• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.10-10
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• 2004

유전율이 서로 다른 물질을 나노 크기로 주기적으로 배열하여 황자 띠간격(Photonic bandgap)을 이루게 하는 광결정(Photonic crystal)에 인위적인 결함을 부가하여 광파워 분배 및 Mux/Demux 등 광회로 기능 수행을 할 수 있도록 집적화한 광도파로 소자가 미래형 정보통신사회를 위한 초고집적화, 초고속화, 저전력 및 신기능 등의 특성을 위하여 요구된다. 이러한 나노 광결정 소자는 다양한 방법으로 제작이 시도되고 있는데, 나노 임프린트 기술은 실장밀도가 높으며, 수십 나노급의 패턴이 주기적으로 배열된 구조물의 성형에 큰 장점이 있어서 본 연구에서 다루어졌다.(중략)

• The Journal of the Acoustical Society of Korea
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• v.28 no.8
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• pp.796-805
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• 2009

In this paper, a fabrication process for PZT preform of 1-3 type piezo-composite were studied using powder injection molding (PIM). The viscosity and the Pressure-Volume-Temperature (PVT) characteristics of the fabricated PZT feedstock were analyzed. The filling patterns, pressure, temperature distributions, and forming defects of the preform were analyzed with 3D TIMON commercial packages during PIM process. Also the fabrication conditions and the delivery system of the preform were optimized during the entire PIM process. Based on the simulated results, the preform having uniform distributions of the PZT rod was fabricated with the PIM process.

• Composites Research
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• v.27 no.4
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• pp.174-181
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• 2014

This study describes viscoelasticity analysis of carbon-fiber reinforced polymer matrix composite material. One of the most important problem during high temperature molding process is residual stress. Residual stress can cause warpage and cracks which can lead to serious defects of the final product. For the difference in thermal expansion coefficient and change of resin property during curing, it is difficult to predict the final deformed shape of carbon-fiber reinforced polymer matrix composite. The consideration of chemical shrinkage can reduce the prediction errors. For this reason, this study includes the viscoelasticity and chemical shrinkage effects in FE analysis by creating subroutines in ABAQUS. Analysis results are compared with other researches to verify the validity of the subroutine developed, and several stacking sequences are introduced to compare tested results.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.186-192
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• 1999

Dang-Chin feldspar powder with the mean particle size of 9.1 $\mu\textrm{m}$ was added to the synthesized mullite powder with the particle size of +325∼-200 mesh and the powder compact was prepared by PLPP(pressureless powder packing method). Densification behaviors were observed in sintering temperature range of 1200∼1400$^{\circ}C$. The binder solution of 4% PVA was infilterated into packed powder to the suitable strength. The PLPP method makes it possible to form compacts without clay as plasticizer. Therfore there was no defect caused by phase transition after sintering. Additionally, we observed the dense microstructure by the melting of feldspar. When the mullite compacts with feldspar of 30% were sintered at 1300$^{\circ}C$-4 hrs, we obtained the dense microstructure with zero water absorption and porosity <1%. When these compacts were sintered longer than 4 hrs at 1300$^{\circ}C$ or higher than 1400$^{\circ}C$, the examggerated grain growth of mullite was observed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.8
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• pp.889-897
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• 2011

In this work, we investigated the theoretical forming limit models for Zircaloy-4 and Zirlo used for spacer grid of nuclear fuel rods. Tensile and anisotropy tests were performed to obtain stress-strain curves and anisotropic coefficients. The experimental forming limit diagrams (FLD) for two materials were obtained by dome stretching tests following NUMISHEET 96. Theoretical FLD depends on FL models and yield criteria. To obtain the right hand side (RHS) of FLD, we applied the FL models (Swift's diffuse necking, M-K theory, S-R vertex theory) to Zircaloy-4 and Zirlo sheets. Hill's local necking theory was adopted for the left hand side (LHS) of FLD. To consider the anisotropy of sheets, the yield criteria of Hill and Hosford were applied. Comparing the predicted curves with the experimental data, we found that the RHS of FLD for Zircaloy-4 can be described by the Swift model (with the Hill's criterion), while the LHS of the FLD can be explained by Hill model. The FLD for Zirlo can be explained by the S-R model and the Hosford's criterion (a = 8).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.11
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• pp.4950-4955
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• 2012

A bolt manufacturing process is completed with continuous forging. Technical and economical success of each process will depend on the appropriate process design and metal mold design for each procedure. This study aims to analyze the moldings of first and second steps among the multi-step molding processes of SCM435 bolt by use of the finite element method in order to achieve the reasonable process. Since the processes of first and second steps analyzed by use of the finite element method consist of axial symmetry, the transformed configuration of material satisfy the dimensions expected in process. In addition, the uniflow line formed in material becomes smooth and consistent over the entire process. Therefore neither molding of material nor inherent defect is expected.

• Clean Technology
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• v.18 no.2
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• pp.155-161
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• 2012

The purpose of this study is to remove paraffin wax binder effectively from powder injection molded part using supercritical fluids in powder injection molding process. For a thin powder injection molded part about 1-2 mm thickness, paraffin wax binder can be removed rapidly without any defect by traditional supercritical extraction process which has fixed high temperature and pressure condition. But, for a thick powder injection molded part, there are limitations in removing paraffin wax binder by the fixed high process condition because crack occurs at the beginning step. Therefore, here we studied variable condition debinding process that starts with mild process condition at the beginning step and then increase the process conditions simultaneously at each step. To find out the initial process condition that has the highest extraction yield without any defect for each sample thickness, we investigated various supercritical debinding conditions using 1-4 mm thickness ceramic injection molded sample. By using the variable condition debinding process that starts with the initial process condition at the first step and then increasing process conditions simultaneously at each step (temperature from 333.15 to 343.15 K, pressure from 12 to 27 MPa, and $CO_2$ flow rate from 1.5 to 10 L/min), over 95% of paraffin wax binder was removed from the 4 mm thick (10 mm diameter) ceramic injection molded disk samples within 5 hours.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.1
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• pp.25-32
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• 2010

With the latest automobile technology, though the third generation common rail system requires high injection pressures up to 1,800bar, the next generation diesel engine is expected to require more higher pressures than the third generation. The common rail pipe requires higher strength because it is one of the parts in the common rail system, which is influenced directly by fuel under high pressure. Preform design is very important for preventing head of the common rail pipe from folding in the heading process. In this study, die angle, curvature, outer diameter of die and length of trapped part are selected as main parameters to obtain best preform shape minimizing radius of folding. Therefore optimal design is carried out by finite element analysis and Taguchi method through main parameters. Results of the finite element analysis have good agreements with those of the experiments in the actual field.

• Journal of Korea Foundry Society
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• v.43 no.4
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• pp.187-193
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• 2023

Shell core making is an excellent process in terms of formability and desanding, but when the molten aluminum comes into con- tact with the shell core, gas generation by pyrolysis of the resin is inevitable. In addition, when the ventilation is inadequate, pores will remain inside the casting, which can directly lead to defects of the casting. While studies on the gas generation behavior of shell core making have been reported, the modeling of gas generation has not been extensively investigated. We will develop a gas evolution analysis method that considers the relationship between temperature and gas quantity for the core to be developed. We then use the developed method to analyze the flow and solidification behavior of metal molten metal during core mold design and low-pressure casting of cylinder head products, and predict the occurrence of casting defects to derive a casting method that min- imizes the occurrence of defects.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.174-174
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• 2013

현재 자동차 강판 시장에서는 승객들의 안전 확보와 연비 향상을 위하여 자동차 강판의 경량화 및 고장력화가 급속히 진행되고 있다. 더불어 소비자는 더욱 아름답고 멋있는 외관을 추구하면서 정교한 디자인이 가능할 수 있도록 높은 성형성을 갖는 강판에 대한 요구도 또한 증대되고 있다. 따라서 강도와 성형성을 동시에 확보할 수 있는 DP형, TRIP형 등의 다양한 컨셉을 갖는 변태강화형 고장력강에 대한 개발 요구가 점점 심화되고 있으나 이들 고장력강의 상 제어를 위하여 첨가된 Si, Mn등의 성분들이 표면에 안정한 산화물을 형성하기 때문에 이러한 고장력강은 표면 품질이 열위한 것으로 보고 되고 있다. 따라서 기존 연구에서는 열처리중 표면으로 확산되어 올라오는 Si, Mn 산화물의 저감을 위하여 분위기 중 산소농도나 노점등을 조절하거나, 산화전처리, 선도금처리 등을 통하여 Si, Mn 의 표면 선택산화를 제어하여 도금 결함을 최소화하려는 연구가 많이 진행되고 있다. 그러나 이러한 연구들은 대부분 강판 표면에서의 산화/환원의 반응에 대한 분위기 요인을 제어하는 연구들이며 실제 Si, Mn등의 산화성 원소들이 어떠한 조건에서 어떠한 경로들을 통해서 이동하여 표면으로 올라오는지에 대한 연구는 부족한 상황이다. 따라서 본 연구에서는 산화성 원소들의 표면 확산 거동에 대한 고찰을 위하여 다양한 열처리 온도 조건을 통한 표면 도금성 경향, 합급화 경향 및 표면 분석결과를 바탕으로 확산 거동에 대한 경향을 밝히고자 하였다.