• 기계저널
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• 제56권7호
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• pp.51-54
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• 2016

이 글에서는 티타늄 합금의 절삭가공 시 공구수명을 향상시키기 위해 적용하는 액체질소를 사용한 극저온가공에서, 공구의 냉각 균일성을 향상시키기 위한 방법으로 극저온간접냉각(Indirect cryogenic cooling) 방식을 소개한다.

• 한국정밀공학회지
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• 제34권4호
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• pp.237-241
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• 2017

Cryogenic machining uses liquid nitrogen (LN2) as a coolant. This machining process can reduce the cutting temperature and increase tool life. Titanium alloys have been widely used in the aerospace and automobile industries because of their high strength-to-weight ratio. However, they are difficult to machine because of their poor thermal properties, which reduce tool life. In this study, we applied cryogenic machining to titanium alloys. Orthogonal cutting experiments were performed at a low cutting speed (1.2 - 2.1 m/min) in three cooling conditions: dry, cryogenic, and cryogenic plus heat. Cutting force and friction coefficients were observed to evaluate the machining characteristics for each cooling condition. For the cryogenic condition, cutting force and friction coefficients increased, but decreased for the cryogenic plus heat condition.

• Tribology and Lubricants
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• 제6권2호
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• pp.50-59
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• 1990

일잔적으로 세라믹재료는 강도, 내식성, 내열성, 내마모성의 성질 등이 우수하여 신소재로서의 응용폭이 점점 확대되고 있으나, 가공성이 난삭재로 피삭성의 개발이 시급한 과제로 대두되고 있다. 본 연구에서는 가공 중 절삭열을 억제시키는 방안으로 극저온 내부 냉각공구시스템을 제작하고, 냉매로 액화질소를 순환 공급하면서 이때 난삭재인 세라믹 가공의 피삭성 향상의 가능성을 실험적으로 검토하였다.

• 한국기계가공학회지
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• 제15권6호
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• pp.129-135
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• 2016

There have been many types of development and commercialization efforts for superconducting power applications with the continuous development of High Temperature Superconducting (HTS) conductors. In particular, HTS power cables are going to be commercialized in real power grids. A cryogenic refrigeration system should be used to keep it below 77 K, and its required cooling capacity continuously increases as the unit length of the HTS power cable increases. Among the many kinds of cryogenic refrigerator, a reverse Brayton refrigerator that uses turbo expanders is a promising refrigerator due to its efficiency and reliability. Among the various components in refrigerators, the cryogenic turbo-expander is the most important part for increasing efficiency and assuring reliability. The design of a 300 W class turbo-expander is described in this paper prior to the development of a 10 kW class turbo expander, which is the required capability for the commercialization of a HTS power cable. The impeller shape and rotation speed are determined based on the cycle analysis. The Eigen frequency and harmonic analysis are conducted with gas bearings at cryogenic temperatures to determine the operational stability.

• 한국정밀공학회지
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• 제34권3호
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• pp.185-189
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• 2017

Recently, titanium alloys have been widely used in aerospace, biomedical engineering, and military industries due to their high strength to weight ratio and corrosion resistance. However, it is well known that titanium alloys are difficult-to-cut materials because of a poor machinability characteristic caused by low thermal conductivity, chemical reactivity with all tool materials at high temperature, and high hardness. To improve the machinability of titanium alloys, cryogenic cooling with LN2 (Liquid Nitrogen) and nanofluid MQL (Minimum Quantity Lubrication) technologies have been studied while turning a Ti-6Al-4V alloy. For the analysis of turning process characteristics, the cutting force, the coefficient of friction, and the surface roughness are measured and analyzed according to varying lubrication and cooling conditions. The experimental results show that combined cryogenic cooling and nanofluid MQL significantly reduces the cutting forces, coefficients of friction and surface roughness when compared to wet condition during the turning process of Ti-6Al-4V.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.381-383
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• 2005

극저온 압연중인 알루미늄 합금의 미세조직의 변화 - 집합조직의 발전과 결정립 크기 및 형상 변화 -를 예측할 수 있는 오일러리안 유한요소 해석을 수행하였다. 패스 당 압하율 $30\%$ 인 연속 세 패스의 압연공정을 시뮬레이션 하여 얻은 결과는 실험에서 관측된 것과 비슷한 경향을 보여, 본 연구의 해석모델의 타당성을 입증하였다.

• 소성∙가공
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• 제13권5호
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• pp.449-454
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• 2004

The annealing behavior of a 5083 Al alloy deformed at cryogenic temperature was investigated, focusing on the evolution of microstructures and mechanical properties. Especially, the effects of annealing temperature, $150~300^{\circ}C$, and time, 3∼60min., on microstructures and mechanical properties of the sheets received 85% reduction at cryogenic temperature were investigated. The optimization of the annealing conditions resulted in a mixture of equiaxed grains and elongated subgrains, exhibiting a good combination of uniform elongation and high strength.

• 한국기계가공학회지
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• 제15권6호
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• pp.136-141
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• 2016

The purpose of this study is to examine the basic design of a submerged cryogenic pump, which is a two stage impeller pump. We limited this study to the impeller design of the submerged pump. We calculated its velocity triangle based on the impeller blade configuration and, in order to check its natural frequency, we carried out a modal test using a finite element method (FEM) analysis. Basically, modal test results had quite similar to FEM analysis.

• 한국정밀공학회지
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• 제15권4호
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• pp.36-43
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• 1998

We experimented turning SCM440, called difficult-to-cut materials in general, using tungsten carbon tool(PIO) in order to elevate machinability by a new cutting method. The cutting tool designed and made to study was cooled to -17$0^{\circ}C$ in about 1 minute by liquid nitrogen. Then, we operated cryogenic cutting by cooling tool with liquid nitrogen and stuided the effect about cutting force, chip thickness, surface roughness, behavior of tool wear and cutting temperature. In addition, we investigated the possibility that sur face roughness of workpiece can be predicted analyzing cutting characteristics.

• 한국기계가공학회지
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• 제16권2호
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• pp.56-62
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• 2017

In this research, reverse engineering was applied to the product manufactured by "Vanzetti" from Italy to develop a localized cryogenic submerged pump used in small-scale LNG liquefaction plants. The results of modal analysis of the impeller and shaft confirmed that the resonance frequency of the impeller and shaft played an important role in the rotor. Modal analysis of the rotor confirmed that the forcing frequency had no influence on the resonance phenomenon.