• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.1
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• pp.8-14
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• 2022

A computer simulation was performed to investigate the heat source distribution and temperature distribution of a laser having multiple characteristics. To simulate the actual size of a welding specimen, the temperature distributions at 0 s, 1 s, and 2 s were analyzed by increasing the domain size to 50 mm in length and 25 mm in width in a material of the same thickness. As indicated by the results, because of the characteristics of metals with high thermal conductivity, the temperature at the welding center line and the temperature distribution at the offset position were not significant. When the core part was cooled by irradiating with a laser, it cooled at a rate of up to 500 ℃/s. In contrast, when the laser was irradiated to the ring part, the cooling proceeded at a rate of over 1800 ℃/s. Comparing the relative numerical values rather than the absolute values, it was found that the cooling rate was approximately 3.6 times faster when the laser was irradiated through the ring than when the laser was irradiated through the core. As a result of irradiating with the same heat source (at 100 W) into the core, ring, and ring + core, it was confirmed that the highest temperature was irradiated to the ring part and the lowest temperature was irradiated to the core part.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.1058-1062
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• 1997

Development of laser induced chemical etching technologt with KrF laser are carried out in this study for micromachining of silicon wafer. The paper is devoted to experimental identification of excimer laser induced mechanism of silicon under chlorine pressures(0.02~500torr). Experimental results on pulsed KrF excimer laser etching of silicon in chorine atmosphere are presented. Etching rate dependency on laser fluence and chlorine pressure are discussed on the basis of experimental analysis, it is concluded that accurate digital micro machining process of silicon wafer can achieved by KrF laser induced chemical etching technology.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.598-601
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• 2000

We investigated the fabrication of Si nanoparticle and $C_{60}$ thin films by pulsed laser ablation. As a result, we observed visible green photoluminescence spectra in the Si/C$_{60}$ multilayer films after laser annealing. It is considered that this green photoluminescence is occurred from SiC particles, which is produced reaction of Si nanoparticles with $C_{60}$ via laser annealing.ing.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.732-737
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• 2005

Distal 3D Real Object Duplication System(RODS) consists of 3D Scanner and Solid Freeform Fabrication System(SFFS). It is a device to make three-dimensional objects directly from the drawing or the scanning data. In this research, we developed an office type SFFS based on Three Dimensional Printing Process and a industrial SFFS using Dual Laser. An office type SFFS applied sliding mode control with sliding perturbation observer(SMCSPO) algorithm for control of this system. And we measured process variables about droplet diameter measurement and powder bed formation etc. through experiments. Also, in order to develop more elaborate and speedy system for large objects than existing SLS process, this study applies a new Selective Multi-Laser Sintering(SMLS) process and 3-axis dynamic Focusing Scanner for scanning large area instead of the existing $f\theta$ lens. In this process, the temperature has a great influence on sintering of the polymer. Also the laser parameters are considered like that laser beam power, scan speed, scan spacing. Now, this study is in progress to eveluate the effect of experimental parameters on the sintering process.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.10
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• pp.134-147
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• 2001

Laser cladding process accompanies phase transformations from melting (on heating) through solidifying (on cooling) at the same time within a small material volume and to final solid phase. The phase transformations are not reversible, but an irreversible thermodynamic process; they accompany either absorption or release of thermal energy (referred to latent heat) during transformation. Yet, most analyses on materials processed by laser as a heat source have been performed on models of neglecting the latent heat in the process and those did not Justify the simplification. With literatures on the laser material process, we have not place an answer to how little the assumption affects on analyses. This led us to our current study: the effects of latent heat on thermo-mechanical analysis. To this end, we developed a fairly accurate program accommodating an algorithm for enforcing the latent heat whenever necessary and ran it combining with ABAQUS$^{TM}$. The simulation techniques we used in this study were verified by directly comparing our prediction with experimental publications elsewhere; our numerical results agreed accurately with the experiments. On the effects of the latent heat, we performed two alternatives about considering the latent heat in analysis, and compared each other. As a result, we found that more accurate conclusions might come out when considering the latent heat in process analyses.s.

• ETRI Journal
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• v.46 no.2
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• pp.347-359
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• 2024

A simultaneous transfer and bonding (SITRAB) process using areal laser irradiation is introduced for high-yield and cost-effective production of mini- or micro-light-emitting diode (LED) display panels. SITRAB materials are special epoxy-based solvent-free pastes. Three types of pot life are studied to obtain a convenient SITRAB process: Room temperature pot life (RPL), stage pot life (SPL), and laser pot life (LPL). In this study, the RPL was found to be 1.2 times the starting viscosity at 25℃, and the SPL was defined as the time the solder can be wetted by the SITRAB paste at given stage temperatures of 80℃, 90℃, and 100℃. The LPL, on the other hand, was referred to as the number of areal laser irradiations for the tiling process for red, green, and blue LEDs at the given stage temperatures. The process windows of SPL and LPL were identified based on their critical time and conversion requirements for good solder wetting. The measured RPL and SPL at the stage temperature of 80℃ were 6 days and 8 h, respectively, and the LPL was more than six at these stage temperatures.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.1
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• pp.29-33
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• 2014

Recently, Difficult-to-cut materials are used in many manufacturing industry. But the difficult-to-cut materials are difficult-to-cutting process. So difficult to cut material cutting process was used after heat treatment through preheating for easy cutting process. In this study, Inconel 625 was preheating using laser heat source in computer simulation. Laser heat source temperature applied $1290^{\circ}C$ that suitable preheating temperature for Inconel 625. And temperature effects such as temperature distribution for moving heat source studied apply to similar actual process condition. Simulation results for heat treatment effects through temperature distribution verified.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.6
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• pp.795-802
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• 1998

For measuring the thermal diffusivity by laser flash method, raw data have to be calibrated using temperature data. We have developed in-process calibration method and polynomial calibration in which thermal diffusivity can be calibrated during measuring, This method is different from existing temperature pre-process calibration method and exponential calibration having various source of error. Using this new calibration method, measurement accuracy was improved about 1∼2% compare to the value by the existing method. We also studied more accurate fitting curve as in Figure 4 was shown the result of measuring output characteristics of IR radiometer with temperature. As illustrated in data, in-process calibration method and polynomial calibration equation is proper than pre-process calibration method and exponential calibration.

• Journal of Welding and Joining
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• v.33 no.6
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• pp.36-41
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• 2015

In the automotive industry, TWB hot stamping process is broadly adapted to reduce weight of the car and improve fuel efficiency. However, the process faces a problem of weakened strength of the welded zone after hot stamping process, due to the fact that Al-Si elements of the coating layer penetrating the welded zone. In this study, filler wires with high percentages of carbon and manganese is adapted during laser welding process to secure the strength of the fusion zone. In addition, wire feeding speed and laser welding speed are optimized by sample test.

• 제어로봇시스템학회:학술대회논문집
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• 1991.10a
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• pp.252-257
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• 1991

This paper proposed that the eddy-current measurement method can be used a means of in-process measuring the hardening depth in Laser surface treatment process. Also, this paper deal with the numerical analysis of magnetic flux distribution and experimental result of measurement. In Laser heat treatment process of steels, a thin layer of the substrate is rapidly heated to austenitizing temperature and subsequently cooled at a very fast rate due to the self-quenching by heat conduction into the bulk body, to produce a martensite structure which have low magnetic permeability. The eddy-current measurement method depends on the properties of material to be measured such as electric conductivity, magnetic permeability and geometry. In this paper, the hardening depth was measured by detecting relevant magnetic permeability changes caused by heat treatment of steels.