• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1645-1650
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• 2003

A numerical and experimental study is made of thermal behavior of a hot chuck which is specially designed for flip-chip bonders. The hot chuck consists of radiant heat sources and a heated plate of very high conductivity, which is for achievement of high-speed heat-up. A simplified numerical model is developed to simulate unsteady thermal behavior of the heated plate. Parallel experimental work is also conducted for a prototype of the hot chuck. Based on the experimental data, the numerical model is tuned to improve the reliability and accuracy. Design analysis using the numerical model is conducted. The results of numerical computations illustrate that the radiant heater system adopted in this study satisfies the key design requirements for a high-performance hot chuck.

• 한국기계가공학회지
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• 제14권5호
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• pp.68-74
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• 2015

In the present work, a series of numerical calculations have been conducted on the cooling of a hot surface using an air/water mist jet. In some cooling processes, such as in the glass-tempering process, direct contact between the cold water drops and the hot surface should be avoided, because this may cause surface cracks due to the sharp temperature gradients. Thus, the main focus of this study is finding the appropriate operating conditions for maximum cooling without direct contact between the drops and the surface. A series of numerical experiments have been performed, and, at the same time, those results were compared with those of the previous experiments for verification purposes. The effects of droplet impinging velocity, hot plate temperature, and liquid loading ratio for mono-dispersed drops of various sizes were studied in detail.

• 소성∙가공
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• 제18권3호
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• pp.251-255
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• 2009

Since fastener bolt for airplane require high specific strength and corrosion resistance, Ti-6Al-4V alloy is widely used. However, the Ti-6Al-4V bolt is generally manufactured by cutting and rolling because of their poor workability. The aim of present work is to develop hot forming technology for high strength Ti-6Al-4V. Various heat-treatments were applied to specimen in order to increase hot-workability and prevent galling with die. Multiple forging were simulated with FE code to determine optimum process parameters including specimen temperature, strain rate, local strain, and thermal shrinkage. Forged samples were heat-treated again to increase their mechanical properties.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.287-290
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• 2002

Stainless steel used widely in various fields of industry have the characteristics of difficulty-to-cut. This difficulty comes from its peculiarity, for example work hardening, vibration, etc. And these peculiarity on the cutting process have an effect on tool wear or life shortness of tools. To solve these problems several method have been developed. Hot-machining is one way of these method. when a material is heated, organization of material is soften. So cutting process becomes easy. When such a hot-machining method applies on drilling process and then heated material is processed, cutting force is less than usual drilling process cutting force. In this paper, cutting force is compared heated SUS 304 with usual SUS 304. And shape of chips is also compared.

• 한국재료학회지
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• 제16권7호
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• pp.435-438
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• 2006

The hot pressing was employed to prepare Fe-doped $CoSb_3$ skutterudites and their thermoelectric properties were investigated. Single phase ${\delta}-CoSb_3$ was successfully obtained by the hot pressing under 60MPa at 773 K for 2 hrs. Iron atoms acted as electron acceptors by substituting cobalt atoms. Thermoelectric properties were remarkably improved by the appropriate doping. $Co_{0.7}Fe_{0.3}Sb_3$ was found as an optimum composition for the best thermoelectric property in this work.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.417-420
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• 2009

The hot forming process of a CAM for vessel engine was designed by finite element (FE) simulation and experimental analysis. An aim of process design was to achieve the near-net shaped CAM forgings by hot forging process. Based on the compression test results of the low alloy steel, deformation processing map was generated using the superposition approach between the dynamic materials model (DMM) and flow stability and/or instability criteria. From the processing map, the initial heating temperature was determined as $1200^{\circ}C$. FE analysis was simulated to predict the formation of rolling defects and deformed shape with different forging designs. Optimum process design suggested in this work was made by comparing with the CAM for vessel engine manufactured by actual forging process.

• 대한기계학회논문집B
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• 제32권8호
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• pp.629-635
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• 2008

Recently, microturbines have received attention as a small-scale distributed power generator. Since the exhaust gas carries all of the heat release, the microturbine CHP (combined heat and power) system is relatively compact and easy to maintain. Generating hot water or steam is usual method of heat recovery from the microturbine. In this work, a heat recovery unit producing hot water was installed at the exhaust side of a 30 kW class microturbine and its performance characteristics following microturbine power variation was investigated. Heat recovery performance has been compared for different operating conditions such as constant hot water temperature and constant water flow rate. In particular, the influence of water flow rate and hot water temperature on the recovered heat was analyzed.

• 한국표면공학회지
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• 제36권1호
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• pp.42-47
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• 2003

Hot-dip galvanizing process is used widely in industry to achieve corrosion resistant coatings. Poor drainage during this process often leads to problems such as icicle formation and bridging In this work, mild steel specimens were hot-dip galvanized. Influence of the addition of bismuth, aluminum and both (bismuth and aluminum) to the zinc bath on the zinc drainage were determined. Bismuth additions improved the drainage significantly. Zinc bath containing 0.1 wt.% Bi and 0.025∼0.05 wt.% Al showed uniformity of coatings. Industrial trials with this bath composition showed reduction in zinc consumption, reduction of ash and dross, and good luster of workpiece.

• 소성∙가공
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• 제13권5호
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• pp.435-440
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• 2004

The temperature in hot forming of metallic materials, such as hot extrusion and hot forging, ranges from $300^{\circ}C$ to $900^{\circ}C$. Correspondingly, the die also exhibits high temperatures close to that of a work piece and its life is limited generally by high temperature fatigue. Thus, the analysis of high temperature fatigue would need the mechanical properties over the wide ranges of temperature. However, very few studies on the high temperature fatigue of brittle materials have been reported. Especially, the study on the fatigue behavior over such transition temperature regime is very rare. In this paper, the stress-strain curves and stress-life curves of a die steel such as STD61 are experimentally obtained. The wide ranges of temperature from $300^{\circ}C$ to $900^{\circ}C$ are considered in experiments and the transition temperature zone is carefully examined.

• 한국식품위생안전성학회지
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• 제35권1호
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• pp.60-67
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• 2020

본 연구에서는 고추의 수확 및 유통 단계에서 미생물 오염 수준과 그 발생원인을 확인하였고, 이를 바탕으로 수온도는 냉장 보관 보다 상온 보관일 때 미생물 오염 수준이 더 높은 것으로 나타나 냉장 보관이 미생물 오염 예방에 더 효과적인 것으로 나타났다. 추가로 소형 플라즈마를 이용하였을 때 초기 균 수 대비 5일차에서 일반세균 3.0 log CFU/g 감소, 대장균군, 효모/곰팡이는 불검출로 나타났고 플라즈마 발생장치 없는 경우 5일차에 대장균군이 2.1 log CFU/g 수준으로 검출되어 소형 플라즈마 발생장치가 보관 및 유통과정 중의 미생물의 저감에 효과적일 것으로 판단되었다. 이상의 결과로 볼 때 수확단계에서 미생물학적 위해요소 발생원인 중 하나인 작업자의 장갑을 주기적으로 교체하고 현장에서 쉽게 수행 가능한 냉장 유통 방법과 신선 고추의 수확 후 보관 및 유통 중에 소형플라즈마 장치를 이용한다면 고추의 미생물 오염을 감소시키는데 효과적인 것을 확인할 수 있었다. 또한 고추 이외에도 다른 신선농산물의 수확, 선별 단계나 유통단계에 미생물의 오염을 예방 또는 저감화 하는데 이용이 가능할 것으로 생각된다.