• 한국농공학회지
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• 제28권2호
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• pp.87-92
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• 1986

The differential equation, which can determine the dynamic critical loads for low parabcoic arches, is derived in this study. The dynamic critical loads of the parabolic arches subjected to a concentrated step load are nummerically analyzed for the changes of load positions. In cases of arches with different end conditions (both hinged, fixed hinged, both fixed), the effect of end conditions and that of the rises are investigated in detail. The summary of the results are the following: 1)The snapthrough does not occur when the rise of arch is very low, and the bifurcation appears clearly as the rise of arch increases. 2)The regions in which the dynamic critical loads are not defined for the both ends fixed are broader than that for the both ends hinged. 3)For all case, the load positions of minimum dynamic critical loads exsit at the near position from the end hinged. Thus, the results obtained in present study show that the magnitude of dynamic critical loads, the load positions of minimum dynamic critical loads and the regions in which the dynamic critical loads are not defined depend on end conditions of arches.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.589-592
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• 2003

In the machining process of micros shape by using high-precision machining system and micro end-mill, it is important for machining characters of tools to be grasped in order to stably use tools of micro end-mill. In this study. we carried out an analytical experiment of basic machining features by using end-mill tools for the purpose of damage prevention and manufacture of high quality when the tools of micro end-mill are used. This experiment used a micro machining system with high precision and a variety of end-mill tools commercialized from tens to hundreds microns in diameter. To establish an optimal machining condition without tool damage, cutting force was analyzed according to the changes of tool diameter and cutting conditions such as cutting speed. feed rate, depth of cut. And an examination was performed for the shape and surface illumination of machining surface according to the changes of machining conditions. Based on these micro machining conditions, micro square pillar, cylinder shaft. thin wall with high aspect ratio, and micro 3-D structures such as micro gear and fan were manufactured.

• 한국기계가공학회지
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• 제20권1호
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• pp.57-65
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• 2021

With the increased utilization of CAM programs, end-mill processing is most commonly used for machining and metal processing. In particular, hole or shaft machining has high assembly precision, which inevitably leads to high utilization of end mills. However, the analysis of quality characteristics according to the process conditions of end mills is not performed systematically at the site, causing poor quality and productivity. The most influential factor of quality is the runout of the end mill. In this paper, the number of turns of the end mill, number of tool blades, cutting direction, and artificial runout volume were determined to identify the correlation between the epicenter, cylindricality, and surface roughness. Two types of end mills, three levels of runout, three levels of rotational speed, and two cutting directions were considered and 36 rounds of hole processing were conducted. For the analysis of shape characteristics according to the set process variables, the experimental planning method was applied to the measured specimen and the processing characteristics were analyzed according to the runout of the end mill through correlation analysis.

• 전자공학회논문지SC
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• 제47권2호
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• pp.35-42
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• 2010

본 논문은 A/D 변환기(Analog-to-Digital Converter) 회로에서 신호선의 터미네이션 조건이 crosstalk에 의해 왜곡되기 쉬운 특성을 가지며 동작 주파수가 높아짐에 따라 이에 대한 주의가 더욱 요구된다. 그중에서도 아날로그 신호인 입력 신호와 레퍼런스 전압 신호는 crosstalk에 의해 왜곡되기 쉬운 아날로그 신호이면서, A/D 변환 전체의 동작 성능을 좌우하는 신호들이다. 이 두 신호들은 각각의 회로 구성에 따라 독특한 터미네이션 조건을 가지므로 본 논문에서는 주파수 영역에서 임피던스 불일치 조건을 고려한 crosstalk를 모델링하고 해당 터미네이션 조건이 crosstalk에 미치는 영향을 확인한다. 먼저, A/D 변환기 회로에서 두 신호의 회로 구성을 파악한 후 near-end와 far-end에서 임피던스 불일치를 고려한 crosstalk 모델을 유도한다. 유도한 crosstalk 모델을 이용하여 입력 신호의 near-end와 터미네이션 임피던스 불일치와 레퍼런스 전압 신호의 far-end 커패시턴스 터미네이션이 crosstalk에 미치는 영향을 예측하고, 실험을 통해 예측 결과를 확인한다. 신호선으로는 가장 널리 사용되는 microstrip 구조를 사용하였으며 skin effect에 의한 손실 증가를 반영하였다.

• 한국생산제조학회지
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• 제26권4호
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• pp.402-409
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• 2017

Selection of optimal cutting conditions is important for improving productivity and implementing efficient process control in metal machining. In this study, improvement of cutting conditions in machining using end-mills is studied by using deep-layered neural networks, which comprise an input layer, output layer, and two hidden layers. System networks are designed with inputs as cutting conditions, and they output the cutting force. A pseudo-inverse network is designed that has the adjustable cutting condition as output and cutting force and other cutting conditions as input. The combination of the system network and pseudo-inverse network enables selection or improvement of cutting conditions that results in the expected cutting force.

• KSTLE International Journal
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• 제3권1호
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• pp.17-22
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• 2002

Roughing of tool steel in its hardened state represents a real challenge in the die and meld industry and process improvement depends on research of tool material, coating technique, and lubrication. However, roughing of hardened steels generates extreme heat and without coolant flooding, tool material cannot withstand the high temperature without choosing the right tools with proper coating. This research conducted milling tests using coated ball end mills to study effects of cutting conditions and geometric parameters of ball end mills on the machinability of hardened tool steel. KP4 steel and STD 11 heat treated steels were used in the dry cutting as the workpiece and TiAIN coated ball end mills with side relief angle of 12$^{\circ}$ was utilized in the cutting tests. Cutting forces, tool wear, and surface roughness were measured in the cutting tests. Results from the experiments showed that 85 m/min of cutting speed and 0.32 mm/rev of feed rate were optimum conditions for better surface finish during rough cutting and 0.26mm/rev with the same cutting speed are optimum conditions in the finish cutting.

• 아태비즈니스연구
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• 제9권4호
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• pp.157-180
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• 2018

This paper empirically analyzes how working conditions of employees and executives affect Korean companies' survival. To this end, a survival analysis based on the accelerated failure time model is conducted from the end of December 2012 to the end of September 2018 on the 2012 year-end financial data for corporations whose common stocks have ever been listed either in the KOSPI market or in the KOSDAQ market with fiscal year ending at the end of December. The analysis shows that the average wage level per employee and the number of executives relative to the number of employees threaten while the average duration of service for female employees prolongs firm survival. Here, the average wage level per employee has turned out to worsen firm survivability regardless of the gender of employees in question while the average duration of service improves firm survivability only in case the employees are female: the average duration of service for male employees or the entire employees has turned out not to have any statistically significant influence on firm survival. The average compensation per executive and the percentage of temporary employees have turned out not to have any statistically significant influence on firm survival while the percentage of female employees has shown statistically significant positive influence on firm survival in some, although not all, models employed in our study. These results are expected to be a good reference in the course of our reaching agreements regarding the improvement of working conditions either between firms and employees or among the members of the entire society.

• Design & Manufacturing
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• 제11권2호
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• pp.46-50
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• 2017

EPS used in lost foam casting elastic modulus is extremely low. So it is necessary to derive machining conditions for effective cutting. Therefore this study were analyzed end-milling machining conditions to affecting the surface roughness of EPS foam. The machining conditions were set to depth, feed, and RPM at 3-level. And 18experimental conditions were derived using mixed orthogonal array. The most important condition for surface roughness is RPM. In addition, RPM machining condition range test that can realize surface roughness less than $10{\mu}m$ was performed. he range of RPM conditions is more than 15,000. However the range of RPM conditions is a condition that is difficult to use in actual field. In the future variance analysis and experiments are needed to derive the range of machining conditions available.

• 대한수학회논문집
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• 제14권1호
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• pp.1-12
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• 1999

The faithful bi-module \ulcornerM\ulcorner with its endomorphism ring End\ulcorner(M) such that M\ulcorner is flat (in other words, End\ulcorner(M)-flat, or endo-flat)and with a commutative ring R containing an identity has been studied in this paper. The chain conditions of a faithful endo-flat module \ulcornerM relative to those of the endomorphism ring End\ulcorner(M) having the zero annihilator of each non-zero endomorphism are studied.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.25-29
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• 1998

One of the crucial problems that must be solved in a computerised unmanned machining environments requires the development of algorithm in order to predict the reliable cutting conditions on surface roughness. This paper is to develop the mathematical models for choosing the suitable cutting conditions and assist a comprehensive understanding of its machinability properties for cutting process by Ball End Mill. The mathematical equations developed to predict the surface results. It has been found that theoretical results obtained from the empirical equations agree with the experimental results of surface roughness.