Upload
galahad666
View
214
Download
0
Embed Size (px)
Citation preview
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
872 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 3, MARCH 2012
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
REIS et al.: INVESTIGATION ON INTERRUPTIONS IN THE PRESENCE OF MAGNETIC FIELDS 873
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
874 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 3, MARCH 2012
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
REIS et al.: INVESTIGATION ON INTERRUPTIONS IN THE PRESENCE OF MAGNETIC FIELDS 875
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
876 IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 40, NO. 3, MARCH 2012
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.