• Journal of Welding and Joining
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• v.18 no.1
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• pp.91-96
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• 2000

Characteristics of the weld defect, such as a blowhole and a pit in lap-jointed fillet Co₂ welds of Zn-coated steel sheet were studied in order to make clear the sequence of the blowhole formation during welding. Main conclusions obtained are as follows: 1) Blowhole, wormhole and pit were found in fillet welds, although the optimum welding condition of 200A-23V-100cm/min was applied. 2) Zn was only detected at the solidification boundary at the early stage of the blowhole formation. 3) Most of the blowholes was started to form at lap-joint by the Zn vapor. With increasing of the Zn vapor and its pressure, the blowhole was develope to th bed surface until the completion of weld solidification. 4) The behavior of the blowhole in growth was similar to that of the columnar dendrite during welding.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.33 no.11
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• pp.1256-1261
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• 2009

Today, implementation of the defect detection in laser welding has been researched for a long time, but most studies have been made around thin plate within $1{\sim}3mm^t$. Therefore, this study was measured and analyzed light emission signals of the induced plasma in $CO_2$ laser lap welding of $6mm^t$ Zn primer-coated steel, and based on this analysis, research made an investigation into possibility of monitoring in thick plate welding. It was been analyzing the measured signals by RMS and FFT processing, as a results, we were able to confirm definite difference of two signals between humping bead and sound bead. Thus, possibility of real time monitoring in $CO_2$ laser lap welding verified experimentally.

• Journal of Welding and Joining
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• v.19 no.6
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• pp.630-635
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• 2001

The characteristics of spatter generation in the short circuit transfer region of $CO_2$ welding was investigated. Spatteriing phenomena could be classified into three types : Type I generated due to the abrupt increase of arc voltage in arcing duration. Type II by the gas ejection from molten metal and Type III generated by the arc instability at the moment of arc re-ignition just after short circuiting. Main observed types were dependent on the chemical composition of welding wires. The case of YCW12 wires was mainly composed of spatters generated by Type l and Type II, while most, spatters in YCW11 wires were generated by Type II and Type III.

• Journal of Welding and Joining
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• v.28 no.3
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• pp.36-41
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• 2010

High Mn steel has been developed for automotive applications since the steel has an excellent combination of strength and ductility. However, from the viewpoint of welding, high Mn steel has a few problems related to its chemical composition. This paper describes characteristics of dissimilar $CO_2$ laser welding for expanding application of high Mn steel. From this work it was cleared that dissimilar laser welded joint between high Mn steel and carbon steel had poor formability due to the formation of martensite within weld metal. In order to improve ductility of welded joint, the method of controlling the dilution ratio of high Mn steel was suggested.

• International Journal of Korean Welding Society
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• v.1 no.1
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• pp.17-22
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• 2001

Because the quantitative relationships between welding parameters and welding result are not yet blown, optimal values of welding parameters for $CO_2$ robotic arc welding is a difficult task. Using the various artificial data processing methods may solve this difficulty. This research aims to develop an expert system for $CO_2$ robotic arc welding to recommend the optimal values of welding parameters. This system has three main functions. First is the recommendation of reasonable values of welding parameters. For such work, the relationships in between the welding parameters are investigated by the use of regression analysis and fuzzy system. The second is the estimation of bead shape by a neural network system. In this study the welding current voltage, speed, weaving width, and root gap are considered as the main parameters influencing a bead shape. The neural network system uses the 3-layer back-propagation model and a generalized delta rule as teaming algorithm. The last is the optimization of the parameters for the correction of undesirable weld bead. The causalities of undesirable weld bead are represented in the form of rules. The inference engine derives conclusions from these rules. The conclusions give the corrected values of the welding parameters. This expert system was developed as a PC-based system of which can be used for the automatic or semi-automatic $CO_2$ fillet welding with 1.2, 1.4, and 1.6mm diameter the solid wires or flux-cored wires.

• Journal of Welding and Joining
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• v.17 no.3
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• pp.26-35
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• 1999

On the laser weld production line, a slight alteration of the welding condition changes the bead size and the strength of the weldment. The measurement system is produced by using three photo-diodes for detection of the plasma and spatter signal in $CO_2$ laser welding. The relationship between the sensor signals of plasma or spatter and the bead shape, and the mechanism of the plasma and spatter were analyzed for the bead size estimation. The penetration depth and the bead width were estimated using the multiple regression analysis.

• Laser Solutions
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• v.11 no.1
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• pp.32-35
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• 2008

In the remote welding system using $CO_2$ laser, laser beam can be rapidly transferred to a workpiece by moving mirrors of scanner system. So, it makes reducing the cycle time of welding process. We can also use and apply various patterns of weld beads by linear controlled mirrors. But most of the domestic car makers have usually applied use stitch-shaped weld bead. In that case, we don't have the merit of remote welding system efficiently. Therefore, in this paper, we investigated the characteristic of weld strength according to patterns of weld bead on $CO_2$ laser welding. And we also studied the relationship between shape of weld bead and value of tensile load.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.4 no.4
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• pp.54-60
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• 2005

In a $CO_2$ inverter welding machine, stable arcs can be generated and a welding performance that is a goal of welding can be improved when stable electric power with a low voltage and a high current is supplied to a electrode that is the secondary part (output load terminal) and the base metal. For such a stable power supply, therefore, the AC arc welding machine, the thyristor welder, and the inverter welder have been developed in order according to development of the power electronics techniques. Up to now, the thyristor welding machine is still broadly used but the application volume is gradually reduced by development of the inverter welder. Because the welding performance of the inverter welder is very good and the weight and size of the welder is remarkably light and small. The final goal of this research is to develop the voltage loss compensator that is a drawback of the inverter welder and improve the welding performance using the developed compensator.

• Journal of Welding and Joining
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• v.26 no.5
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• pp.29-35
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• 2008

In this paper concentrate on the comparison of the thermal and mechanical characteristics in Butt joint of ship structure AH32 steel by using hybrid welding and conventional SAW. For this purpose, fundamental welding phenomena of hybrid process using $CO_2$ Laser and MIG is investigated by the experiments and characteristics of thermal and welding residual stress distribution of welded joint in SAW and hybrid welding are understood from the result of FE numerical simulation and experimental values. From the result of this study, it is understood that Laser-MIG hybrid welding have high potential, make substantial saving of time and manufacturing cost and may proves its self robust in the butt joining of thick AH32 steel ship structural plate in the near future.

• Journal of Welding and Joining
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• v.23 no.5
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• pp.14-19
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• 2005

In high speed $CO_2$ welding, it has been blown to produce no sound bead with undercut or humping bead. In this study welding phenomena through synchronized high speed camera and output welding voltage and current waveform has been analyzed. For the purpose to improve a welding bead, effect of short circuit current rise slope has been examined. With commercial power source it was produced no sound bead by instantaneous short circuit, long arc period and stubbing at welding speed 2.5mm/min Humping bead or undercut were showed by instantaneous short circuit and long arc period. Also, the weld bead was not formed during the long short circuit period after stubbing start and long arc extinguishment period after wire sticking by failure of arc regeneration, because the droplet was not transferred to weld pool. With increasing short circuit current rise slope the frequency of stubbing was decreased and the normal short circuit rate was increased. A control of short circuit current rise slope was effective factor in high speed welding.