• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.365-372
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• 2004

The laser welding and its analysis were carried out using high power 6kW $CO_2$ laser for high strength steels such as DP, TRIP and conventional high strength steels. Bead on plate welding of thin sheet was examined to investigate the effect of weld variables of laser welding, and to obtain optimum welding condition. In order to investigate the formability of welded high strength steels, LDH test was added on this work. At high welding speed, the partial penetration was obtained by low heat input. Meanwhile, porosity was formed in the bead at low weld speed because of extremely higher heat input. The optimum welding condition of welding was derived from bead width, penetration and hardness property. It was shown that the DP steels had lower porosity level and smooth bead shape, therefore better laser weldability than TRIP steels and conventional high strength steels. In addition, LDH test shows that the welded DP steels have about $90\%$ formability value of base metal, although TRIP steel and conventional high strength steels have about $80\%$ formability value of its base metal.

• Proceedings of the KWS Conference
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• 1999.10a
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• pp.23-26
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• 1999

• Proceedings of the KWS Conference
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• 1998.05a
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• pp.217-222
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• 1998

• Proceedings of the KWS Conference
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• 1994.05a
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• pp.60-61
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• 1994

• Journal of Welding and Joining
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• v.30 no.5
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• pp.51-56
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• 2012

The purpose of this study is to evaluate the distortion and the residual stress of GTA tubular welds between tube and head. In order to do it, the heat input model for GTA welding process was first developed by experiment and FE analyses. The welding distortion and the residual stress distribution of the tubular welds according to welding pass and various restraint degrees were evaluated by using FEA with the heat input model. From FEA results, it was found that the residual stress and the radial distortion at the weld toe of tube part decrease with a decrease in the number of welding pass. However, the maximum residual stresses in each direction of tubular welds are almost constant regardless of the external restraint degree. It was mainly due to the high internal restraint of the welds.

• Journal of Electrical Engineering and Technology
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• v.2 no.3
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• pp.366-372
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• 2007

Joining thin aluminum alloy is difficult using most welding techniques. Many of the problems are associated with bum-through by the high heat input. Common welding techniques are TIG (Tungsten Inert Gas), MIG (Metal Inert Gas), and PULSE-MIG welding. The method provides more control of the heat balance in the welding arc by taking advantage of the different arc characteristics obtained with each of the two polarities. In this paper, we proposed a new welding method by control DSP 320C32, and the characteristic and experiment result-voltage, current, welding bead, and penetrations by this method are presented.

• Journal of Welding and Joining
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• v.25 no.3
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• pp.18-27
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• 2007

Laser welding process is widely used in the industrial field due to its numerous advantages: a small heat affected zone(HAZ), deep penetration, high welding speed, ease of automation, single-pass thick section capability, enhanced design flexibility, and small distortion after welding. The objective of this research works is to investigate the influence of the process parameters, such as the welding fur metals with CW Nd:YAG lasers. The bead-on-plate and Lap welding experiments are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the welding quality of the cross section, tensile stress behavior and the hardness of the welded part are investigated in comparison of the Nickel coated and Nickel uncoated S45C steel. As a result of experiment, nickel coated S45C Steel showed more even weld zone than Nickel uncoated counterpart upon lap welding. Also, it showed relatively small amount of internal defects and spatter, and Nickel coated S45C showed better weldability than Nickel uncoated S45C steel. The optimum welding process upon lap welding of Nickel coated S45C steel is when each laser power is 1900W; focal positions is -1mm; welding speed is $0.9{\sim}1.0m/min$. The heat input was $4.178{\sim}4.36{\times}103J/cm^2$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.455-467
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• 2017

In this study, a finite element analysis of a cylindrical multi-pass weldment for dissimilar metals was performed. The effects of the heat input method and weld bead generation method were considered. We compared two heat input methods: the heat flux method and the temperature method. We also compared two weld bead generation methods: the element birth method and the quiet element method. Although the results of the thermal analysis show deviations between the two heat input methods, the welding residual stresses were similar. Because the areas exposed to high temperature were similar and the strength of the material was very low in high temperature (above the $1000^{\circ}C$), the effects of the weld bead temperature were insignificant. The distributions of the welding residual stress were similar to each other. However, gaps and overlaps occurred on the welding boundary surfaces when the element birth method was applied. The quiet element method is more suitable for a large deformation model in order to simulate a more accurate weld shape.

• Journal of Welding and Joining
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• v.22 no.4
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• pp.65-72
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• 2004

The aim of this study is to investigate the optimum drawing parameter for BAS111 welded tubes. The BAS111 aluminium alloy tubes with 25.4mm in external diameter and 1.5mm in thickness for heat-exchangers were manufactured by high frequency induction welding with the V shaped convergence angle 6.8$^{\circ}$ and power input 50㎾. With increasing the reduction of area (1.6, 5.8, 11.5, 14.2, 18.5, 22.5%) by drawing, tensile strength was increased and elongation was decreased. With increasing the reduction of area by drawing, hardness in weld metal increased rapidly, while that of base metal increased slowly. In the specimen with the outer diameter smaller than 22mm, hardness of weld metal was higher than that of base metal. The optimum drawing parameter of area reduction was estimated about 15% because of the work hardening of welds.

• Proceedings of the KWS Conference
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• 2006.05a
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• pp.121-123
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• 2006

The aim of present study is to investigate the effect of welding parameters and heat treatment conditions on the formability of the laser welded silicon steel sheet. It was found that there is optimum range of the heat input ($0.6{\sim}0.7kJ/cm$) and gap distance ($0.125{\sim}0.150mm$) for the high tensile strength and the avoidance of the fracture in weld metal, Also, it was essential for the improvement of formability to perform pre- and post-welding heat treatment which cause the uniform mixture of base metal and welding consumable.