• Journal of Korea Foundry Society
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• v.12 no.3
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• pp.210-219
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• 1992

The measurement of the apparent and tap density for Al-Pb-X(Sn,Sn-Si) powders produced by centrifugal atomizer showed that the larger theoretically calculated densities the larger those densities. And tap densities were not over 50% of the theoretical densities. The nip angle of Al-5wt%Pb alloy powders produced with 38000 r.p.m. of disk rotation was $3^{\circ}$ degree larger than that of Al-8.5wt%Pb-3wt%Sn(-4wt%Si, 8wt%Si) with 50000 r.p.m. The effects of roll gap and rolling speed on thickness and density of the single strips by rolling were that rolling speed increasing the thickness and density of strip decreased and roll gap increasing, the thickness of strip increased but the density decresed. The compactibility of Al-Pb-X with Al by rerolling showed that the coarse powder-strips were better than fine powder-strips. From the SEM study with EDX analysis on the sintered strips, it was found that Pb and Sn were segregated with maximum size $5{\mu}m$, and Si existed surrounding the segregation zone. After sintering the clad strips at $500^{\circ}C$, the pores, which were spherical with $5{\mu}m$ of mean diameter, partly remained around the particles of alloy powders area, while completely disappeared at clad interface. The hardness of strips of alloy powders decreased linearly with increasing sintering temperature.

• Transactions of the Korean hydrogen and new energy society
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• v.28 no.6
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• pp.663-668
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• 2017

SOFC anode fabricated core-shell using machano-fusion method using core with submicron size Ni, nano size YSZ for shell. Using prepared core-shell, depending on the thickness of the shell, we studied how the characteristics of sintering and SOFC cell change by sintering the anode. The Ni-YSZ core-shell has a Ni core of 0.5 to $1.2{\mu}m$ over 2 to 7 YSZ of 15 to 20 nm is, and as the high speed mixing time increases, the YSZ number increases and the shell thickness becomes uniform increased. When the fuel electrode is manufactured with core-shell, it has superior sintering property, has grain of uniform size compared with the one synthesized by general mixing, the falling path is short, the conductors (electrons and ions) connection is excellent, the electrical conductivity has become excellent. The thicker the shell, the lower the electrical conductivity. When the thickness of shell ranged from 46 to 139 nm and 61 to 81 nm, the performance was the highest and the ASR was the smallest.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.119-126
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$ balls were fabricated using different raw materials, sintering aids and sintering conditions, Commercially available Si3N4 ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 9.525mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) mjcrostructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$Phase.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.4
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• pp.23-29
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• 2004

In this study, four kinds of $Si_3N_4$-based ceramic cutting tools with different sintering time were fabricated to investigate the relation among mechanical properties, grain size and tool life. They were used to turn gray cast iron at a cutting speed of 330m/min and depth of cut of 0.5mm and 1mm in dry, continuos cutting conditions. Multiple linear regression model was used to determine the relations among the mechanical property, grain size and the density. It was found that the combination of hardness and fracture toughness showed a good relation with tool life. It was also shown that hardness was the most important single element for the tool life.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.923-928
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• 1997

An MCP (Microchannel Plate) is a secondary electron multiplier to detect and amplify electrons. An MCP has many rnicrochannels whose diameters range from 10 to 100pm and whose lengths range from 40 to 100times of the diameter. Each microchannel of the MCP amplifies electrons over IOOOtimes by the secondary electron emission. Even though MCPs have high performance for electron amplification, the application of MCPs is limited to high performance electronic equipments because of their high fabricating cost and the limit of increasing their size due to the conventional fabrication process. Therefore, in this work, microchannels of the MCP are manufactured by micro-drilling to reduce the cost of the MCP and to increase their size. Alumina green body with epoxy binder was machined for fabricating microchannels using a high speed air turbine spindle and micro-drills with diamond grinding abrasives. Then alumina MCP was fabricated through the sintering of the machined alumina green body.

• Tribology and Lubricants
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• v.15 no.2
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• pp.150-155
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• 1999

The rolling fatigue lives (RFL) of five kinds of silicon nitride balls were investigated. Four kinds of Si$_3$N$_4$balls were fabricated using different raw materials, sintering aids and sintering conditions. Commercially available Si$_3$N$_4$ball was also studied for comparison. All the balls were finished up to the dimensional accuracy of Grade 10 defined in KS B 2001 (Steel Balls fer Ball Bearings) with a size of 9.525 mm. RFL tests were then conducted under the initial theoretical maximum contact stress 6.38 GPa and the spindle speed 10,000 rpm. Gear oil was provided by oiled race as lubricant. The results of RFL test indicated the prerequisitic conditions for the long rolling life of Si$_3$N$_4$ball : (1) the high density, (2) microstructures consisted of small uniformly distributed grains, (3) little glassy phase in grainboundary, and (4) little crystalline phase and secondary phase that induces residual thermal stress due to the differences of thermal expansion coefficient with Si$_3$N$_4$phase.

• Journal of Powder Materials
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• v.19 no.2
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• pp.117-121
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• 2012

Tool steels serve a large range of applications including hot and cold workings of metals and injection mouldings of plastics or light alloys. The high speed steels (HSS) are specifically used as cutting tools and wear parts because it has high strength, wear resistance and hardness along with appreciable toughness and fatigue resistance. From the view of HSS microstructure, it can be described as metallic matrix composites formed by a ferrous with a dispersion of hard and wear resistant carbides. The experimental specimens were manufactured using the PIM with T42 powders (50~80 vol.%) and polymer (20~50 vol.%). The green parts were debinded in n-hexane solution at $60^{\circ}C$ for 8 hours and thermal debinded at an $N_2-H_2$ mixed gas atmosphere for 8 hours. Specimens were sintered in high vacuum ($10^{-5}$ Torr) and various temperatures.

• Journal of the Korean Ceramic Society
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• v.47 no.5
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• pp.365-372
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• 2010

This paper was to evaluate the influence of kiln process parameter(kiln angle, kiln rotating speed) of lightweight aggregate using waste glass and bottom ash with industrial by-products on thermal conductivity, density, water absorption, fracture load and porosity by response surface analysis. In the results of surface plot and contour plot, it has verified that kiln residence time of lightweight aggregate increase as kiln angle and rotating speed decreases. For this reason, pore size and quantity tend to increase by active reaction of forming agent. It seems to be that increase in pore size and quantity have caused decreasing density, fracture load and thermal conductivity, and increasing water absorption. In conclusion, optimization of kiln process parameter on thermal conductivity, density, water absorption, fracture load and porosity by response surface analysis are kiln angle 2.4646%, kiln rotating speed 40.7089 rpm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.732-737
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• 2005

Distal 3D Real Object Duplication System(RODS) consists of 3D Scanner and Solid Freeform Fabrication System(SFFS). It is a device to make three-dimensional objects directly from the drawing or the scanning data. In this research, we developed an office type SFFS based on Three Dimensional Printing Process and a industrial SFFS using Dual Laser. An office type SFFS applied sliding mode control with sliding perturbation observer(SMCSPO) algorithm for control of this system. And we measured process variables about droplet diameter measurement and powder bed formation etc. through experiments. Also, in order to develop more elaborate and speedy system for large objects than existing SLS process, this study applies a new Selective Multi-Laser Sintering(SMLS) process and 3-axis dynamic Focusing Scanner for scanning large area instead of the existing $f\theta$ lens. In this process, the temperature has a great influence on sintering of the polymer. Also the laser parameters are considered like that laser beam power, scan speed, scan spacing. Now, this study is in progress to eveluate the effect of experimental parameters on the sintering process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.7
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• pp.602-609
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• 2008

This paper presents experimental optimization of process parameters for a newly developed SFF(Solid Freeform Fabrication) system. Two critical process parameters, layering thickness and curing period, which have a large effect on the quality of the product, are optimized through experiments. Specimens are produced using layering thicknesses of 60, 80, 100, 120, 140, and $160\;{\mu}m$ and curing periods of 0, 10, 20, and 30 minutes under the same processing conditions, i.e., build-room temperature, feed-room temperature, roller speed, laser power, scan speed, and scan spacing. The specimens are tested to compare and analyze performance indices such as thickness accuracy, flatness, stress-strain characteristics, and porosity. The experimental result indicates that layering thickness of $80{\sim}100\;{\mu}m$ and curing period of $20{\sim}30$ minutes are recommended for the developed industrial SFF system.