• 대한기계학회논문집B
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• 제20권10호
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• pp.3313-3321
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• 1996

A fundamental study in cooling and solidification process focused on ice storage was performed, including the interesting phenomena of density inversion, supercooling and dendritic ice. A numerical study was performed for natural convection and ice formation in the cooling and freezing processes with supercooling in a space between double cylinders. When water was cooled under the freezing point by a cooling wall in a cavity, solidification was not started at once, but a subcooled region was formed near the wall. Especially, when the cooling rate was low, subcooled region extended to a wide area. However, after a few minutes, supercooling is released by some triggers. Dendritic ice is suddenly formed within a subcooled region, and a dense ice layer begins to be developed from the cooling wall. Due to the difficulties, most previous studies on solidification process with numerical methods had not treated the supercooling phenomena, i.e. the case considering only the growth of dense ice. In this study, natural convection and ice formation considering existence of supercooling and dendritic ice were analyzed numerically with using finite difference method and boundary fixing method. The results of numerical analysis were well compared with the experimental results.

• 한국정밀공학회지
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• 제27권8호
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• pp.98-104
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• 2010

It has been reported that the photopolymer solidification in the stereolithogrpahy process is mainly depend on the laser exposure conditions such as laser power and scanning speed. However, these researches were focused on the vertical laser exposure onto the surface of the photopolymer. In this research, we developed a mathematical model for the photopolymer solidification under the inclined laser beam exposure. Using the developed mathematical model, the photopolymer solidifications were simulated varying inclined laser exposure conditions. Developed mathematical model was in good agreement with the experimental result. This research can be applied to improve the surface roughness in the stereolithogrpahy process.

• 산업경영시스템학회지
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• 제38권1호
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• pp.44-51
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• 2015

When manufacturing die casting mold, generally, the casting layout design should be considered based on the relations of injection system, casting condition, gate system, and cooling system. According to the various relations of the conditions, the location of product defects was differentiated. High-qualified products can be manufactured as those defects are controlled by the proper modifications of die casting mold with keeping the same conditions. In this research, Computer Aided Engineering (CAE) simulation was performed with the several layout designs in order to optimize the casting layout design of an automotive part (Housing). In order to apply them into the production die-casting mold, the simulation results were analyzed and compared carefully. With the filling process, internal porosities caused by air entrapments were predicted and also compared with the modification of the gate system and overflow. With the solidification analysis, internal porosities occurring during the solidification process were predicted and also compared with the modified gate system. The simulation results were also applied into the production die-casting mold in order to compare the results and verify them with the real casting samples.

• 한국전기전자재료학회논문지
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• 제20권6호
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• pp.561-565
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• 2007

Because of a good wear resistance and a stable contact resistance, Ag-CdO is widely used as electrical contact material. But, the Cd-oxide mainly exists as a coarse particle and adversely affected to environment. As a reason, $Ag-SnO_2$ alloy has been developed. The Sn-oxide maintains stable and fine particle even at high temperature. In order to investigate the effect of Misch metal (Mm) additional that affects the formation of the oxide and the formation of fine matrix Ag, we studied the microstructures and properties of Ag-Sn-In(-Mm) material fabricated by rapid solidification process. The experimental procedure were melting using high frequency induction, melt spinning, and internal oxidation. The Mm addition makes Ag matrix more fine than no Mm addition. The reason is that the addition of Misch metal decreased a latent heat of fusion of alloy, as a result the rapid solidification effect of alloy is increased. The maximum hardness shows at 0.3 wt%Mm. after that the hardness is decreased until 0.4 wt% Mm, but still larger than no Mm addition alloy. At 0.5 wt% Mm alloy, the precipitation of Misch metal causes a decrease of hardness than no Mm addition alloy.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2104-2113
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• 2002

A finite element model is developed for the process of squeeze casting of metal matrix composites (MMCs) in cylindrical molds. The fluid flow and the heat transit. are fundamental phenomena in squeeze casting. To describe heat transfer in the solidification of molten aluminum, the energy equation is written in terms of temperature and enthalpy are applied in an axisymmetric model which is similar to the experimental system. A one dimensional flow model simulates the transient metal flow. A direct iteration technique was used to solve the resulting nonlinear algebraic equations, using a computer program to calculate the enthalpy, temperature and fluid velocity. The cooling curves and temperature distribution during infiltration and solidification were calculated fer pure aluminum. Experimentally, the temperature was measured and recorded using thermocouple wire. The measured time-temperature data were compared with the calculated cooling curves. The resulting agreement shows that the finite element model can accurately estimate the solidification time and predict the cooling process.

• 한국전기전자재료학회논문지
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• 제32권4호
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• pp.341-348
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• 2019

This paper reports the microstructure and electrochemical properties of Si-Al-Fe ternary amorphous alloys prepared by rapid solidification as an anode for lithium secondary batteries. The microstructure was analyzed using XRD and HR-TEM with EDS mapping. In accordance with DSC analysis, annealing was performed to crystallize the active nano-Si in the amorphous alloy. Thus, nano-Si forms (~80 nm) embedded in the matrix alloy, such as $Fe_2Al_3Si_3$, $FeSi_2$, and $Fe_{0.42}Si_{2.67}$, were successfully synthesized. The electrode based on the Si-Al-Fe ternary alloy delivered an initial discharge capacity of approximately $700mAh^{g-1}$, and exhibited a high Coulombic efficiency of 99.0~99.6% from the $2^{nd}$ to $70^{th}$ cycles.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.51-54
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• 2003

The continuous casting is primarily a heat-extraction process in which the heat transfer at various cooling zones profoundly influences quality of products. So development of numerical model is necessarily needed for more specific and clear investigations upon heat transfer mechanism at mold and secondary cooling zones. In this study, heat transfer coefficients which shows the characteristic of heat transfer mechanism in mold are calculated for more exact analysis with temperatures measured in bloom mold using optimal algorithm, and finally the validity of cooling conditions at secondary cooling zone which is actually used at field for 30 Ton bloom type continuous casting of 0.187%C is investigated. From the results of solidification analysis, the characteristic of bloom mold shows good agreements with that of previously studies by other authors and optimized cooling conditions for 0.187%C are presented.

• 한국주조공학회지
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• 제16권6호
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• pp.550-555
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• 1996

A stochastic model, based on the coupling of the finite volume(FV) method for macroscopic heat flow calculation and a two-dimensional cellular automaton(CA) model for treating microstructural evolution was applied-for the prediction of microstructural evolution in squeeze casting. The interfacial heat transfer coefficient at the casting/die interface was evaluated as a function of time using an inverse problem method in order to provide a quantitative simulation of solidification sequences under high pressure. The effects of casting process variables on the formation of solidification grain structures and on the columnar to equiaxed transition of an Al-4.5wt%Cu alloy in squeeze casting were investigated. The calculated solidification grain structures were in good agreement with those obtained experimentally.

• 대한기계학회논문집
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• 제16권2호
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• pp.348-355
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• 1992

Casting structures and properties are determined by the solidification speed in the metal mold. The heat transfer characteristics of the interface between the mold and the casting is one of the major factors that control the solidification speed. According to Sully's research, the thermal resistance exists due to the air-gap formation at the mold-casting interface during the freezing process and the interface heat transfer coefficient is used to describe the degree of it. In this study, one-dimensional Stefan problem with air-gap resistance in the cylindrical geometry is considered and heat transfer characteristics is numerically examined. The temperature distribution and solidification speed are obtained by using the modified variable time step method. And the effects of the major parameters such as mold geometry, thermal conductivity, heat transfer coefficient and initial temperature of casting on the thermal characteristics are investigated.

• 한국주조공학회지
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• 제12권3호
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• pp.203-209
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• 1992

Directional solidification of Al-Ti peritetic alloys was carried out using Upward Continuous Casting Process. The morphology of a solid-liquid interface and solidification microstructures were investigated under various crystal growing conditions. The experimental results were compared with those attained by the Bridgman method. The cell spacing of the Al-Ti peritetic alloys and the primary dendrite arm spacing of the Al-Ti peritetic alloys decreased with an increase in pulling speed. The primary ${\beta}$ phase of the Al-Cr and Al-Ti peritectic alloys did not appear in solidification microstructures because of the depleted solute contents in the melt ahead of the solid-liquid interface.