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파이버 레이저의 스테인리스강 용접시 인프로세스 모니터링을 위한 유기 플라즈마와 방사신호간의 상관성 연구(II) - 후판 용접시 측정신호의 특성 변화 -
이창제,김종도,Lee, Chang-Je,Kim, Jong-Do 대한용접접합학회 2014 대한용접·접합학회지 Vol.32 No.6
On this study, we researched the in-process monitoring during fiber laser welding as well as on the first paper. On the previous/formal study, we analyzed the change of emission signal on thin plate welding. On this study, however, we analyzed RMS and FFT with emission signals in laser welding on lap joint and butt joint of 8mm-thick 316L stainless steel. As the result, the movement of specific frequency peak was observed according to welding speed changes. Furthermore, frequency peak as a result of FFT on the thick plate welding are much clearer than on the thin plate welding. Therefore, it is expected that the welding parameter changes can be predicted in case of applying FFT to in-process monitoring.
이창제(Chang Je Lee),조경래(Gyong Rae Cho),김의간(Uei Kan Kim),김동혁(Dong Hyuk Kim),도덕희(Deog Hee Doh) 한국가시화정보학회 2016 한국가시화정보학회지 Vol.14 No.2
In this study, a Masked Omni-Directional Integration(MODI) method for pressure calculation is proposed using the Particle Image Velocimetry (PIV) data. To obtain the velocity field, the Affine PIV method was adopted. Synthetic images were generated for a solid body rotation. Calculation on the pressure was based on the Navier-Stokes equation. The results obtained by the MODI were compared with those obtained by theoretical pressure and by the Omni-Directional Integration(ODI) method. It was shown that the minimum error by the proposed MODI method was attained when the mask size was 1.
API강재의 파이버레이저 용접시 유기하는 플라즈마의 방사특성 (III) - 보호가스가 플라즈마 방사 신호에 미치는 영향 -
이창제,김종도,김유찬,Lee, Chang-Je,Kim, Jong-Do,Kim, Yu-Chan 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.3
Ar, $N_2$, and He are the conventional kind of shield gas that are used for laser welding. Many researches on the impact of laser welding shield gas have been done, and it is on going until now. However, there are few studies that analyze the changes and differences of the plasma emission signal. Therefore, in this study, we evaluated the change in the penetration characteristics according to the type of shield gas during fiber laser welding impacts to the plasma signal. As a result, if was checked that the difference in molecular weight of Ar, $N_2$, and He affects to the amount of spatter, and also found that the measured plasma radiation signal changes similar to the order of the molecular weight of the gases. Especially, clear change on the signal intensity per each shield gas was measured through RMS, and found that the shield gas was nothing to do with the FFT analyzed result.
API강재의 파이버레이저 용접시 유기되는 플라즈마의 방사특성 (II) -용접조건과 방사신호의 관련성-
이창제,김종도,김유찬,Lee, Chang-Je,Kim, Jong-Do,Kim, Yu-Chan 대한용접접합학회 2012 대한용접·접합학회지 Vol.30 No.4
Laser welding by fiber laser accompanied by a lot of spatter and humping bead. This is because the deep and narrow keyhole usually form due to high beam quality. So the weld bead is formed defects, because the plasma jet with a high vapor pressure make the molten pool on keyhole wall scattered. For such a reason, unstable behavior of keyhole is difficult to monitor laser welding by using the laser induced plasma. Mostly, fiber laser welding of thick plates most be influenced by this effect. Therefore, fiber laser welding has been difficult to apply the sole. Thus, laser welding monitoring based on plasma measurements have much difficulty in measurements and analysis of signal. In this study, influence of the plasma emission signal according to welding speed and laser power in fiber laser welding analysed by using RMS and FFT analysis. We can verify that RMS value of the plasma emission signal changes with welding parameters in fiber laser welding, and aspect ratio greater than 1, the peak of FFT frequency had been moved in accordance with welding parameter.