• Journal of Welding and Joining
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• v.15 no.2
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• pp.72-80
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• 1997

The spatter generation rate of GMA welding with $CO_2$ gas shielding was measured with the change of welding conditions such as wire feeding rate and welding voltage and then the results were analized with the accompanying changes in metal transfer mode and in bead geometry. The spatter generation rate (SGR) was relatively low not only wit the short circuit transfer but with the truely globular transfer mode. However, the SGR resulted with the mixed mode were consistantly high. The resultant wave pattern of mixed mode was due to the coexistance of short-circuit and globular transfer and characterized by the frequent appearance of instantaneous short circuit. Considering the result of SGR and that of bead geometry, it could be concluded that when the wire feeding rate (or welding current) was either low or high, the optimum bead shape could be obtained along with the low spatter generation. However, in the middle range of wire feeding rate, the optimum bead shape was only obtained in the mixed mode condition resulting in the high spatter generation.

• Journal of Welding and Joining
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• v.15 no.3
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• pp.47-55
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• 1997

Dynamic characteristics of the short circuit mode are investigated using the Volume of Fluid (VOF) method. When the initial molten drop volume, contact area and wire feed rate are given, rate change of the molten bridge profiles, pressure and velocity distributions are predicted. The electromagnetic force with proper boundary conditions are included in the formulation to consider the effects of welding current. It is found that the molten metal is transferred to the weld pool mainly due to the pressure difference caused by the curvatures in the initial stage, and electromagnetic force becomes dominant factor in the final stage of short circuit transfer. Necking occurs at the contact position between the molten drop and weld pool, and the initial molten drop volume and welding current have significant effects on break-up time.

• Journal of Welding and Joining
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• v.19 no.5
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• pp.486-491
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• 2001

The effect of S content in welding wires on spattering characteristics and droplet transfer phenomena was studied. In MAG welding using 80%Ar-$20%CO_2$ shielding gas, spattering characteristics and droplet transfer phenomena were varied with S content of wire. Sulfur addition in wire reduced surface tension of droplet and weld pool, and made arc more stable in MAG welding. With increasing S content, the spattering ratio and the ratio of large size spatter ($d{\geq}1.0mm$) were reduced in short circuit transfer mode. In spray transfer mode, spattering ratio, however was increased when sulfur was added more than 0.020wt.% because surface tension of droplets and weld pool was reduced too much even though arc stability was improved.

• Journal of Welding and Joining
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• v.16 no.3
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• pp.95-101
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• 1998

Waveforms of $CO_2$ gas shielded arc welding in short circuit transfer mode was studied with the waveform analysis program, which can calculate various waveform factors such as number of short circuit event, mean and standard deviation of short circuit time and arc time. The calculated values of these factors were correlated independently or in combination with the spatter generation rate to figure out the most reliable index for evaluating spatter generation and further for arc stability. As a result this study, it was confirmed that the spatter generation tends to decrease with the increase of short circuit frequency. Further to this, it was also found that as the short circuit frequency increases the short circuit event becomes more uniform resulting in the decrease of standard deviations ($\sigma$values) of short circuit time and arc time. This result demonstrated that these factors are strongly correlated with each other and thus any one of these factors can be used for the evaluation index. In the discussion, however, short circuit frequency was proposed for the most practical index in evaluating the arc stability of short circuit transfer mode since it is the one which could be monitored in-process condition without any complex caculation process.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.39-46
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• 1998

$CO_2$ gas shielded arc welding has been characterized with its harsh arc compared to Ar-based shielding gases and with its high level of spattere specially in welding current range of 250~300 amperes. In this range of welding current, the metal transfer mode showed to be changed from short circuit to globular with the increase of welding voltage resulting in so-called the transitional mode in which both modes of transfer appeared together. To characterize the transitional mode, the short circuit events were divided into two groups, i.e. normal short circuit (N.S.C) which has short circuit time $(t_s)$ over 2msec and instantaneous short circuit (I.S.C) of $t_s$$\leq$2msec. The experimental results showed that the number of N.S.C decreased almost linearly with the increase of welding voltage and appeared to be not related with spatter generation rate. However I.S.C became to be pronounced in the transitional condition and its number reached the maximum value at around 29.0 volts. Considering the relation with the spatter generation rate, it was found that the number of I.S.C had a very strong correlation with the spatter generation rate of the transitional condition. It was further demonstrated that spatter generation rate decreased quite linearly with the decrease of I.S.C frequency. It implies that I.S.C is the most important waveform factor controlling the spatter generation of the transitional mode, i.e. in the middle range of welding current. Based on these results, It was discussed that in the transitional mode the basic concept of waveform control for suppressing spatter generation would be different from the one applied for typical short circuit transfer mode of low welding current.

• International Journal of Korean Welding Society
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• v.1 no.2
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• pp.1-6
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• 2001

A weld quality assessment method is proposed in this work, which can be applied to the short-circuit mode in GMAW. Information about the welding signal trajectory, distribution of the signal duration at each sub-regions and short-circuit frequency is used to evaluate the weld quality. The weighted penalty, which is determined experimentally, is imposed for each abnormal signal. Performance of the proposed method is compared with the Simpson's method under the conditions of shielding gas reduction, workpiece surface contamination and joint gap in the butt and fillet welds. Although the proposed method predicts the weld quality with reasonable accuracy, further modification and extension to other metal transfer modes are needed as a further study.

• Journal of Welding and Joining
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• v.12 no.4
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• pp.76-84
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• 1994

Droplet transfer modes due to welding conditions and the effect of Ca in welding wire on droplet transfer were investigated. Droplet transfer mode in CO$_{2}$ welding was classified into 2 modes, that is, short circuit and globular transfer, with increasing welding current and voltage. With increasing Ca content in wire, repulsive pressure due to vaporization of Ca was considerably increased. In short circuit transfer region, arcing time was increased and droplet transfer cycle was decreased, with increasing Ca content. In globular transfer region, welding condition for globular transfer was lower current region, with increasing Ca content.

• Journal of Welding and Joining
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• v.14 no.5
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• pp.106-112
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• 1996

The effects of Ti addition in welding wire on the spatter generation and the droplet transfer phenomena were investigated. With increasing Ti content the spattering rate was decreased but the ratio of large size spatter (D $\geq$ 1. 0mm) was increased in both short circuit and globular transfer mode of $CO_2$welding. In short circuit transfer region, the arcing time was increased and the droplet transfer frequency was decreased with increasing Ti content In globular transfer region, the transition current and voltage to globular transfer was lowered and the welding condition region for stable globular transfer was widened with increasing Ti content.

• Journal of Welding and Joining
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• v.14 no.5
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• pp.145-150
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• 1996

The variation of spatter generation in gas metal arc welding with welding conditions and wire compositions was investigated and interpreted in terms of arc stability. The transition range from a short circuit mode to a spray mode in the mixed gas welding showed an unstable arc and generated the largest amount of spatters. Titanium reduced spatters only in the globular mode of $CO_2$welding and silicon and manganese showed the same effect The effect of silicon and manganese, however, was no longer seen when titanium was added simultaneously to the wire. It is believed that deoxidizers easily form oxides on the anode and make the arc stable even in DCRP welding. The wires with deoxidizers also showed low short circuit frequency, resulting in the increase of large size spatters.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.63-72
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• 1998

In this study, the effects of the current pulsing conditions, on the spatter generation rate during the $CO_2$ gas metal arc welding (GMAW) were investigated. Normally using the inverter type power supply, of which the welding current waveform was regulated to reduce the spatter generation rate, but in this study pulsing was imposed on the welding current. Observation of the metal transfer phenomena during the pulsed current GMAS indicated that the droplet transfer from the electrode via the short circuit transfer and the repelling transfer mode could be minimized by selecting optimum combinations of pulsing parameters, which include base and peak current, base and pak duration. It was also demonstrated in this study that proper combinations of the pulsing parameters led to reduce generation of spatters during GMAW shielded by $CO_2$ gas.