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Experiments and computer simulation analysis of impact behaviors of micro-sized abrasive in waterjet cutting of thin multiple layered materials

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中国有色金属学会会刊：英文版 2012年第S3期22卷 864-869页

作者： Jung-Han LEE kang-Su PARK myung chang kang Bo Sik kang Bo Sung SHIN Engineering Research Center Pusan National University National Core Research Center Pusan National University Mechanical System Safety Research Division Korea Institute of Machinery and Materials

The abrasive waterjet (AWJ) is now widely used in the advanced cutting processes of polymers,metals,glass,ceramics and composite materials like thin multiple-layered material (TMM).Various research and development efforts have recently been made to understand the science of ***,the interaction mechanism between a workpiece and high-velocity abrasive particles still remains a complicated *** this work,the material removal mechanisms of AWJ such as micro penetration and micro dent were experimentally *** addition,a new computer simulation model considering high strain rate effect was proposed to understand the micro impact behavior of high-velocity micro-sized abrasives in AWJ cutting.

关键词： abrasive waterjet thin multiple layered materials micro-sized abrasive micro penetration micro dent

Surface effects of hybrid vibration-assisted femtosecond laser system for micro-hole drilling of copper substrate

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中国有色金属学会会刊：英文版 2012年第S3期22卷 801-807页

作者： Jung-Kyu PARK Ji-Woon YOON myung-chang kang Sung-Hak CHO Nano Machining Laboratory Korea Institute of Machinery and Materials Department of Nano-Mechatronics University of Science and Technology National Core Research Center for Hybrid Materials Solution Pusan National University

The ultrafast laser based hybrid machining system was studied and a novel approach was demonstrated to improve laser machining quality on metals by vibrating the optical objective lens with a low frequency (500 Hz) and various displacements (0-16.5 μm) during a femtosecond laser machining *** laser used in this experiment is an amplified Ti:sapphire femtosecond (10-15 s) laser system that generates 100 femtosecond pulses having an energy of 3.5 mJ/pulse with a 5 kHz repetition rate at a central wavelength of 790 *** is found that both the wall surface finish of the machined structures and the aspect ratio obtained using the frequency vibration assisted laser machining are improved compared with those derived via laser machining without vibration assistance.

关键词： femtosecond laser hybrid machining vibration-assisted machining surface roughness aspect ratio

Optical diffraction gratings embedded in BK-7 glass by low-density plasma formation using femtosecond laser

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Transactions of Nonferrous Metals Society of China 2011年第A01期21卷 165-169页

作者： Jung-Kyu PARK Sung-Hak CHO Kwang-Ho KIM myung-chang kang Nano Machining Laboratory Korea Institute of Machinery and Material Daejeon 305-343 Korea National Core Research Center for Hybrid Materials Solution Pusan National University

The optical embedded diffraction gratings with the internal refractive index modification in BK-7 glass plates were demonstrated using low-density plasma formation excited by a high-intensity femtosecond （130 fs） Ti： sapphire laser （λp=790 rim）. The refractive index modifications with diameters ranging from 400 nm to 4 gm were photoinduced after plasma formation occurred upon irradiation with peak intensities of more than 1 ×10^13 W/cm2. The graded refractive index profile was fabricated to be a symmetric around the center of the point at which low-density plasma occurred. The maximum refractive index change （An） was estimated to be 1.5x10 2. Several optical embedded gratings in BK-7 glass plate were demonstrated with refractive index modification induced by the scanning of low-density plasma formation.

关键词： BK-7 glass plate diffraction grating refractive index modification plasma formation femtosecond laser

Characteristics of damaged layer in micro-machining of copper material

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中国有色金属学会会刊：英文版 2009年第B09期19卷 295-300页

作者： Dong-Hee KWON Jeong-Suk KIM myung-chang kang Se-Hun KWON Jong-Hwan LEE School of Mechanical Engineering Pusan National University National Core Research Center for Hybrid Materials Solution Pusan National University Department of Mechatronics Busan College of Korea Polytechnic Ⅶ

The study on damaged layer is necessary for improving the machinability in micro-machining because the damaged layer affects the micro mold life and micro machine parts. This study examined the ultra-precision micro-machining characteristics, such as cutting speed, feed rate and cutting depth, of a micro-damaged layer produced by an ultra-high speed air turbine spindle. The micro cutting force, surface roughness and plastic deformation layer were investigated according to the machining conditions. The damaged layer was measured using optical microscope on samples prepared through metallographic techniques. The scale of the damaged layer depends on the cutting process parameters, particularly, the feed per tooth and axial depth of the cut. According to the experimental results, the depth of the damaged layer is increased by increasing the feed per tooth and cutting depth, also the damaged layer occurs less in down-milling compared with up-milling during the micro-machining operation.

关键词：机械加工性微观特征损伤层铜材样品制备技术微型机器切削速度切削深度

Distribution of electric field for carbon nanotube assembly: Experiments (II)

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Transactions of Nonferrous Metals Society of China 2011年第A01期21卷 121-125页

作者： Soongeun KWON Soo-Hyun KIM Kwang-ho KIM myung-chang kang Hyung-woo LEE Department of Mechanical Engineering Korea Advanced Institute of Science and Technology (KAIST) Daejeon 305-701 Korea National Core Research Center for Hybrid Materials Solution Pusan National University

The distribution effect of electric field on the alignment and attachment of carbon nanotubes （CNTs） were investigated. The experimental results were compared with the simulation results according to three different shaped electrodes. In previous simulation, the round shaped electrodes were expected to be more effective for aligning and attaching a single CNT between two electrodes than conical or rectangular shaped electrodes. To verify the simulation results, three different shaped electrodes were introduced and a single multi-walled carbon nanotube （MWNT） was attached. The optimal conditions for aligning and attaching MWNTs such as the frequency, applied voltage and concentration of MWNTs solution were investigated. Through repeated experiments, frequency of 100 kHz-10 MHz, applied voltage of 0.3-1.3 V^s/~m, concentration of 5 ktg/mL in MWNTs solution were obtained as a possible condition range to attach MWNTs. Under these conditions, the yield of MWNTs attachment between two electrodes was up to 70%. In previous simulation, furthermore, it was verified that the size of the stable or quasi-stable region made CNTs aligned and attached on different shaped electrodes from the comparison of the experimental and simulation results. Most single MWNT attachment was accomplished on the round shaped electrodes.

关键词： carbon nanotubes dielectrophoresis round shaped electrode simulation

Dielectrophoretic assembly of semiconducting single-walled carbon nanotube transistor

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Transactions of Nonferrous Metals Society of China 2011年第A01期21卷 126-129页

作者： Se-Hun KWON Young-Keun JEONG Soongeun KWON myung-chang kang Hyung-Woo LEE National Core Research Center for Hybrid Materials Solution Pusan National University Department of Mechanical Engineering Korea Advanced Institute of Science and Technology (KAIST) Daejeon 305-701 Korea

A novel burning technique for making a semiconducting single-walled carbon nanotubes （SWNTs） transistor assembled by the dielectrophoretic force was suggested. The fabrication process consisted of two steps. First, to align and attach a bundle of SWNTs between the source and drain, the alternating （AC） voltage was applied to the electrodes. When a bundle of SWNTs was connected between two electrodes, some of metallic nanotubes and semi-conducing nanotubes existed together. The second step is to burn the metallic SWNTS by applying the voltage between two electrodes. With increasing the voltage, more current flowed through the metallic SWNTs, thus, the metallic SWNTs burnt earlier than the semiconducting one. This technique enables to obtain only semi-conducting SWNTs connection in the transistor. Through the 1--V characteristic graph, the moment of metallic SWNTs burning and the characteristic of semi-conducing nanotubes were verified.

关键词： single-walled carbon nanotube (SWNT) semi-conducting carbon nanotube burning technique dielectrophoresis

Structural considerations in friction welding of hybrid Al_2O_3-reinforced aluminum composites

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Transactions of Nonferrous Metals Society of China 2011年第A01期21卷 42-46页

作者： In-Duck PARK Choon-Tae LEE Hyun-Soo KIM Woo-Jin CHOI myung-chang kang Busan Metropolitan City Hall Fundamental Industries Division 2001 Jungang-ro Yeonje-gu Busan 611-735 Korea Department of Automotive & Mechanical Engineering Silla University Research & Development Center Sam-Ho precision 1256-1 Daejeo2-dong Gangseo-gu Busan 618-807 Korea National Core Research Center for Hybrid Materials Solution Pusan National University

Comparative studies on the relationship between the welding parameters and joining efficiency in the friction welding of hybrid Al203-reinforced aluminum composites were conducted. Metal matrix composites （MMCs） with 37% （volume fraction） aluminum particle were joined by friction welding. The results show that the effects of the rotation speed on the reduction rate of particle size are greater than those of the upset pressure, and the area of the MMC weld zone decreases as the joining efficiency increases, while it is considered that the joining efficiency does not increase as the reduction rate of particle size decreases. During the macro-examination of the bonding interlace, a gray discolored region was observed on the bonding interface, and the center of the region was dark gray. After the micro-examination of the bonding interface, base metal made some second particulate formed by condensed alumina particulate but discoloration part distributed minute alumina particulate without second particulate. Consequently, it was also observed that rotational speed of 3 000 r/min and upset pressure of 63.6 MPa showed a very ***.

关键词： friction welding hybrid aluminum composite bonding interface joining efficiency metal matrix composite

Comparative study on discharge conditions in micro-hole electrical discharge machining of tungsten carbide (WC-Co) material

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中国有色金属学会会刊：英文版 2009年第B09期19卷 114-118页

作者： Hyun-Seok TAK chang-Seung HA Dong-Hyun KIM Ho-Jun LEE Hae-June LEE myung-chang kang National Core Research Center for Hybrid Materials Solution Pusan National University Department of Electrical Engineering Pusan National University

WC-Co is used widely in die and mold industries due to its unique combination of hardness, strength and wear-resistance. For machining difficult-to-cut materials, such as tungsten carbide, micro-electrical discharge machining(EDM) is one of the most effective methods for making holes because the hardness is not a dominant parameter in EDM. This paper describes the characteristics of the discharge conditions for micro-hole EDM of tungsten carbide with a WC grain size of 0.5 μm and Co content of 12%. The EDM process was conducted by varying the condenser and resistance values. A R-C discharge EDM device using arc erosion for micro-hole machining was suggested. Furthermore, the characteristics of the developed micro-EDM were analyzed in terms of the electro-optical observation using an oscilloscope and field emission scanning electron microscope.

关键词：电火花加工碳化钨钴难切削材料硬质合金放电扫描电子显微镜微孔模具行业

Characteristic evaluation of Al_2O_3/CNTs hybrid materials for micro-electrical discharge machining

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Transactions of Nonferrous Metals Society of China 2011年第A01期21卷 28-32页

作者： Hyun-Seok TAK chang-Seung HA Ho-Jun LEE Hyung-Woo LEE Young-Keun JEONG myung-chang kang National Core Research Center for Hybrid Materials Solution Pusan National University Department of Electrical Engineering Pusan National University

The characteristic evaluation of aluminum oxide （A1203）/carbon nanotubes （CNTs） hybrid composites for micro-electrical discharge machining （EDM） was described. Alumina matrix composites reinforced with CNTs were fabricated by a catalytic chemical vapor deposition method. A1203 composites with different CNT concentrations were synthesized. The electrical characteristic of A1203/CNTs composites was examined. These composites were machined by the EDM process according to the various EDM parameters, and the characteristics of machining were analyzed using field emission scanning electron microscope （FESEM）. The electrical conductivity has a increasing tendency as the CNTs content is increased and has a critical point at 5% A1203 （volume fraction）. In the machining accuracy, many tangles of CNT in A1203/CNTs composites cause violent spark. Thus, it causes the poor dimensional accuracy and circularity. The results show that conductivity of the materials and homogeneous distribution of CNTs in the matrix are important factors for micro-EDM of A1203/CNTs hybrid composites.

关键词： A1203/CNTs hybrid materials micro-electrical discharge machining micro-hole electrical conductivity