• Journal of Welding and Joining
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• 제18권3호
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• pp.76-82
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• 2000

In this study, three-dimensional heat flow in laser beam welding for deep penetration was analyzed by using F.E.M common code, and then the results were compared with the experimental data. The models for analysis are full penetration welds and are made at three different laser powers (6, 9.9, 4.5 kW) with two different welding speeds (5.8mm/s, 5mm/s). The characteristics of thermal absorption by the workpiece during deep penetration laser welding can be represented by a combination of line heat source through the workpiece and distributed heat source at the top surface due to the plasma plume above the top surface. This gives an insight into the way in which the beam interacts with the material being welded. The analyses performed with the combined heat source models show comparatively good agreement between the experimental and calculated melt temperature isotherm, i.e, the fusion zone boundary. The results are used to explain the "nail head" appearance of fusion zone, which is quite common in laser beam welds.eam welds.

• 한국레이저가공학회지
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• 제2권2호
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• pp.42-51
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• 1999

This study has been performed to investigate into some effects of the output power and traverse speed of laser beam on the microstructures, hardness and fatigue resistance of the ductile iron surface-hardened by $CO_2$ laser defocussed beam. Optical micrographs have shown that with increasing the output power and decreasing the traverse speed, the martensite was coarsened and some retained austenite were appeared in ductile iron. The microstructures of hardening zone were composed of bull's eye and some nodular graphite dissolved structures by the effect of self quenching. Fatigue fracture characteristics of ductile iron have appeared in the high stress and low stress ranges. The fracture initiated at nodular graphites in the surface hardened layer due to the stress concentration caused by a notch effect. The interior graphite nodules were broken away or popped out during crack propagation. Fatigue test has shown that values of fatigue strength considerably increased with increasing output power at a given traverse speed.

• 한국기계가공학회지
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• 제10권1호
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• pp.31-37
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• 2011

Recently, the technology of surface treatment is being more important which affects the material cost reduction and substitution to the expensive material. The material used for the mechanical processing should have not only high intensity, but also strength toughness, wear resistance and corrosion resistance. In order to increase the durability and have better quality of the parts using such kind of tooling material, various kinds of research of the surface hardening through many kinds of heat resources is being done and practically applied. In this study, the characteristics of hardening surface zone for high strength of the press die material through laser beam irradiation are researched. In this study, it is experimentally observed by the status of the surface morphology, tensile strength, the hardness distribution of the base metal and wear condition by the surface hardness pattern by the laser beam based on the process parameters of $CO_2$ laser by using SM45C and STD11 used for press tool. Through this research, the characteristics of surface hardened zone for high strength of the thin metal by laser beam irradiation is done.

• 한국광학회지
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• 제3권4호
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• pp.222-226
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• 1992

$Ar^{+}$레이저로 펌핑되는 Nd:glass레이저를 제작하여 그 특성을 조사하였다. 레이저 공진기는 오목거울 두 개와 98% 고반사 평면경, 그리고 Brewster 각도로 놓인 Nd:glass 의 이득 매질로 구성되었으며, 효율적인 펌핑을 위해서 $Ar^{+}$레이저 광선을 공진기 길이 방향으로 입사하여 공진모우드의 beam waist에서 초점이 맺히도록 하였다. Nd:glass의 열존도도가 작아서 흡수된 펌핑빔에 의해 생성된 잔열로 인한 매질의 손상이 우려되기 때문에 mechanical chopper 로 펌핑빔을 100Hz로 끊어서 입사하여 잔열의 생성을 줄였다. 1.5W로 펌핑될 때 Nd:glass 레이저의 출력은 70mW이었고 발진이 되는 문턱에서의 펌핑파워는 520mW이었으며 slope efficiency는 7.4%이었다.

• 한국레이저가공학회지
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• 제4권1호
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• pp.29-38
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• 2001

This work was carried out to investigate the welding behavior of thin A3003 Al alloy sheets by Nd : YAG laser beam. Considering bead shape and mechanical properties, the laser pulse shapes selected were two kinds of 2-division and 3-division by varying power level and pulse duration. In order to obtain optimum conditions, the factorial design method and central composite design method were applied. Tensile test, optical microscopy, micro hardness test and TEM analysis were performed. Due to the annealing caused by thermal effect during laser welding, precipitates were coarsended. The HAZ was softened and failed during tensile test. The hardness of HAZ was lower than that of base metal, since the heat input relieved the work hardening effect and caused grain growth.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.945-947
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• 2009

We developed a new laser irradiation (BLDA: Blue Multi-Laser-Diode Annealing) system. The system forms the uniform line beam, which is constructed by 48 pieces of semiconductor lasers. This new system has achieved high laser output stability and the highly accurate beam shape by adopting a reliable laser control, the auto-focus control in addition to an original laser photosynthesis technology and the beam homogenizing technology. It was confirmed to crystallize the Si films effectively with good quality.

• Journal of Welding and Joining
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• 제9권1호
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• pp.23-31
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• 1991

Laser beam weldability of zircaloy-4was investigated using a pulsed Nd: YAG laser of 200W average power. Mechanical properties of laser and GTA bead-on-plate welded zircaloy-4 test specimens were compared. The influence of plasma generated during laser welding was analyzed and optimum laser welding parameters were investigated.

• 한국레이저가공학회:학술대회논문집
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• 한국레이저가공학회 1999년도 춘계학술발표대회 논문개요집
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• pp.1-4
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• 1999

• 한국기계가공학회지
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• 제20권2호
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• pp.1-7
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• 2021

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℃, 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.

• 한국레이저가공학회지
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• 제12권4호
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• pp.12-16
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• 2009

The engineering ceramic is one of the materials advantageous in various conditions with high strength, endurance at high temperature, abrasion resistance and corrosion resistance, etc. However, due to high strength and high brittleness, ceramic incurs high costs and long time on finishing process required after sintering. So a process for obtaining wanted measurements of them has been studied using the high temperature which makes ceramics softened and heat affected recently. This study makes an estimate of laser-assisted machining (LAM) if an economically practical process for manufacturing precision silicon nitride ceramic parts using laser beam. In this study, mechanical properties of silicon nitride at high temperature were observed. And during the LAM, it was observed that cutting force and tool wear were reduced and oxidation of machined surface was increased according to a increase of laser power.