• 대한기계학회논문집A
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• 제36권10호
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• pp.1221-1226
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• 2012

핫 스탬핑은 오스테나이트 변태 온도 이상에서 프레스 성형 후 급속히 냉각되는 고강도 부품을 제조하는 성형 방법이다. 매우 적은 양의 보론 성분을 가지고 있는 보론강은 핫 스탬핑에 사용되는 재료 중의 하나이다. 본 연구의 목적은 열처리 조건에 따르는 기계적 성질과 에릭슨 커핑 시험에 의하여 성형성을 조사하는 것이다. 다양한 온도에서 다이��칭은 대기 시간을 달리하여 실시하였다. 1173 K-0s에서 ��칭 후 TWB는 1203 MPa의 인장 강도를 얻었다. 이것은 모재 인장강도(1,522 MPA)의 79 %이다. 금형 온도(298, 523, 673 K)에 따른 보론강 TWB의 성형성은 차이가 크지 않았다. 그러나 성형 속도가 증가함에 따라 성형성이 감소하는 것을 확인할 수 있었다.

• 열처리공학회지
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• 제27권5호
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• pp.242-252
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• 2014

A comparative study was performed on the microstructures and the mechanical properties of STD11 and 8Cr steel. The specimens were quenched from $1030^{\circ}C$ and tempered at $240^{\circ}C$ and $520^{\circ}C$. Vickers hardness, impact toughness and tensile tests were conducted at various tempering temperatures. Microstructural characterization to measure grain size, volume fraction of retained austenite and distribution of carbides was carried out by using SEM, EBSD, TEM and X-ray diffraction techniques. Due to finer $M_7C_3$ carbides dispersed, 8Cr steel showed larger impact toughness and plasticity than STD11 irrespective of the tempering temperature. While 8Cr steel had lower hardness in as-quenched state and after tempering at $240^{\circ}C$ owing to smaller carbide content and more retained austenite, it was harder after tempering at $520^{\circ}C$ due to larger precipitation hardening from finer $M_{23}C_6$.

• 대한기계학회논문집A
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• 제26권6호
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• pp.1120-1126
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• 2002

Machining characteristics of tool steels manufactured by electro slag casting process has been investigated in this study. For the estimation of machinability, turning and drilling tests are carried out. The chip shapes at various velocities are investigated for the comparison of turning workabilities of tool steels because the chip shapes reflect characteristics of cutting resistance. In case of drilling test, feed motor currents measured by a hall sensor are used as a measure for the drilling resistance. The machining characteristics of the tool steels are strongly correlated with tensile properties, such as tensile strength, hardness, and ductility. In case of turning workability, it was found to be favoured by the higher tensile strength, while the opposite is true far the drilling workability. The electro-slag casted materials show better turning workability in the viewpoint of chip shapes and, the quenching-tempered electro-slag casted material has relatively better drilling machinability than that of the annealed one.

• 대한기계학회논문집
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• 제18권11호
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• pp.2954-2966
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• 1994

The characteristics and good corrosion resistance at room and elevated temperatures led to increasing application of Ti-alloys such as aircraft, jet engine, turbine wheels. In forging of Ti-alloy at high temperature, die chilling and die speed should be carefully controlled because the flow stress of Ti-alloy is sensitive to temperature, strain and strain-rate. In this study, the forging of turbine disk was numerically simulated by the finite element method for hot-die forging process and isothermal forging process, respectively. The effects of the temperature changes, the die speed and the friction factor were examined. Also, local variation of process parameters, such as temperature, strain and strain-rate were traced during the simulation. It was shown that the isothermal forging with low friction condition produced defect-free disk under low forging load. Consequently, the simulational information will help industrial workers develope the forging of Ti-alloys including 'preform design' and 'processing condition design'. It is also expected that the simulation method can be used in CAE of near net-shape forging.

• 대한기계학회논문집
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• 제9권6호
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• pp.725-731
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• 1985

본 논문에서는 Chen, Kobayashi에 의한 강소성 유한요소법 프로그램을 이용하 여 마찰조건 및 형상비(H$_{O}$/D$_{O}$)가 0.75, 1.0, 1.5에 따른 금형 접촉면상의 응력분포 및 반경방향 증분량 그리고 번형률 분포 등을 고찰하고 실제로 알루미늄과 .alpha.-황동의 두 종류 재료를 사용하여 이론과 동일한 마찰조건과 형상비에 대해 실험함 으로써 그 변형 특성을 F.E.M. 결과와도 비교 고찰하였다. 또한 시편 실험에서 파괴 시까지 실험하여 그 형상도 살펴보았으며 이전 연구와도 비교하여 보았다.

• 한국분말재료학회지
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• 제22권3호
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• pp.157-162
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• 2015

SKD11(ASTM D2) tool steel is a versatile high-carbon, high-chromium, air-hardening tool steel that is characterized by a relatively high attainable hardness and numerous, large, chromium rich alloy carbide in the microstructure. SKD11 tool steel provides an effective combination of wear resistance and toughness, tool performance, price, and a wide variety of product forms. Adding of CNTs increased the performance of mechanical properties more. 1, 3 vol.% CNTs was dispersed in SKD11 matrix by mechanical alloying. SKD11 carbon nanocomposite powder was sintered by spark plasma sintering process. FE-SEM, HR-TEM and Raman analysis were carried out SKD11 carbon nanocomposites.

• 한국기계가공학회지
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• 제16권3호
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• pp.131-137
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• 2017

In this study, we evaluated the surface roughness of mold and injected parts manufactured by polycarbonate (PC) injection molding. The mold surface was polished to produce six differentiated roughnesses with 12 areas using stones (#800, #1200), sandpapers (#800, #1200), and diamond compounds (#8000, #14000). Injected parts were created using 20mm/s injection speed, 80 bar holding pressure for 5 seconds, and $70^{\circ}C$ cooling water. Injected parts surface roughness (Sa) was measured randomly in 10 of 30 using an interferometer (NewView8000, zygo, USA). In the same way, mold surface was measured randomly 10 times on 12 polished areas. Surface roughness of molds and injected parts were compared, and a regression equation to predict mold surface roughness was proposed for specific injection molding parameters.

• 대한기계학회논문집
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• 제16권4호
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• pp.658-666
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• 1992

본 연구에서는 고속, 연속장업으로 이루어지고 있는 스템핑 공정에서 금형과 강판간의 접촉-슬립에 따른 마찰 및 윤활특성의 성능을 평가할 수 있도록 한 원형단면 형상의 드로오비드 마찰실험장치를 활용하여 가압력, 윤활유 특성, 드로잉 속도와 강 판의 표면특성 등에 따른 자동차용 냉연강판과 도금강판의 마찰계수와 드로오비드 저 항력에 대한 테이터 베이스를 구축하고자 한다.

• 한국정밀공학회지
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• 제29권2호
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• pp.161-169
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• 2012

Recently, a study for the functional surface production of super hydrophobic of natural and biomimetic artificial has attracted much attention. To make process methods of super hydrophobic surface has a variety of ways such as lithography, etching, and laser ablation. However, we were used ultra-shot pulse laser ablation process which has the virtue of more environmental friendliness and simple process. In this paper, we were fabricated a multiplicity of super hydrophobic patterns on mold surface(NAK80) using by optimizing the laser processing conditions and it was transferred on PDMS. Also, we measured contact angle super hydrophobic patterns on PDMS. The result showed there is no patterns on PDMS were measured 94 degrees, by contrast, optimized super hydrophobic patterns on PDMS was 157 degrees. Therefore we fabricated super hydrophobic surface on mold. Based on these experimental results, it is possible to mass production using ultra shot pulse laser ablation of super hydrophobic pattern and to be applied for a variety of industries.

• 한국정밀공학회지
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• 제19권3호
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• pp.101-106
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• 2002

This paper presents an experimental investigation of high speed machining of dies and molds. Several critical issues involved with the high speed machining of QRO90 tool steel of hardness up to HRc62, have been studied and explained from a detail analysis of experimental observations. The experiments were performed using ball end mills. The effect of different process parameters on tool life and surface finish produced was also investigated. The cutting parameters involved were; cutting speeds in the range of 100 to 40 / m/min, axial depth of cut from 0.1 to 0.5mm, pick feed of 0.1 to 0.5mm. Run out and acceleration signals were observed during the experiment to investigate cutting slates. Compressed air and flood coolant were used and the effect of coolant on tool life was also determined.