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니켈도금된 S45C강의 연속파형 Nd:YAG 레이저 겹치기용접 특성
유영태,신호준,Yoo, Young-Tae,Shin, Ho-Jun 대한용접접합학회 2007 대한용접·접합학회지 Vol.25 No.3
Laser welding process is widely used in the industrial field due to its numerous advantages: a small heat affected zone(HAZ), deep penetration, high welding speed, ease of automation, single-pass thick section capability, enhanced design flexibility, and small distortion after welding. The objective of this research works is to investigate the influence of the process parameters, such as the welding fur metals with CW Nd:YAG lasers. The bead-on-plate and Lap welding experiments are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the welding quality of the cross section, tensile stress behavior and the hardness of the welded part are investigated in comparison of the Nickel coated and Nickel uncoated S45C steel. As a result of experiment, nickel coated S45C Steel showed more even weld zone than Nickel uncoated counterpart upon lap welding. Also, it showed relatively small amount of internal defects and spatter, and Nickel coated S45C showed better weldability than Nickel uncoated S45C steel. The optimum welding process upon lap welding of Nickel coated S45C steel is when each laser power is 1900W; focal positions is -1mm; welding speed is $0.9{\sim}1.0m/min$. The heat input was $4.178{\sim}4.36{\times}103J/cm^2$.
유영태(Young-Tae Yoo),황희주(HeeJu Hwang) 한국산업경영학회 2023 경영연구 Vol.38 No.1
Due to COVID-19, people around the world have to adapt to a new lifestyle, and the real economy has been hit hard. Firms have considered and implemented various strategies to survive the economic shock starting in 2020. In this study, the free cash flow of individual firms was mainly observed at the period of COVID-19. It was found that firms listed on the Korean capital market during and after the pandemic strategically use free cash flow. At the time of the pandemic with high uncertainty, free cash flow was held, and it was confirmed that free cash flow was exhausted by reducing uncertainties and securing stable investment in new industries. This study has a contribution in that it reviewed the entire Korean capital market for free cash flow control activities. In preparation for similar shocks that may occur in the future, it is possible to confirm the expected response of the capital market in advance, and at the same time propose the necessary policy implications for the government authorities. COVID-19로 인하여 전 세계인은 새로운 생활방식에 적응해야 했으며 실물경제도 엄청난 타격을 받았다. 기업들은 2020년을 기점으로 경제 충격에서 생존하기 위한 다양한 전략을 고민하였으며 이를 실행해 왔다. 본 연구에서는 COVID-19 시점에 개별 기업의 잉여현금흐름(Free Cash Flow)을 주로 관찰하였다. 팬데믹기간 및 그 직후 한국 자본시장에 상장한 기업들은 잉여현금흐름을 전략적으로 사용하는 것으로 나타났다. 불확실성이 매우 높은 팬데믹 시점에는 잉여현금흐름을 보유하였으며, 팬데믹 이후 기간에는 불확실성 감소와신산업에 대한 안정적 투자처 확보 등으로 잉여현금흐름을 소진하는 것을 확인하였다. 본 연구는 잉여현금흐름 조절 활동에 대하여 한국 자본시장 전체를 검토하였다는 데에 그 기여점이 있다. 향후 발생하는 유사 충격에 대비하여 예상되는 자본시장의 반응을 미리 확인할 수 있고, 정부 당국에 필요한 정책적 함의를 동시에제안한다.
CW Nd:YAG 레이저를 이용한 중탄소강과 오스테나이트계 스테인레스강의 이종금속 용접
유영태(Young Tae Yoo),신호준(Ho Jun Shin),안동규(Dong Gu Ahn),임기건(Kie Gon Im),신병헌(Byung Heon Shin) Korean Society for Precision Engineering 2006 한국정밀공학회지 Vol.23 No.3
Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests arc carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stress-strain behavior and the hardness of the welded metal are investigated. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding quality is l600W of the laser power, 0.85m/min of welding speed and 4ℓ/min of pressure for shielding gas.
연속파 Nd:YAG 레이저를 이용한 치아교정 급속 구개확장장치 용접특성
유영태(Young Tae Yoo),양윤석(Yun Seok Yang),신호준(Ho Jun Shin) Korean Society for Precision Engineering 2010 한국정밀공학회지 Vol.27 No.2
The Purpose of this paper is to weld a rapid palatal expander using a continuous wave Nd:YAG laser. The rapid palatal expander has become a useful treatment method for severe maxillary transverse deficiencies and posterior crossbites. Rapid maxillary expansion is a well-established method to correct transverse maxillary deficiency and arch length discrepancy. The major process parameters studied in the present laser welding experiment were the positions of focus, laser power and travel speed of laser beam. We measured the fusion zone size and its shape using an optical microscope for the observation of cross-sectional area and tension stress of a rapid palatal expander welded. Through the experimental investigation, the optimum speeds and power of laser without deficiencies of weld cross-sectional area were obtained.
연속파형 Nd:YAG 레이저를 이용한 금형강의 보수용접 특성에 관한 연구
유영태(Young Tae Yoo),신호준(Ho Jun Shin) Korean Society for Precision Engineering 2010 한국정밀공학회지 Vol.27 No.11
In this study, wire was used as the filler material for the laser repair welding, and the phenomenon in which the supplied filler material was melted and beaded down into the specimen was examined with varying laser powers and welding speeds. The optimal processing condition was found to be the laser power of 1,300 W, the welding speed and feed wire supply speed of 0.5 m/min and the defocused distances of +2㎜. At this time, the heat input(E) was 65 ~ 75 J/㎟, and no internal defect occurred. When repair welding was carried out as the optimal processing for the part that had an external defect with the radius of 2㎜, the filler metal was melted, resulting in the volume smaller than the defect part and thus causing the part unfilled. Therefore, it was found to be necessary to carry out repair welding two to three times by multiple passes rather than does it only once by single pass.
유영태(Young-Tae Yoo),최병재(Byeong-Jae Choi),김진우(Jin-Woo Kim) 한국기계가공학회 2021 한국기계가공학회지 Vol.20 No.3
Typical implants are not specified the screw structure and the surface process according to the bone quality of the human body. The purpose of this study is to complement the shortcomings of the existing implant surface processing method. It is to propose a surface processing method that increases the adhesion between the implant and bone tissue by increasing the surface area per unit area of the implant. It is very important to establish precise and systematic process parameters when surface treatment of implants using lasers. Therefore, we intend to develop a process so that the implant can be a biocompatible structure using a Q-switching Nd:YAG laser with a wavelength of 1.06um. Implant surface treatment technology through this study will be used in the industry.
연속파형 Nd:YAG 레이저를 이용한 SM45C 중탄소강의 레이저표면경화 특성
유영태(Young Tae Yoo),신호준(Ho Jun Shin),안동규(Dong Gu Ahn) Korean Society for Precision Engineering 2005 한국정밀공학회지 Vol.22 No.11
Laser surface hardening technologies have been used to improve characteristics of wear and to enhance the fatigue resistance for automotive parts. The objective of this research work is to investigate the influence of the process parameters, such as. power of laser and defocused spot position, on the characteristics of laser heat treatment for the case of SM45C medium carbon steel. CW Nd:YAG laser is selected as the heat source. The optical lens with the elliptical profile is designed to obtain a wide heat treatment area with a uniform hardness. From the results of the experiments, it has been shown that the maximum hardness is approximatly 780 Hv when the power and the travel speed of laser are 1,095 Wand 0.6 m/min, respectively. In addition, the hardening width using the elliptical lens was three time larger than that using the defocusing of laser beam.