RESEARCH PAPER

Governing parameters affecting fume generation in short-circuitMAG welding

Américo Scotti & Valter Alves de Meneses

Received: 28 October 2013 /Accepted: 4 March 2014 /Published online: 30 March 2014# International Institute of Welding 2014

Abstract The operating parameters of the short-circuitingMAG process are expected to have a significant effect onfume generation. Despite this, no conclusive results on thissubject have been presented in current literature. The objectiveof this work was to determine the most significant governingparameters affecting fume generation, by attempting to isolateeach parameter from the others as much as possible. Severalwelding tests were carried out, and the effect of short-circuiting current, arc length (welding voltage), arcing time,and droplet diameters before detachment were investigated.The results show that the increase in each of these parameterscontributes to a higher fume generation rate, and their effectbecomes more significant when they act together.

Keywords MAGwelding . Fume . Process parameters .

Current . Electric arcs . Voltage

1 Introduction

MIG/MAG welding is one of the most commonly appliedprocesses in manufacturing industries. A very common oper-ational mode of this process is short-circuiting transfer. Asdescribed by Scotti et al. [1], in the short-circuiting mode,there must be a contact (short-circuit) between the droplet

under formation and the pool before drop detachment. Duringthe short-circuit periods, the arc extinguishes. At the sametime, a liquid metal bridge is formed and then grows as thedroplet is sucked into the molten pool (by surface tension). Asthe initial short-circuit current is low, there is insufficientelectromagnetic force to constrict (pinch effect) the metalbridge. The current increases progressively, heating the wireby Joule effect (absence of anodic heating at this stage), andthe bridge is pinched by the combined effect of the surfacetension and the increasing electromagnetic forces (pinch ef-fect). It is recognized that in conventional short-circuit MAGwelding, there may be a problem with spatter generation if theparameters are not properly set. On the other hand, it is alsoexpected that higher metal transfer stability in short-circuitingMAG welding will lead to increased fusion, improved beadfinish, and reduced spatter generation.

There are several references in the current literature corre-lating fume generation with spatter. Dennis et al. [2] report 6to14% of fume as coming from spatter. Zimmera et al. [3]believe that the formation of welding spatter can have asignificant effect on the composition of the fume, and its rateof formation (spatter represents a large surface area fromwhich further evaporation can occur and increase the forma-tion of fumes). However, some authors claim that the ejectedspatter particles are too large to remain airborne, and they donot contribute directly to fume generation. According toBosworth and Deam [4], micro-spatter (very fine droplets ofliquid metal formed by effects such as wire explosion of theneck or shorting to the weld pool) can form fume and shouldbe avoided. But in a recent work, Meneses et al. [5], studyingthe effect of the metal transfer stability (spatter generation) onfume generation, found that a condition with greater transferstability does not generate less fume quantity, despite the factthat this condition generates less spatter.

Hilton and Plumridge [6] and Mendez et al. [8] claim thatthe fumes released during MIG/MAG processes are

Doc. IIW-2437, recommended for publication by Commission XII “ArcWelding Processes and Production Systems.”

A. Scotti (*)Center for Research and Development of Welding Processes,UFU—Federal University of Uberlandia, Uberlandia, MG, Brazile-mail: ascotti@ufu.br

V. A. de MenesesIFMA—Federal Institute of Maranhao, São Luis, MA, Brazile-mail: alves_de_meneses@yahoo.com.br

Weld World (2014) 58:367–376DOI 10.1007/s40194-014-0122-2

composed of oxides and metallic vapors, originated predom-inantly from the wire, while the base metal usually contributesless than 10 % of the total fume. These authors also mentionthat lower oxidation potentials in shielding gases cause fewerfumes to be created. Cooper et al. [7] point out that the intenseheat produced by a MIG/MAG arc is the responsible forevaporation of some metals, and Mendez et al. [8] claim thatthe generation of fumes depends mainly on the evaporation ofmetal from the electrode. Yamazaki et al. [9] suggest thatmetal vapor is projected into the air from the arc jet, undergo-ing oxidation and condensing rapidly into the fine particlesthat constitute the fumes; the temperature in these droplets ismuch higher than that of the metal in the weld pool. Bosworthand Deam [4] summarize fume formation mechanismsexplaining that the weld pool and workpiece are considerablycolder than the droplet and act as a sink for metal vapor. Metalvapor that does not condense onto the weld pool and work-piece escapes and mixes with air to form a fine dispersion ofmetal oxide particulate (fumes).

These previous studies on fume generation from MIG/MAG welding do not isolate the effect of separate processvariables and are mainly related to free flight transfer ratherthan the short-circuiting mode. Heile and Hill [10], for in-stance, suggest that increasing welding current increases fumegeneration rate (FGR) by raising the temperature of the dropsurface. However, higher current decreases the residence timeyet increases the number of drops (these effects may canceleach other out). They also say that voltage is proportional to thearc length, which also affects droplet residence time in the arcand therefore also to FGR. Sterjovski et al. [11, 12] explain thathigher voltages, corresponding to greater arc lengths, increasefume generation by exposing a larger surface area of moltenweld metal to the atmosphere for a longer period of time. Butthe authors do not mention that when voltage is increased,other parameters, such as current, can also vary concomitantly.

For short-circuit metal transfer, fume rate has also beenshown to have a direct correlation with voltage, but asshown by Meneses et al. [5], in the short-circuiting range,the increasing fume generation rate at higher voltage is notdue to either spatter (as consequence of lower metal transferstability) or long arc lengths alone. They demonstrated thatthe following interrelated factors are likely to govern fumegeneration:

Higher short-circuiting current (Isc);Longer arc length (higher voltage);Longer arcing time (tarcing);Larger droplet diameters before detachment (∅drop).

Menezes et al.’s finding are in accordance with those ofPires et al. [13], who, in their review, reported that, in spite ofknowing the sources of fumes, it is difficult to separate theindividual effect of each factor, as many of them are

interrelated. Pires et al.’s observations also confirm the find-ings of Garcia and Scotti [14] who claim that some effects, suchas characteristics of the metal transfer (arcing time, etc.), canpredominate over the effect of current level and gas composi-tion. Gray et al. [15] also refer to the influence of indirectparameters, i.e., short-circuiting current, pointing out thathigher levels of secondary inductance in the power sourcereduce the current rise and peak current during short-circuitingand therefore decrease FGR.

The previous studies reported above indicate that thereremains a challenge to determine the role played by each ofthe individual factors on fume generation rate in short-circuiting MIG/MAG welding. Thus, the objective of thiswork was to evaluate the weight of each of the factors pointedout by Meneses et al. [5].

2 Methodology and experimental procedures

In an attempt to determine the effect on fume generation rateof the governing parameters pointed out in the previous workby Meneses et al. [5], a series of experiments was planned insuch a way that fume data from bead-on-plate weldmentscould be isolated and correlated with measures such asshort-circuiting current (Isc), arc length, arcing time (tarcing),and droplet diameter before detachment (∅drop).

Two different commercial power sources were utilized inthis work in order to facilitate the objectives of each experi-mental trial. The first power source, an inverter Power Wave455 STT, was set to operate in constant voltage mode byselecting the program “Conventional GMAW with gasshielding and positive polarity”. Thus, voltage (Vset), wirefeed speed (WFS), and inductive factor (Ind) were the threesettable parameters. This power source is referred hereafter aspower source 1.

The second power source, referred henceforth as powersource 2, was a TransPuls Synergic (TPS) 5000 cold metaltransfer (CMT) MV. With this power source, three specialfunctions were used. The first (denoted here as PULS) wasused for welding in pulsedMIG mode. The setting parameterswere, consequently, the desired current and arc length trim-ming. The built-in synergic command provides the pulseparameters and the wire feed speed to fit the desired currentfor a given combination of wire diameter, wire composition,and shielding gas composition. The second function of powersource 2 applied in this work was also a synergic command,but for short-circuiting welding. This operational function isdesignated here as SYN and requires only the desired currentand values for inductance and arc length trimming. The built-in synergic command also provides the arc voltage and thewire feed speed to fit the desired current for a given wire andshielding gas. The third function, branded as CMT, is aspecially controlled short-circuiting metal transfer system

368 Weld World (2014) 58:367–376

developed by the manufacturer, in which, by sensing the arcvoltage, the current is reduced and the wire feeding is reversedbackward during most of the short-circuit (almost current-freematerial transfer). Just after the moment of droplet detach-ment, current is recovered. Again, a synergic command pro-vides the arc voltage and the wire feed speed to fit the desiredcurrent for a given combination of wire and shielding gas.

Plain carbon steel (ASTM 1020) was used for the testplates, and the torch was positioned at 10±1° pull direction(drag angle) in flat position. The wire was a 1.2-mm AWSER70S-6, shielded by Ar+25 % CO2 or 100 % CO2. A targetmean current (Im=150±2 A) was used for all trials.

The amount of fume emission was measured by means ofan apparatus (Fig. 1) and procedure established in the standardAWSF1.2:2006 [16]. The fume collecting glass-fiber filter padis specified by the standard ASTMC800 [17]. Before carrying

out the fume emission tests, the system was calibrated accord-ing to the recommended standard procedure.

3 Determination of the individual governing factor effectson fume generation

3.1 Influence of the short-circuiting current (Isc) on fumegeneration

In an attempt to isolate the effect of short-circuiting current (Isc)on fume generation, the inductance was set at three levels (high,medium, and low inductances) using power source 1.When theinductance setting is changed for a given welding condition, theaverage values of short-circuiting current (Isc) and short-circuiting time (tsc) will also change. For higher inductances,Isc will become lower, but at the same time, tsc will becomelonger. However, from different short-circuiting times, no effectof fume generation is expected, since, with no arc, the generatedheat on the droplet surface would not be enough to causevaporization. In addition, no significant effect of the inductancesetting on tarcing is predictable, since the wire melting rate isconstant during arcing periods (wire feed rate was notchanged). Consequently, for the conditions of “adequate arc”lengths, no significant effect of the inductance setting on drop-let diameters before detachment (∅drop) is expected. The inval-idation of this approach to isolate the effect of Isc wouldmaterialize if the correlation between ∅drop and tarcing couldnot be expected. Thus, one can say that the experimentalapproach to isolate the effect of Isc is potentially correct.

Table 1 presents the experimental design and results. Thevariations in the contact tip to work-distance (CTWD) are dueto the need to maintain the required target average current(150±2 A) constant for the same wire feed rate. As seen, thearc length was also intentionally set with three levels (“long”,“adequate”, and “short”) at two setting inductances (low andmedium inductances), by increasing the setting voltage (Vset)for a giving inductance set. The reason for including thesevariations in the experimental matrix is that for the sameinductance, Isc increases as arc gets longer. However, in thiscase, Isc is not isolated any longer. The lack of influence ofinductance on mean voltage (Vm) is justified by the fact thatthe power supply was an electronic one, set to maintain aconstant voltage. It is important to mention that a span of 8 Vis large but still covering the short-circuit transfer range (aproper welding parameter setting for production, not alwaysobserved, should be in the middle of the span range, with atolerance of ±1 V).

A stability index (IVsc) as established by Rezende et al. [18]and Scotti et al. [19] was used in this work to classify the metaltransfer stability for a given short-circuit MAG weld. Thelower IVsc, the more stable the metal transfer, fewer spattersare produced. The highest metal transfer stability (lowest IVsc)

Fig. 1 Fume collecting apparatus according to standard AWS F1.2:2006(on the left) and an illustration of the glass-fiber pad after use (on theright)

Weld World (2014) 58:367–376 369

was reached at the average setting voltage (21 V), but theoutcomes show that the change in inductance does interferewith the metal transfer regularity (1.1 to 1.7, from low to highinductances at the “adequate” arc length), as much as Vset does(1.3/1.4 to 1.9/1.7, from “short” through “long” arc lengths at“low” and “medium” inductances, respectively); in practice,inductance is used as a secondary factor in metal transferstability control. It must also be pointed out that it is notexpected to keep the same short-circuiting current values for“short” and “long” arcs at the same inductance setting.

The aim of the planned approach seems to have beenachieved; comparing data from the highest metal transferstability (adequate arc length) trials, decreasing Isc values(402, 329, and 259 A) were achieved as inductance increased(from low to high settings), tsc increased only marginally(0.0027, 0.0031, and 0.0041 s). As predicted, the dropletdiameter ∅drop kept approximately the same (1.1, 1.2, and1.2 mm) and tarcing was not significantly affected (0.0143,0.0136, and 0.0140 s) by inductance setting. Summarizing,the only significant effect of inductance changes was on Isc(lower inductance, higher Isc).

Figure 2 shows the relationship between inductance andshort-circuit current (Isc) and fume generation rate. As can beseen, the decrease of Isc also decreases FGR, but the effect is notconsistent from medium to high inductance (one can observe aminimum at the medium inductance setting, 0.13 g/min, incontrast to 0.14 g/min for high’s, although the standard devia-tion of these two measurements is in the other of 0.01 g/min,i.e., the difference is not statically significant). Another reasonfor the differences in the influence of Isc on FGR between lowto medium inductances (ΔFGR=−0.04/min) and medium tohigh inductances (ΔFGR=+0.04/min) could also be attributedto the resultant minimum value of tarcing at medium inductancesetting. As shown in item 3.3, the longer the arcing time, themore fume generated. It must be pointed out that since anelectronic power source was used, increased “inductance”means reduced rate of rise of current, but there is no automat-ically any stored energy to inject into the arc.

Even though only a slight and uncertain influence of Isc onFGR is indicated, the authors propose that increasing Iscshould generate more fumes for the following reasons (Fig. 3):

During the contact between the droplet and the weld pool,a higher Isc could cause some metal boiling to take place,in particular on surface of the meniscus formed betweenthe droplet and the pool just before the detachment;During the arcing times (tarcing), the arc starts with highercurrent values (when Isc just starts to decay), which mayenhance evaporation of the forming droplet and/or in-crease evaporation from the pool surface under the initialarc phase.

But it must be remembered that:

(a) When Isc increases, to keep the same average current(Im), tarcing may become shorter if tsc is the same;

Table 1 Experimental matrix to determine the short-circuiting current effect on fume generation (mean values from three replications—power source 1)

Experimental factors (powersource 1)

Settings Monitored Determined

Vset

(V)CTWD(mm)

Im (A) Um (V) IVsc Isc (A) tsc (s) tarcing (s) ∅drop

(mm)FGR(g/min)

Low inductance (short arc) 17 14 151±1 15.1±0.0 1.3±0.0 309±31 0.0033±0.0000 0.0074±0.0001 0.9±0.0 0.08±0.01

Low inductance (adequate arc) 21 12 149±1 18.7±0.0 1.1±0.1 402±8 0.0027±0.0000 0.0143±0.0003 1.1±0.0 0.17±0.01

Low inductance (long arc) 25 9 149±0 22.4±0.0 1.9±0.0 521±5 0.0033±0.0000 0.0374±0.0007 1.7±0.0 0.27±0.02

Medium inductance (short arc) 17 15 151±1 14.8±0.1 1.7±0.2 287±19 0.0033±0.0003 0.0064±0.0004 0.9±0.0 0.05±0.00

Medium inductance (adequate arc) 21 12 150±2 18.6±0.1 1.4±0.1 329±8 0.0031±0.0001 0.0136±0.0026 1.1±0.0 0.13±0.00

Medium inductance (long arc) 25 9 151±1 22.4±0.0 1.7±0.2 411±18 0.0040±0.0001 0.0357±0.0025 1.5±0.0 0.22±0.02

High inductance (adequate arc) 21 12 150±1 18.7±0.1 1.7±0.2 258±36 0.0041±0.0001 0.0140±0.0024 1.2±0.0 0.14±0.01

Wire/gas=1.2-mm AWS ER70S-6, Ar+25 % CO2; WFR=3.0 m/min; TS=17.36 cm/min

Fig. 2 Short-circuiting currents (Isc) and fume generation rates (FGR) asa function of setting inductances

370 Weld World (2014) 58:367–376

(b) If Isc is higher, the arc will probably restart (after theshort-circuit ends) with a long arc length (a parameterthat has been shown to be a factor influencing fumegeneration);

(c) If Isc is higher, the wire melting rate is higher at themoment of arc restart (also a factor which may be re-sponsible for increased fume generation).

Thus, assuming that the objective of isolating the Isc effectsucceeded, one can deduce that Isc is a less significantgoverning parameter on fume generation (in general thehigher Isc, more fumes are generated).

3.2 Influence of the arc length on fume generation

Analyzing the results presented in Table 1, for the three levelsof arc length (long, adequate, and short) at two setting induc-tances (low and medium), the relationship between arc lengthand FGR is shown in Fig. 4. Higher values at low inductance

can be justified by the parallel effect of the short-circuitingcurrent (Isc). As seen in Fig. 5, Isc increased significantly as thearc gets longer, accompanied by a significant increase of FGR.However, from Figs. 6, 7, and 8, which illustrate the othertendencies shown in Table 1, it appears that there is nostatistical tendency for tsc to increase as the arc gets longer,despite the increase of FGR (Fig. 6). However, both tarcing and∅drop presented clear tendencies to increase as arc gets longer,as seen in Figs. 7 and 8, respectively, and, in these cases, FGRwas also augmented. These results indicate that there are othergoverning parameters acting concurrently with arc length inaddition to Isc.

In an attempt to isolate the effect of arc length on fumegeneration, a new series of testes was planned using thespecial functions of the power source 2. Two shielding gaseswere used to verify the repeatability of tendencies. By usingthe equipment set to work in pulsed synergic mode, it waspossible to vary the arc length by varying the “Trimmer”command (which in fact sets the wire feed speed—WFS—tohave different arc lengths at the same mean current), keepingthe remaining parameters constant. As the pulsed transfer

Fig. 3 Proposed mechanism forfume generation based on theshort-circuit current (Isc)

Fig. 4 Relationship between arc length and fume generation rate (FGR)using the data presented in Table 1

Fig. 5 Short-circuiting currents (Isc) and fume generation rates (FGR) asa function of arc length

Weld World (2014) 58:367–376 371

mode was used, the arcing time and droplet diameter beforedetachment are defined by the pulsing parameters, as shown inTable 2. Thus, it can be considered that only arc length waschanged in these experiments.

As seen in Fig. 9, the longer the arc (confirmed by themonitored mean voltage), the greater the FGR. This resultconfirms the findings already presented in the literature, but inthis case, the results are independent of other factors, nowwiththe warranty of no dependence of other factors. For instance,Quimby and Ulrich [20] demonstrated for approximately thesame current, wire, and shielding gas, that fume rates rise asvoltage is increased through the short-circuit mode. However,these authors do not mention potential changes in othergoverning parameters as voltage was increased.

It is important to point out that, considering that the wirefeed speed (WFS) was slightly higher for the short arc condi-tion in the present work, there was more melted material perunit of time, consequently more fumes generated per unit oftime. Thus, one could consider that for the same WFR, theeffect of arc length on FGR would be even more distinctive. Itis also important to mention that the very low values of FGRdetermined is in total agreement with data from other authors,

among them were Rosado et al. [21] and Wallace et al. [22].According to the latter, fume levels were significantly lowerfor the pulsed than for conventional MAG welding in mea-surements in industrial plants and not only in laboratorydeterminations. They suggest that this fume reduction is dueto the ability of pulsed current to transfer metal droplets fromthe wire, through the arc, to the work piece, with minimumheat. Mendez et al. [8], on the other hand, suggest that thereduced fume generated by pulsed current is due to the smallerdroplet size (less metal is vaporized). Their calculations indi-cate that the surface temperature at the tip of the electrodeincreases with droplet size and, however, they show thatdetaching the droplet after it has remained in the arc for arelatively long time as in globular transfer would not beexpected to yield any improvements.

3.3 Influence of arcing time on fume generation

In the effort of isolating the effect of arcing time on fumegeneration, a series of experiments were carried out using thespecial functions of the power source 2: synergic control withconventional constant voltage short-circuit transfer (SYN) and

Fig. 6 Short-circuiting times (tsc)and fume generation rates (FGR)as a function of arc length

Fig. 7 Arcing times (tarcing) andfume generation rates (FGR) as afunction of arc length

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“cold metal transfer” (CMT). Two shielding gases were used,a blend Ar+15 % CO2 and pure CO2. In both cases, it isexpected that the power source should maintain the same arclengths for different gases, but the mean voltage should in-crease at a higher content of CO2. Higher CO2 levels requirehigher voltage (Um) and a lower wire feed speed (WFS) toachieve the same arc length. When changing from the argonbased mixture to pure CO2, a longer arcing time is expectedfor each drop detachment.

Table 3 shows the outcomes of these welding tests. TheCMT function provides a very short arc, as evidenced by thearc voltage measurements (13.9 for Ar+15% CO2 and 16.3 Vfor 100 % CO2) and very stable metal transfer (IVsc rangingfrom 0.10 to 0.16). Now, comparing the results from synergicand CMTmodes, for the same shielding gas andmean current,a lower FGR is observed for CMT, despite the fact that Isc washigher. In addition to a lower voltage (presumably shorter arclength), the arcing time tarcing, although longer, was lesseffected by the change of shielding gas with the CMT mode.This suggests that arc length and arcing time effects prevailover the effect of the short-circuiting current. The low FGRfigures found with CMT (Table 3) are slightly higher butsimilar to those achieved with the pulsed mode (Table 2).These findings are in agreement with the FGR results pub-lished by Pires et al. [23].

Figure 10 shows that the longer arcing time (tarcing) corre-sponds to a higher FGR. The difference in tarcing from the twoshielding atmospheres was more significant for the synergicfunction, as much as its effect on FGR. It is noteworthy that byconsidering lower wire feed speeds (WFS) to the 100 % CO2

shielded conditions, whichmeans less meltedmaterial per unitof time, consequently less fume generated per unit of time,one could consider that for the sameWFR, the effect of arcingtime on FGR would be even more distinguishing.

More spatters and poorer stability (higher IVsc) were expectedwith pure CO2 shielding, but as shown in a previous work [5],there is no straight correlation between spatter and FGR. Inaddition, no significant increase in the droplet size before

Tab

le2

Experim

entalm

atrixto

determ

inethearclength

effecton

fumegeneratio

n(valuesfrom

tworeplications

foreach

condition—power

source

2)

Test

Operatio

nmode(pow

ersource

2)Regulated

Monito

red(A

r+15

%CO2)

Determined

Trim/Ind

I set(A

)Ip

(A)

Ib(A

)tp

(ms)

tb(m

s)I m

(A)

I RMS(A

)Um(V

)WFS

(m/m

in)

∅drop(m

m)

FGR(g/m

in)

PULS1&

2Pulse

(longarc)

22/0

177

509/512

33.8/30.0

1.45/1.45

6.18/6.33

152/150

227/227

27.4/27.3

5.55/5.54

1.0/1.0

0.05/0.05

PULS3&

4Pulse

(shortarc)

17/0

178

525/515

29.2/32.6

1.45/1.45

6.52/6.32

148/150

228/226

25.8/25.9

5.63/5.67

1.0/1.0

0.01/0.01

Fig. 8 Droplet diameters before detachment (∅drop) and fume generationrates (FGR) as a function of arc length

Weld World (2014) 58:367–376 373

detachment (∅drop) was observed. The short-circuiting time (tsc)was slightly different between the two gases, but as discussedearlier, fume emission is not expected to increase as a function oftsc. Table 3 also shows that a change in shielding gas results invery little change in Isc for CMT. The use of CMT seems to beeffective in isolating the effect of tarcing on fume generation.

However, in the synergic mode, the attempt to isolate theeffect of tarcing was not totally successful. Despite the dropletsize (∅drop) being similar and the effective tsc being low, theshort-circuiting current (Isc) was increased when 100 % CO2

was used. As seen in item 3.1, a higher Isc tends to increaseFGR. The combined and convergent effects (longer tarcing andhigher Isc) may explain the higher significance of tarcing onFGR when the synergic mode was used. It should also betaken into account in this analysis that in welding processes,with arc interruption, such as with short-circuiting transfer(and to some extend pulsed transfer), the effect of the heatfrom the arc on the droplet surface is time dependent.

The significance of tarcing on FGR has been demonstrated bythese experiments, and the reduced influence of this factorwhen the CMT mode was applied is also shown. Overall, it isshown here that tarcing is a governing parameter on fume gen-eration (the longer the arcing time, the more fume generated).

3.4 Influence of the droplet diameters before detachment(∅drop) on fume generation

In the attempt to analyze the effect of droplet diameters beforedetachment (∅drop) on fume generation, the data from Table 1were used. As illustrated in Fig. 8, the larger the droplet beforedetachment, the higher the FGR (consistently for two condi-tions and in a sensitive way). However, the conditions (arclength) that led to larger ∅drop also tended to increase Isc andtarcing. Thus, the attempt to isolate the influence of ∅drop onFGR was inconclusive. Based on the present data, it is how-ever unlikely that there is an inverse relationship between∅drop and FGR. When the four factors (arc length, Isc, tarcing,and ∅drop) are considered, it appears that higher values areassociated with increased fume emission. Mendez et al. [8] T

able3

Experim

entalm

atrixto

determ

inethearcing

timeeffecton

fumegeneratio

n(valuesfrom

tworeplications

foreach

condition—power

source

2)

Test

Operatio

nmode/shieldinggas%

CO2

Regulated

Monito

red

Determined

Trim/Ind

I set(A

)I m

(A)

I RMS(A

)Um(V

)WFS(m

/min)

IVsc

I sc(A

)t sc

(ms)

t arcing(m

s)∅

drop

(mm)

FGR

(g/m

in)

SYN1&

2Sy

nergic/15%

CO2

0/0

153

148/152

153/157

18.4/17.7

3.71/3.68

0.67/0.70

228/227

3.3262/3.3631

7.6918/7.3599

1.2/1.2

0.09/0.07

SYN3&

4Sy

nergic/100

%CO2

8/0

148

148/148

155/154

20.8/21.1

3.31/3.39

0.99/0.95

263/261

2.8156/2.7610

16.6322/16.9273

1.3/1.3

0.20/0.19

CMT1&

2CMT/15%

CO2

0/0

155

152/152

173/171

13.9/13.9

4.30/4.36

0.10/0.11

307/299

6.0778/5.8585

6.3389/6.1326

1.1/1.1

0.02/0.02

CMT3&

4CMT/100

%CO2

0/0

176

151/152

172/172

15.8/16.7

4.26/4.28

0.16/0.13

313/298

7.6218/6.4598

7.6721/6.8335

1.2/1.2

0.05/0.05

Fig. 9 Arc voltage and fume generation rates (FGR) as a function of arclength

374 Weld World (2014) 58:367–376

present interesting models to explain heat transfer through thedroplet (faster heat transfer implies lower droplet temperaturesand less evaporation). Following their reasoning and extend-ing it to short-circuit transfer, it is reasonable to claim that anyeffect of droplet size on FGR would happen only duringarcing time of a short-circuiting transfer (the reason for thecorrelation between these two factors found in the results),when the droplet regime would be similar to large-like glob-ular metal transfers (highest FGR).

4 Conclusions

By isolating the controlling parameters under the experimentalconditions applied here (short-circuiting MAG welding, with1.2-mm AWS ER70S-6 wire shielded with either Ar+25 %CO2 blend or 100 % CO2, maintaining fixed the averagecurrent of 150 A, and the travel speed of 17.4 cm/min, weld-ments carried out on plain carbon steel plates in flat position),it was concluded that higher short-circuiting currents, longerarc lengths, and long arcing times each increase fume gener-ation rate (mass of fume per unit of time), but if they acttogether in the same direction, which is normal as a result ofshort-circuiting MAG welding, the combined effect on fumeemission is significant. However, the isolation of the effect ofdroplet diameters before detachment on FGR was not possi-ble, but there is no evidence that a larger droplet could lead tolower FGR.

Acknowledgments The authors would like to express their gratitude tothe Federal University of Uberlandia, Brazil, through its Center forResearch and Development of Welding Processes (Laprosolda), for thelaboratory support for fume quantification. They also would like thankingthe Brazilian councils for research development, CAPES, and CNPq forthe financial support.

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