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화상처리에 의한 Gas Tungsten Arc 용접에서의 용융지폭제어에 관한 연구
김동철,이세헌,엄기원,Kim, Dong-Cheol,Rhee, Sehun,Um, Ki-Woan 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.9
The feedback control systems of welding process using visual information can improve weld qualities. However, it is very difficult to get the visual information of weld pool since the light intensity of welding arc is much stronger than that of the weld pool. To explore the possibility of extending the capability of automatic welding machines, a study of a closed loop controlled welding system consisted of a GTA welding machine, a vision system, a stepping motor system and a digital computer was undertaken. Particularly, in this system, a CCD camera with a long wavelength pass filter was used to get a better weld pool image. Subsequently, an image analysis technique has been developed to measure the weld pool width. Using this weld pool width measurement, a colsed loop control system adjusted welding speed to maintain a constant weld pool width.
철도차량 접촉기의 신뢰성 분석 및 교환주기 결정에 대한 연구
박민흥(Minheung Park),이세헌(Sehun Rhee) 한국신뢰성학회 2017 신뢰성응용연구 Vol.17 No.4
Purpose: The purpose of this study is to determine the replacement cycle applied age replacement policy by reliability analysis based on railway vehicle contactor’s failure history data. Method: We performed reliability analysis based on railway vehicle contactor’s failure history data. We found a suitable distribution by goodness of fit test and predicted the reliability through estimation of scale & shape parameter. Considering cost information we determined the replacement cycle that minimize the opportunity cost. Result: Suitable distribution was the Weibull and scale parameter & shape parameter are estimated by reliability analysis. The replacement cycle was predicted and MTTF, B6 percentile life were suggested additionally. Conclusion: We confirmed that failure rate type of railway vehicle contactor is degradation model having a time dependent characteristic and examined the replacement cycle in our country’s operating environment. We expect that this study result contribute to railway operation agency for maintenance policy decision.
알루미늄 합급의 레이저 가공에서 인장 강도 예측을 위한 회귀 모델 및 신경망 모델의 개발
박영환(Young Whan Park),이세헌(Sehun Rhee) Korean Society for Precision Engineering 2007 한국정밀공학회지 Vol.24 No.4
Aluminum alloy which is one of the light materials has been tried to apply to light weight vehicle body. In order to do that, welding technology is very important. In case of the aluminum laser welding, the strength of welded part is reduced due to porosity, underfill, and magnesium loss. To overcome these problems, laser welding of aluminum with filler wire was suggested. In this study, experiment about laser welding of AA5I82 aluminum alloy with AA5356 filler wire was performed according to process parameters such as laser power, welding speed and wire feed rate. The tensile strength was measured to find the weldability of laser welding with filler wire. The models to estimate tensile strength were suggested using three regression models and one neural network model. For regression models, one was the multiple linear regression model, another was the second order polynomial regression model, and the other was the multiple nonlinear regression model. Neural network model with 2 hidden layers which had 5 and 3 nodes respectively was investigated to find the most suitable model for the system. Estimation performance was evaluated for each model using the average error rate. Among the three regression models, the second order polynomial regression model had the best estimation performance. For all models, neural network model has the best estimation performance.
CFRP-Aluminum 이종소재의 Self-Piercing Rivet 접합
전남기(Nam-Ki Jeon),이세헌(Sehun Rhee),감동혁(Dong-Hyuck Kam) 대한용접·접합학회 2018 대한용접·접합학회지 Vol.36 No.3
In response to the environmental regulations and market forces for fuel economy, automotive industry has continued trying to apply lightweight multi-materials for weight reduction. Carbon fiber reinforced plastics (CFRP) is one of the most attractive structural materials because of its high strength to weight ratio. CFRP-metal dissimilar joints are inevitable to realize a variety of CFRP-metal hybrid designs. However, conventional fusion joining methods for metals are not applicable to CFRP-metal dissimilar joints. In this study, considering the process productivity and the joint reliability, self-piercing rivet (SPR) is investigated to join CFRP and aluminum panels. The SPR joint quality such as head height, interlock, bottom thickness is considered to find an optimal combination of the processing parameters, which include rivet, die, and punch force. In the tensile lap shear test of CFRP-aluminum SPR joints, the first fracture load is found to be a better parameter for representing the joint quality over the max fracture load because of the discontinuous property of CFRP panel. The first fracture load achieved in this study is up to 4.4 kN for SPR lap joint with 1.8 mm thickness CFRP upper and 2.0 mm Al5083-O lower.
커버 플레이트를 이용한 이종 3겹 저항 점 용접성 평가
심정현(Junghyun Shim),이세헌(Sehun Rhee) 한국생산제조학회 2016 한국생산제조학회지 Vol.25 No.5
Low carbon steel is usually used as the outer panel with low base metal resistance compared to the inner reinforced panel made with high strength steel, which makes it difficult to form a robust nugget. To overcome welding problems of a dissimilar three-sheet combination made of SGACEN, DP980 and CP1180, a cover plate was inserted between the upper electrode and SGACEN. The quality of the nugget was analyzed by comparing the welding signals and cross sectional images under maximum heat input both with and without the cover plate. To analyze the mechanical of weld properties, a hardness test analysis was conducted. To enhance the reliability of experimental results, temperature distributions were obtained using a simulation program. The method of inserting a cover plate led to a change in the heat input, which induced a larger nugget size between SGACEN and DP980.