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이종 폴리머 소재의 레이저 투과 용접 시 결함의 실험적 평가
최대철(Dae Cheol Choi),신기훈(Ki-Hoon Shin),한영구(Young Gu Han),홍민철(Min Cheol Hong),정성균(Seong-Kyun Cheong),정종설(Jong-Seol Jeong),나기정(Ki Jung Na),유호훈(Ho Hoon Ryu) 한국생산제조학회 2021 한국생산제조학회지 Vol.30 No.2
In this study, the laser process parameters were determined at which surface and sectional defects begin to occur during the laser-transmission welding of two heterogeneous polymer materials. Specifically, laser-transmission welding of PMMA and PC/ABS with thicknesses of 2 mm each was conducted using a thulium laser with a wavelength and focusing diameter of 2 μm and 1 mm, respectively. The experimental results show that the laser power at the time of defect occurrence also increases proportionally as the laser scan speed increases, but the corresponding energy density decreases. In addition, the ratio of the welding width to the laser diameter at defect occurrence slightly decreases from 1.25 to 1.13 with increasing scan speed. Based on the experimental results, it is necessary to increase the laser scan speed and power simultaneously within the allowable range in terms of energy efficiency and production time during laser-transmission welding.
최대봉(Dae-Bong Choi),유기한(Ki-Han Yu),김수태(Soo-Tae Kim) 한국기계가공학회 2008 한국기계가공학회 춘추계학술대회 논문집 Vol.2008 No.-
High speed machining is the core technology that influences the performance of machine tools, and the high speed motor spindle is widely used for the high speed machine tools recently. The important problem in this spindle is to reduce and minimize the thermal effect by motor and bearing. This paper presents the thermal characteristics analysis of a high speed motor spindle system consisted of angular constant ball bearings and built-in motor with oil-jet lubrication. The analysis of thermal characteristic of spindle is performed according to the oil-jet lubrication by using finite element method. This result can be applied to the design and manufacture of the high speed spindle.
최대정(Dae Jung Choi),이영성(Young Sung Lee),김응도(Eung-Do Kim),안동기(Dong-Ki Ahn),신병준(Byung-Joon Shin) 대한정형외과학회 2014 대한정형외과학회지 Vol.49 No.3
목적: 대한정형외과학회 의학연수교육의 인식도를 조사하여 전통적인 학회식 의학연수교육의 장단점을 평가하고자 하였다. 대상 및 방법: 대한정형외과학회의 학회식 및 웹기반 의학연수교육에 대한 인식도를 근무현황, 정보기술에 대한 친밀도, 학회식 및 웹기반 의학연수교육에 대한 장단점에 대하여 웹(web) 설문 조사하였다. 결과: 수신 3,427명 중 유효 응답은 168건(4.9%)이었다. 응답자의 74.4%는 근무시간과 맞지 않아서(35.7%)와 학회가 대도시에서 개최되어 거리가 멀어서(13.2%) 등의 이유로 의학연수교육에 자주 참석하지 못하였다. 학회식 의학연수교육의 장점은 임상적 문제에 대하여 다른 회원이 어떻게 생각하는지 알 수 있다(64.3%)로, 단점은 비슷한 내용의 학회가 많고(60.1%), 짧은 시간에 강의가 이루어져 심도 있는 공부가 되지 못한다(53.0%)로 조사되었다. 웹기반 의학연수교육이 구축 시 웹컨텐츠는 수술 술기 및 조언(tip)에 관한 요구가 가장 많았으며(49.0%), 강의 슬라이드(44.6%)나 동영상(37.6%) 형태로 제공되는 것을 선호하였다. 웹기반 의학연수교육의 필요성에 대하여서는 응답자의 95.5%에서 긍정적으로 답하였다. 결론: 학회식 의학연수교육에서의 비교적 짧은 교육 시간과 질의 문답의 부족을 보완하고, 지역적, 시간적 장애의 단점을 보완할 수 있는 웹기반 의학연수교육의 필요성에 높은 요구를 보였다. Purpose: Awareness on continuing medical education (CME) of the Korean Orthopaedic Association (KOA) was investigated in order to augment the weak educational points of the conventional academic CME. Materials and Methods: The web-survey was conducted in the KOA on the awareness of conventional academic or web-based CME. The questionnaire included working conditions, intimacy of informational technology, and strengths and weaknesses of academic and web-based CME. Results: Among 3,427 emails sent, 168 (4.9% of effective response rate) responses were received. Of the responders, 74.4% of the responders could not attend CME frequently because of working time (35.7%) and a distance far from the working place (13.2%). The merits of academic CME included as the opportunity for considerations of other members’ thoughts on some clinical matters (64.3%); however, the weak points were holding several similar conferences (60.1%) and too short time for adequate study (53.0%). They wanted that surgical procedures and tips (49.0%) to be provided in the form of lecture slides (44.6%) or movie clips (37.6%) in web-based CME. 95.5% of the responders showed positive response regarding the need for web-based CME. Conclusion: Results of the survey showed high needs and interests in web-based CME, which could support the weaknesses of the academic CME with less time for education and limited accessibility to CME due to time or space barriers due to their working conditions.
조기연(Ki Youn Cho),박재규(Jae Gyu Park),최대원(Dae Won Choi),김기현(Gi Hyun Kim),한민현(Min Hyeon Han) 한국자동차공학회 2012 한국자동차공학회 학술대회 및 전시회 Vol.2012 No.11
It was analyzed the relationship between the bead profile and tire performance using passenger and light truck tires. At this time, test tires have the same size and load index by manufactured in the ten tire brand. And it was measuring the contact pressure of bead section under the different inflation pressure conditions. Also, spring rate test was proceeded to get the spring constant of test tires. As a result, rim flange and bead hill are proportional to the inflation pressure. But bead seat is not influenced by inflation pressure. In case of passenger, lateral and longitudinal spring constant are influenced by the contact pressure of bead section. But in case of light truck, these are not influenced by the contact pressure of bead section.
강윤환,최대기,이윤용,이원국 ( Yun Whan Kang,Dae Ki Choi,Youn Yong Lee,Won Kook Lee ) 한국화학공학회 1991 Korean Chemical Engineering Research(HWAHAK KONGHA Vol.29 No.2
The concentration profiles of the ternary system(acetone/methanol/water) in a distillation column were predicted by the following four different solutions: the general or approximately linearized solutions of Maxwell-Stefan equation, two solutions with the assumptions of the constant number of overall gas phase mass transfer unit(N_(OG)) along the dispersion height or the constant binary Murphree efficiency. The experiments were performed in a 5 ㎝ I.D. distillation column with 5 plates under the conditions of the liquid flow rate of 2.0 g-mole/min and total reflux. The calculated concentration profiles were compared with the experimental data. It showed that the concentration profiles with the constant binary Murphree efficiency were severely deviated from the experimental data, but the profiles of the other three methods were in good agreements.