• 한국정밀공학회지
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• 제24권12호
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• pp.42-49
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• 2007

When micro holes are machined by EDM, machining characteristics of machined holes are changed according to the machining conditions. Typical machining conditions are the kind of dielectric fluids, capacitance and ultrasonic vibrations. They influence electrode wear, machining time, radial clearance and taper angle. In this paper, machined holes whose depths are 300, 500, $1000\;{\mu}m$ are observed for each machining conditions. Using deionized water as a dielectric fluid makes electrode wear small, machining time short, radial clearance large and taper angle small. High capacitance makes electrode wear high. Ultrasonic vibrations make electrode wear large, machining time short, radial clearance small and taper angle small. From the results of experiments, the optimal machining conditions were obtained to machine highly qualified micro holes.

• 한국정밀공학회지
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• 제22권7호
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• pp.47-53
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• 2005

Microholes with high aspect ratio are required in microstructures. Among various methods for producing the microhole, micro electrical discharge machining (MEDM) is very effective and useful process. But, it is difficult to machine the high aspect ratio holes below $100\;{\mu}m$ in diameter because machining condition becomes unstable due to bad removal of debris at deep hole. In this paper, ultrasonic vibration is applied to MEDM work fluid to make a high aspect ratio micro hole. It is shown that the vibration is effective in circulating the debris and increasing the machining rate. As a result, produced was a micro hole with $92\;{\mu}m$ entrance diameter, $81\;{\mu}m$ exit diameter and aspect ratio 23.

• 한국공작기계학회논문집
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• 제13권2호
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• pp.104-111
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• 2004

Ultrasonic machining is a non-thermal, non-chemical, md non-electorial material removal process, and thus results in minimum modifications in mechanical properties of the brittle material during the process. Also, ultrasonic machining is a non-contact process that utilize ultrasonic vibration to impact a brittle material. In this research characteristics of micro-hole machining for brittle materials by ultrasonic machining(USM) process have been investigated. And the effect of ultrasonic vibration on the machining conditions is analyzed when machining fir non-conductive brittle materials using tungsten carbide tools with a view to improve form and machining accuracy.

• 한국기계가공학회지
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• 제14권3호
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• pp.105-111
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• 2015

Ultrasonic machining (USM) does not involve heating or any electrochemical effects, and subsequently causes low surface damage, has small residual stress, and does not rely on the conductivity of the workpiece. These characteristics are suitable for the machining of brittle materials, such as glass or ceramics. However, USM for brittle materials generates cracks on the workpiece while machining, especially at the hole exit with a small diameter. In this study, wax coating was used to deposit wax on the back side of the workpiece to decrease the occurrence of cracks at the exit holes in USM, and it was finally removed with a cleaning process. The experimental results show that this technique is beneficial for restricting the occurrence of cracks in glass or ceramics.

• 대한기계학회논문집A
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• 제37권2호
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• pp.213-218
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• 2013

초음파 가공(Ultrasonic Machining:USM)은 새로운 기계가공기술 분야 중의 하나이다. 초음파 가공 과정은 비열, 비화학, 그리고 비전도의 방법이기 때문에 공작물 재료의 물리적, 화학적 변화가 없다. 이러한 특성으로 인해 초음파 가공기술은 유리, 세라믹 등과 같은 취성재료의 가공에 적합하다. 그러나 단점으로는 초음파 진동을 이용하여 취성재료를 가공하는 경우 크랙이 빈번하게 발생한다. 본 논문에서는 유리와 세라믹의 미세 구멍가공에서 다구찌 방법을 이용하여 크랙발생을 최소화하는 최적의 가공조건을 얻고자 하였다. 이를 통해 공작물의 입구 및 출구에서 발생하는 크랙 현상을 감소시켰다.

• 한국정밀공학회지
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• 제22권4호
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• pp.52-59
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• 2005

When a micro hole is machined by EDM with a cylindrical electrode, the hole diameter is different at the inlet and the outlet of the micro hole. The taper shape of the micro hole is caused by not only wear of the electrode but the eroded particles. The eroded particles cause secondary discharge during machining the micro hole. As a result, the diameter of the inlet becomes larger than that of the outlet. In this paper, a new method is proposed to reduce the difference in diameter between the inlet and the outlet of the hole. Observed was that the feed depth and machining time affect the formation of taper shape On this experimental basis, ultrasonic vibration was applied to reduce machining time, and capacitance was changed during machining to use the difference in discharging energy of different capacitances. Using the proposed method, a straight micro-hole was fabricated.

• 한국기계가공학회지
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• 제13권6호
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• pp.119-126
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• 2014

Micro-holes of conductive ceramic are required in micro structures. Micro-electrical discharge machining (Micro-EDM) is an effective machining method since EDM is as process for shaping hard metals and complex-shaped holes by spark erosion in all kinds of electro-conductive materials. However, as the depth of micro hole increases, the machining condition becomes more unstable due to inefficient removal of debris between the electrode and the workpiece. In this paper, micro-EDM was performed to evaluate machining characteristic such as electrode wear, machining time, taper angle, radial clearance with varying voltage and ultrasonic vibration on 10 vol.% Carbon-nanotube reinforced conductive $Al_2O_3$ composite fabricated by spark plasma sintering in previous research.