극초단 레이저의 물질작용 및 바이오메디컬 미세가공과 접합공학의 응용

최해운,Choi, Hae-Woon 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.4

HUD용 다파장 레이저 광학부품 설계 및 분석

최해운,Choi, Hae Woon 한국레이저가공학회 2014 한국레이저가공학회지 Vol.17 No.1

Head up display is in increasing demand for advanced devices in the modern luxury vehicles. It helps drivers focus on driving environment on the road. While HUD technology with LED has advanced, the brightness in daylight can be still an issue to be resolved. Laser light source is a possible solution to overcome the brightness problem and optimal optics design is required for the best performance. Sample design of optics is proposed and detail procedure of lens design evaluation is presented in this paper. The results were characterized by using a ray tracing method and qualitative analysis for spot and DEE is also presented. The overall error or image distortion remained in the target range of $25{\mu}m$ and the simulated image demonstrated possible use in the automotive applications.

극초단 레이저를 이용한 PC-TEMs 초정밀 가공에 대한 연구

최해운(Hae Woon Choi) Korean Society for Precision Engineering 2011 한국정밀공학회지 Vol.28 No.1

3차원 부품 레이저 용접용 스캐너 광학 최적설계

최해운(Hae Woon Choi) 한국기계가공학회 2020 한국기계가공학회지 Vol.19 No.6

In this paper, we present the results of our research to perform 3D laser scanning functions by adding a focusing lens to a conventional 2D laser scanner. For the optical design, the ray-tracing technique was used along with a total of four lenses as the variable incident focusing lens, the collimating lens, and the F-Theta lens. As design variables, the curvature of the incident focusing lens (Lens #1) was assumed to be us, l mm and sumed mm, and the incident angles were set at 0cidenus, l. In addition, the distance between the focusing lens and the collimating lens was set to vary from 5 mm to 15 mm. When the incident focal length was varied from 5 mm to 15 mm, the exit focal length was calculated to vary from 67.5 mm to 56.8 mm for the lens with R = 100 mm and from 108.5 mm to 99.0 mm for the lens with R = 150 mm. When the incident angle was 0°, the focal aberration was only slightly observable at 10㎛ in both the x- and y-direction. At 7.5° was the focal aberration of approximately 20~50㎛ was measured at 20㎛. To investigate the chromatic aberration of the designed optical device, the distortion of the focus was observed when the 550 nm beam was simulated on lens designed for a 980 nm wavelength.

소형 2차원 레이저 스캐너용 F-theta 렌즈 역설계

최해운(Hae Woon Choi) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.3

리모트 용접용 2D 스캐너 F-theta 렌즈의 역설계가 광선 추적기법을 사용하여서 수행이 되었다.렌즈의 곡면 및 렌즈간 거리를 변수로 설정하고 초점거리를 Marginal Ray Height 로 설정하여, 상용 광선추적기법 프로그램을 사용하여 무한반복 최적화를 수행 하였다. 최종목표 값을 설정 후 Merit Function에 정의된 기준에 따라, 최종 초점거리와 초점의 크기를 최종 목표 값 가중치로 설정하였다. 최적화된 렌즈는 총 4매이며, 벤치마킹된 상용렌즈의 초점거리(185mm) 보다는 다소 근거리인 137mm로 최적화 되었지만, 초점의 크기는 레이저 입사각에 따라 RMS 기준 1.3m, 6.2m 그리고 16.1m로 계산 되었으며, 이는 상용렌즈에 근접하는 성능을 구현한다. 입사각별 왜곡도를 중첩 하여서 비교 분석한 결과, 입사각 0°와 12.5°에서는 기존 렌즈와 거의 유사한 형태로 나타나는 것을 볼 수가 있어, 본 연구에서 제안된 역설계기법이 사용자 환경에 따라서 효과적으로 적용되어 최적설계가 이루어질 수 있을 것으로 기대가 된다. In this study, a reverse design of the F-theta lens was proposed for a 2D scanner in remote welding applications. The curvature and distance of the lens were set as variables, and the focal length of the lens was set as the marginal ray height. The ZEMAX commercial software was used to perform a simulation with unlimited iterations for the optimization process. The target value was optimized using the internal Merit function with the weight factors of focal length and spot diameter. The number of lenses was four, and the focal length obtained from the results was 135mm that is slightly less than that of the commercial lens, which is set with a focal length of 185 mm. The calculated spot diameters are 1.3m, 6.2m, and 16.1m for 0°, 12.5° and 23° of incident laser beam, respectively. It is expected that an optimized lens design is possible by performing the reverse design of a lens by the ray tracing method.

하이브리드 용접방식을 이용한 박판 및 후판용접공정

최해운(Hae Woon Choi),신현명(Hyun Myung Shin),임문혁(Moon Hyuk Im) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.11

An application of innovative laser+GMA hybrid welding process is presented for reducing bead humping defects in high speed welding and increasing side wall fusion in narrow groove welding without torch or wire oscillation. In this hybrid process, the laser heat input is applied adjacent to the weld pool at a relatively low power density to produce a wider, flatter weld bead. In bead on plate in sheet metal gauges, the hybrid process was able to produce hump-free welds from 70ipm (~1780㎜/min) to over 150ipm (~3810㎜/min) of the travel speed compared to the un-assisted GMAW process. A square-butt joint in 15mm A572 Gr50 steel welds was investigated. A square butt joint with a gap of 3.2㎜ was filled with 6 passes. Liquid Nitrogen calorimetry and innovative CO₂ laser reflective optics were also developed to demonstrate the concept of hybrid welding.

극초단 레이저를 이용한 기공성 세라믹 드릴링시 발생하는 레이저빔 산란해석

최해운(Hae Woon Choi) 한국레이저가공학회 2012 한국레이저가공학회지 Vol.15 No.4

Laser beam can be either absorbed or scattered in porous ceramic material and its optical characteristics need to be understood. Electro-magnetic multiphysics software was used to simulate and understand the actual scattering phenomena in porous materials. 785nm femtosecond laser was irradiated on the surface of ceramic material and strong scattering occurred in drilling process. The computer results showed the scattering and absorption phenomena of Aluminum oxide were a mixture of dielectric and metallic material. The computer simulation showed the laser beam was almost extinct at the aspect rate of 5 approximately.

Analysis of Heat Transfer by Various Laser Beam Patterns in Laser Material Process

Hae-Woon Choi(최해운) 한국기계가공학회 2018 한국기계가공학회지 Vol.17 No.5

In laser material processing for high thermal conductivity, the thermal effect of laser beam shape was examined through computer simulations. In this paper, a circular beam with a focal radius of 500 μm, an elliptical beam with a major axis of 4 mm and a minor axis of 1 mm, and a rotating beam with a focal radius of 500 μm and an angular velocity of 5 rad/sec were compared. Simulation results showed that there was no clear difference in the maximum temperature between the circular focus and the elliptical shape, but the heating and cooling rates were different. The simulation result for a laser beam rotating in a circular pattern with a radius of 5 mm showed an asymmetric temperature rise due to the combination of linear and rotational motion. At points where the rotational and linear speeds combined, the temperature gradually rose and reached the maximum temperature; whereas at points where the rotational and linear speeds were attenuated, the temperature tended to gradually decrease after reaching the maximum temperature. Based on the results of this study, the authors expect to be able to optimize laser material processing by designing patterns of laser beams.

Analysis of Optical Characteristics of Oil Immersion Lens in Aqueous Environment

Hae Woon Choi(최해운) 한국기계가공학회 2019 한국기계가공학회지 Vol.18 No.11

The oil immersion method can be used to create objective lenses with long working distances without sacrificing the focusing resolution for laser processing. In this study, a space in which air or oil can be filled was formed in the middle of a lens for analyzing the optical properties of a liquid-oil immersion lens. As the refractive media, air and oils of different refractive index values (1.2 and 1.5, respectively) were used. A simulation was conducted in the ZEMAX software environment using the ray-tracing technique, and the performance of the oil immersion lens was verified by determining its image distortion and focal length (FL) in each medium. In the case of air, the calculated FL was 0.813 ㎜, whereas the imaged FLs were 1.594 ㎜ and 8.126 ㎜ when the refraction indices were 1.2 and 1.5, respectively. The FL of an oil immersion lens could be increased considerably. In terms of image distortion, the oil immersion lens exhibited little distortion at the center in all cases, but different degrees of image distortion were observed at different points away from the center depending on the refraction index degree.

Analysis of Laser Heat Distribution in Al-Cu Welding

Hae Woon Choi(최해운) 한국기계가공학회 2021 한국기계가공학회지 Vol.20 No.2

A computer simulation was performed to study the effectiveness of temperature on the type of laser heat source in the context of the heterogeneous welding of aluminum and copper materials. Three different types of heat sources were used in the computer simulation: 1) Single Beam Straight Scan, 2) Single Beam Wobble Scan, and 3) Dual Beam Straight Scan. Among these sources, dual beam straight scan was found to be the most effective from the viewpoint of heat source control. Because the difference between the melting temperatures of copper and aluminum is approximately 400°C, a clear separation of heating temperature was required, and the dual beam straight scan provided superior controllability in this regard. When using the dual beam, the temperature of the 90:10 split was considerably easier to control than that of the 50:50 split. The optimal offset was calculated to be 4 mm off to the copper side, where the melting temperature and thermal conductivity were higher. In this manner, computer simulation was effectively used for determining the optimal laser beam hear source control without performing an actual laser welding experiment.