• Journal of Ship and Ocean Technology
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• v.11 no.3
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• pp.14-23
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• 2007

Welding processes cause undesirable problems, such as residual stresses and deformations due to the thermal loads imposed by local heating, melting, and cooling processes. This paper presents a computational modeling technique to simulate the Gas Metal Arc Welding (GMAW) process, emphasizing the effect of the melting bead on the residual stress distribution. Both a three-bar analogy and a three-dimensional thermo-mechanical finite element analysis are carried out in order to explain the effect. Element (de)activation, enthalpy, and adjustment of the reference temperature of thermal strain are considered with respect to the effect of the weld filler metal added to the base metal during a thermo-elastic-plastic analysis. Stress distributions obtained by the present study are compared with measured values and available data from other studies. The effect of the melting bead on the residual stress distribution is discussed and demonstrated.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.6
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• pp.20-28
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• 2003

This paper presents development of a high speed rotating arc sensor system using a microprocessor based controller with tracking function for a complicate curved fillet welding line, The welding tip connected to the torch body is eccentrically positioned from the centerline of the torch, The area during one rotating cycle is divided into 4 regions of front, rear, right and left in welding direction of the torch tip to determine the horizontal deviation between the welding seam and the torch position. The average value at each region is calculated using the regional current values and a low pass filter incorporated with the moving average method is implemented. The effectiveness of the developed system is proven through the experimental results for several kinds of complicate curved fillet welding lines.

• Journal of Welding and Joining
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• v.13 no.1
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• pp.156-166
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• 1995

Experimental models which are able to determine the deviation between weld line and weaving center by measuring the weld current during welding were proposed for the gas metal arc welding process. The models were used for developing a weld seam tracking system which controls the weaving speed of a welding torch. However, it was revealed that the tracking result of the system is affected by the welding conditions. Thus an arc sensor system was developed by using fuzzy control approach for overcoming the difficulty of modelling the nonlinear process. The rule base and parameters of the fuzzy control system were determined on the basis of the results of experiments. This fuzzy control system has shown the successful tracking capability for the wide operating range of welding conditions.

• Journal of Ocean Engineering and Technology
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• v.16 no.2
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• pp.53-59
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• 2002

This paper shows the experimental results controlling the height of surface and back bead in GMAW by analyzing the unexpected gaps between base metals produced in welding and by controlling welding velocity due to the variation of the gap between base metals in thin-plate welding. The back bead behavior and burn-through in I-type butt joint $CO_2$ welding of thin mild steel are analyzed in the views of short circuit time ratio and short circuit frequency. It is shown through experimental consideration that the short circuit time ratio method is more reasonable than the short circuit frequency method in analyzing the formulation of back bead under changing the gap between base metals. Based on the these results, welding manipulator is designed so as to satisfy the bead height control in real time by measuring the short circuit time ratio. To show the effectiveness of the developed bead formulation control system, the experiment is implemented under two welding conditions such as increasing gap from 0mm to 0.8mm and gradually increasing gap from 0mm to 1.2mm. The experimental results show that the bead formulation can be controlled uniformly in spite of the variation of the gap between base metals.

• Journal of Welding and Joining
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• v.27 no.1
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• pp.59-64
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• 2009

In order to determine the One-Drop One-Pulse(ODOP) condition of the pulsed gas metal arc(GMA) welding, the drop detaching phenomenon during the peak time is investigated using the force-displacement model. The drop detaching criterion is established based on the displacement of the pendant drop, and the forces exerted on the drop are calculated using the Modified Force Balance Model(MFBM). The effects of wire melting on the drop size and force are included in the force-displacement model. While the peak current has most significant effects on the drop detaching time, the initial drop mass prior to the peak time also influences drop transfer. The calculated results show good agreements with the experimental data, which implies that the ODOP condition can be predicted using the force-displacement method.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.2053-2058
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• 2008

Extruded aluminium panels have been widely used for railway vehicle structures because of their light specific weight and other merit. In the past, GMAW (Gas Metal Arc Welding) and GTAW (Gas Tungsten Arc Welding) were mainly used to join aluminium panels. But recently friction stir welding (FSW) is widely used. due to its lots of advantage. In this study aluminium A6005-T6 which are used for car body structures was chosen. The influence of main parameters such as : pin rotating speed, welding speed, shoulder diameter, pin length and tilting angle on mechanical properties was examined. Optical microscope observation, micro hardness test and tensile test were carried out. Tensile strength of the stir welded plates is 74% of that of the base material.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.293-295
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• 2004

For the evaluation of corrosion resistance, Al 6061-T6 alloy was welded by Friction Sti. Welding(FSW) and Gas Metal Arc Welding(GMAW) evaluated by Tafel method and immersion test. The Tafel and immersion test results indicated that GMA weld was severely attacked compared with those of friction stir weld. It may be mainly due to the galvanic corrosion mechanism act on the CMA weld.

• Journal of Welding and Joining
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• v.21 no.2
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• pp.50-56
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• 2003

Metal matrix composites(MMC) consist of metal matrix into which is distributed a second solid phase. The normal intension is to develop a material with superior mechanical properties (for example increased toughness, stiffness and wear resistance) compared to those inherent in the matrix component. In this study, WC-12%Co/low carbon steel MMC overlays have been prepared by Gas Metal Arc Welding(GMAW) according to feeding rate of WC-12%Co grit. The macro and microstructures were examined using optical microscopy (OM) and scanning electron microscopy(SEM) each other. The characteristics of hardness and wear resistance have been investigated. WC-12%Co/low carbon steel MMC overlays which have been taken good beads without porosity and cracks were manufactured by method of GMAW. Matrix of overlayed surface was seen as fish bone and faceted dendrite structures. It was known that structures were iron tungsten carbides, Fe$_{6}$W$_{6}$C which have been occurred by melting of WC-12%Co grits. After MMC had been tested by block-roll wear test it was known that WC-12%Co/low carbon steel MMC has a excellent wear resistance by exiting Fe6w6c and WC-12%Co grit. The consequence was that region of overlay with Fe$_{6}$W$_{6}$C phase has been showed a model of adhesive wear, but region of overlay with WC-12%Co grit was restrained as a result of mechanism that wear of WC-12%Co grit is not adhesive but fracture.racture.

• Journal of Welding and Joining
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• v.16 no.5
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• pp.119-133
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• 1998

To implement full automation in pipe welding, it si most important to develop special sensors and their related systems which act like human operator when detecting irregular groove conditions. In this study, an automatic pipe Gas Metal Arc Welding (GMAW) system was proposed to full control pipe welding procedure with intelligent sensor systems. A five-axes manipulator was proposed for welding torch to automatically access to exact welding position when pipe size and welding angle were given. Pool status and torch position were measured by using a weld-pool image monitoring and processing technique in root-pass welding for weld seam tracking and weld pool control. To overcome the intensive arc light, pool image was captured at the instance of short circuit of welding power loop. Captured image was processed to determine weld pool shape. For weld seam tracking, the relative distance of a torch position from the pool center was calculated in the extracted pool shape to move torch just onto the groove center. To control penetration of root pas, gap was calculated in the extracted pool image, and then weld conditions were controlled for obtaining appropriate penetration. welding speed was determined with a fuzzy logic, and welding current and voltage were determined from a data base to correspond to the gap. For automatic fill-pass welding, the function of human operator of real time weld seam control can be substituted by a sensor system. In this study, an arc sensor system was proposed based on a fuzzy control logic. Using the proposed automatic system, root-pass welding of pipe which had gap variation was assured to be appropriately controlled in welding conditions and in torch position by showing sound welding result and good seam tracking capability. Fill-pass welding by the proposed system also showed very successful result by tracking along the offset welding line without any control of human operator.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.5
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• pp.2019-2024
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• 2011

The effect of the wear of contact tips on the weld beads made by a Gas Metal Arc Welding(GMAW) process was studied. In order to correlate between the wear of tips and beads, the droplet transfer was investigated by a high speed camera and waveform shapes, and the condition of beads was examined by a low magnification camera as well. It was found that the worn contact tip had caused to shift the contact point between the tip and the welding wire which resulted in nonuniform beads. In addition, the worn contact tip had changed the welding resistance and brought about the arc instability during welding.