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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.
A Study on Heat Flow Affects on Multiplies Dissimilar Material Laser Beam Welding
Hae-Woon Choi(최해운) 한국기계가공학회 2024 한국기계가공학회지 Vol.23 No.3
The results of a numerical analysis of the joining of copper and aluminum in a laser welding process are presented. The laser beam was arranged parallel to the two spots with a 1 mm offset and the layers in two cases were studied to determine the heat flux tendency. For the Cu-Al-Cu layer, the heat flows in a two-dimensional tendency. The heat flow from the more conductive material to the less conductive material acted as a heat shield. However, in the Al-Cu-Al layer, heat flows in a three-dimensional trend. The heat flow from the less conductive material to the more conductive material acted as a heat sink that redistributed the heat flow to adjacent layers with higher thermal conductivity. Comparing the heat flux along the z-direction or thickness, it was found that the Al-Cu-Cu laminated material had more than three times higher thermal conductivity than the Cu-Al-Cu laminated material, supporting three-dimensional directional heat transfer and efficient laser welding. The heat distribution in multilayer materials by laser welding is an important analysis step to understand the heat flow for high weld quality and high productivity processes.
3차원 광경화성 수지와 폴리아세테이트 수지의 레이저 접합해석
최해운(Hae Woon Choi),윤성철(Sung Chul Yoon) 대한기계학회 2015 大韓機械學會論文集A Vol.39 No.7
본 논문에서는 격자가 있는 광경화성수지와 폴리아세테이트 수지의 레이저 접합해석에 대한 실험적 결과와 컴퓨터시뮬레이션 결과를 비교분석하였다. 3차원 격자형상은 MJM 방식의 3D 프린터를 사용하였고, 접합은 다이오드 레이저를 사용하였다. 5Watt ~ 7Watt 범위에서 경계면에 조사된 레이저는 유리천이온도에 도달 후 상면의 격자사이로 침투되어 기계적인 접합이 이루어졌다. 컴퓨터 시뮬레이션 결과, 분포 온도를 통해서 열유동방향을 예측할 수 있었으며 분석을 통해서 접합의 원리를 이해할 수 있었다. 접합실험에서 최대 입열조건인 고출력 저속에서의 2scan 접합이 최소 입열조건이 저출력 고속 조건의 4 scan 보다는 훨씬더 효과적인 것으로 나타났고, 일정수준(Threshold) 이상의 최소에너지 즉, 유리천이온도 이상이 되어야만 효과적인 것을 알 수가 있었다 In this study, experimental and computer simulation results are compared and analyzed. Three-dimensional (3D) fabricated matrices from an MJM 3D printer were joined with poly-acetate thermoplastic polymers using a diode laser. A power range of 5-7 W was used to irradiate the boundary of two polymers. The heated polymers flowed into the matrices of the 3D fabricated structure, and reliable mechanical joining was achieved. Computer simulation showed the temperature distribution in the polymers, and flow direction was estimated based on the flux and temperature information. It was found that the more than the minimum energy threshold was required to effectively join the polymers and that two scans at low-speed were more effective than four scans at high speed.
최해운(Hae Woon Choi) 한국기계가공학회 2019 한국기계가공학회지 Vol.18 No.2
A new experimental approach is proposed to detect a specific polymer dissolved in a liquid. Distinctive optical properties were found using a laser scattering technique when there is a polymer compound with almost no difference in optical properties (index of refraction) in a liquid phase. The index of refraction, which determines the refraction of light, is obtained by dissolving PCL and PLA. The used samples are biodegradable materials with similar properties and dissolved in a mixture of Chloroform 7: Methanol 3. To predict the optical properties, a 632-nm diode laser was used as the light source of the device, and an integrating sphere was used as the light receiver. Although PCL and PLA had a similar index of refraction of 1.46-1.48, the dissolved PCL showed a relative transmittance of 43%, and the dissolved PLA had a relative transmittance of 34%. The difference in optical properties of the pure polymer compound in the solid state or liquid state is not significantly different, and the difference in the dissolved state in the specific solvent is remarkable because the solubility differs in a specific solution and is randomly distributed.
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.