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나노초 가시광 레이저 펄스를 이용한 사파이어 미세천공 공정의 해석
오부국,정영대,김남성,김동식,O, Bu-Guk,Jeong, Yeong-Dae,Kim, Nam-Seong,Kim, Dong-Sik 한국레이저가공학회 2009 한국레이저가공학회지 Vol.12 No.1
Engineering ceramics as sapphire are widely used in industry owing to their superior mechanical and corrosion properties. However, micromachining of sapphire is a considerable challenge due to its transparency. Recently, direct ablation of sapphire has been demonstrated with a visible laser pulse at sufficiently high laser intensity. In this work, the theoretical model for pulsed laser ablation of sapphire is suggested and numerical analysis is carried out using the model. Sapphire ablation begins with plasma generation by the laser interaction with surface defects, impurities and contaminations in the initial stage of machining. Subsequent absorption of the visible laser beam can be explained by three mechanisms: metalization of sapphire surface due to the EUV radiation from the hot plasma, increments of surface roughness and temperature-dependent absorption coefficient. Comparison of the computation results with experimental observation indicates that the proposed model of sapphire is reasonable.
실리콘 박막이 레이저 가공 시 발생하는 광기계적 손상 해석
오부국,김동식,김태현,전은숙,김남성 한국레이저가공학회 2008 한국레이저가공학회 학술대회 논문집 Vol.2008 No.-
Photomechanical damages of single-crystal silicon under 6 ns laser pulse (Nd:YAG) ablation at intensities of 1~20 GW/㎠ are studied through the scanning electron microscope investigation of the ablated samples and numerical simulations simultaneously. The effects of various parameters (beam size, irradiance, sample thickness, and crater shape) were investigated by using numerical model which is developed in this work considering the recoil pressure and the surface evaporation.
오부국,김동식 한국레이저가공학회 2003 한국레이저가공학회지 Vol.6 No.3
Pulsed laser ablation is important in a variety of engineering applications involving precise removal of materials in laser micromachining and laser treatment of bio-materials. Particularly, detailed numerical simulation of complex laser ablation phenomena in air, taking the interaction between ablation plume and air into account, is required for many practical applications. In this paper, high-power pulsed laser ablation under atmospheric pressure is studied with emphasis on the vaporization model, especially recondensation ratio over the Knudsen layer. Furthermore, parametric studies are carried out to analyze the effect of laser fluence and background pressure on surface ablation and the dynamics of ablation plume. In the numerical calculation, the temperature, pressure, density, and vaporization flux on a solid substrate are obtained by a heat-transfer computation code based on the enthalpy method. The plume dynamics is calculated considering the effect of mass diffusion into the ambient air and plasma shielding. To verify the computation results, experiments for measuring the propagation of a laser induced shock wave are conducted as well.
펨토초 레이저 금속 가공시 발생하는 열충격 수치계산 프로그램 개발
오부국,김동식,김재구,이제훈 한국레이저가공학회 2008 한국레이저가공학회지 Vol.11 No.1
It has been recognized that laser dicing of wafers results in low mechanical strength compared to the conventional sawing techniques. Thermal shock generated by rapid thermal loading is responsible for this problem. This work presents a two-dimensional ultra-short thermoelastic model for numerical simulation of femtosecond laser ablation of metals in the high-fluence regime where the phase explosion is dominant. Laser-induced thermoelastic stress is analyzed for Ni. The results show that the laser-induced thermal shock is large enough to induce mechanical damages.
피코초 레이저를 이용한 고세장비 미세 홀가공의 실험적 연구
오부국,김종기,김두영,이승기,정수화,홍순국,Oh, Bukuk,Kim, Jongki,Kim, Dooyoung,Lee, Seungkey,Jeong, Soohoa,Hong, Michael 한국레이저가공학회 2015 한국레이저가공학회지 Vol.18 No.2
Pressure-drop in a micro-channel is critical when a hole diameter is less then 100um with the high aspect ratio, more than 40. To minimize these pressure loss for micro-channel applications is important and there would be the best hole diameter, taper angle, and their combinations. In this work, the parametric study for laser drilling of anodized material is conducted to obtain the micro-channel hole with high aspect ratio.
피코초 레이저를 이용한 양극산화 알루미늄 미세 홀 가공의 실험적 연구
오부국,방준호,김종기,임성묵,이승기,정수화,홍순국,Oh, B.K.,Bang, J.H.,Kim, J.K.,Lim, S.M.,Lee, S.K.,Jeong, S.H.,Hong, S.K. 한국레이저가공학회 2014 한국레이저가공학회지 Vol.17 No.2
Aluminum has been widely used in the electric applications because of light metals. When mechanical element is periodically moving with contacting other surfaces, the anodizing process for aluminum is useful for avoiding the abrasive damage. The anodized element has quietly different characteristics with respect to the distribution of hardness and crystal structure. In this work, the laser drilling of anodized surface is studied experimentally. Fusion drilling method - laser drilling with inert gas blowing - is used. The effect of various process parameters (gas pressure, laser power, focus position) is investigated with respect to the hole size and circularity.