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금속표면 특성향상을 위한 Iaser peening 효과
정진만(Chin-Man Chung),백성훈(Sung-Hoon Baik),김정수(Joung-Soo Kim),이상배(Sang-Bae Lee) 한국레이저가공학회 2008 한국레이저가공학회지 Vol.11 No.3
The effect of a laser peening on the surface residual stress of SUS 304 was investigated using a second harmonic Nd:YAG laser beam. The energy density and the diameter of the laser beam were 400 mJ/㎟ and about 1㎜, respectively. According to the test results, the effect of a laser peening for improving the surface residual stress was not big enough to induce a high compressive stress on the SUS 304 surface. This is thought to be attributed to the small radius of the laser beam used in this study, even though its energy density is big enough. From this study, it can be concluded that to induce a recognizably high compressive stress on a metal surface, the energy density as well as the size (diameter) of the laser beam should be large enough to generate surface plasma with a high energy to have a big impact to a metal surface.
김동언(Kim, Dong-Eon),이홍기(Lee, Hong-Gi),한홍식(Han, Hong-Sik),정영규(Jung, Yung-Gyu),서형석(Suh, Hyung-Suck),정진화(Chung, Chin-Wha),임민수(Lim, Min-Soo),곽승근(Kwak, Seung-Keun),오만수(Oh, Man-Soo),최준혁(Choi, June-Hyuk) 한국신재생에너지학회 2008 한국신재생에너지학회 학술대회논문집 Vol.2008 No.05
Pohang Wind Energy Research Center (PoWER-C) is developing a 3 MW Radial Flux Permanent Magnet (RFPM) Synchronous Generator for offshore Wind Energy Converter (WEC). The blade rotor rpm is 15.7 and the gear ratio is set to be 92.93. The nominal generator rpm at the rated load is about 1459. Baseline design with surface mounted PM magnets are completed. However, there is some concern about the excessive eddy current heating in the magnets. To alleviate this problem, another design with embedded magnet is going on. With embedded magnets, the generator length should be increased to compensate the increased flux leakage. But the field fluctuation in the magnets due to the slots are greatly reduced. This means less eddy currents and lower magnet operating temperature. In this report, engineering efforts for embedded rotor is presented.
열복사의 색수차 공간여과를 이용한 레이저 용접 감시기술
김민석,백성훈,박승규,정진만,김철중 한국레이저가공학회 1999 한국레이저가공학회지 Vol.2 No.2
An innovative real-time weld monitoring technique using chromatic filtering of the thermal radiation from a weld pool is developed. This thermal radiation from the weld pool is focused on an aperture and the transmitted thermal radiation is monitored at two wavelengths with high-speed single-element detectors. Due to the chromatic aberration introduced in the focusing optics, the transmittance curve of thermal radiation varies by the wavelength. Owing to this difference in the transmittance, the local variation of thermal radiation from the weld pool can be monitored by processing the two spectroscopic signals from two detectors. In this paper, the algorithms to monitor the laser power on the weld specimen and the focus shift are investigated and the performances of laser power and focus monitoring are shown for a pulsed Nd:YAG laser welding. The monitoring of the weld pool size variation is also discussed.
Nd:YAG 레이저빔에 의한 인코넬 600 합금의 용접에 관한 연구
김재형,김철중,김도훈,정진만 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.8
Lap joint welding of 1.2 ㎜ thick Inconel 600 plate was performed by Nd:YAG laser. Welding parameters such as pulse width, repetition rate, peak power and scanning speed, were varied in this experiment. The optimum welding condition observed were 6-12ms pulse width, 15-50㎐ repetition rate, 1.5-3.0㎾ peak power and 288-360㎜/min scanning speed. Cracks were not observed in the weldment. An aspect ratio of 0.7-1.4 was obtained by means of controlling the above parameters. Microscopic analysis revealed that the weldment consisted of a planar front solidification zone which formed at the initial stage of solidification, and a cellular-dendrite solidification zone produced by rapid cooling. Epitaxial growth from base metal was also observed. Post-welding heat treatment was performed in order to relieve residual stresses induced by welding. Results obtained from the Huey test and ABI test, the optimum heat treatment condition was observed at 5 min. annealing at 640-700℃. It was found that the susceptibility to intergranular corrosion attack of the weldment was approximately three times higher than that of the base metal and the base metal corroded more severely than the weldment. This occurrence is believed to be caused by the sensitization of the base metal by heat input during welding. It was also observed that the intergranular corrosion rate was also accelerated as heat treatment temperature was increased. ABI tests showed that residual tensile stress was present in the weldment and was subsequently relieved by post-welding heat treatment.