• 한국정밀공학회지
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• 제22권8호
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• pp.17-26
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• 2005

Dissimilar-metal welds(DHWs) are used widely in various industrial applications due to the pratical importance from the technical and economic aspect. However, DMWs have several fabricative and metallurgical drawbacks that can often lead to in-service failures. For example, the most pronounced fabrication faults are hot cracks. Recently, DMWs have used the various of heat source to decrease such as faults. In this paper, the weldability on dissimilar metal welds of Austenite stainless steel and Low carbon steel using a continuous wave Nd:YAG laser was experimentally investigated. Experiments were conducted to determine effects of welding parameters, on eliminating or reducing the extent welding zone formation at dissimilar metal welds and to optimize those parameters that have the most influence parameters such as focus length, power, beam speed, shielding gas, and wave length of laser.

• 한국정밀공학회지
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• 제23권3호
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• pp.47-55
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• 2006

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stress-strain behavior and the hardness of the welded metal are investigated. From the results of the investigation, it has been shown that the optimal voiding condition without defects in the vicinity of the welded area and with a good welding quality is 1600W of the laser power, 0.85m/min of welding speed and $4{\ell}/min$ of pressure for shielding gas.

• 한국정밀공학회지
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• 제20권10호
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• pp.65-73
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• 2003

The effect of pre-heating on the mechanical properties of laser welding joints has been investigated for the case of SM45C carbon steel welded by a cw Nd:Y AG laser. The occurrence of porosity and cracking was inspected in various welding conditions to find the optimal welding parameters. The results of laser welding experiment with pre-heating technique showed that porosity and cracking can be reduced significantly in most of welding conditions and the welded joints have improved mechanical properties, such as higher tensile strength and better durability.

• Journal of Welding and Joining
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• 제26권5호
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• pp.90-96
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• 2008

The objective of this paper is to investigate the effects of the laser power, the material thickness, comer angles, and the loop size on the formation of the comer in the cutting of Inconel 718 super-alloy sheet using high-power CW Nd: YAG laser. In order to investigate the influence of comer angles and loop sizes on the melted area and the formation of comer in the sharp comer, angular cutting tests and loop cutting tests were carried out. The results of the angular cutting tests were shown that the melted area is minimized and the melting mode is changed from nose melting in the thickness direction to the secondary melting induced by the attached dross when the comer angle is $90^{\circ}$. Through the results of loop cutting tests, the variation of the melted area and the comer shape in the sharp comer according to the loop size were examined. In addition, it was shown that a proper loop size is approximately 3 mm. The results of above experiments will be reflected on the knowledge base to generate optimal cutting path of the laser.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 추계학술대회 논문집
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• pp.93-94
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• 2006

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2006년 추계학술발표대회 개요집
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• pp.216-218
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• 2006

The application of aluminium alloy is increasing for lightweight and high quality transport vehicle. In this study, therefore, it is intended to apply the high speed hybrid welding method for marine grade aluminium alloy(A5083) used for shipbuilding that consists of 3 kW CW Nd:YAG laser and MIG welding process. For this purpose, the characteristics of process parameters(laser & arc combine angle and focal position of hybrid head to specimen) are investigated for hybrid fillet joint. This study also describes determination of heat distribution using finite element model of the T-joint fillet weld using the in-house solver which has been validated for different type of welding problems.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2006년도 춘계 학술대회 개요집
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• pp.248-250
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• 2006

The study on a surface transformation hardening of a rod-shaped SM45C carbon steel is carried out by using CW Nd:YAG laser. Conventionally, $CO_2$ laser has been usually used as a laser source for a transformation hardening. however, it is needed to an additional absorbent coating like a colloidal graphite owing to a lower absorbtion rate. On the other hand, no cost and post-removal process of coating is required to Nd:YAG laser, due to a higher absorbtion rate relatively. Moreover, there is a merit which is capable of building up the more flexible processing system resulted from a beam delivery through a optical fiber. In this study, we were going to recognize characteristics of a transformation hardening using a optic head with a gaussian beam distribution.

• 한국생산제조학회지
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• 제20권6호
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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.

• Journal of Welding and Joining
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• 제19권3호
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• pp.317-324
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• 2001

This study deals with high power Nd:YAG laser welding of thin steels for small pressure vessels. Full penetration welding at the overlap joint was performed so as to assure sufficient weld strength. Results showed that mid-depth weld size reduced drastically with increasing the travel speed. Position of focus had little effect on the bead formation even though short focal system was used. However, the shape factor and the bead width had closely related with the position of focus. Based on the microstructural inspection, acceptable weld was obtained when the overlap clearance was controlled up to 20% of the base metal thickness. In the case that the joint contained more clearance than the critical value, both the tensile shear strength and the tear strength were reduced. Results also demonstrated that shielding gases were proved to play a key role as far as the bead formation characteristics was taken into consideration. Blowing dry air through 5mm in diameter nozzle produced narrower bead cross-section than that of argon or nitrogen shielding.

• 비파괴검사학회지
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• 제28권4호
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• pp.372-376
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• 2008

We report experimental results on the correlations between welding penetration depth and the frequencies of the radiation from the welding pool. Various welding samples such as SUS304, brass, SUS316, etc. have been investigated with 2 kW CW Nd:YAG laser welding machine. The radiation signals from the plume generated by the interactions between the welding sample and laser with respect to the defocusing length was measured with fiber system collecting the plume signal. Analysis of the frequencies by using fast Fourier transform (FFT) shows that the penetration depth is deep as plume signal frequencies are low, shallow penetration depth for high frequencies. Frequencies up to 250 Hz for obtained signals can be analyzed with the discrete FFT. This is the useful method fur closed loop control of the laser power with respect to the welding penetration depth and is used for real time inspection of the welding quality.