06140585

7/27/2019 06140585

1/7

870 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 3, MARCH 2012

Investigation on Welding Arc Interruptionsin the Presence of Magnetic Fields:

Welding Current InfluenceRuham Pablo Reis, Amrico Scotti, John Norrish, and Dominic Cuiuri

AbstractArc interruptions and, therefore, oscillation in theamount of energy and molten wire delivered to the plate have beenobserved during tandem pulsed gas metal arc welding (GMAW). Itappears that these instabilities are related to the magnetic interac-tion between the arcs. In order to clarify the possible mechanismsinvolved, this paper tries to mimic the tandem GMAW arc in-terruptions. External magnetic fields were dynamically applied toGTAW arcs in constant current mode to verify their resistance toextinction as a function of current level and direction of deflection.

High-speed filming was carried out as an additional tool to un-derstand the extinction mechanism. The influence of the weldingcurrent level on the arc resistance to extinction was established:The higher the welding current, the more the arc resists to theextinction. The arc deflection direction has minor effect, but arcsdeflected backward have more resistance to extinction.

Index TermsArc interruption, GTAW, magnetic deflection,tandem GMAW.

I. INTRODUCTION

I N TANDEM gas metal arc welding (GMAW), two wiresare fed through two electrically isolated contact tips intoa single weld pool. The existence of magnetic interaction be-

tween the arcs is widely recognized. In a review carried out byYudodibroto et al. [1], it is stated that tandem GMAW can

employ any metal transfer mode, but the most flexible per-

formance for the vast majority of applications is obtained

with the pulsed-current mode. The same review points out

disagreements concerning the role of pulse synchronization

on the process stability; a number of studies indicate that

tandem GMAW has superior stability with an antiphase pulse

synchronization, while others suggest that it is better to apply

a pulse phase shift of 0.51 ms or even that synchronization is

unnecessary. Yudodibroto et al. [1] conclude from experimental

work reported in the same review that, with a 6-mm interwire

distance and 0

torch leading angle, pulse synchronization doesnot significantly influence the stability of the process, and

Manuscript received August 15, 2011; revised December 6, 2011; acceptedDecember 29, 2011. Date of publication January 27, 2012; date of currentversion March 9, 2012. This work was supported in part by the FederalUniversity of Uberlndia (UFU), Uberlndia, Brazil, by the University ofWollongong, Wollongong, Australia, through their infrastructure, and by CNPqthrough project 300671/08-3.

R. P. Reis and A. Scotti are with the Centre for Research and Development ofWelding Processes, Federal University of Uberlndia (UFU), 30400-902 Uber-lndia, Brazil (e-mail: [email protected]; [email protected]).

J. Norrish and D. Cuiuri are with the Welding Engineering ResearchGroup, University of Wollongong, Wollongong, N.S.W. 2522, Australia(e-mail: [email protected]; [email protected]).

Digital Object Identifier 10.1109/TPS.2012.2182781

apparent influence of the pulse synchronization on the process

stability is verified at higher leading angles.

With the electrodes positioned side by side (twin GMAW)

and the mean current below the transition level, out-of-phase

current pulses reduce the deviations of the arcs and influence

the penetration profile of the weld beads, but they are not

necessarily beneficial for bead formation [2]. Using the stan-

dard deviation of arc voltage in the pulse and backgroundperiods of current as evaluation criterion for arc stability in

twin GMAW, it is claimed that out-of-phase current pulses do

not have a statistically significant influence on the stability of

the arcs [2]. According to these studies, there is no evidence

that out-of-phase current pulses can impose any reduction in

arc and droplet attractions at high-current levels in the GMAW

processes with two wires [2], [3]. Andersson et al. [4] presumed

that synchronization is not necessary above 1215-mm inter-

wire distances, since, in their experiments, arc attractions were

not appreciable. For short interwire distances, they mention

that some synchronization is more important than the type of

synchronization itself [4]. Andersson et al. [4] also introduced a

fundamental stability mechanism in tandem GMAW apart fromarc interactions that are not often mentioned and weld pool

dynamics, which is related to the shape of the weld pool, as a

function of the interwire distance. Keeping the pool in a steady-

state standing wave is likely to result in a stable process and

high-quality welds. Scotti et al. [3] also investigated the rela-

tionship between pulsing current and pool oscillation, but they

concluded that the natural frequency of the pool determines the

process stability.

In most of the studies which deal with arc interactions,

stability assessment has been related only to bead formation and

spatter formation. However, the problems of arc interruption

and, therefore, oscillation in the amount of energy and moltenwire delivered to the plate have been observed during tandem

pulsed GMAW in experiments conducted by the authors of

this paper and also by Ueyama et al. [5]. One hypothesis

raised for this phenomenon linked it to the magnetic field

generated between the two adjacent arcs and their stiffness.

As a result of these magnetic fields and resultant forces, the

arcs are deflected toward each other depending on the operating

parameters (interwire distance, current level, shielding gas, etc.)

[5]. The present authors and Ueyama et al. [6] found that the

problem is more pronounced in the trailing wire.

External magnetic fields have, however, been used to control

welding arcs. Marques [7] built a device for this purpose but

0093-3813/$31.00 2012 IEEE

7/27/2019 06140585

2/7

REIS et al.: INVESTIGATION ON INTERRUPTIONS IN THE PRESENCE OF MAGNETIC FIELDS 871

found that the arc could be destabilized if the magnetic field

produced was too large. The concept of using an alternated/

external magnetic field to oscillate welding arcs was also

patented in the 1960s by Greene [8]. Currently available com-

mercial equipment uses controlled ac power supplies to oscil-

late the welding arcs.

Considering the importance of the subject and the lack ofmore comprehensive studies on arc interruptions during tandem

GMAW, the objective of this paper was to investigate the effect

of the welding current and direction of deflection in the stiffness

of welding arcs under the influence of external magnetic fields.

The intention is to correlate the outcomes of this paper with arc

interruptions that occur in tandem GMAW.

II. METHODOLOGY

Before detailing the methodology used to evaluate the factors

that govern welding arc interruptions, two basic points need to

be emphasized.

1) First, there is a basic electromagnetic effect. If an electri-

cal charge travels inside a magnetic field, it will be sub-

jected to a force with a defined direction and magnitude,

which changes the direction of the traveling charge and,

hence, the arc direction. A more detailed explanation has

been given in an earlier publication [9].

2) Second, when an interaction (attraction) between the arcs

takes place in tandem GMAW, it is difficult to attribute

a phenomenon to a unique cause, since many variables

and potential causes are often acting concurrently and are

themselves interrelated. When the pulsed-current mode

is used, for instance, the magnetic field generated by the

leading and trailing arcs is periodically changing and sothe size and stiffness of these arcs. Most importantly,

these features for each arc are changed by both their

own current magnitude and the magnetic field of the

neighboring arc. In the following work, stiffness is

taken to be the resistance of the arc column to be deflected

under the influence of a magnetic field.

Thus, in order to verify if the magnetic field generated by

one arc can be unambiguously responsible for extinguishing

the other arc in tandem GMAW, a simplified approach to the

problem is proposed. A single independently controlled GTAW

arc operating in constant-current mode is subjected to a sudden

change of external magnetic field. This mimics the effect on thesecond arc in tandem welding during the pulsing phase of the

first/leading arc. This procedure is used to assess the GTAW arc

resistance to extinction by the external magnetic field. With this

method, the influence of variables such as welding current level,

direction of deflection, arc length, electrode angle (trailing or

pushing the weld pool), high-frequency current pulsing, etc.,

on a single arc resistance to extinction could be independently

and repeatedly verified.

A. Experimental Rig for Tests With GTAW Arcs

Fig. 1 shows the experimental rig. In order to provide

the external magnetic field, an electromagnet was devised.A pair of wound copper coils from commercial contactors

Fig. 1. Rig used for the GTAW arc stiffness assessment.

(electromechanical switching devices) was used, and two mag-

netic cores were built by stacking thin sheets of silicon steel

(high magnetic permeability and low hysteresis) together, using

anaerobic adhesive. As detailed in the figure, the cores were

extended to maintain high magnetic flux density at the center

point between the coil poles. An adjustable 48-V dc powersource was used to provide the current necessary to produce the

magnetic field of desired magnitude. While the current flowing

through the electromagnet coils is responsible for generating

the magnetic flux density, the voltage applied on the coils

was taken as the experimental reference for the magnetic field

strength, as it is directly proportional to the coil current (Ohms

law) and is more conveniently measured.

The conversion from coil voltage (V) to magnetic fluxdensity (M) was reached by measuring (using a teslameter)the magnetic flux density for different coil voltages applied

(from 3 to 48 V). The probe was placed right in the center

of a 40-mm interpole distance (no arc), with a welding sample

placed 2 mm below the electromagnet. Magnetic flux densitiesas high as 7.2 mT were reached, which are comparatively

higher than the values (5 mT) used in magnetic arc oscillation

studies [10]. Equation (1) fits the points of the electromagnet

characterization (relationship between magnetic flux density

produced and voltage applied on the coils), with a correlation

index of 0.9993

M = 0.154 V 0.0946. (1)

The resultant magnetic flux density produced by the afore-

mentioned device would be a way of indirectly measuring the

magnetic field acting on the arc inasmuch as the actual magneticfield acting on the arc cannot be straight measured due to the

improper environment. One must take into account that the

electromagnetic field generated by the arc will interact with the

imposed magnetic field. Moreover, the magnetic flux density

obtained by (1) represents the magnetic field at the center of the

interpole distance, rather than the real spatial field distribution;

as the arc is deflected, the density of the magnetic flux acting

on its core reduces. Even considering these limitations, the

magnetic flux density acting on the arc was considered to be the

value at the center point of the interpole distance measured in

air, onward called apparent magnetic flux density. Moreover,

for a given welding condition, the higher the apparent magnetic

flux density required to extinguish the arc, the higher the arcstiffness (arc resistance to extinction).

7/27/2019 06140585

3/7


For the tests with arc, as seen in Fig. 1, an aluminum arm

(paramagnetic) held the electromagnet cores perpendicular to

the GTAW torch, perpendicular to the welding direction, and

adjacent to the arc region. A low-carbon-steel test plate (300 50 2 mm) was tightly preset 2 mm below the electromagnetand 10 mm above a moving welding table (at a welding travel

speed of 41 cm/min), while the torch and electromagnet stayedfirmly in place. The GTAW welding torch was mounted perpen-

dicular to the test plate, and an EWTh-2 electrode (diameter =2.4 mm; tip angle = 30) shielded by argon (14 L/min) wasused in DCEN with a secondary chopper electronic power

source. During the tests, the magnetic field was rapidly applied

when the arc was around the mean point of the test plate,

allowing enough time for arc stabilization. The effects of the

welding current level on the arc resistance to extinction were

evaluated with the arc being deflected backward and, in terms of

comparison, also with the arc being deflected forward. For each

current level assessed, the voltage applied on the electromagnet

that produced the magnetic field capable of extinguishing the

arc was registered and then converted to apparent magnetic

flux density through (1). High-speed filming synchronized with

the arc electrical transients at 2000 Hz was carried out as an

additional tool to investigate the deflections and extinctions.

III. EXPERIMENTAL PROCEDURES,

RESULTS, AN D DISCUSSIONS

A. Welding Current Influence on Arcs Deflected Backward

For each value of welding current, the magnetic flux density

was progressively increased up to a point where the arc was

extinguished. For each current value, the voltage applied onthe electromagnet was increased in 1-V steps. A longer than

usual arc length (10 mm) was used to ensure that the magnetic

flux density range provided by the electromagnet would be

able to extinguish the arc (higher sensitivity) in all tests. If the

extinction occurred, the voltage was increased by 1 V again,

and another test was carried out to confirm that the region of

arc extinction had indeed been reached. The voltage value of

1 V below this last level was considered for the GTAW arc

resistance to extinction (arc extinction limit), as recorded in

Table I.

As shown in Fig. 2, the arc extinction limit curve has a

slightly parabolic tendency for the current range tested; thehigher the electrical current flowing through the arc, the more

the arc resists to the extinction. This type of result was expected

considering the fact that the welding current is responsible for

the formation of plasma jet [9] and for arc stiffness as pointed

out by Lancaster [11]. However, the overall situation is not

so straightforward. As the current rise gives more stiffness to

the arc, it also increases the magnetic force acting on the arc.

As the magnetic force acts on each charged particle, the arc

is deflected as soon as it leaves the electrode. The intensity of

the resultant deflection is a balance; the self-induced magnetic

field associated with the arc generates the plasma jet, and the

external magnetic field (from an external source, from another

arc, or from an unbalanced magnetic field that produces arcblow) deflects the arc.

TABLE IWELDING CURRENT VALUES EVALUATED AND RESPECTIVE

APPARENT MAGNETIC FLUX DENSITIES NEEDEDTO CAUSE THE GTAW ARC EXTINCTION

Fig. 2. Relationship between GTAW current and resistance to arc extinctionwhen the arc is deflected backward (arc length = 10 mm).

As discussed by Reis et al. [9], if a welding arc is deflected

by a magnetic field, it changes its path and so its plasma jet

direction. In addition, since the magnetic field force is directly

related to the charged particle velocity, in other words, to the

welding current, the gain in plasma jet intensity by raising the

current could be counteracted by the increase in magnetic force

and consequent arc deflection. High arc deflections may lead

to a higher risk of extinction. Thus, the effect of the welding

current on the arc resistance to extinction might be relatedto effects beyond the plasma jet. Because of the parabolic

tendency observed, these effects might be nonlinear, as is the

plasma jet effect.

Fig. 3 shows how a GTAW arc set at 50 A is extinguished.

In order to make any effect more evident, the electromagnet

voltage was set at 19 V (2 V more than the arc extinction limit).

As the magnetic flux density produced by the electromagnet is

raised (as indicated by the electromagnet voltage), the arc is

deflected. At various times, there were spikes in the arc voltage

signal, where arc extinction appears imminent. For some rea-

son, the arc recovers and resists extinction as the electromagnet

voltage continues to rise. At a certain point, the arc is deflected

so far that the electrical circuit is broken, that is, the arc isextinguished. This is most likely to occur when the arc voltage

7/27/2019 06140585

4/7


Fig. 3. Arc extinction at 50 A; arc deflected backward (arc length = 10 mm).

Fig. 4. Regions close to the electrode and plate being the last to disappear(detail of Fig. 3).

approaches the open circuit voltage of the welding power

source, so the power source is no longer able to maintain currentflow through the arc. Consequently, the arc voltage rises to

the open-circuit-voltage value, while the welding current drops

to zero. The regions close to the electrode and plate give the

impression to be the last to be extinguished (detailed in Fig. 4),

and the arc seems to be broken somewhere in the arc column.

It is important to mention that, despite the fact that the arc

operated in a spot mode at the attachment with the work piece,

none of the high-speed videos showed any perceptible arc

jumping or walking action. It was noticed from the sequence

of high-speed images that the arcs expanded and contracted

during the rapid spikes (kinking action), but the position of

attachment to the work piece remained the same. Thus, thedisplacement of the area of connection between the arc and

work piece seen in the figures presented in this paper is a result

of magnetic deflection dynamics.

As shown in Fig. 5, at a welding current of 95 A, the arc was

extinguished in the same way as shown in Fig. 3. However,

it required more extensive deflection, which, in turn, required

a greater rise in the magnetic flux density to be applied. In

this case, the electromagnet voltage was set at 32 V (2 V

over the arc extinction limit). Just before being extinguished,

the arc again showed signs of imminent extinction through

voltage spikes, similar to those observed in the case for a

welding current of 50 A (Fig. 3). A larger number of these

voltage spikes were observed near the arc extinction limit(electromagnet voltage at 30 V).

Because the arc contains charged particles (electrons and

ions), if it is subjected to an external, perpendicular, and

uniform magnetic field, these charged particles experience a

magnetic force that is always perpendicular to both the velocity

of the particle and the magnetic field that created it; this creates

a curved path called cyclotron motion [12]. This effect is

evident in the shape of the arc leaving the electrode tip (region

1 in Fig. 6) when it is deflected. However, at a certain point

along its extension, the arc must change its direction as it needs

to reach the plate to maintain the welding circuit (region 2 in

Fig. 6). The distinction between these paths gets more evidentas the arc deflection progresses.

Fig. 7 shows the event in more detail (at 50-ms intervals). In

this case, a 50-A arc was subjected to a magnetic field well

beyond (10 V over) the arc extinction limit. Even with the

much more intense magnetic field, the same small spikes were

observed in the voltage signal just before arc extinction. In this

case (a 50-A GTAW arc subjected to a 27-V electromagnet

voltage), the extinction took place when the arc voltage reached

approximately 54 V. By zooming in on the time when a 50-A

arc was extinguished by a 19-V electromagnet voltage (Fig. 3),

it was verified that the arc was extinguished at around 52 V.

These values indicate that the arc voltage at the extinction

moment might be independent of the magnetic flux density.

In fact, extra tests with 120-A GTAW arcs deflected backward

showed that the arc voltage at the extinction moment ranged

from 38 to 47 V regardless of the magnetic flux density applied.

Fig. 8 shows the arc voltage values at the moment of ex-

tinction for various values of welding current. Again, a random

effect was observed, which indicates that there is no influence

of the welding current on the arc voltage value when the arcs are

extinguished. However, there seems to be a voltage range within

which the arc extinction takes place (3757 V). It is worth

noting that the exact moment that the arc is truly extinguished

is very difficult to determine since all the images presented here

deal with the visible light emitted by the arc, which depends onoptical filters used, camera shutter speed, etc. However, to be

7/27/2019 06140585

5/7


Fig. 5. Arc extinction at 95 A; arc deflected backward (arc length = 10 mm).

Fig. 6. Characteristic shape assumed by the arc when it is largely deflected in

consequence of an intense and external magnetic field.

Fig. 7. Arc extinction at 50 A when the arc is deflected backward by amagnetic field much greater than thearc extinction limit (arc length = 10 mm).

consistent throughout this paper, the moment of arc extinction

was always considered as the point where the welding currentstarts to fall to zero.

Fig. 8. Arc voltage values at the moment of extinction by backward deflectionfor various welding current levels.

Despite using GTAW arcs in this work, the results found here

match the results from Ueyama et al. regarding the influence of

base current level in the number of arc interruptions occurring

in tandem pulsed GMAW [5], [6], [13]. Ueyama et al. showed

that the number of interruptions falls as the base current is

raised. This agrees with the trend observed in the results pre-

sented earlier, demonstrating a markedly increased resistance

to arc extinction as the welding current is increased (Fig. 2).

B. Welding Current Influence on Arcs Deflected Forward

The same approach applied in Section III-A was duplicated

for these tests where the arc is deflected forward. Table II shows

the current values observed and the respective magnetic flux

densities needed to cause arc extinction in each case. Fig. 9

shows how the arc extinction limit curve changes when the arc

is deflected forward.

Compared to the situation where the arc is deflected back-

ward, the arc extinction limit curve for forward deflection is

slightly lower. This displacement becomes even more pro-

nounced as the current flowing through the arc is increased.There seems to be no straightforward explanation for this effect.

7/27/2019 06140585

6/7


TABLE IIWELDING CURRENT VALUES EVALUATED AN D RESPECTIVE

APPARENT MAGNETIC FLU X DENSITIES NEEDEDTO CAUSE THE GTAW ARC EXTINCTION

Fig. 9. Relationship between GTAW current and resistance to arc extinctionwhen the arc is deflected forward (arc length = 10 mm).

Fig. 10. Comparison between extinctions of arcs deflected (top images)forward and (bottom images) backward under the same welding conditions.

However, it may be related to the interaction between the arc

and the weld pool and/or plate, since the condition of the

surface where the arc meets the plate, as it is deflected and

eventually extinguished, might be different for each case. In thecase where the arc is deflected backward, higher temperatures

exist over the molten metal or the heated surface if the arc is

deflected beyond the weld pool. For the case where the arc is

deflected forward, the arc is deflected toward the cold plate

surface. The more pronounced effect at high-current levels may

be related to higher temperature differences between the regions

ahead and under the arc in this case.

Fig. 10 compares the extinctions of arcs deflected forward

and backward under the same welding conditions. Both extinc-

tions followed similar patterns. Despite working with visible

light emitted from the arc (and the corresponding risk of

misinterpretation), the heat from the plate close to the arc may,

in fact, contribute with metal vapor to assist arc ionization,thus improving its resistance to extinction. The fact that the arc

is deflected forward does not seem to have any effect on the

arc voltage values when the extinctions take place. The values

were randomized and also tended to fit in the arc voltage range

defined in Fig. 8.

Despite the differences between the welding situations in

the tests being conducted with GTAW arcs and in the case of

common tandem GMAW arcs, the results presented here agreewith previous findings for arc interruptions in tandem GMAW.

For Ueyama et al. [5], [6], [13], in tandem GMAW, trailing

arcs are more prone to interruptions than leading ones. In the

case of the present work, when the arc is deflected forward, it is

comparable to the case in tandem GMAW where the trailing arc

is deflected or pulled forward by a high current in the leading

arc. Similarly, the arc deflected backward in the experiments

presented here is comparable to the case in tandem GMAW

where the leading arc is deflected or pulled backward by

a high current in the trailing arc. However, the explanation

adopted in this paper for the differences in resistance to ex-

tinction of GTAW arcs deflected forward and backward cannot

be sustained for the tandem GMAW arc case. During tandem

GMAW, the arcs, whether deflected forward or backward, are

always over the molten metal or the work piece heated surface.

There are clear differences between the tandem GMAW

process and the GTAW experiment used, which include differ-

ences in the arc length, the presence of a second energy source

(second arc) on the work piece, the frequency of the magnetic

field oscillations, etc. All these differences might have led to

overlooking key factors that may determine the reason for the

incidence of more arc interruptions in trailing arcs in tandem

GMAW. It must also be remembered that the cathode in the

GTAW system is a thermionic emitter unlike the plate cathode

in GMAW and, in addition, that the thermal conditions in atandem GMAW situation are unlike those of a single GTAW

arc. Thus, the reason for the occurrence of more arc interrup-

tions in trailing arcs in tandem GMAW remains unclear, and

the complexity of this welding process (two intimate electrical

arcs) still stands as a challenge to fully understand this issue.

IV. CONCLUSION

Considering the results presented and discussed, the conclu-

sions can be summarized as follows.

1) Welding arcs affected by magnetic fields as in tandem

GMAW, magnetic arc oscillation, etc., can be readilyextinguished or interrupted if the magnetic flux density

is high enough.

2) The resistance to arc extinction is increased as the arc-

ing current is also increased, regardless of the direc-

tion of deflection (forward or backward). This explains

why tandem GMAW trailing arc interruptions can be

avoided by increasing the current in the trailing arc when

the magnetic field produced by the leading arc is high

(pulse current level), which is actually achieved by using

almost-in-phase current pulses.

3) The resistance of the GTAW arc to extinction seems to be

affected by the direction of deflection, with arcs deflected

backward slightly offering more resistance to extinctionsthan those deflected forward.

7/27/2019 06140585

7/7


4) The arc voltage values at the moment of extinction do not

seem to be dependent on the strength of the externally ap-

plied magnetic field nor are the voltage values dependent

on the welding current level used. However, all the arcs

tended to be extinguished within a range of voltages, well

above values measured in normal steady-state operation.

5) The arc voltage at extinction is likely to be affected bythe power source dynamic characteristics, and this may

account for the scatter in the arc extinction voltages.

REFERENCES

[1] B. Y. B. Yudodibroto, M. J. M Hermans, and I. M. Richardson, The In-fluence of Pulse Synchronisation on the Process Stability During TandemWire Arc Welding, IIW Doc XII-1910-06.

[2] M. F. Motta, J. C. Dutra, R. Gohr, Jr., and A. Scotti, A study on out-of-phase current pulses of the double-wire MIG/MAG process with insulatedpotentials on coating applications, Welding Cutting, vol. 4, no. 1, pp. 2632, 2005.

[3] A. Scotti, C. O. Morais, and L. O. Vilarinho, The effect of out-of-phasepulsing on metal transfer in twin-wire GMA welding at high current

level, Welding J., vol. 85, no. 10, pp. 225230, 2006.[4] IIW Doc. No. XII-1895-06 J. Andersson, E. Tolf, and J. Hedegrd, The

Fundamental Stability Mechanisms in Tandem-MIG/MAG Welding, andHow to Perform Implementation.

[5] T. Ueyama, T. Onawa, M. Tanaka, and K. Nakata, Occurrence of arcinterference and interruption in tandem pulsed GMA weldingStudy ofarc stability in tandem pulsed GMA welding (Report 1), Quart. J. Jpn.Welding S oc., vol. 23, no. 4, pp. 515525, 2005.

[6] T. Ueyama, T. Uezono, T. Era, M. Tanaka, and K. Nakata, Solution toproblems of arc interruption and arc length control in tandem pulsed gasmetal arc welding, Sci. Technol. Welding Joining, vol. 14, no. 4, pp. 605614, May 2009.

[7] P. V. Marques, Desenvolvimento e avaliao de um sistema para sol-dagem TIG mecanizada, M.S. thesis, Univ. Federal Minas Gerais,Belo Horizonte, Brazil, 1984.

[8] W. J. Greene, Magnetic Oscillation of Welding Arc, US Patent2 920183, Jan. 1960.

[9] R. P. Reis, D. Souza, and A. Scotti, Models to describe plasma jet, arctrajectory and arc blow formation in arc welding, Welding World, vol. 55,no. 34, pp. 2432, 2011.

[10] Y. H. Kang and S. J. Na, A study on the modeling of magnetic arcdeflection and dynamic analysis of arc sensor, Welding J., vol. 81, no. 1,pp. 813, 2002.

[11] J. F. Lancaster, The Physics of Welding, 2nd ed. Oxford, U.K.: PergamonPress, 1986.

[12] R. L. Stenzel, Single Particle Motion in Electric and Magnetic Fields,accessed in April 12, 2011. [Online]. Available: http://www.physics.ucla.edu/plasma-exp/beam/

[13] T. Ueyama, T. Ohnawa, T. Uezono, and M. Tanaka, Solution to problemsof arc interruptionand stablearc lengthin tandempulsed GMA weldingStudy of arc stability in tandem pulsed GMA welding (Report 2),Welding Int., vol. 20, no. 8, pp. 602611, 2006.

Ruham Pablo Reis, photograph and biography not available at the time ofpublication.

Amrico Scotti, photograph and biography not available at the time ofpublication.

John Norrish, photograph and biography not available at the time ofpublication.

Dominic Cuiuri, photograph and biography not available at the time ofpublication.

Documents

06140585