• Journal of Korea Foundry Society
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• v.42 no.4
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• pp.218-225
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• 2022

For hydrogen-vehicle applications (air pressure control valve housing, APCVH), an investigation was conducted to determine how micro-defects in a high- pressure die-casted Al alloy (industrial code: ALDC12) could be controlled by means of a post-treatment using an organic-based impregnation solution in order to improve the air- tightness of the die-casted Al sample. Two different impregnation solutions were proposed and its test results were compared to a imported product from Japan with respect to the processing variables used. A structural investigation of the components under study was conducted by means of computer tomography and 3D X-ray micro-CT. These observations revealed that the use of the impregnation treatment to seal micro-defects led to highly significant and beneficial changes which were attributed mainly to interconnections among inherent micro-pores. A leak test after impregnation revealed that the performance improvement rate of the die-casted Al sample was ~70% for INNO-01. Therefore, the developed impregnation solutions offer an effective strategy to control the micro-defects found in various vehicle parts via die-casting.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.93-96
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• 2003

Recently, various bulk metallic glasses (BMG's) haying good mechanical and chemical properties were developed. BMG's can easily be deformed in the supercooled liquid region, via viscous flow mechanism. In our previous work, we evaluated the deformation behavior and some other basic properties of Z $r_{41.2}$ $Ti_{13.8}$C $u_{12.5}$N $i_{10}$B $e_{22.5}$ alloy. In this study, we investigated the micro forming of Z $r_{41.2}$ $Ti_{13.8}$C $u_{12.5}$N $i_{10}$B $e_{22.5}$ alloy. The process condition was chosen based on the viscosity data from TMA, and superalloy and Si wafer with micro patterns on the surface were used as forming die. The alloy showed good replication of the patterns. However, some stripe patterns, resembling scratches, appeared on the deformed alloy surface. These scratches can be reduced or eliminated by polishing before forming.ing.ore forming.ing.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.4
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• pp.387-394
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• 2017

This paper develops a pump system for patient with chronic pain or cancer. The pump module is consists of two micro-valve and membrane. The micro-valve is operated by a solenoid. With two solenoid valves which are connected via a drug transport line, the inlet and outlet are completely blocked. A silicon rubber membrane located between the two valves makes the flow-rate constant without any backflow. This pump module can control the flow-rate of drugs by controlling the time that the valves are opened and closed. The reservoir consists of a drug chamber and a gas chamber. As the gas chamber encloses the drug chamber, propellant gas which is injected into the gas chamber pressurizes the drug chamber regardless of volume of the drug chamber. To design the pump module, analysis a constant efficiency test, and accuracy test for the pump module were conducted.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.4
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• pp.63-69
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• 2007

The two-photon stereolithography (TPS) process is a promising technique for the fabrication of real three-dimensional (3D) nano/micro-structures via application of a femto-second laser, In TPS, when a near-infrared ultrashort-pulsed laser is closely focused onto a confined volume of photocurable resin, only the local area at the center of the focus is cured. Therefore, real 3D microstructures with resolution under the diffraction limit can be fabricated through a layer-by-layer accumulative technique, This process provides opportunities to develop neo-conceptive nano/micro devices in IT/BT industries, However, a number of issues, including development of effective fabrication methods, highly sensitive and functional materials, and neo-conceptive devices using TPS, must be addressed for the realization of industrial application of TPS. In this review article, we discuss our efforts related to TPS: effective fabrication methods, diverse two-photon curable materials for high functional devices, and applications.

• Korean Journal of Optics and Photonics
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• v.13 no.2
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• pp.117-122
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• 2002

Some 10$\times$10 micro-lens arrays of a period of 300 ${\mu}{\textrm}{m}$, a thickness of 17 ${\mu}{\textrm}{m}$, and a focal length of 2.2 mm are fabricated by exposing a thick layer of photoresist through a grayscale mask via UV proximity printing. The grayscale mask is fabricated in a holographic film by reducing (6.6X) a high-resolution black-and-white film where a grayscale patters of a micro-lens array designed by a computer has been written using a film recorder. The proposed method has the advantage of a low fabrication cost, a fill-factor of almost 100% and the ease of realizing an aspheric lens.

• Transactions of Materials Processing
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• v.13 no.1
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• pp.9-14
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• 2004

Recently, various bulk metallic glasses (BMG's) having good mechanical and chemical properties were developed. BMG's can easily be deformed in the supercooled liquid region, via viscous flow mechanism. By using the viscous flow, the very low pressure is needed to deform the materials. In this study, we investigated the structural transition and deformation behavior of Vitreloy 1 (Zr/sub 41.2/Ti/sub 13.8/Cu/sub 12.5/Ni/sub 10/Be/sub 22.5/) using TMA and DSC. We applied the results to the micro forming process. The forming condition was chosen based on the viscosity data from TMA, and Si wafer with micro patterns on the surface was used as a forming die. The deformed surface was analyzed by SEM and 3D Surface Profiling System. The alloy showed good replication of the patterns. Quantitative measurement of roughness was useful to evaluate the replication. Surface condition of the deformed surface was determined by the initial surface condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.6 s.237
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• pp.904-912
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• 2005

The flow in a microchannel is usually characterized as a low Reynolds number (Re) so that good mixing is quite difficult to be achieved. In this regard, we developed a novel chaotic micromixer, named Barrier Embedded Kenics Micromixer (BEKM). In the BEKM, the higher level of chaotic mixing can be achieved by combining two general chaotic mixing mechanisms: (i) splitting/reorientation by helical elements inside the microchannel and (ii) stretching/folding via periodically located barriers on the channel wall. The fully three-dimensional geometry of BEKM was realized by a micro-stereolithography technology, in this study, along with a Kenics micromixer and a circular T-pipe. Mixing performances of three micromixers were experimentally characterized in terms of an average mixing color intensity of phenolphthalein. Experimental results show that BEKM has better mixing performance than other two micromixers. Chaotic mixing mechanism, proposed in this study, could be integrated as a mixing component with Micro-Total-Analysis-System, Lab-on-a-chip and so on.

• Korean Journal of Materials Research
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• v.25 no.6
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• pp.265-268
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• 2015

ZnO micro/nanocrystals at large scale were synthesized through the thermal evaporation of Al-Zn mixtures under air atmosphere. The effect of synthetic temperature and time on the morphology of the micro/nanocrystals was examined. It was found that the temperature and time affected the morphology of the ZnO crystals. At temperatures below $900^{\circ}C$, no crystals were synthesized. At a temperature of $1000^{\circ}C$, ZnO crystals with a rod shape were synthesized. With an increase in temperature from $1000^{\circ}C$ to $1100^{\circ}C$, the morphology of the crystals changed from rod shape to wire and granular shapes. As the time increased from 2 h to 3 h at $1000^{\circ}C$, tetrapod-shaped ZnO crystals started to form. XRD patterns showed that the ZnO crystals had a hexagonal wurtzite structure. EDX analysis revealed that the ZnO crystals had high purity. It is believed that the ZnO nanowires were grown via a vapor-solid mechanism because no catalyst particles were observed at the tips of the micro/nanocrystals in the SEM images.

• Journal of the Microelectronics and Packaging Society
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• v.31 no.3
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• pp.62-66
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• 2024

A statistical approach to inspection of the 3-D shape of micro solder balls is proposed, where an optical method with spatially arranged LED and specular reflection is used. The reflected image captured by a vision system was analyzed to calculate the relative displacements of LED's in the image. Also, the statistics of displacements for the micro solder balls contained in a captured image are used to detect existing defects, and the usefulness of the proposed method is shown via experiments.

• Journal of the Korean Ceramic Society
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• v.54 no.1
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• pp.43-48
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• 2017

In this study, we investigate the effect of additive size on the densification and thermal conductivity of AlN ceramics with $MgO-CaO-Al_2O_3-SiO_2$ (MCAS) additives. Micro-sized MCAS powder prepared via melting and nano-sized MCAS powder synthesized via the polymeric complex method are used as sintering additives. We analyze the densification behavior of AlN added with 5 wt.% of MCAS by dilatometry as well as by isothermal sintering in the temperature range of $1300{\sim}1700^{\circ}C$. AlN exhibits higher sinterability with nano-MCAS than with micro-MCAS, and both specimens approach their maximum densities when sintered at $1600^{\circ}C$ for 4 h. The thermal conductivities of AlN with 5 wt% of nano- and micro-MCAS additives sintered at $1600^{\circ}C$ are 82.6 and 32.0 W/mK, respectively. We find that nano-MCAS is more effective in sintering of AlN ceramics at lower temperatures, and thus for enhancing their thermal conductivities.