• Journal of the Korean Society for Precision Engineering
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• v.29 no.1
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• pp.87-95
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• 2012

In recent years, laser-arc hybrid welding has begun to be adopted for assembly welding of automotive bodies and parts, because the hybrid welding process can weld lapped steel sheets having a larger gap than is possible with laser welding. In this paper, to predict the twist deformation by the hybrid welding when brackets are welded in B pillar of a passenger car, the residual stress using CAE is analyzed and the deformation result of CAE is compared with the measured deformation. First of all, after modeling heat source as intended to be expressed with laser-arc hybrid welding method, heat source fitting is done with welding conditions and a section of welding part obtained through specimen test. In case of heat source functions, laser used conical source and arc used double ellipsoid source. Through the local model analysis, elements which are located in the center of the model are selected. The elements are called WME(Welding Macro Element). This WME is extruded in the welding lines and welding phenomenon of complex parts is accomplished. The deformation amount after hybrid welding is got through a simulation, the validity of simulation is verified by measuring the panel and comparing with the simulation result.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.9
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• pp.5419-5424
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• 2014

A weld scallop is a small quadrant or half circle type hole installed in the weld line cross area for easy welding operation. Many types of T-bars with a scallop can be welded in a block assembly stage in shipbuilding. The difficulties arise from the fact that scallops are to be filled by build-up welding after welding of the cross line is complete. In this study, a non-scallop block joint welding method was developed using special type CBM (ceramic backing material). The wedge shaped CBM was devised to insert a CBM into just the V groove of weld line cross area without weld scallop. A saw-toothed shape was adopted for easy cutting of the unnecessary part in the CBM fitting process. The applicability of the developed method was verified through welding experiments based on the yard welding conditions.

• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.9-14
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• 2018

The piping system of a nuclear power plant plays a role of transferring high energy fluid to equipment and various devices. The safety and soundness of these piping systems are very closely related to the operability of the power plant. In the case of a welded part of a small diameter pipe, it may grow as a microcrack due to a lack of penetration, and it may grow to a size that affects the safety of the pipe due to the influence of mechanical vibration and fatigue load. Resonance refers to an increase in energy as the natural frequency of an object coincides with the frequency applied to the external force. When this resonance occurs, the frequency is the resonance frequency. In this study, when defects exist in the welds of small diameter pipe, the natural frequency of the pipe changes and resonance may occur. Since these resonances are likely to cause fatigue damage to the piping, resonance frequency changes due to the size and shape of the defects are analyzed and evaluated. As a result of the vibration test, the resonance frequency tended to decrease as the depth of the defect deepened, and the influence was larger when the defect existed at the bottom of the top of the trough. Also, it was confirmed that the Transverse cracks had an effect on the resonance frequency in the presence of the cracks in the weld bead, compared to the longitudinal cracks. As a result of this study, it is expected that the cause of the defect and the condition of the pipe can be monitored because the resonance frequency tendency according to the shape of the crack is analyzed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.8
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• pp.1374-1380
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• 2002

Recently, the use of Robot increase little by little for the purpose of developing a welding quality and productivity in the welding part. It is more important to contact the seam for arc welding before moving a welding robot. There are two types of method to contact the seam namely contact and non-contact type largely. In this paper, image processing sensor(a kind of non-contact sensor) is concerned to track the seam by using laser diode and CCD camera. A structured laser diode's light illuminated on the weld groove and the reflected shape is introduced by CCD camera. The image board captures this image and software analyzes this image. The robot is moved and welded exactly as acquired image X-Y data is changed with robot's X-Y value. Also, most of seam tracking are considered by changing the program simply in case of the different weld groove of plane surface.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.759-765
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• 2016

The PTO (Power Take-Off) shaft for aircraft, with welded construction using multiple thin membranes, was developed in the 1950s to improve the elasticity of the part. As it is lightweight, stable at high speeds, and has good flexibility, it is used in most of the fighter aircraft. It connects the AMAD (aircraft mounted accessory drive) gearbox with the EMAD (engine mounted accessory drive) gearbox and transmits the rotational power between them. It operates in the high speed range of 10,000-18,000 rpm. In this study, the safety of the PTO shaft made of Ti alloy was investigated using finite element analysis, and the ability to transmit power was demonstrated through a high-cycle fatigue test conducted in a laboratory. Further, the life of the ball joints of the aircraft under high-cycle fatigue test conditions was predicted, and the wear characteristics were analyzed.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2001.05a
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• pp.460-464
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• 2001

Recently, the use of Robot increase little by little for the purpose of developing a welding quality and productivity in the arc welding part. It is more important to contact the seam for arc welding before moving a welding robot. There are two types of method to contact the seam namely contact and noncontact type largely In this paper, image processing sensor(a kind of non-contact sensor) is concerned to track the seam by using laser diode and CCD camera. A structured laser diode's light illuminated on the weld groove and the reflected shape is introduced by CCD camera. The image board captures this image and software analyzes this image. The robot is moved and welded exactly as acquired image X-Y data is changed with robot's X-Y value. Also, most of seam tracking are considered by changing the program simply in case of the different weld prove of plane surface.

• Journal of Welding and Joining
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• v.17 no.5
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• pp.47-54
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• 1999

It is well known that solidification cracking often occurs in welds of root pass for one-side welding under the conditions of high welding currents and speeds. In this study, the solidification in 590MPa class steel for pressure vessels SPPV490 was investigated by using flux-cored arc welding(FCAW) with 4 types of welding wires and welding conditions of 200∼280A and 2.8∼ 4.2mm/sec. In order to compared the result of cracking in SPPV490, 0.2%C steel for welded structure of SWS400 and 0.45%C steel for machine structural SM45C were also used as base metals. As the results, all the cracks formed in some welding conditions were observed near the center of weld bead. The solidification cracks were generally initiated near the upper surface of bead and propagated toward the inner part. The solidification cracking generally increased with welding current and welding speed in the same base metal and welding material. In cracking susceptibility, SPPV490 showed higher cracking susceptibility than SWS400 in all welding conditions and welding materials. It was considered that cracking susceptibility could not be evaluated with the hardness of weld metals. The cracking ratio increased with decreasing of a/b(a and b; the width of the upper surface and the back surface of the bead) as shape factor of bead. The cracking tendency with shape factor of bead was extended under the condition of higher welding currents.

• 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 $4.178{\sim}4.36{\times}103J/cm^2$.

• Journal of Welding and Joining
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• v.26 no.6
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• pp.81-91
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• 2008

The weldability of resistance spot welding of TRIP1180 steels for automobile components investigated enhance in order to achieve understanding of weld fracture during tensile-shear strength (TSS) test. The main failure modes for spot welds of TRIP1180 steels were nugget pullout and interfacial fracture. The peak load to cause a weld interfacial failure was found to be related to fracture toughness of the weld and the weld diameter. Although interfacial fracture occurred in the spot welded samples, the load-carrying capacity of the weld was high and not significantly affected by the fracture mode. Substantial part of the weld exhibits the characteristic dimple (or elongated dimple) fractures on interfacial fractured surface also, dimple fracture areas were drawmatically increased with heat input which is propotional to the applied weld current. In spite of the high hardness values associated with the martensite microstructures due to high cooling rate. The high load-carrying ability of the weld is directly associated with the area of ductile fracture occurred in weld. Therefore, the judgment of the quality of resistance spot welds in TRIP1180 steels, the load-carrying capacity of the weld should be considered as an important factor than fracture mode.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1221-1226
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• 2012

The hot-stamping technique is a forming method used for manufacturing high-strength parts, in which a part is cooled rapidly after press forming above the austenite transformation temperature. Boron steel, which contains a very small amount of boron, is one of the materials used for hot stamping. The purpose of this study is to investigate the mechanical properties of boron steel according to the heat-treatment conditions and the formability by using an Erichsen cupping test. Die quenching from various temperatures was conducted for different elapsed heat-treatment times. Laser-welded boron steel after quenching at 1173 K-0 s has a tensile strength of 1203 MPa. This is 79% of the tensile strength of the base metal (1522 MPa). The formability of boron steel was not significantly different from that at the mold temperature. However, it decreased with increasing forming speed. These properties provide practical information for the use of boron steels for hot stamping.