• Korean Journal of Metals and Materials
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• v.47 no.11
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• pp.722-727
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• 2009

The bipolar plates are not only the major part of the polymer electrolyte membrane fuel cell (PEMFC) stack in weight and volume, but also a significant contributor to the stack costs. Stainless steels are considered to be good candidates for bipolar plate materials of the PEMFC due to their low cost, high strength and easy machining, as well as corrosion resistance. In this paper, 316L stainless steel with and without nitrogen ion implantation were tested in simulated PEMFC environments for application as bipolar plates. The results showed that the nitride formed by nitrogen ion implantation contributed the decrease of the interfacial contact resistance without degradation of corrosion property. The combination of excellent properties indicated that nitrogen ion implanted stainless steel could be potential candidate materials as bipolar plates in PEMFC. Current efforts have focused on optimizing the condition of ion implantation.

• Design & Manufacturing
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• v.16 no.1
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• pp.9-14
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• 2022

A lot of research is being done on metal materials to improve the lifespan of molded parts. As a result, excellent mold materials have been developed that withstand high hardness at high temperatures and frictional heat generated from high-speed cutting. In this study, the press mold life of powder high-speed tool steel and general high-speed tool steel was compared. Powdered high-speed steel is composed of alloying elements such as tungsten, maldividene, cobalt, chromium, and vanadium in steel, which improves wear resistance compared to high-hardness and high-speed tool steels. The mold parts of both steel types were manufactured in the same way from heat treatment to machining, and the powder high-speed tool steel was 66HRC and the high-speed tool steel was 61HRC. As a result of the experiment, it was observed that the number of punching of powder high-speed tool steel was improved by 40-50%, and powder high-speed tool steel had fewer impurities, uniform texture, and excellent surface structure. It has a microscopic structure.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.6
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• pp.28-41
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• 1994

An efficient algorithm is proposed to select the proper tools and generate their paths for NC rough cutting of dies and molds with sculptured surfaces. Even though a milling process consists of roughing, semi-finishing, and finishing, most material is removed by a rough cutting process. Therfore it can be said that the rough cutting process occupy an important portion of the NC milling process, and accordingly, an efficient rough cutting method contributes to an efficient milling process. In order work, the following basic assumption is accepted for the efficient machining. That is, to machine a region bounded by a profile, larger tools should be used in the far inside and the region adjacent to relatively simple portion of the boundary while smaller tools are used in the regions adjacent to the relatively complex protion. Thus the tools are selected based on the complexity of the boundary profile adjacent to the region to be machined. An index called cutting path ratio is proposed in this work as a measure of the relative complexity of the profile with respect to a tool diameter. Once the tools are selected, their tool paths are calculated starting from the largest to the smallest tool.

• Journal of the Korea Safety Management & Science
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• v.15 no.4
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• pp.179-184
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• 2013

An accident from machine work is often fatal to the worker. This accident is mostly preventable through perfect process jig. In case of this machine work, however, the disaster frequently occurred because of the design which is not considered the beginning of product design, post-process and mass process of production. As for sand casting method, this has the merits of the production; the product is easily produced by manual labor. On the other hand, this method has the demerits of a bigger dimensional error contrary to other mass process of production. When the sand casting product is in machine work, there are various problems such as unsafe fix and excessive cutting, product desorption and rapid life depreciation of equipment and tools. Considering the characteristics of sand casting method, it is accepted as difficulty to improve the problems. In this study, it suggests shell mold method for mold instead of the machine work after the sand casting of the circle shape container product. And the surface accomplishes the following average of surface roughness Ra$9.94{\mu}m$ of machine work with the casting of flask mold by shell mold method. In accordance with the simplification of processing process and reducing the average thickness variation by mass production of product with detailed appearance, it has a good influence on safety accident prevention caused by production and damaged product. It is confirmed that making higher degree of size precision of all machine work product is possible to increase the safety and productivity, reduce the processing process and improve environment.

• Korean Journal of Materials Research
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• v.2 no.3
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• pp.172-179
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• 1992

$Al_2O_3/ZrO_2$ composites were fabricated by pressureless sintering from commercial powders and/or nano composite powder of $Al_2O_3/ZrO_2$. The Properties of the composites such as density, strength, hardness and fracture toughness were evaluated. Microstructures and fracture surfaces ware also examined. The flexural strength remains unchanged(~640 MPa) as long as the content of commercial powders is not extreamly high, and depends on microstructures of the composites. Fracture toughness(4.3-5.3 $Mpa{\cdot}m^{1/2}$) increases with increasing content of commercial powders. Fractography shows that failure-initiating sources are 1)surface flaws resulting from machining damage, 2)crack-shaped voids formed due to $ZrO_2$ agglomeration, and 3)surface separation caused by inhomogeneous blending and by sinterability difference between nato composite powder and commercial powders of $Al_2O_3/ZrO_2$. Failure mode of the composites was mainly transgranular.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.770-776
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• 2003

#140 mesh and #600 mesh wheels were adopted to grind (111) and (100) oriented single crystalline silicon wafer and the grinding induced change of the surface integrity was investigated. For this purpose, microroughness, residual stress and phase transformation were analyzed for the ground surface. Microroughness was analyzed using AFM (Atomic Force Microscope) and crystal structure was analyzed using micro-Raman spectroscopy. The residual stress and phase transformation were also analyzed after thermal annealing in the air. As a result, microroughness of (111) wafer was larger than that of (100) wafer after grinding. It was observed using Raman spectrum that the silicon was transformed from diamond cubic Si-I to Si-III(body centered tetragonal) or Si-XII(rhombohedral). Residual stress relaxation was also shown in cavities which were produced after grinding. The thermal annealing was effective for the recovery of the silicon phase to the original phase and the residual stress relaxation.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.4
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• pp.93-100
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• 2002

The current from the feed motor of a machine tool contains substantial information about the machining state. There have been many researches that investigated the current as a measure for the cutting farces. However it has been reported that this indirect measurement of the cutting farces from the feed motor current is only feasible in low frequency. In this research, it was presented that the bandwidth of the current monitoring can be expanded to 130 Hz. And the unusual behavior of the current was examined in this bandwidth. The cross-feed directional cutting force influences the machined surface of the workpiece, which makes it necessary to estimate this force to control the roughness of the machined sulfate. The current exists in the stationary feed motor, and it can give the useful information on the quality of the machined surface. But the unpredictable behavior of the current prevents applying the current to prediction of the cutting state. Empirical approach was conducted to resolve the problem. As a result, the current was shown to be related to the accumulation of the accumulation of the infinitesimal rotation of the motor. rotation of the motor. Subsequently the relationship between the current and the cutting force was identified.

• Journal of KIISE:Computing Practices and Letters
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• v.5 no.4
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• pp.385-394
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• 1999

제품을 설계하는 디자이너나 엔지니어는 많은 시간과 노력을 들이지 않고서 그들이 설계한 3차원 제품 모델에 대한 사실적인 이미지를 원한다. 디자인 프로세스의 초기인 개념 설계에서부터 설계검증, 그리고 가공 과정에서 사실적인 이미지가 매우 유용하므로, 대부분의 주요 CAD 제작사는 그들의 CAD 소프트웨어에 고급 렌더링 기능을 추가하고 있다. 상용의 CAD/CAM 모델러에서는 NURB 곡면을 기초로 모델링을 수행하므로, NURB 곡면을 렌더링할 수 있는 패키지가 필요하다. VIF(Visual InterFace) 렌더링 라이브러리는 A-buffer 방식과 Ray tracing 방식의 두 가지 고급 렌더링 모드를 제공한다. 다각형은 물론 NURB 곡면을 입력으로 받아 사용자가 설정한 표면의 각종 계수, 원하는 view와 설정된 광원에 따라 이미지를 만들고 다양한 형태로 출력시킬 수 있는 다양한 기능을 제공한다. 본 논문에서는 VIF 렌더링 라이브러리에 대한 구조와 기능별로 분류된 함수에 대하여 설명하며, 실제로 CAD/CAM 시스템과 통합되어 구상설계에서부터 3차원 설계 모델링에 이르기까지의 제조공정에서 설계검증 툴로써 어떻게 활용되고 있는가에 대하여 기술한다.Abstract Engineers and industrial designers want to produce a realistic-looking images of a 3D model without spending a lot of time and money. Photo-realistic images are so useful from the conceptual design, through its verification, to the machining, that most major CAD venders offer built-in as well as add-on photo-realistic rendering capability to their core CAD software. Since 3D model is consists of a set of NURB surfaces in commercial CAD packages, we need a renderer which handles NURB surface as well as other primitives.A new rendering library called VIF (Visual InterFace) provides two photo-realistic rendering modes: A-buffer and Ray tracing. As an input data it takes NURB surfaces as well as polygonal data and produces images in accordance with the surface parameters, view and lights set by user and outputs image with different formats. This paper describes the overall architecture of VIF and its library functions classified by their functionalities, and discusses how VIF is used as a graphical verification tool in manufacturing processes from the conceptual design to 3D modeling.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.473-479
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• 2017

CrN coatings have been used as protective coatings for cutting tools, forming tools, and various tribological machining applications because these coatings have high hardness. Cr-Al-N coatings have been investigated to improve the properties of CrN coatings. Cr-Al-N coatings were fabricated by a hybrid physical vapor deposition method consisting of unbalanced magnetron sputtering and arc ion plating with different working pressure and substrate bias voltage. The phase analysis of the composition was performed using XRD (x-ray diffraction). Cr-Al-N coatings were grown with textured CrN phase and (111), (200), and (220) planes. The adhesion strength of the coatings tested by scratch test increased. The friction coefficient and removal rate of the coatings were measured by a ball-on-disk test. The friction coefficient and removal rate of the coatings decreased from 0.46. to 0.22, and from $2.00{\times}10^{-12}m^2/N$ to $1.31{\times}10^{-13}m^2/N$, respectively, with increasing bias voltage. The tribological properties of the coatings increased with increasing substrate bias voltage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.105-111
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• 2013

The spindle is the main component in machine tools. The static and dynamic characteristics of the spindle directly affect the machining accuracy of workpieces. The characteristics of the spindle depend on the shaft size, bearing span, built-in motor location, and so on. Therefore, the appropriate selection of these parameters is important to improve the spindle characteristics. This paper presents the analysis of the static and dynamic characteristics and optimization design of a 40,000-rpm high-speed spindle. Statistical analysis for optimization and finite element analysis were performed. This study uses the response surface method to optimize the objective function and design factors. The targets are the natural frequency and displacement. The design factors are the shaft length, shaft diameter, bearing span, and motor location. The optimized design provides better results than the initial model, and these results are expected to improve the static and dynamic characteristics of the spindle.