• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.936-936
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• 2006

Bulk amorphous materials have been intensively studied to apply for various advanced industry fields due to their high mechanical, chemical and electrical properties. These materials have been produced by several techniques such as mechanical alloying, melt spinning and gas atomization, etc. Among them, the atomization is the most potential technique for commercialization due to high cooling rate during solidification of the melt and mass productivity. However, the amorphous powders still have some limitations because of their low ductility and toughness. Therefore, intensive efforts have to be carried out to increase the ductility and toughness. In this study, the Ni-based amorphous powder was produced by the gas atomization process. And in order to increase the ductile toughness, ductile Cu phase was coated on the Ni amorphous powder by spray drying process. The characteristics of the as-synthesis powders have been examined and briefly mentioned. The master alloy with $Ni_{57}Zr_{20}Ti_{16}Si_2Sn_3$ was prepared by vacuum induction melting furnace with graphite crucible and mold. The atomization was conducted at $1450^{\circ}C$ under the vacuum of $10^{-2}$ torr. The gas pressure during atomization was varied from 35 to 50 bars. After making the Ni amorphous powders, the spray drying was processed to produce the Cu -coated Ni amorphous composite powder. The amorphous powder and Cu nitrate solution were mixed together with a small amount of binder and then it was sprayed at temperature of $130^{\circ}C$ and rotating speed of 15,000 R.P.M.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.6
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• pp.117-124
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• 2017

In this study, we investigated the optimization of process conditions by using the Six Sigma process, design of experiment (DOE) method and response surface method (RSM) to resolve dimensional deviation and appearance problems arising from the shortened process time of the mobile phone rear cover. The analysis of the trivial many was performed by 2-sample T-test and cooling time, and mold temperature and packing pressure were selected as the vital fews affecting the overall width of the product. The optimal conditions of the process were then studied using the DOE and the RSM. We analyzed the improvement effects by applying the selected optimal conditions to the production process and the results showed that the difference between the mean value and target value of the overall width stood at 0.01 mm, an improvement of 88.89% compared to current process that fell within the range of standard dimension. The short-term process capability stood at $4.77{\sigma}$, which implied an excellent technology level despite a decrease by $0.22{\sigma}$ compared to the current process. The difference in process capability decreased by $2.44{\sigma}$ to $0.41{\sigma}$, showing a significant improvement in management capability. Ultimately, the process time of the product was shortened from 18.3 seconds in the current process to 13.65 seconds, resulting in a 34.07% improvement in production yield.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1649-1657
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• 2010

We have investigated the unexpected phenomena on the surface of molded GFRP composites. The major cause of the unevenness, as a result of which the surface becomes rough, is a shrinking of the matrix in the process of holding pressure and cooling temperature. The higher holding pressure load in a molding process and the lower demolding temperature in an annealing experiment, the better GFRP composites moldings improved its appearance. In addition, by taking the holding pressure and demolding temperature into consideration, we evaluate the process that causes the surface unevenness and the variation in the fiber projection height.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.4
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• pp.267-271
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• 2018

A high directivity TIR (total internal reflection) lens in the UV-A region was designed using a silicone resin, and a UV light source module with a maximum irradiation density of $150mW/cm^2$ was fabricated. The beam angle of the TIR lens was designed to be $8.04^{\circ}$ and the maximum diameter of the TIR lens was Ø13.5. A silicone resin having a UV transmittance of 93% and a refractive index of 1.4 at a wavelength of 365 nm was used, and the lens was manufactured using an aluminum mold, from which silicone could be easily released. The module was fabricated in a metal printed circuit board of COB (chip on board) type using a $0.75{\times}0.75mm^2$ UV chip. A jig was used to adjust the focal length between lens and chip and to fix the position of the lens. The optical characteristics such as illumination distributions of the lens and module were designed using 'LightTools' optical simulation software. The heat dissipation system was designed to use a forced-air cooling method using a heat-sink and fan.

• Journal of the Korean Applied Science and Technology
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• v.41 no.1
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• pp.46-57
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• 2024

In this study, the various process conditions for high-power DC Magnetron Sputtering (DCMS) on the surface roughness of carbon thin films were investigated. The optimal conditions for Si/C coating were 40min for deposition time, which does not deviate from normal plasma, to obtain the maximum deposition rate, and the conditions for the best surface roughness were -16volt bias voltage and 400watt DC power with 1.3x10-3torr chamber pressure. Under these optimal conditions, an excellent carbon thin film with a surface roughness of 1.62nm and a thickness of 724nm was obtained. As a result of XPS analysis, it was confirmed that the GLC structure (sp² bonding) was more dominant than the DLC structure (sp³ bonding) in the thin film structure of the carbon composite layer formed by DC sputtering. Except in infrequent cases of relatively plasma instability, the lower bias voltage and applied power induces smaller surface roughness value due to the cooling effect and particle densification. For the optimal conditions for Graphite/C composite layer coating, a roughness of 36.3 nm and a thickness of 711 nm was obtained under the same conditions of the optimal process conditions for Si/C coating. This layer showed a immensely low roughness value compared to the roughness of bare graphite of 242 nm which verifies that carbon coating using DC sputtering is highly effective in modifying the surface of graphite molds for glass forming.

• Journal of Bio-Environment Control
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• v.22 no.4
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• pp.432-438
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• 2013

A study was conducted to examine the effect of maturity and precooling ($60%/0^{\circ}C$ and $80%/4^{\circ}C$), and light illumination on the storage life of 'Maehyang' strawberry meant for export. Fruits at 60% and 80% ripened stage were harvested from a commercial greenhouse in Jinju on April 3, 2012. Harvested fruits were transported to the precooling system within 30 minutes. Transported fruits were precooled the $4^{\circ}C$ for 2 hours and $0^{\circ}C$ for 5 hours by a forced draft cooling system, and then stored at $6^{\circ}C$. During the storage, the fruits were examined for their changes in hardness, soluble solid content, quality grade, acidity, Hunter value, weight loss, and the incidence of gray mold (Botrytis cinerea) at an interval of two days from April 5 to April 17. Hardness was decreased until 7th days and it was changed to increase at 9th days. Treatment of 60% maturity, $0^{\circ}C$ precooling and no light illumination of strawberry were shown the highest value in freshness. The soluble solid content harvested in 80% maturity strawberry was higher than 60% maturity strawberry until the third day. Quality grade decreased rapidly in 80% maturity stage with light illumination strawberry in comparison to the 60% maturity stage of strawberry. Hunter value 'L' and 'a' showed a rapid change in 60% maturity stage of strawberry. Weight loss decreased rapidly in 80% maturity, $0^{\circ}C$ precooling, and no light illumination of strawberry treatments. Gray mold incidence was found the most at 60% maturity, $4^{\circ}C$ precooling, and light illumination of strawberry. The results from our study indicate that effectiveness for keeping the freshness of strawberry was best achieved by harvesting in low maturity, precooling at $0^{\circ}C$, and with no light illumination.

• Corrosion Science and Technology
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• v.12 no.1
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• pp.1-6
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• 2013

Recently Digital TV industry has drastically been moving the illuminating system, which causes an obvious product change from PDP and LCD to LED model to provide high-definition image. Due to strong competition in the digital industry, TV manufacturers make a great efforts to reduce production cost by using low-priced materials such as steels instead of aluminum and plastic etc. In this paper we have developed a new low-priced electrogalvanized steel sheet, which has a black resin composite layer, to substitute conventional high-priced PCM steel and plastic mold for rear cover panel in the digital TV. The black resin composite was prepared by mechanical dispersion of the mixture solution that consists of high solid polyester resin, melamine hardener, black pigment, micronized silica paste, polyacrylate texturing particle and miscellaneous additives. The composite solution was coated on the steel sheet using roll coater followed by induction furnace curing and cooling. Although the coated layer has a half thickness compared to the conventional PCM steels having $23{\mu}m$ thickness, it exhibits excellent quality for the usage of rear cover panel. The new steel sheet was applied to test products to get quality certification from worldwide electronic appliance customers. Detailed discussion provides in this paper including preparation of composite solution, roll coating technology, induction curing technology and quality evaluation from customers.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.1
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• pp.221-243
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• 1997

The objective of this study was to characterize the mechanical properties of $Y_{2}O_{3}$-containing glass infiltrated ceramic core material, which was made by pressureless powder packing method. A pure alumina powder with a grain size of about $4{\mu}m$ was packed without pressure is silicon mold to form a bar shaped sample, and applied PVA solution as a binder. Samples were sinterd at $1350^{\circ}C$ for 1 hour. After cooling, $Y_{2}O_{3}$-containing glass($SiO_{2},\;Y_{2}O_{3},\;B_{2}O_{3},\;Al_{2}O_{3}$, ect) was infiltrated to the sinterd samples at $1300^{\circ}C$ for 2 hours and cooled. Six different proportions $Y_{2}O_{3}$ of were used to know the effect of the mismatch of the thermal expansion coefficient between alumina powder and glass. The samples were ground to $3{\times}3{\times}30$ mm size and polished with $1{\mu}m$ diamond paste. Flexural strength, fracture toughness, hardness and other physical properties were obtained, and the fractured surface was examined with SEM and EPMA. Ten samples of each group were tested and compared with In-Ceram(tm) core materials of same size made in dental laboratory. The results were as follows : 1. The flexural strengths of group 1 and 3 were significantly not different with that of In-Ceram, but other experimental groups were lower than In-Ceram. 2. The shrinkage rate of samples was 0.42% after first firing, and 0.45% after glass infiltration. Total shrinkage rate was 0.87%. 3. After first firing, porosity rate of experimental groups was 50%, compared with 22.25% of In-Ceram. After glass infiltration, porosity rate of experimental groups was 2%, and 1% in In-Ceram. 4. There was no statistical difference in hardness between two materials tested, but in fracture toughness, group 2 and 3 were higher than In-Ceram. 5. The thermal expansion coefficients of experimental groups were varied to $4.51-5.35{\times}10^{-6}/^{\circ}C$ according to glass composition, also the flexural strengths of samples were varied. 6. In a view of SEM, many microparticles about $0.5{\mu}m$ diameter and $4{\mu}m$ diameter were observed in In-Ceram. But in experimental group, the size of most particles was about $4{\mu}m$, and a little microparticles was observed. The results obtained in this study showed that the mismatch of the thermal expansion coefficients between alumina powder and infiltrated glass affect the flexural strength of alumin/glass composite. The $Y_{2}O_{3}$-containing glass infiltrated ceramic core made by powder packing method will takes less time and cost with sufficient flexural strength similar to all ceramic crown made with slip casting technique.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.7
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• pp.2919-2924
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• 2011

The automatic drawer is used to absorb the movement shock and adjust its velocity when it opens and closes. The tube in shock-absorber is the cylindrical case which surrounds its parts and is made of acetal. The purpose of this study is to determine the quality stability of the tube in the shock-absorber in injection molding process. The tube which had been manufactured in the process with 4 cavity cooling unit was used. In this study, the analysis and test are carried out to determine its quality stability. Which are the quality analysis with numerical simulation and performance tests of the tube compared with one of foreign make. It is calculated that the injection press is 87.6 MPa and the deflections in X, Y, Z directions are ranged in 0.07~1.00 mm. When the researched tube is compared with the foreign made tube, the maximum bending compressive load is 231 kgf higher, average axial compressive load is 0.05 kgf higher, and the roughness(Ra) on the inner surface is $0.02\;{\mu}m$. lower. In the result, it is known that the quality of researched tube in injection mold process is stable and its performance is superior.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.499-508
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• 2016

Injection molding is a method for manufacturing many products, wherein a plasticized resin is injected into a mold at high pressure and hardened. According to the method, the product can be manufactured into various forms, and the mass production of up to tens of thousands of products is possible. The purpose of this study was to determine the process conditions for manufacturing a door latch for automobiles, through an analysis of the injection molding method. To calculate an appropriate injection flow for injection molding, a primary analysis for comparing the injection time, pressure, flow pattern, consolidation range, shear stress, shear rate, and weld line, as well as a secondary analysis for determining the conditions for stabilizing the molding temperature, holding pressure, and cooling process, were conducted. The characteristics of injection molding, and their influence on the product quality are discussed. No weld line and pores were observed on the products that had been manufactured based on the process conditions determined above. In addition, there were no flaws regarding the deformation compared to the prototype. Therefore, the manufacture of a product under the conditions determined in this study can reduce the defect rate compared to the existing production, and the process is also more competitive due to reduced production time.