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액화질소를 이용한 오픈 셀 실리콘 폼의 냉동 절삭조건 최적화
황지홍(Jihong Hwang),조광희(Kwang-Hee Cho),박민수(Min-Soo Park) 한국생산제조학회 2014 한국생산제조학회지 Vol.23 No.1
Open-cell silicon foam is difficult to cut using conventional machining processes because of its low stiffness. That is, open-cell silicon foam is easily pressed down when the tool is engaged, which makes it difficult to remove the material in the form of chip. This study proposes an advanced method of machining open-cell silicon foam by freezing the material using liquid nitrogen. Furthermore, the machining conditions are optimized to maximize the efficiency of material removal and minimize the usage of liquid nitrogen by conducting experiments under various machining conditions. The results show that open-cell silicone foam products with free surface can be successfully machined by employing the proposed method.
정지연(Jiyeon Jung),황지홍(Jihong Hwang) Korean Society for Precision Engineering 2021 한국정밀공학회지 Vol.38 No.8
The objective of the present study was to investigate the relationship between surface roughness and touch perception of surfaces with randomly spaced, irregular features. Two sets of specimens with top surfaces consisting of triangular peaks and valleys were modeled and 3D-Printed by varying the height of the peak, the depth of the valley, and the width between two intersections of the peak or valley with the center line. For one set of specimens, values of these variables were kept constant within a specimen but varied across specimens. For the other set of specimens, values of these variables were randomly selected in given ranges within a specimen while ranges were varied across specimens. The level of touch perception of each specimen was then measured using a questionnaire consisting of 16 adjectives related to touch perception and a 7-point Likert scale. Measured data were statistically analyzed and compared between different sets of specimens. Results indicated that it was inappropriate to directly apply findings of the previous studies for surfaces with regularly spaced, geometrically well-defined features to surfaces with randomly spaced, irregular features.
순수 2차원 절삭에서 속도화상입자계측(PIV)을 이용한 주변형 영역 내 변형률 분포 고찰
이주호(Joo Ho Lee),이은호(Eunho Lee),황지홍(Jihong Hwang) 한국생산제조학회 2019 한국생산제조학회지 Vol.28 No.1
In the present study, a system for direct observation and quantitative analysis of the chip formation process in 2-D orthogonal machining was developed. The system consists of an optical system for high-speed photographing of the shear zone at high temporal and spatial resolution and an image analysis system for calculating the strain rate and strain distributions from the acquired images using particle image velocimetry. The effects of cutting conditions, such as cutting edge radius and depth of cut on the deformation behavior in the shear zone, were investigated by comparing the strain rate and strain distributions obtained using the developed system. The results indicate that the developed system can be utilized to enhance the understanding of the mechanics of machining and the development and validation of machining models.
폴리머 층 전사 및 처짐 현상을 이용한 곡선 형태의 PMMA 나노채널 제작
조영학(Young Hak Cho),김성동(Sung Dong Kim),황지홍(Jihong Hwang) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.1
We present a simple and low-cost method to fabricate poly(methyl-methacrylate) (PMMA) nanochannels with various shapes by combining the standard optical lithography with a PMMA layer transfer and collapse technique. We utilized PMMA membrane reflowing/collapsing phenomena into microchannels to fabricate nanochannels at both corners of arbitrarily-shaped microchannels. This allows nanochannels with various shapes such as curved nanochannels as well as straight nanochannels to be easily fabricated since the shape of the microchannel determines the shape of the nanochannels. This nanochannel fabrication method is simple, flexible, and low-cost since the standard optical lithography with low-resolution optical masks can be used to fabricate nanoscale channels as small as 100 nm wide with various shapes. Also, the sealing of nanochannels can be naturally achieved while the nanochannels are formed through the polymer layer transfer and collapse.
안일혁(Il-Hyuk Ahn),김익현(Ik-Hyun Kim),황지홍(Jihong Hwang) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.3
The material removal mechanism in machining is significantly affected by the cutting edge geometry. Its effect becomes even more substantial when the depth of cut is relatively small as compared to the characteristic length which represents the shape and size of the cutting edge. Conventionally, radius or focal length has been employed as the characteristic length with the assumption that the shape of cutting edge is round or parabolic. However, in reality, there could be various ways to determine the radius or focal length even for the same tool edge profile, depending on the region to be considered as cutting edge in the measured profile and the constraints to be set in constructing the best fitted circle or parabola. In this regard, the present study proposes various models to determine the characteristic length in terms of radius or focal length. Their physical compatibility are validated by carrying out 2D orthogonal cutting experiments using inserts with a wide range of characteristic length (30 ? 180 μm in terms of radius) and then by investigating the correlation between the characteristic length and the cutting forces. Such validation is based on the common belief that the larger the characteristic length is, the blunter the cutting edge is and the higher the cutting forces are. Interestingly, the results showed that the correlation is higher for the radius or focal length obtained with a constraint that the center of best fitted circle or the focus of the best fitted parabola should be on the bisectional line of the wedge angle of tool.