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대기압 Ar/O<sub>2</sub> 플라즈마 표면처리된 자동차용 냉연강판의 표면특성 및 접착특성평가
이찬주,이상곤,박근환,김병민,Lee, Chan-Joo,Lee, Sang-Kon,Park, Geun-Hwan,Kim, Byung-Min 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.4
Cold rolled steel sheet for automotive was treated by Ar/$O_2$ atmospheric pressure plasma to improve the adhesive bonding strength. Through the contact angle test and calculation of surface free energy for cold rolled steel sheet, the changes of surface properties were investigated before and after plasma treatment. The contact angle was decreased and surface free energy was increased after plasma treatment. And the change of surface roughness and morphology were observed by AFM(Atomic Force Microscope). The surface roughness of steel sheet was slightly changed. Based on Taguchi method, single lap shear test was performed to investigate the effect of experimental parameter such as plasma power, treatment time and flow rate of $O_2$ gas. Results shows that the bonding strength of steel sheet treated in Ar/$O_2$ atmospheric pressure plasma was improved about 20% compared with untreated sheet.
이정구 ( Chung Ku Rhee ),박근환 ( Geun Hwan Park ) 한국의료윤리학회 2005 한국의료윤리학회지 Vol.8 No.1
Both medical ethics and medical English are being taught in most of the premedical courses in Korea since both subjects are considered to be very important in medical education. We have taught medical ethics using English texts in medical English class of premedical course. Students were given tasks of various tests, reports, and presentations in English and part of the lectures were given in English. We have investigated the effectiveness of this type of teaching medical ethics in English using questionnaire survey to premedical students, medical students, and residents who have completed medical ethics in English class at their premedical periods. The survey questioned mainly in the following three areas; if they could understand medical ethics and it was helpful in making ethical decisions at their resident time although it was taught in English, if the class was helpful for their advanced medical ethics class at their medical course and making ethical decisions at their resident time, and if the English they have learned in the class has helped their study of medicine through the medical school and resident time. Most of them responded favorably to all the three questions. In conclusion, teaching medical ethics in medical English class in premedical course appears to be an effective way of teaching both medical ethics and medical English at the same time.
핫스템핑 공정에서 가열온도 및 유지시간을 고려한 22MnB5의 단일겹치기 저항 점용접 조건 최적화
최홍석(Hong Seok Choi),김병민(Byung Min Kim),박근환(Geun Hwan Park),임우승(Woo Seung Lim),이선봉 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.10
본 연구에서는 핫스템핑 소재로 사용되는 보론합금강판 22MnB5의 단일 겹치기 점용접에서 용접부의 강도 향상을 위한 최적화를 수행하였다. 최적화 과정은 다구찌 실험계획법에 의해 행해졌으며 공정변수는 전류, 가압력 및 통전시간으로 선정하였고, 잡음인자로서 핫스템핑 시 소재의 가열온도와 유지시간을 고려하였다. 가열조건에 따라 22MnB5 표면의 알루미늄 도금층과 모재 간의 확산반응에 의해 화합물층 두께에 산포가 발생하였으며 이러한 산포는 너겟의 형성에 영향을 미치는 것을 알 수 있었다. 한편 용접부의 인장전단강도를 목적함수로 하였을 때, 이러한 가열조건에 강건한 최적의 용접 조건은 전류 8㎄, 가압력 4kN, 통전시간 18cycle로 선정되었다. 최적 조건의 검증 결과 용접부의 인장전단강도 는 32kN으로서 요구되는 규격인 23kN보다 크게 증가되었다. In this study, optimization of the process parameters of the resistance spot welding of a sheet of aluminum-coated boron alloyed steel, 22MnB5, used in hot stamping has been performed by a Taguchi method to increase the strength of the weld joint. The process parameters selected were current, electrode force, and weld time. The heating temperature and heating time of 22MnB5 are considered to be noise factors. It was known that the variation in the thickness of the intermetallic compound layer between the aluminum-coated layer and the substrate, which influences on the formation of nugget, was generated due to the difference of diffusion reaction according to heating conditions. From the results of spot weld experiment, the optimum weld condition was determined to be when the current, electrode force, and weld time were 8㎄, 4kN, and 18 cycles, respectively. The result of a test performed to verify the optimized weld condition showed that the tensile strength of the weld joint was over 32kN, which is considerably higher than the required strength, i.e., 23kN.