In this study, we propose a novel and simple fabrication method of the microfluidic device, with high-aspect-ratio (HAR) microchannel for microparticle separation under viscoelastic fluid flow. To fabricate the HAR (> 10) microfluidic device comprised of the Si channel and PDMS mold, basic MEMS processes such as photolithography, reactive ion etching and anisotropic wet etching of Si wafer were used, and then plasma bonding with mechanical alignment between the Si channel and PDMS mold was conducted. The width of the microchannels was determined by the difference between the Si channel width and the master width for the PDMS mold. On the other hand, the heights of the Si channel and PDMS mold could be controlled by the KOH etching time and spin-coating speed of SU-8, respectively. The HAR microfluidic device whose microchannel had 10 μm width and 100 μm height was successfully fabricated, and used to separate microparticles without other external forces. The effect on the particle focusing position and focusing width under viscoelastic fluid was investigated, depending on the flow rate and the microparticle size. It is expected that precise manipulation as well as high-throughput separation of microparticles, can be achieved using the microfluidic device with HAR microchannel.
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Process for the Fabrication of Nickel Material High Aspect-ratio Digital PCR Partition GeeHong Kim, HyungJun Lim, SoonGeun Kwon, Hak-Jong Choi Journal of the Korean Society for Precision Engineering.2024; 41(8): 663. CrossRef
In this paper, a microfluidic co-culture system comprising an embedded polydimethylsiloxane (PDMS) microstencil was fabricated. The fabricated co-culture system has two micro-channels separated with a PDMS microstencil membrane. Master molds for microchannels and stencil membranes were fabricated by photolithography, then used for casting of PDMS devices. The stencil membrane was 10 thick, with holes 10-μm large in diameter. The fabricated system co-cultured two types of cells (HepG2, NIH-3T3 Cells) successfully for seven days. The viability and stability of the cells were verified through LIVE/DEAD® staining and analysis. Additionally, albumin secretion of HepG2 cells was measured for seven days, using an HSA ELISA kit. The measured data were analyzed, to compare the activity of HepG2 cells. Results confirmed that cells can be co-cultured in the fabricated microfluidic system.
There are various conduit structures such as arteries, veins, and airways in the human body, and they play critical roles in each tissue/organ. However, in recent years, the demand for artificial substitutes for the damaged conduit structure-based tissues and organs has significantly increased as dietary life has rapidly changed. Accordingly, various studies have been conducted, to develop a conduit structure of biocompatible polymers. In this study a 5 mm-diameter conduit structure was developed, using electrospinning process. An electrospinning setup equipped with a cylindrical-rod collector was constructed to fabricate a fibrous conduit structure, and then the impacts of process conditions on morphological and mechanical properties were investigated. Finally, it was shown that the mechanical properties of the fibrous conduit structure in circumferential direction, can be controlled by the electrospinning process conditions.
Microchannels machining can be used to make micro molds for microfluidic chips. The fluid flow in the channel can be controlled, by changing the cross sectional shape of the channel. V-shaped channels with a specific angle are not easily made with the etching process. This study presents the mechanical machining of microchannels of V-shaped cross section, on cemented carbide (WC-Co). In this study, to reduce tool wear in the process of machining, the micro conical tool was fabricated using polycrystalline diamond (PCD). The tool wear of the conical tool and form accuracy of channels, were investigated during V-shaped microchannel machining.
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Micro Hole Machining Characteristics of Glassy Carbon Using Electrical Discharge Machining (EDM) Jae Yeon Kim, Ji Hyo Lee, Bo Hyun Kim Journal of the Korean Society for Precision Engineering.2025; 42(4): 325. CrossRef
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In this study, we demonstrated a triboelectric nanogenerator composed of a vertical column, and a cylindrical shell, for omnidirectional wind energy harvesting. With a simple structure using a metal wire, the height between the two triboelectric materials can be maintained, and the Al coated shell can also be electrically connected to the electrode. When the shell is deformed by wind, its Al layer and Polytetrafluoroethylene (PTFE) on the outside of the column can be triboelectrically charged. Thus, wind energy can be harvested through a triboelectric energy conversion mechanism. In particular, due to the high flexibility of the shell, the nanogenerator operates even at wind speeds as low as 1 m/s. Although the output voltage is asymmetrical depending on the wind direction due to the metal wire, it was experimentally confirmed that the device can harvest wind energy from all directions. The measured output RMS power was approximately 15 μW at a wind speed of 6 m/s.
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Wind-powered Triboelectric Nanogenerator Using Contact-separation of Two Cylindrical Structures Jong-An Choi, Jingu Jeong, Mingyu Kang, Soonjae Pyo Journal of the Korean Society for Precision Engineering.2023; 40(12): 939. CrossRef
In this study, the disturbance torque that maintains the gimbal at a specific angle during the centrifugal acceleration test was analyzed. Newton"s Second Law for Rotation was applied, to calculate the disturbance torque. A Theoretic solution for calculating the disturbance torque was derived, by separating the horizontal/vertical components of the moment of inertia. The Theoretic solution was verified, by numerical analysis (RecurDyn) of the simplified Gimbal model. To include the effect of acceleration, the distance between the central axis of the gimbal and the accelerated test equipment was applied as 0 and L (non-Zero). As a result of the analysis, it was found that the main disturbance torque is not related to acceleration, but to self-centrifugal force caused by rotation. A centrifugal acceleration test was conducted, to verify the operational performance of gimbal. The disturbance torque was calculated, by measuring the torque used to operate the gimbal"s motor. The result was compared with the disturbance torque, calculated by the Theoretic solution of the gimbal. The error between the result of test and Theoretic solution of torque was less than 4.5%.
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A study of Tuned Mass Damper (TMD) Application for Mass Imbalance and Vibration Reduction in Gimbal Systems for High-speed Maneuverable Vehicles Jun-Soo Kim, Dong-Kyun Lee, Jong-Kuk Lee, Hyeon-Jun Cho, Ji-in Jung Journal of the Korean Society for Precision Engineering.2024; 41(11): 857. CrossRef
Cambolt that has two slot shape in thread, have been widely used to adjust wheel alignment in Hyundai and Kia motors. These slots in thread make stress more concentrated, and lead to yield more easily. This paper describes the optimizing process of the Cambolt figure, to maximize the yield load. Contribution of the Cambolt design factors to yield load was verified, through actual test and finite element analysis. Using the DFSS (Design for Six Sigma) method, we optimized the design factors of Cambolt, and confirmed the yield load was enhanced. This new Cambolt can provide more stable wheel alignment joints, by using a higher range of preload.
Energy devices in modern society require high efficiency, carbon neutrality, and the capability of distributed power generation. A fuel cell is an energy conversion device, that satisfies all of these requirements. However, most fuel cells use hydrogen as a fuel, and more than half of hydrogen is currently produced through hydrocarbon reforming, resulting in significant energy loss. Additionally, the storage and supply of hydrogen require costly systems, and a large amount of energy is consumed during compression or liquidation processes. This paper develops a solid oxide fuel cell, that uses hydrocarbon directly as fuel to resolve this problem. A small amount of Ru is mixed with the Ni-based electrode, for the effective internal reforming of hydrocarbons. For rapid deposition of YSZ electrolytes, we developed a reactive sputtering process, using a DC power source. The developed thin-film solid oxide fuel cell, showed a performance of 76 mW/cm² at 500℃ using methane as fuel.
This paper presents an improved formulation, to estimate the sliding friction torque of deep groove ball bearings (DGBBs). Running torque of rolling element bearings, is directly associated with heat generation in rotating machines. Among the components of running torque, sliding friction is a major friction source in ball bearings. For DGBBs, sliding friction is dominated by spinning and differential sliding between balls and races. This paper addresses the sliding friction torque components of DGBBs: Spinning friction, differential sliding friction due to the ball rotation, and differential sliding friction due to the ball orbital motion. An efficient and accurate computational method is proposed for the individual sliding friction sources, based on pure rolling lines in the elliptical contact area between the balls and races. The proposed method applies an updating algorithm, for estimating more accurate information about the pure rolling lines. The proposed method was validated in terms of comparison with other methods, and with the empirical formulae provided by a bearing manufacturer. Simulations were also conducted to investigate the impacts of important parameters on the sliding friction torque in DGBBs.
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Study on Thermo-mechanical Modeling and Analysis of High-speed Angular Contact Ball Bearings Under Oil-jet Lubrication Gilbert Rivera, Shinhyang Park, Chan-sik Kang, Dongjoo Kim, Seong-Wook Hong Journal of the Korean Society for Precision Engineering.2024; 41(7): 569. CrossRef
Analytical formulation for sliding friction torque in cylindrical roller bearings Gilbert Rivera, Patrick John Po, Chan-sik Kang, Seong-Wook Hong Journal of Mechanical Science and Technology.2024; 38(9): 4669. CrossRef
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Metal additive manufacturing processes such as directed energy deposition process (DED), can be used to manufacture high value metal parts, with improved mechanical properties and efficiency. However, parts produced by DED can suffer from excessive temperature gradients, and heat accumulation due to the deposition process. The purpose of this study was to investigate the impact of the deposited area on thermos-mechanical characteristics for the case of deposition of Inconel 718 powder, on the AISI 1045 substrate, using the DED process through finite element analyses (FEAs). Nine types of FE models were developed. Temperature dependent cooling conditions were analyzed, and applied to the model. Laser heat source was defined, as the three-dimensional volumetric heat source based on the Gaussian distribution model. Temperature dependent properties were assigned to the models. The influence of the width and the length of the deposited region, on residual stress distributions in the vicinity of deposited region were investigated. Additionally, the impacts of the deposited area on deformation characteristics were examined.
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