• Journal of Welding and Joining
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• 제11권1호
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• pp.52-61
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• 1993

Laser welding of ASTM no. 1060 Al plate with a pulsed Nd: YAG laser of 200W average power was performed for end capping of KMRR nuclear fuel elements In this research, we performed basic welding experiments. Firstly, laser output parameters which affect laser welding parameters were studied by changing laser input parameters for effective welding of 1060 Al plates. We found that laser power density and pulse energy are important parameters for smooth bead shape. Secondly, welding parameters which affect weld width-to-depth ratio were studied by changing power density and pulse energy, shielding gas, and defocusing. We found that power density must be higher than 0.3 Mw/cm$^{2}$ pulse energy must be higer than 3 J. travel speed must not exceed 200mm/sec, laser focus must be existed beneath 2-3mm from plate surface and helium is proper shielding gas. Thirdly, we studied the weld defects of Al-1060 such as crack and porosity in lap-joint welding. We designed new welding geometry for crack free welding of Al-1060 plates, and obtained crack free weldment but with lack of fusion. However, with Ti, Zr grain refiner elements, we can weld Al plates without solidification hot crack. Finally, we studied the origin of porosity by changing shielding gas. And we found that porosity was resulted from entrapment of shielding gas by the collapsing keyhole.

• 한국레이저가공학회지
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• 제6권2호
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• pp.27-33
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• 2003

A laser shock cleaning technology is a new dry cleaning methodology for the effective removal of small particles from the surface. This technique uses a plasma shock wave produced by a breakdown of air due to an intense laser pulse. In order to optimize the laser shock cleaning process, it needs to evaluate the cleaning performance quantitatively by using a monitoring technique. In this paper, an acoustic monitoring technique was attempted to investigate the laser shock cleaning process with an aim to optimize the cleaning process. A wide-band microphone with high sensitivity was utilized to detect acoustic signals during the cleaning process. It was found that the intensity of the shock wave was strongly dependent on the power density of laser beam and the gas species at the laser beam focus. As a power density was larger, the shock wave became stronger. It was also seen that the shock wave became stronger in the case of Ar gas compared with air and N$_2$ gas.

• 한국레이저가공학회지
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• 제6권1호
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• pp.25-31
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• 2003

5052 aluminum alloy sheets of 2mm thickness were butt welded using a continuous wave Nd:YAG laser with and without Ar shielding gas. Vickers hardness, transverse-weld tensile and bulge tests were carried out to investigate the effect of Ar shielding gas on the mechanical properties and formability of laser welds. Porosity in the weld metals was investigated using an optical microscope. Mechanical properties and formability of 5052 aluminum alloy laser welds were degraded compared to those of base metal. However, those properties were improved due to the reduced size and number of porosity when Ar shielding gas was used.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.914-917
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• 2002

Fabrication of micro carbon structures and patterns using laser-assisted chemical vapor deposition is studied. Argon ion laser and ethylene were used to grow micro carbon rod through pyrolytic decomposition of the reaction gas. The influence of reaction gas pressure and incident laser power on the diameter and growth rate of the micro carbon rod was experimentally investigated. The diameter of micro carbon rods increases linearly with respect to the laser power but is almost independent of the reaction gas pressure. Growth rate of the rod changes little with gas pressure when the laser power remains below 1W. When the carbon rod was grown at near threshold laser power, a very smooth surface is obtained on the rod. By continuously moving the focusing lens in the direction of growth, a micro carbon rod with a diameter of 28 ${\mu}{\textrm}{m}$ and aspect ratio of 100 was fabricated.

• Journal of Welding and Joining
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• 제31권3호
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• pp.60-65
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• 2013

Ar, $N_2$, and He are the conventional kind of shield gas that are used for laser welding. Many researches on the impact of laser welding shield gas have been done, and it is on going until now. However, there are few studies that analyze the changes and differences of the plasma emission signal. Therefore, in this study, we evaluated the change in the penetration characteristics according to the type of shield gas during fiber laser welding impacts to the plasma signal. As a result, if was checked that the difference in molecular weight of Ar, $N_2$, and He affects to the amount of spatter, and also found that the measured plasma radiation signal changes similar to the order of the molecular weight of the gases. Especially, clear change on the signal intensity per each shield gas was measured through RMS, and found that the shield gas was nothing to do with the FFT analyzed result.

• 한국정밀공학회지
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• 제19권7호
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• pp.106-115
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• 2002

Growth characteristics of micro carbon structures fabricated by laser-assisted chemical vapor deposition are studied. Argon ion laser and ethylene were used as the energy source and reaction gas, respectively, to grow micro carbon rod through pyrolytic decomposition of the reaction gas. Experiments were performed at various conditions to investigate the influence of process parameters on growth characteristics such as the diameter or growth rate of the micro carbon rod with respect to reaction gas pressure and incident laser power. Reaction gas pressure in experiments ranges from 200 to 600Torr and the incident laser power from 0.3 to 3.8W. For these conditions, the diameter of the rod increases linearly with respect to the laser power but is almost independent of the reaction gas pressure. Growth rate of the rod changes little with gas pressure when the laser power remains below IW. For a constant reaction gas pressure, the growth rate increase with Increasing laser power, but the rate of increase decreases gradually, implying that the chemical vapor deposition condition changes from a kinetically-limited regime to a mass-transport-limited regime. When the carbon rod was grown at near threshold laser power, a very smooth surface is obtained on the rod. By continuously moving the focusing lens in the direction of growth, a micro carbon rod with a diameter of 287${\mu}{\textrm}{m}$ and aspect ratio of 100 was fabricated..

• 한국연소학회지
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• 제11권3호
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• pp.26-35
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• 2006

This work forcus on the development of gas sensor that measure the concentrations of exhaust gas using diode laser, Each diode laser for exhaust gas measurement is set to work at near-IR using both DA and WMS methods. Also use of fiber-coupled optical elements makes such a sensor rugged and easy to align. The results showed that gas concentrations of $O_2$, CO, $CO_2$, NO are accurately measured within ${\pm}2%$ error. The application of WMS method increased the beam intensity 2-3 times higher than DA method. It were experimentally compared WMS (Wavelength Modulation Spectroscopy) with DA (Direct Absorption) for the accuracy.

• Journal of Welding and Joining
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• 제7권4호
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• pp.12-21
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• 1989

Laser beam welding parameters have experimentally investigated, using a continuous wave 3kW $CO_2$ laser with the various travel speeds, beam mode and laser beam power in low carbon steels. An optimum position of focus and the effect of shielding gas on penetration depth with varying the flow range of 0.5 to 5.1m/min have been combined to investigate the effect of laser power and travel speed on penetration depth and bead width. It is found that the optimum position of focus in 3kW class laser is 0.5 to 1.5mm below the surface of the material. The flow rate of shielding gas affects the penetration depth and He is more effective than Ar. The penetration depth in laser welds of low carbon steels is between two and four times of the bead width. Laser beam welding of butt joints in 2mm thick carbon steel has been carried out to establish a weldability lobe. The lobe indicating acceptable welding conditions is introduced.

• Bulletin of the Korean Chemical Society
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• 제11권3호
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• pp.214-220
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• 1990

We have studied the Infrared Multiphoton Dissociation (IRMPD) of 1-bromo-3-chloropropane by using the pulsed $CO_2$ laser. The product yields and the HCl/HBr branching ratios in IRMPD of $BrCH_2CH_2CH_2Cl$ are studied under the focused beam geometry as a function of buffer gas (He) pressure, laser energy, and photolysing wavelength. It is observed that the total dissociation yield has a laser energy dependence of 1.8-2.0 power order and the branching ratio is very slightly dependent on the pulse energy for the laser lines employed. The dependences of total dissociation yield and branching ratio on the buffer gas pressures show that the dissociation yield monotonically decreases and the branching ratio slightly decreases with the increase of the buffer gas pressure. The Energy-Grained Master Equation (EGME) was applied to explain the laser pulse energy and the buffer gas pressure(He) dependence of the dissociation yield and the branching ratio.

• 대한치과기공학회지
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• 제30권1호
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• pp.49-55
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• 2008

In this study, to provide the fundamental data on stable connection method for successful implants prosthesis, We fabricated the solder joint of gold alloy bar specimens by gas flame soldering method and laser welding and soldering method. It compared and studied the tensile strength of two soldering method by universal testing machine. The results using universal testing machine were as follow : The mean of tensile strength of solder joint bar in gas flame soldering method specimens was 363.89 $\pm$17.62 MPa, and the mean strength of laser welding and soldering method was 125.91 $\pm$ 19.66 MPa, so gas flame soldering method was better than laser welding and soldering method and the finding better way to improve tensile strength is needed in laser welding method. On weak loading condition and the part which is needed an accuracy, laser welding method is more effective and on long-span prosthesis and frequent chewing loading part, laser welding technique is recommended first and applying additional gas flame soldering technique would be better for making much more successful prosthesis.