• Journal of the Korean Society of Marine Environment & Safety
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• v.3 no.2
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• pp.13-21
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• 1997

This paper describes the effectiveness of laser pulse shaping in eliminating weld defects such as porosity, cracks and undercuts in pulsed Nd:YAG Laser welding. A large porosity was formed in a keyhole mode of deep penetration weld metal of any stainless steel. Solidification cracks were present in Type 303 with about 0.3%s. The conditions for the formation of porosity were determined in further detail in Type 316. With the objectives of obtaining a fundamental knowledge of formation and prevention of weld defects, the fusion and solidification behavior of a molten puddle was observed during laser spot welding of Type 310S. through high speed video photographing technique. It was deduced that cellular dendrite tips grew rapidly from the bottom to the surface, and consequently residual liquid remained at the grain boundaries in wide regions and enhanced the solidification cracking susceptibility. Several laser pulse shapes were investigated and optimum pulse shapes were proposed for the reduction and prevention of porosity and solidification cracking.

• Journal of Welding and Joining
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• v.29 no.2
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• pp.88-93
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• 2011

This study produced hypereutectic Al-Si clad layer on 1050 Al alloy by a novel laser cladding method. Pure Si powder was mixed with organic binder to make fluid paste which could be screen-printed on the 1050 Al alloy plate. Pulsed Nd:YAG laser was irradiated on the Si paste layer to melt and alloy with Al substrate. Different laser power of 99 W, 179 W and 261 W, was used to see the difference of the microstructure, composition and hardness of the clad layers. When laser power of 179 W was used, the clad layer had overall Si content of 38wt% and composed of fine primary Si particles and fine eutectic phase. At laser power of 261 W, the clad layer had overall Si content of 24wt% and composed of mainly fine eutectic phase. Vickers hardness of HV176.7 and HV150.3 on the clad layer was obtained at laser power of 179 W and 261 W, respectively.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.35-41
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• 2016

The experimental study has been performed through residual stress using the Ti6Al4V, investigate the effect of laser shock peening on laser welding process residual stress of Ti6Al4V welds in a reduce safety weld zone. This research evaluated the effects of shock waves from laser shock peening with a pulsed Nd:YAG laser on Ti6Al4V welding specimens, through the analysis of the residual stress of the specimens. The residual stress could be formed by the depth of 1 mm if the proposed method of reducing the residual stress is performed in the optimal condition. The welded structures and products during the production process increase the mechanical property of repeated stress, which could be expected to extend the fatigue life of the structure.

• Laser Solutions
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• v.2 no.2
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• pp.18-26
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• 1999

An innovative real-time weld monitoring technique using chromatic filtering of the thermal radiation from a weld pool is developed. The thermal radiation from the weld pool is focused on an aperture and the transmitted thermal radiation is monitored at two wavelengths with high-speed single-element detectors. Due to the chromatic aberration introduced in the focusing optics, the transmittance curve of thermal radiation varies by the wavelength. Owing to this difference in the transmittance, the local variation of thermal radiation from the weld pool can be monitored by processing the two spectroscopic signals from two detectors. In this paper, the algorithms to monitor the laser power on the weld specimen and the focus shift we investigated and the performances of laser power and focus monitoring are shown for a pulsed Nd:YAG laser welding. The monitoring of the weld pool size variation is also discussed.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.176-180
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• 2002

During the last two decades the laser beam has progressed from a sophisticated laboratory apparatus to an adaptable and viable industrial tool. Especially, in its welding mode, the laser offers high travel speed, low distortion, and narrow fusion and heat-affected zones (HAZ). The principal obstacle to selection of a laser processing method in production is its relatively high equipment cost and the natural unwillingness of production supervision to try something new until it is thoroughly proven. The major objective of this work is focused on the combined features of gas tungsten arc and a low-power cold laser beam. Although high-power laser beams have been combined with the plasma from a gas tungsten arc (GTA) torch for use in welding as early as 1980, recent work at the Ohio State University has employed a low power laser beam to initiate, direct, and concentrate a gas tungsten arcs. In this work, the laser beam from a 7 watts carbon monoxide laser was combined with electrical discharges from a short-pulsed capacitive discharge GTA welding power supply. When the low power CO laser beam passes through a special composition shielding gas, the CO molecules in the gas absorbs the radiation, and ionizes through a process known as non-equilibrium, vibration-vibration pumping. The resulting laser-induced plasma (LIP) was positioned between various configurations of electrodes. The high-voltage impulse applied to the electrodes forced rapid electrical breakdown between the electrodes. Electrical discharges between tungsten electrodes and aluminum sheet specimens followed the ionized path provided by LIP. The result was well focused melted spots.

• Proceedings of the Korean Society of Laser Processing Conference
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• 2005.06a
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• pp.45-47
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• 2005

• Proceedings of the Korean Society of Laser Processing Conference
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• 2005.11a
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• pp.42-45
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• 2005

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.4
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• pp.523-532
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• 1999

This study is aimed to obtain fundamental knowledge of pulse laser welding phenomena the authors investigated the structure and composition of evaporated particles of Al alloys in air and in the Ar atmosphere during pulsed laser welding. The ultra-fine particles of 5 to 100nm diameter in a globular or irregular shape were formed in laser-induced plasma and the main structure was $MgAl_2O_4$ The composition of particles was ifferent depending on the power density of a laser beam; namely under the low power density conditions magnesium was predominant in the parti-cles while aluminium content increased with an increase in the power density. These results were attributed to evaporation phenomena of metals with different boiling points and latent heats of vaporization. On the other hand the number density of laser-induced plasma species was obtained by Saha's equation. it was confirmed that the number density depends upon the plasma tempera-ture and total pressures.

• Proceedings of the KWS Conference
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• 2008.05a
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• pp.32-32
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• 2008

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.5
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• pp.567-574
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• 2007

Aluminum and aluminum alloys have high rate of lightness, recycling property and excellent specific strength. Fields using them have been widening because they ould satisfy both energy reduction and high efficiency in manufactures production. But they have many problems on welding due to high thermal conductivity and reflectivity, so the study to solve these problems ate proceeding actively around the world. This study was purposed to improve weldability and spread application range for aluminium alloys by using the unique property of aluminium which absorb high energy around $800{\mu}m$ wavelength and the higher temperature, the mote absorbtion of laser beam on preheating by multi-wavelength laser beam(pulsed Nd:YAG laser + diode laser with $808{\mu}m$ wavelength). The favorable mechanical properties were acquired by the test results of strength, hardness and leak of weld metal which had reduced its defect like crack and so on.