• Journal of Welding and Joining
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• v.27 no.4
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• pp.26-31
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• 2009

• Journal of Welding and Joining
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• v.34 no.5
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• pp.13-18
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• 2016

Toshiba has developed a laser peening system for PWRs(pressurized water reactors) as well after the one for BWRs(boiling water reactors), and applied it for BMI(bottom-mounted instrumentation) nozzles, core deluge line nozzles and primary water inlet nozzles of Ikata Unit 1 and 2 of Shikoku Electric Power Company since 2004, which are Japanese operating PWR power plants. Laser pulses were delivered through twin optical fibers and irradiated on two portions in parallel to reduce operation time. For BMI nozzles, we developed a tiny irradiation head for small tubes and we peened the inner surface around J-groove welds after laser ultrasonic testing (LUT) as the remote inspection, and we peened the outer surface and the weld for Ikata Unit 2 supplementary. For core deluge line nozzles and primary water inlet nozzles, we peened the inner surface of the dissimilar metal welding, which is of nickel base alloy, joining a safe end and a low alloy metal nozzle. In this paper, the development and the actual application of the laser peening system for PWR power plants will be described.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.6
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• pp.720-728
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• 2011

Lap joint welding conducts low carbon steel plates using a 2.0kW continuous wave Nd:YAG laser beam. The specimen is composed of thin plate of 20 sheets. Process Variables contain two controlled parameters of the laser power and the welding speed. In order to quantitatively examine the characteristics of the lap welding, the welding quality of the cut section, stain-stress behavior, and the hardness of the welded part are investigated. The weld width difference between the top and the bottom because the welding speed is increased. The reason, cooling rate is decreased because of fast welding speed. When the heat input is higher, larger volume of the base metal will melt and the welding heat has longer time to conduct into the bottom from the top. The microstructure and tensile properties of the joints are investigated in order to analyze the effects of heat input on the quality of laser welded specimen. From the results of the investigation, We observe that welding quality is good for the laser power of 1800W, and laser welding speed from 1.8m/min to 2.2m/min.

• Proceedings of the Korean Society of Laser Processing Conference
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• 2006.11a
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• pp.17-20
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• 2006

In the remote welding system using $CO_2$ laser, laser beam is rapidly deflected by moving mirrors of scanner system and has focusable distance over 1000mm from workpiece. From such arrangement, various advantages and disadvantages arise. Remote welding is a highly efficient laser process. As the mirrors of the scanner system allow positioning speeds exceeding 700m/s, it becomes possible to reduce the welding cycle time. On the other hand, as there no the provision of shielding gas which is normally required for beam powers exceeding 3kW, may become difficult task. Therefore, In this study, the influence of the various penetration of back bead by the different laser welding speed on the weld seam formation without shielding gas was investigated.

• 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.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.9
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• pp.63-70
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• 2022

Laser welding has attracted great attention as a tool used to join electrical steel coils. In this study, laser butt welding for electrical steel coil joining was conducted using the Taguchi method. It was found that structural defects such as void sand cracks were not produced in welds. This indicated that the performance of laser welding in electrical steel was excellent. According to the Taguchi analysis, the total welding quality index (TWQI) considering the bead height and roughness and tensile strength of the weld joint was almost evenly affected by laser power, welding speed, and focal position. The optimum welding conditions to maximize the TWQI were a laser power of 1220W, welding speed of 90 mm/s, and a focal position of 1mm. The regress model predicting the TWQI was also developed using the surface response method. We found that the model predicts measured values with an average error of 16.36%.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.339-344
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• 1999

For the Tailor Welded Blank sheet used for automobile body panel, the characteristics of fatigue strength and crack propagation behavior were studied. The thickness of specimen was machined to be same (0.9mm+0.9mm) and different (0.9mm+2.0mm). As a base test, mechanical properties around welding zone were examined. The results indicated that there were no significant decreases in mechanical properties, but hardness around welding bead is 2.3 times greater than base material. The fatigue strength was the highest when the loading direction was parallel to the welding direction, which was about 85% of tensile strength of base material. It was decreased by 8.5% when the thickness of specimen and base material was different, and it is increased by 25% when pre-strain was applied. The crack propagation rate was noticeable decreased around welding line and rapidly increased as it passed by welding line. Reviewing the shape of the crack propagation, crack width around welding line was wide around the welding zone due to retardation of crack growth, but it became narrow passing welding line due to decreased toughness.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.112-112
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• 2009

레이저 용접은 아크 용접에 비해 상대적으로 빠른 용접과 깊은 용입이 가능하며, 낮은 열입력을 가지는 장점이 있다. 하지만 알루미늄 합금 용접 시 균열 감수성의 증가 및 용접강도가 저하되는 단점을 가지고 있다. 이러한 단점을 극복하는 방법으로 모재의 화학조성을 제어하는 방법과 부가적인 용접와이어를 공급하는 방법이 제안되었으나 레이저 용접에 적용하기 쉽지 않다. 아크 용접과 전자빔 용접에서는 열원에 오실레이션을 적용하여 결정립 구조를 제어하여 용접강도를 증가하는 방법이 제안되었다. 따라서 본 연구에서는 알루미늄 합금 5J32-T4의 용접균열 저감 및 용접강도 향상을 위해 레이저 위빙을 적용하였다. 1mm 두께의 알루미늄 5J32-T4를 사용하였으며, 4kW급 디스크 레이저와 레이저용 스케너를 이용하여 레이저 위빙을 구현하였다. 고온균열을 평가하기 위해 자기구속형 균열 평가방법을 사용하였으며, 용접강도를 평가하기 위해 겹치기 용접을 수행한 시편을 이용하였다. 고온균열 실험결과 레이저 위빙 적용 시 직선 용접에 비해 균열 감수성이 감소한 것을 확인하였다. 전단인장강도 측정결과 레이저 위빙의 적용에 따라 직선 용접에 비해 높은 전단인장강도의 확보가 가능하였다.

• Journal of Welding and Joining
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• v.23 no.6
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• pp.43-48
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• 2005

This work was carried out to obtain sound welds and to select a most suitable binary metal joint among three different dissimilar binary metal combinations such as Zr-4/Ta, Mo/Ta and Ti/Ta(seal tube/sensor sheath) joints fur the instrumented nuclear fuel irradiation test. To do this, Taguchi experimental method was employed to optimize the experimental data. In addition, metallography, micro-focus x-ray radiography and hardness test were conducted to examine the welds. From the weld bead appearance, penetration depth and bead width as well as weld defects standpoint, Zr-4/Ta joint is suggested for the circumferential joining between a seal tube and a sensor sheath. The optimized welding parameters based on Zr-4/Ta joint are suggested as well.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.8
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• pp.681-685
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• 2015

Hastelloy C-276 composed of Cr, Mo, and Ni is a versatile, corrosion-resistant alloy with numerous industrial applications including its use in nuclear reactors, general chemical plants, and as a superconducting base material. Of especial significance, it can be used as a thin-sheet type whereby lap-joint welding is occasionally necessary. The main welding problems for thin-sheet metals are deformation and burn-through from an excessive heat input. Laser welding can minimize these problems because it has a high energy density and low heat effect on the base material. In this study, the laser-welding characteristics of lap-joint Hastelloy C-276 sheet metal were determined. The criteria of the laser-welding variables were chosen using a heat-conduction analysis, and the optimal welding parameters were selected by experimenting with an Nd:YAG laser.