in machining process. Femtosecond laser is a micro machining technology that is able to drill a small nozzle without damaging the nozzle exit. In this experiment, a small nozzle of combustion was fabricated by using a femtosecond laser. The fabricated nozzle of combustion provided a very small nozzle diameter with clean nozzle exit without wrinkling or collateral damage.

• 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.

• 한국생산제조학회지
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• 제19권3호
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• pp.419-425
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• 2010

To machine the micro hole, laser machining system is widely used, however, the system cannot fabricate the micro hole with high aspect ratio and good surface finish. To break the obstacles, the high frequency vibration mechanism with PZT (Piezoelectric Transducers) is proposed in this paper. The mechanism will vibrate the laser beam in vertical direction so that the aspect ratio and surface finish may be higher than the conventional. The mechanism vibrates the eyepiece of laser optics. In addition to the benefits, the mechanism enables us to have high precision and flexibility. It decreases burr and debris during machining. And it is able to machine various materials of workpiece. This research include high frequency and large travel range of the proposed mechanism. The PZT motion of mechanism and analysis on the sensitivity of design parameters are extracted from a finite element method (FEM) simulation. In the analysis, the target vibration mode without parasitic motion is designated to have the target frequency and high amplitude.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.487-488
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• 2006

Picosecond (ps) laser micro-machining has emerged as an attractive method of fabricating high-precision microstructures, especially in metals. In this paper, a metallic mold for diffraction gratings is fabricated with a mode-locked 12 Ps $Nd:YVO_4$ laser. Laser pulses with a wavelength of 355nm are irradiated on the surface of NOK 80, a mold material, to generate line patterns. In order to minimize the line width, laser power is set just above the ablation threshold of NOK 80. Results show that the spectrum from the fabricated mold is good enough for some industrial application.

• 대한기계학회논문집A
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• 제38권9호
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• pp.967-972
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• 2014

우수한 광투과성 및 경도를 지닌 유리는 바이오, 전자, 광학 등의 분야에서 널리 활용되고 있다. 하지만, 유리는 경도가 높고 깨지기 쉬워 일반적으로 특수가공법을 이용하여 가공이 이루어진다. 그 중 레이저는 공구가 불필요하며 가공 속도가 빠르다는 장점을 지니고 있지만 유리의 높은 광투과성 때문에 가공에 적용하기에는 많은 제약이 따른다. 이에 저출력의 나노초 펄스 레이저로 유리 가공을 하기 위하여 간접가공법인 레이저 습식 후면 식각공정을 활용하고자 한다. 기존의 연구들에서는 흡수율이 뛰어난 고가의 단파장 레이저 장비를 주로 사용하였으나 본 연구에서는 범용적인 근적외선 레이저 장비를 활용하여 유리 구조물 제작의 가능성을 실험하였다. 특히 깊은 구조물 제작시 발생하는 문제점을 확인하고 이를 해결하기 위해 초음파 부가 공정을 통한 미세 구조물 제작을 수행하였다.

• 한국정밀공학회지
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• 제27권2호
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• pp.34-39
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• 2010

In order to achieve and maintain dimensional accuracy in laser micro-machining, dominant parameters such as laser power and laser focus position need to be monitored and controlled real time. Also, in order to selectively machine multi-layered materials, the material being presently machined need to be recognized. This paper presents an auto-focusing (AF) module to keep laser focus on a large-area surface; a real-time laser power stabilizing module based on optical attenuation; and a laser-induced breakdown spectroscopy (LIBS) module. With these monitoring modules, position error in laser focus on a 4" silicon wafer was kept below $4{\mu}m$, initially $51{\mu}m$, and laser power stability of a UV laser source was improved from 1.6% to 0.3%. Also, the material transition from polyimide to copper in machining of FCCL (flexible copper clad laminate) was successfully observed.