• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.251-255
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• 2003

This paper presents the design, fabrication, and calibration of a piezoelectric polymer-based sensorized microgripper. Electro discharge machining technology is employed to fabricate super-elastic alloy based micro gripper. It is tested to present improvement of mechanical performance. For integration of force sensor on the micro gripper, the sensor design based on the piezoelectric polymer PVDF film and fabrication process are presented. The calibration and performance test of force sensor integrated micro gripper are experimentally carried out. The force sensor integrated micro gripper is applied to perform fine alignment tasks of micro opto-electrical components. It successfully supplies force feedback to the operator through the haptic device and plays a main role in preventing damage of assembly parts by adjusting the teaching command.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1772-1777
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• 2003

This paper presents the design, fabrication, and calibration of a piezoelectric polymer-based sensorized microgripper. Electro discharge machining technology is employed to fabricate super-elastic alloy based micro gripper. It is tested to present improvement of mechanical performance. For integration of force sensor on the micro gripper, the sensor design based on the piezoelectric polymer PVDF film and fabrication process are presented. The calibration and performance test of force sensor integrated micro gripper are experimentally carried out. The force sensor integrated micro gripper is applied to perform fme alignment tasks of micro opto-electrical components. It successfully supplies force feedback to the operator through the haptic device and plays a main role in preventing damage of assembly parts by adjusting the teaching command.

• Journal of the Korean Society for Nondestructive Testing
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• v.10 no.2
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• pp.15-22
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• 1990

Since in-core flux thimble tube wear the due to flow-induced vibration could degrade the integrity of nuclear reactor, the effective detection and interpretation of the wear is important. In order to establish an inspection technique for thimble tubes, an eddy current experiment was performed to determine the optimum test frequency, defect sensitivity and evaluation accuracy. Eddy current probes were designed and fabricated with a theory. Specimens with artificial defects were fabricated using electro discharge machining method. The results from inspection technique developed and on-site inspection showed good applicability.

• Nuclear Engineering and Technology
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• v.30 no.4
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• pp.377-385
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• 1998

Many nuclear power plants have experienced unscheduled shutdown due to the leakage of steam generator tubes. The leakages are normally due to the crack, possibly stress corrosion cracking (SCC) near the tube expansion at the top of tubesheet or at the tangential point of the row-1 U-bend region. The conventional eddy current technique, which makes use of a differential bobbin coil, has been found to be inadequate for the early detection of SCC. During the in-service inspection, therefore, it is a general practice that the rotating pancake coil (RPC) is used for detecting the cracks. Even in using RPC, however, it is difficult to determine the depth of the cracks quantitatively. This paper attempts to determine the detectability and sizing ability of RPC technique for axial or circumferential cracks at the tube expansion region. The simulated cracks with various dimensions were fabricated by electro-discharge machining (EDM) method. Experimental results are discussed with theoretical calculations.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.9
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• pp.881-886
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• 2009

This paper presents a manipulation system consisting of a coarse/fine XY positioning system and an out-of-plane manipulator. The object of the system is to conduct tine positioning and manipulation of micro parts. The fine stage and the out-of-plane manipulator have compliant mechanisms with flexure hinges, which are driven by stack-type piezoelectric elements. In the fine stage, the compliant mechanism plays the roles of motion guide and displacement amplification. The out-of-plane manipulator contains three piezo-driven compliant mechanisms for large working range and fine resolution. For large displacement, the compliant mechanism is implemented by a two-step displacement amplification mechanism. The compliant mechanisms are manufactured by wire electro-discharge machining for flexure hinges. Experiments demonstrate that the developed system is applicable to a fine positioning and fine manipulation of micro parts.

• Transactions of Materials Processing
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• v.29 no.6
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• pp.347-355
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• 2020

The mechanical responses of multilayered aluminum sheet fabricated by roll bonding, i.e., A1050/A3004 (65% A1050, 35% A3004 by thickness), were investigated via combined experiment and finite element (FE) analysis. The mechanical properties were measured using uniaxial tensile tests in various loading directions for the multilayered sheet. The corresponding tests for individual layers were also conducted. The testing samples were prepared by wire electro discharge machining (EDM). Stress-strain curves and Lankford coefficients of the multilayered sheet were then predicted by FE simulations. The measured mechanical properties of the individual layers were utilized as inputs for the simulation. Two yield functions, i.e., isotropic von-Mises and anisotropic non-quadratic Hill1948, were employed. Predicted results were compared with the experimental data and further discussed.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.2
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• pp.38-43
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• 2007

This paper describes ultrasonically assisted grinding used to obtain a glossy surface quickly and precisely. High-quality surfaces are required for plastic injection molding dies used in the production of plastic parts such as dials for cellular phones. Traditionally, in order to finish the dies, manual polishing by a skilled worker has been required after the machining processes, such as electro discharge machining (EDM), which leaves an affected layer, and milling, which leaves tooling marks. However, manual polishing causes detrimental geometrical deviations of the die and consumes several days to finish a die surface. Therefore, a machining process for finishing dies without manual polishing to improve the surface roughness and form accuracy would be extremely valuable. In this study, a 3D positioning machine equipped with an ultrasonic spindle was used to conduct grinding experiments. An electroplated diamond tool was used for these experiments. Generally, diamond tools cannot grind steel because of excessive wear as a result of carbon atoms diffusing into bulk steel and chips. However, ultrasonically assisted grinding can achieve a fine surface (roughness Rz of $0.4{\mu}m$) on die steel without severe tool wear. The final aim of this study is to realize mirror surface grinding for injection molding dies without manual polishing. To do this, it is necessary to fabricate an electroplated diamond tool with high form accuracy and low run-out. This paper describes a tool-making method for high precision grinding and the grinding performance of a self-electroplated tool. The ground surface textures, tool performance and tool life were investigated A ground surface roughness Rz of 0.14 um was achieved Our results show that the spindle speed, feed rate and cross feed affected the surface texture. One tool could finish $5000mm^2$ of die steel surface without any deterioration of the ground surface roughness.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.417-420
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• 2007

Micro parts are usually used of producing by micro-electro-mechanical systems(MEMS). In this paper, we present some fundamental results concerning on the MEMS, extrusion condition on the micro forming characteristics and new micro forward extrusion machine has been developed. In the first step, we manufactured micro dies in two kinds of sections. One is a circle section, another is a cross section. The process for fabricating micro dies combines a deep UV-lithography, anisotropic etching techniques and metal electroplating with bulk silicon based on Ni with a thickness of $50{\mu}m$. The outer diameter of Ni-micro dies is 3mm and the diameter of extrusion section is $270{\mu}m$ for a cross section, $500{\mu}m$ for a circle section. The low linear density polyethylene(LLEPD) in the shape of a pellet has been used of micro extrusion. The billet was placed in a container manufactured by electric discharge machining and extruded through the micro die by a piezoelectric actuator. The micro extrusion has succeeded in a forming such micro parts as micro bars, micro cross shafts.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.118-124
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• 2003

응축기, 증발기, 전열관에 사용되는 Fin Tube는 열전달효율 향상을 위하여 Fin의 높이 를 증가시키고, Tube의 최소두께를 얇게 가공하는 경향으로 발전하고 있다. 따라서, Fin Tube의 와전류탐상(ECT; Eddy Current Testing)에 의한 결함검출에 더욱 어려움이 예상된다. 본 연구에서는 Fin Tube의 Fin 높이를 3단계로 변화시켜 Tube를 제작하고, Tube에 축 방향결함, 원주방향결함, 원형결함을 각각 Fin Tube의 안쪽에 최소두께의 20%, 40%, 60% 의 동일결함율을 갖는 인공결함 시험편을 제작하였다. 제작한 원형결함시험편에 와전류탐상을 수행하여 Fin 높이에 따른 최적주파수의 변화를 연구하였다. Fin높이가 다른 원형결함 시험편에 1~20KHz 주파수를 적용한 결과 최적주파수는 12KHz로 Fin높이에 크게 영향을 받지 않음을 밝혔다 또한 Fin높이에 따른 최적주파수변화는 크지 않으나 Fin 높이가 높을수록 100%관통결함의 위상각(40')에 근접하여 나타났다. 축방향결함, 원주방향결함, 원형결함을 갖는 시험편에 와전류탐상을 수행한 결과 원형결함을 갖는 시험편의 신호 감도가 축방향결함, 원주방향결함보다 좋게 나타났다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.81.2-81.2
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• 2012

To fabricate a metal mold for injection molding, hot-embossing and imprinting process, mechanical machining, electro discharge machining (EDM), electrochemical machining (ECM), laser process and wet etching ($FeCl_3$ process) have been widely used. However it is hard to get precise structure with these processes. Electrochemical etching has been also employed to fabricate a micro structure in metal mold. A through mask electrochemical micro machining (TMEMM) is one of the electrochemical etching processes which can obtain finely precise structure. In this process, many parameters such as current density, process time, temperature of electrolyte and distance between electrodes should be controlled. Therefore, it is difficult to predict the result because it has low reliability and reproducibility. To improve it, we investigated this process numerically and experimentally. To search the relation between processing parameters and the results, we used finite element simulation and the commercial finite element method (FEM) software ANSYS was used to analyze the electric field. In this study, it was supposed that the anodic dissolution process is predicted depending on the current density which is one of major parameters with finite element method. In experiment, we used stainless steel (SS304) substrate with various sized square and circular array patterns as an anode and copper (Cu) plate as a cathode. A mixture of $H_2SO_4$, $H_3PO_4$ and DIW was used as an electrolyte. After electrochemical etching process, we compared the results of experiment and simulation. As a result, we got the current distribution in the electrolyte and line profile of current density of the patterns from simulation. And etching profile and surface morphologies were characterized by 3D-profiler(${\mu}$-surf, Nanofocus, Germany) and FE-SEM(S-4800, Hitachi, Japan) measurement. From comparison of these data, it was confirmed that current distribution and line profile of the patterns from simulation are similar to surface morphology and etching profile of the sample from the process, respectively. Then we concluded that current density is more concentrated at the edge of pattern and the depth of etched area is proportional to current density.