The integrity of laser welded structures is decided with fracture strength and fatigue strength. This study presents fracture behavior considering residual stress in the laser welding. Experiments are conducted and analyses are performed to explore the influence of residual stress on fracture behavior of bead-on laser welded compact specimen. Fracture experiments are performed using ASTM 1820. The performed analyses included thermo-elasto-plastic analyses for residual stress and subsequent J-integral calculation. A modified J integral is calculated in the presence of residual stresses. The J-integral is path-independent for combination of residual stress field and stress due to mechanical loading. The results indicates that the tensile residual stress near crack front bring the low fracture load while the compressive residual stress bring the high fracture load compared to no residual stress specimen. These results quantitatively understand the influence of residual stress on fracture behavior.

Silicon Nitride ($Si_3N_4$), which is widely used in a variety of applications, is hard-to-machine due to its high hardness. At high temperature (e.g. above $1000^{\circ}C$), however, the machinability can be greatly improved. In this work, we used a $CO_2$ laser with a high absorptivity to $Si_3N_4$ of 0.9 to locally heat the surface of a rotating $Si_3N_4$ rod on a lathe. In order to examine the effects of the laser-assisted heating on hardness, an $Si_3N_4$ md is heated to temperatures from 900 to $1800^{\circ}C$ and is rotated at speeds from 440-900 rpm in experiments. When the rod is naturally cooled to room temperature, we measured the Victors hardness (Hv): and observed the surface of HAZ using a scanning electron microscopy (SEM). Energy dispersive spectroscopy(EDS) was used for ingredient analysis. Results showed that when heated at $1600^{\circ}C$, the hardness of $Si_3N_4$ decreased from 1500 Hv to 1000 Hv. Also, in order to predict the depth of HAZ, we numerically analyzed the laser-assisted heating of $Si_3N_4$.

최근 차체 용접의 고속화를 통한 생산성 향상 및 차체 설계의 자유도 향상, 차체 강성 증가를 목적으로 원격 용접, 브레이징 등 다양한 형태로 레이저 적용 기술이 개발되고 있다. 뿐만 아니라, 레이저의 종류에 있어서도 $CO_2$ 레이저, Nd:YAG 레이저, 화이버 레이저, 디스크 레이저등 다양한 형태의 레이저가 사용되고 있으며, 사용자의 목적에 부합하는 여러 형태의 레이저들이 개발되고 있다. 본 연구는 $CO_2$ 레이저 원격 용접의 차체 T/GATE 양산 적용 결과를 바탕으로, 적용 용접점 선정, 용접품질 확보, 생산성 향상을 위한 공정의 최적화 요소들에 대한 개발을 진행하였다.

Laser welding is high power density welding method which is higher speed and productivity, lower thermal deformation, without material restrictions for car body welding. But, in case of zinc coated sheet metal welding, the gap is needed $0.1{\sim}0.2mm$ to avoid weld bead blowup. This paper describe that it used dimple and pressure roller tool to improve laser welding quality for 3-layer zinc coated sheet metal.

레이저를 이용한 폴리머의 융착기술은, 자동차산업에서의 다양한 적용분야에 힘입어 새로운 접합기술로 각광을 받고 있다. 현재까지는, 대부분 작고 간단한 형상의 제품을 융착하는 분야에 많이 적용되어 왔으며, 튼 사이즈의 제품을 대량으로 생산하는 공정에서는 레이저융착이 가지는 다양한 장점에도 불구하고, 프로세스의 안정성, 사출후의 제품변형에 따른 갭의 관리, 작업속도등에 대한 이유로 본격적인 적용을 기피하고 있는 실정이다. 이러한 배경에 의하여 개발된 하이브리드방식(레이저빔+할로겐램프)의 폴리머융착 시스템은, 다이오드레이저에서 출력되는 $800{\sim}980nm$의 레이저파장과 할로겐 램프에서 방사되는 적외선영역의 파장을 동시에 사용함으로써 프로세스의 안장성과 융착효율을 향상시켰다.

Previous studies demonstrated that laser ablation under transparent liquid can result in ablation enhacement and particle removal from the surface. In this work, the liquid-assisted excimer laser ablation process is examined fer polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), Si, and alumina with emphasis on ablation enhacement, surface topography, and debris formation. In the case of PET and PMMA, the effect of liquid is analyzed both fer thin water film and bulk water. As the ablation enhanement by liquid is already known for Si and alumina, the analysis focuses on surface topography and debris formation resulting from the liquid-assisted laser ablation process. The results show that application of liquid increases the ablation rate of PMMA while that of PET remains unchanged even in the liquid-assisted process. It is also revealed that the liquid can significantly improve the surface quality by reducing the debris deposition. However, the surface roughness is generally deteriorated in the liquid-assisted process. The surface toporaphy is found to be strongly dependent on the method of liquid application, i.e., thin film or bulk liquid.

In this study, PID control method was applied to decrease the power fluctuation of the pulse laser which is one of the major processing variables in laser machining process. To stabilize the power fluctuation of the pulse laser, we averaged 10 pulse outputs of Nd:YAG laser operating in 10Hz using boxcar averager, and with taking this averaged output as an input signal, we conducted PID control using optical attenuator which is consisted of half wave plate attached on the stepping motor and polarizer. When PID control was not enabled, the power fluctuation was 4.71% and with PID control, the power fluctuation was 1.86% for 2 hours and 1 hour respectively. As a result, we stabilized the power fluctuation of the pulse laser by 60.5%

Picosecond (ps) laser micro-machining has emerged as an attractive method of fabricating high-precision microstructures, especially in metals. In this paper, a metallic mold for diffraction gratings is fabricated with a mode-locked 12 ps $Nd:YVO_4$ laser. Laser pulses with a wavelength of 355nm are irradiated on the surface of NOK 80, a mold material, to generate line patterns. In order to minimize the line width, laser power is set just above the ablation threshold of NOK 80. Results show that the spectrum from the fabricated mold is good enough for some industrial application.

Recently, mobile information devices, such as cellular phone, PDA(Personal Digital Assistant, PDA) are getting smaller and thinner. Accordingly, ultra precision welding technology is required to manufacture the high performance system for use in the telecommunication industry. In this study, we propose the laser micro welding process. Using ytterbium fiber laser, a wide range of experiments have been carried out for the gold wire-to-gold thin film welding.

We constructed a micro-patterning system that build patterns on a photoresist coated wafer using laser direct writing system. Confocal microscope system was adapted for real-time auto-focusing of the laser writing lens to generate lines of uniform width.

In this paper, actuator based on voice coil motor is designed and estimated to check the capability whether that system is in design specification or not. Design specification is moving range as $20{\times}20mm^2$ a along XY-axis in plane and maximizes bandwidth for high speed. The type of voice coil motor is selected with regarding design specification and minimizes the size of actuator. Flux density of designed voice coil motor is simulated. And PI controller is designed to maximize bandwidth of actuator. Finally, characteristic of designed actuator is simulated and that result reveals the validity of presented design.