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AdvancedgasmetalarcweldingprocessesARTICLEinINTERNATIONALJOURNALOFADVANCEDMANUFACTURINGTECHNOLOGYJULY2012ImpactFactor:1.78DOI:10.1007/s00170-012-4513-5
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ORIGINAL ARTICLE
Advanced gas metal arc welding processes
P. Kah & R. Suoranta & J. Martikainen
Received: 2 May 2012 /Accepted: 11 September 2012 /Published
online: 30 September 2012# Springer-Verlag London Limited 2012
Abstract There is an increased requirement in the automo-tive,
food and medical equipment industries to weld heat-sensitive
materials, such as thin sheets, coated thin plates,stainless steel,
aluminium and mixed joints. Nevertheless,relevant innovations in
arc welding are not widely knownand seldom used to their maximum
potential. In the area ofgas metal arc welding welding processes,
digitalisation hasallowed integration of software into the power
source, wirefeeder and gas regulation. This paper reviews
developmentsin the arc welding process, particularly the effect of
the set-up of the welding process parameters on waveform
deposi-tion. It is found that good weldability, good mechanical
jointproperties and acceptable process efficiency can be
obtainedfor thin sheets through advanced power source
regulation,especially over short circuiting, controlled polarity
and elec-trode wire motion. The findings presented in this paper
arevaluable for waveform and deposition prediction. The needis
furthermore noted for an algorithm that integrates gasflow
parameters and wire motion control, as well as avariable sensor on
the tip of the electrode, permitting flex-ibility of control of the
current and the voltage waveform.
Keywords Arc welding processes . GMAW . Low heatinput .
Productivity . Transfer mode .Waveform . Current .
Voltage
1 Introduction
Arc welding is a group of welding processes in which thearc
generated by electric power is used to melt the wire andweld pool
to allow the joining of parts. However, the
process can face difficulties in welding some materials.The need
to widen the range of weldable materials and toincrease
productivity has contributed to new arc weldingprocesses
modifications. Although the modifications techni-ques were
introduced at the end of the nineteenth century,widespread
implementation of the arc welding process wasnot possible because
of the poor capability of power sourcesto control and provide the
required dynamic and staticcharacteristics. The need to develop the
gas metal arc weld-ing (GMAW) process became associated with
technologicaldevelopment of the power source.
In vehicle construction work, joints between steel andaluminium
are also increasingly being used. In the iron/aluminium phase
diagram, iron or steel and aluminium offervirtually no solubility
with one another. In each mixed ratio,Fe/Al phases occur with
brittle characteristics. Experiencetherefore shows that a
proportion of Al/Fe phases in themolten material of over 10 % must
be avoided in all cases.When using zinc as the filler material, a
joint can be createdbetween these two materials, where the
aluminium is par-tially melted, whereas the steel, to avoid
brittleness in themolten material, may only be moistened. This
means that awelded joint is created on one side and a brazed joint
on theother [1].
The pulse gas metal arc welding (GMAW-P) method canbe used for
any type of ferrous as well as non-ferrousmaterial, even for sheet
metal welding and positional weld-ing, which is very much
challenging with other weldingprocesses. It can reduce corrosive
tendency, hot cracking,spattering and distortion due to the pulsed
nature of current.However, this process depends greatly on the
right selectionof pulse parameters, as the latter affect the weld
microstruc-ture and porosity content of the weld due to their
influenceon weld thermal cycle and arc characteristics [2].
Modern welding power sources have benefited fromdevelopments in
electronics and the introduction of thyris-tors, transistors and
other components. The transistor, for
P. Kah (*) : R. Suoranta : J. MartikainenLappeenranta University
of Technology,P. O. Box 20, 53851 Lappeenranta, Finlande-mail:
[email protected]
Int J Adv Manuf Technol (2013) 67:655674DOI
10.1007/s00170-012-4513-5
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example, can be used as a variable resistor or as an elec-tronic
switch and modern power sources can include anelectronically
analogue controlled chopper or an inverter.This technology has
widened the range of adjustments in thepower source, made welding
suitable for robot applications,and enabled the digitalisation of
feedback from millisecondto nanosecond and intelligent control of
the welding pro-cess. The inverter is a key improvement in the
modern powersource because it quickly responds to digital feedback
controland it has dramatically changed the features of arc control
[3,4]. This study focuses on the principles behind the
newprocesses, highlighting the key improvement in terms ofdroplet
transfer mode control, current and voltage control,wire feeder
control and gas shielding control. A comparisonof each process is
made with the traditional GMAW processand between the different
approaches.
Figure 1 shows the metal transfer mode function of thewelding
voltage (V) and current (A) outputs, which determine
the type of the arc process because their values directly
influ-ence the droplet transfer mode and the stability of the
process.The main difficulty with conventional power sources
wascontrol of these variables during the process. Electronic
anddigital controls enhance the accuracy of the arc. In the
1990s,developments in computer technology made possible thedesign
unlimited amount of waveforms aimed to improvethe timing of arcing
and metal deposition [3, 4].
The metal transfer mode is controlled by power outputregulation.
The International Institute of Welding proposedin 1976 a
classification of droplet transfer and welding pro-cesses (Table 1)
published later by [5, 6]. Technologicalinnovation brought
variation to the welding process and [7]proposed a reassessment of
welding with three main catego-ries: natural metal transfer,
controlled transfer and extendedoperating techniques (Tables 2 and
3) [8].
In earlier wire feeds, the motion was constant and thewire speed
was adjusted to the process. New developmentshave synchronised both
the power source and the wirefeeder to reach an optimised molten
material transfer mode.The process is called, mechanically assisted
droplet depo-sition, which is applied in controlled short circuit
byretracting the wire from the short circuiting [9, 10].
Inaddition, the contact tip-to-work distance (CTWD) is inte-grated
into the control of the arc welding process so that thearc length
is not disturbed by the irregularity of the surfacewelded and
handling monitoring during the manual process[11]. Another
important factor in the welding process iscontrol of the shielding
gas. Regulation of the flow hasbecome part of the algorithm to
optimise the flux accordingto requirements sensed on the tip and
weld pool [12].
The aforementioned innovations have given more optionsto the
welder; rather than following pre-set welding parame-ters
established during design of the power sources, determi-nation of
the welding parameters now depends on theelectronic control or the
computer. This improvement hasgiven rise to new opportunities in
welding heat-sensitivematerials, such as aluminium and stainless
steel, and enabled
Fig. 1 Arc types and their working ranges, solid wire (d01.2
mm)shielding gas: argon-rich mixtures [5]
Table 1 IIW classification ofmetal transfer [6] Transfer modes
Welding process
Free flight transfer Globular Drop Low current GMA
Repelled CO2 shielded GMA
Spray Projected Intermediate current GMA
Stream Medium current GMA
Rotating High current GMA
Explosive SMA (coated electrode)
Bridging transfer Short-circuiting Short arc GMA
Bridging without interruption Welding with filler wire
addition
Slag protected transfer Flux wall guided SAW
Other modes SMA, cored wire, electroslag
656 Int J Adv Manuf Technol (2013) 67:655674
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joining of dissimilar materials and thin sheets or plate
materi-al. The precision and flexibility of machine control has
made itpossible to apply a variety of methods and has also
permittedoptimisation of the choice of electrode diameters,
shieldinggas and material quality, with a significant impact on
both theeconomics of welding and service reliability [8].
The need to increase productivity has resulted in thedevelopment
of high-power range transfer modes. Oneexample of such a transfer
mode is the rotating arc, whichis mainly performed in the T.I.M.E
or RapidMelt [13, 14]process. Distortion, a consequence of the high
energy load,is, however, one of the limits of the process.
2 Advanced power source regulation
This section identifies the main advances that have occurredin
power source regulation of the short circuiting process.The designs
of new arc welding processes aim to overcomethe limitations of
traditional short arc waveform by enablingnew shapes of the arc
curve. The power sources benefit fromenhancement in digital control
and upgraded software,which enables monitoring of every aspect of
the arc. Theshort circuiting is predictable and can be set at a
specifictime. Moreover, the molten material transfer can be
handledso that spatter is minimised.
2.1 WiseRoot process
The WiseRoot process is a metal inert gas (MIG)/metalactive gas
(MAG) modified short arc circuit welding process
developed by KEMPPI Company and is based on control ofthe power
source. An initial version of the process was firstintroduced in
2005 and was called FASTRoot. Recently, thewelding devices and
software were coupled and the processrenamed WiseRoot. The power
source control enables reg-ulation of the short circuit and allows
accurate timing of thetransmission of the filler drop from the
filler into the weldpool. The prefix wise indicates a new approach
whichintegrates improvement in efficiencies and a brand newwelding
process supported by software. The concept com-prises the elements
WiseRoot, WiseThin, WisePenetrationand WiseFusion. In this paper,
attention is, however, givenprimarily to the two first concepts
which make up the newshort arc mode [1517].
In the WiseRoot process, the power source is monitoredby the
wave of the current, which can be analysed in twomain parts; the
short circuit and the arc period (see Fig. 2).In the short circuit
period, the filler wire is transmitted to theweld pool that
materialises on the current curve by a shortpeak at the time when
it contacts the weld pool. The currentis maintained at this
required level to permit the step to becompleted. The current then
increases suddenly, to makedrop detachment possible from the filler
material. The drop-let is formed by maintenance of the current at
that levelduring a certain period of time, followed by a
moderateddecrease of the current till the detachment occurs. As
soonas the transmission to the weld pool has occurred, a
secondphase of the current increase begins and initiates the
arcperiod [15, 16].
The arc period is initiated by an increase of the current tothe
desired level, forming the weld pool and guaranteeing
Table 2 Classification of controlled transfer mode [8]
Metal transfer modes Welding process
Controlled spray Pulsed transfer GMAW using variable frequency
pulse and drop spray transfer
Controlled short circuiting Current controlled dip transfer GMAW
using current controlled power source
Controlled wire feed short circuit mode GMAW with wire feed
oscillation
Table 3 Classification forextended operating modestechniques
[8]
Metal transfer modes Application
Short circuiting GMAW Extended stick out GMAW High deposition
short circuit transfer GMAW
Low frequency pulsed Pulsed mean current for gap filling
Pulsed transfer GMAW Multi-wire Multi-wire GMAW
Low frequency pulsed Modulated pulsed transfer welding of
aluminium
Variable polarity Welding of thin sections and single sided root
runs
Spray transfer GMAW Rotating spray High current extended stick
out
Electrode negative Flux cored wire or special gas mixture
Spray transfer SAW Electrode negative
Extended stick out
AC/variable polarity
Int J Adv Manuf Technol (2013) 67:655674 657
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the penetration of the weld root. The current is then reducedto
an appropriate level to ensure timely formation of thedroplet
during the next short arc [15, 16]. Table 4 presentsan example of a
root pass when welding an X65 pipe. Theprocess allows satisfactory
joints to be achieved with reducedheat input [18].
WiseThin is a MIG/MAG welding process which can beconsidered as
an extension of WiseRoot. The principle isthe same, i.e. usage of a
modified short arc. However,WiseThin differs from WiseRoot in that
it is optimised forwelding of sheet metal [16]. The process is
capable ofachieving similar welds with 525 % less heat input than
aconventional short arc and maintains the same heat input asa laser
welding process [16].
2.2 Surface tension transfer process
Surface Tension Transfer (STT) [19], invented by
LincolnElectric, is a GMAW process based on control of the
shortcircuit transfer process. The process performs withoutchanges
to the voltage settings. Instead, the heat is adjustedby current
control independent of the wire feed speed.Therefore, the change in
electrode length has no consequen-ces on the heat value [20]. STT
devices are equipped withelectronic technology which enables
optimisation of thewaveform and arc characteristics for a specific
application.In addition, the setting programme integrates relevant
factor,such as the joint type, material and thickness, rate of
travel,electrode size and type, as well as the specific arc
shieldinggas. The process is claimed to combine the best aspects
ofthe short arc and TIG processes in a single process [21].
The current control follows a particular waveform, thecurve can
be considered in four main stages that correspond
to the five states of the droplet and the arc. Figure 3 showsthe
waveform and images from a high-speed camera of thetip of the drop
detachment from the filler wire to the weldpool and the re-ignition
of the arc. The process can bedetailed as follows [20]:
& Background current: The background current is in arange
from 50 to 100 amps to keep the arc, as shownin A, in an arc
burning period and to heat the base metal.When the filler wire is
in contact with the weld pool inB, the current is suddenly
decreased to form the droplet.
& Pinch current: The pinch current is applied to permit
thedetachment of the molten filler while monitoring theshrinking
section in C. In D, when the detachment islikely to occur, the
power source control reacts byreducing the current to about 4550 A
to allow a smoothbreak of molten metal from the tip of the
electrode.
& Peak current: The peak current is applied, in E, just
afterthe drop has separated, to allow generation of the plasmathat
pushes the weld pool down, to avoid unexpectedshorting, and to heat
the puddle and the joint.
& Tail-out: The tail-out following E is an
exponentialdecrease by the current control to regulate and
initiatethe next detachment and re-ignition from the back-ground
current.
Table 5 shows examples of results from experimentsperformed on
high-strength low-alloy SA 516 of 5 mmthickness and on a 15Mo3
steam boiler component. Thestudies [20, 21] showed the usability of
STT on sensitiveheat material with CO2 as shielding gas, in the
first case, butalso with an argon and CO2 mixture. In addition, the
resultsshowed directly proportional changes in the fume emissionof
STT with wire feed speed. Analyses of the weld bead
Fig. 2 Current waveform ofWiseRootconventionalshort arc and
sequence ofthe arc [15]
Table 4 Example welding parameters with the WiseRoot process
References Material Groove Wire Shielding gas Wire
speed(m/min)
Welding speed(m/min)
Position
[18] X65 V 50 1.0 LMN Ni1 Ar+18 % CO2 3.53.9 75130 D0780 mm
Width (4.5 mm) and
height (0.5 mm)t045.5 mm
(Pipe)
Structural steel tube I gap 4 mm 1.0 mm G3Si1 3.0 or 2.8
Vertical positionup to downD0110 mm
t04 mm
658 Int J Adv Manuf Technol (2013) 67:655674
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revealed better penetration and superior microhardness.STT
showed the lowest fume formation rate and excellentweld bed
geometry at higher wire feed speeds [22]. Theprocess was
successfully applied in steam boiler produc-tion, with acceptable
joint output quality and higher effi-ciency in the root pass
compared to a conventional GMAWprocess [23].
2.3 Regulated metal deposition (RMD) process
Miller Electric Mfg. Co introduced, in 2004, a new
weldingtechnology process called RMD or regulated metal
deposi-tion. The technology is based on an advanced
softwareapplication for modified short circuit transfer GMAW(MIG
welding) that monitors the electrode current in eachstep of the
short circuiting. The wave profile depends on thematerial being
welded, although the typical waveform shaperemains, as shown in
Fig. 4. The RMD approach is illus-trated in different steps as
follows [24]:
& Wet: Let the ball on the end of the wire wet-out to
thepuddle.
& Pinch: Increase the current to a level high enough
toinitiate a pinch effect.
& Clear: Maintain and slightly increase the pinch current
toclear the short circuit while simultaneously watching forpinch
detection.
& Blink: Upon pinch detection, rapidly decrease the
cur-rent. Pinch detection occurs before the short clears.
Theinverter shuts off and current decays to a low levelbefore the
short circuit breaks.
& Ball: Increase current to form a ball for the next
shortcircuit.
& Background: Drop the current to a low enough level toallow
a short circuit to occur.
& Pre-short: If the background current exists for a
rela-tively long time, the pre-short period drops current to aneven
lower level to make sure arc force does not pushthe puddle back
(e.g. prevents excess agitation).
According to the manufacturer, the RMD softwareprogramme,
working with an inverter-based welding systemand closed-loop
feedback, closely monitors and controls theelectrode current at
speeds up to 50 s (50 millionths of asecond). Moreover, the
software accurately adjusts the re-quired speed and gas combination
for a specific wire diam-eter. Thus, based on the heat history of
the tips, it predictsfuture arc conditions and controls the droplet
transfer ac-cordingly [24, 25]. Table 6 presents an example of
RMDuse, showing the ability to weld line pipe alloy steel P5Band
P91 grade with a significant drop in heat input. Thedecrease in
heat input also benefits line pipe carbon steelX52 grade [26].
Experiments with the process on a nickelalloy have also resulted in
a successful root pass [27].
Fig. 3 Current waveformcontrol of STT andcorresponding drop and
shortarc images [22]
Int J Adv Manuf Technol (2013) 67:655674 659
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2.4 Cold Arc process
The Cold Arc concept is a controlled short circuiting
metaltransfer mode patented by EWM Hightec Welding GmbH
andpresented in 2004. The new MIG/MAG welding process
takesadvantage of a new type of highly dynamic inverter
switching,combined with very fast digital current control. The
digitalsignal processor is used to control the instantaneous
extractionof the power just before re-ignition in a period of less
than 1 s;the peak power in the arc is dramatically reduced when
theshort arc is re-ignited [28]. Figure 5 compares the waveform
ofthe conventional and the Cold Arc process. The first two stepsare
similar to conventional short circuiting; during the arcburning
phase, the electrode approaches the work piece withthe current and
voltage maintained at the required steady level.The arc phase stops
when the electrode touches the work piece.Then the voltage drops
suddenly to almost zero, while thecurrent increases sharply to
allow the pinch effect. The currentis decreased dramatically to
permit a smooth break of the bridgeof the molten metal, preventing
spatter. Immediately after thearc ignites, the outputs is reduced
(Fig. 5a) in a dynamic andcontrolled way. After the arc has been
stabilised, the current israised slightly for a defined short
period of time, known as meltpulse, to create a regular separation.
In addition, the melt pulsecreates a melting cone on the edge of
the electrode, thereforeguaranteeing smooth continuity of the
process [28].
The Cold Arc process has been applied in butt jointing ofthin
sheet plate aluminium grades such as 6XXX, 2XXXand 5XXX, presented
in Table 7. Although the manufacturerclaims other material grade,
the experiment on aluminiumshowed improvement within standard range
concerningmechanical and micro-structure of the joint. Cold Arc,
inlimited condition of iron/aluminium diagram phase exhibitsability
of mixed joint [29].
2.5 ColdMIG process
The ColdMIG process is patented byMERKLE. The process isa
modified short arc process enabled by the use of software tomonitor
the waveform. The application is one of the options inTa
ble5
Examplewelding
parameterswith
theSTTprocess
References
Material
Groove
Wire(m
m)
Shielding
gas
Wirespeed
(m/m
in)
Welding
speed
(m/m
in)
Peakcurrent
Background
current(%
)Volt
Gas
flow
rate
(L/m
in)
[22]
HSLAASA516
Beadon
plate
1.2
CO2
5.00
250
100(40)
1710
FCAW
with
STTmode
5mm
AWSA5.29,Class
E110T5-K
46.24
125(50)
20
7.51
150(60)
23
8.76
175(70)
26
10.00
200(80)
29
[23]
15Mo3
(steam
boiler)
Buttjoint
Ar+
18%
CO2
3150
265
6515
Fig. 4 a RMD current waveform and b current wave Form [24]
660 Int J Adv Manuf Technol (2013) 67:655674
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a multi-process power source. The process is characterised
byoptimization of the voltage and current waveform. Figure 6shows,
in the same frame, a conventional short circuit and theColdMIG
curve. During the short circuit cycle, considerableincrease in the
current reduces the voltage to about zero to allowthe droplet
detachment. The short circuit period is dramaticallyreduced
compared to a conventional short arc, which gives anew shape to
thewaveform in this section, for voltage aswell ascurrent waveform.
The time of the current in this period isreduced and occurs faster.
The consequence is that the shortcircuiting cycle is considerably
reduced, which leads to a dropin heat input generated by the short
arc [30, 31]. Furthermore, topermit a smooth break of the molten
bridge and a stable start ofthe arc, the current is dramatically
decreased during the transi-tion between the molten metal
detachment and the re-ignitionof the arc [31].
2.6 Intelligent Arc control process
Intelligent Arc Control (IAC) is a modified short arc
process;the result of 3 years research by Migatronic and released
in2010. The process benefits from the latest improvements
ininverters and digital control. IAC registers every welding
cycleand adjusts the arc 50,000 times per second. The
softwaremodels and optimises dynamical parameters of the short
arc,
resulting in a highly stable and focused short arc, colder
weld-ing, lower heat input, less distortion and lower power
consump-tion. In addition, the process includes intelligent control
of theflow shielding gas rate [32, 33].
The typical current and voltage waveforms of IAC, shownin Fig.
7, are significantly different from those of a conven-tional short
circuit. During the arcing cycle, the voltage ismaintained at a
considerable level while the current is sharplydecreased and after
the re-ignition steadily reduced to a lowlevel. In this stage, in a
conventional short circuit, both thecurrent and voltage are
maintained at a right level. During theshort circuiting cycle, the
voltage is dramatically reduced andthe current is increased to
allow the pinch effect. After reach-ing the peak, the current and
voltage are suddenly reduced fora cold transfer of the molten metal
and stable transition for there-ignition of the arc. Table 8
presents an example of setting ofmild steel suggested by the
manufacturer. The manufacturerclaims the arc control for mild
steel, stainless steel and othergrades in the software package [32,
33].
2.7 Super-imposition process
The Super-imposition (SP-MAG) process is a modifiedshort arc
circuit patented by Panasonic. SP-MAG aims toovercome some of the
limitations of conventional short
Table 6 Example welding parameters with the RMD process
References Material Groove Wire Shielding gas
[77] P5B grade of P91 Bead on plate ER90S-B9 Ar 90 %+10 %
CO2[27] C-2000 thickness 6.35 mm
flat position AWS G 1Root pass Diameter 1.14 mm 10 % helium0.4
%
CO2balance argonGap:1.271.5 mm Single V groove, 70
included angleTravel speed: 0.5 m/min
Root land:5.08 mm 15.4 V WFS: 5.7 m/min135 A
Fig. 5 Principle of a Cold Arcvoltage and current waveformsand b
Cold Arc power atre-ignition [30]
Int J Adv Manuf Technol (2013) 67:655674 661
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circuiting and constant voltage (CV) processes, such asspatter,
low speed and low heat input. The TAWERS robotseries claims to
successfully gather in one process the bene-fits from pulse and
CVapproaches [3436]. Figure 8a and b,presenting the waveform of the
current and voltage, showimprovements in control of the short
arcing. During theshort arc cycle, the shape of the current and
voltage aresimilar to conventional processes. There are two main
dif-ferences in the arc burning. Firstly, so-called
super-imposition (SP) which time is shortened. The SP
controlprevents the short arc after re-ignition; the tip is made
roundto allow a smooth start of the arc. Secondly, so-called
hyper-stabilisation (HS), which is characterised after the pea, by
adramatic reduction of the current wave curve and a suddenincrease,
then followed by a steady drop along the arcingperiod. In addition,
the HS control suppresses the vibrationof the molten pool, shortly
after re-ignition, to prevent short-arc. Again, this period is
shorter than in a conventional shortcircuit [3436].
An experiment was carried out in the automobile industry[37] to
investigate robotic MAG process welding parameters(Table 9). The
aim was to optimise the process parameters insimilar welding of
steel and dissimilar welding with highstrength and dual phase
steels. The thickness of the work-pieces differed from 1.2 to 3.0
mm. In addition, differentcombinations with various thicknesses
were welded. Theconventional short arc current waveform was used
for com-parison with the SP-MAG waveform. The result showedthat
robotic MAG welding of similar and dissimilar materialjoints can
give welds with satisfactory mechanical andstructural properties,
even with variable gap (02 mm).
2.8 Controlled bridge transfer process
The controlled bridge transfer process (CBT) is a modi-fied
short circuiting process which aims to reduce the heatinput and
spatter when the molten metal touches thepuddle and when the
droplet separates from the electrode.Figure 9 shows the current
waveform of the process. Theprocess senses the contact of the
electrode with the melt-ing pool and reduces the current
dramatically to avoidspatter. The second switching occurs at the
neckingperiod; the process senses the decrease of the cross-section
by the pinch effect and drops the current rapidlyto allow only the
surface tension to perform the moltentransfer in the puddle. The
method overcomes disturban-ces as arising from wire extension,
welding speed, weld-ing position, and the size, shape and viscosity
of themolten droplet, which occur in timed squeezing of thedrop.
The process has been proved to be able to weldstainless steel with
a stable arc in an argon-rich environ-ment [38]. In addition,
electro-negativity (EN)-CBT hasbeen applied successfully and allows
low heat input weld-ing. CBT was suggested by a group of
researchers [38]and is now implemented under the name metal
transferstabilisation by Panasonic Corporation, with the aim
ofimproving the CO2 welding process in MAG [38].
Table 10 presents details of experiments performed withAISI304L
on a lap joint, the section of which varied from0.6 to 2.0 mm. The
results showed low distortion and signi-ficant improvement in
mechanical properties and micro-structure. In addition, low-spatter
and low-fume emissionwere noted compared to the conventional
process [39].
Table 7 Example weldingparameters with the Cold Arcprocess
References Material Groove Wire (mm) Welding speed Current
Volt
[29] 6XXX Butt joint 0.52-mm AlSi5 4080c m/min 68 A 11.6 V2XXX
1.2 mm
5XXX AlMg4.5MnZr
AlMg5
1.2 mm
Fig. 6 Comparison of conventional short arc and ColdMIG
currentand voltage waveform [31]
Voltage
Current
Fig. 7 Voltage and current waveform of the droplet transfer
sequenceof Intelligent Arc ControlSigma Galaxy [32]
662 Int J Adv Manuf Technol (2013) 67:655674
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3 Mechanically assisted droplet transfer
New developments have enabled welding equipment suchas the power
source, wire feeder, and the shielding gas flowregulator to perform
in synergy and obtain an optimisedresult as regards the welding
dynamic characteristic. In theGMAW process, the wire feeder used to
contribute to pro-viding the current and ensuring continuous speed
of thewire. Now use of the filler wire has advanced to a
situationwhere it is fully integrated in the welding process.
Theoverall motion of the wire is forward but it can be reversedat a
specific time to assist in the breaking of the moltenmetal during
detachment into the molten pool. For thispurpose, an inverter
welding current source is used and thecontrol algorithm is
conjugated with the electrode wiremotion [9, 10, 40].
3.1 Cold metal transfer process
The cold metal transfer (CMT) welding process waspatented by
FORNIUS in 2004 and is based on a dip metaltransfer mode. The
system is equipped with a high-speeddigital control, inverters and
a processor that control all theprocess, for instance, the length
of the arc, the current andthe voltage. Whereas the material
transfer in dip transferwelding is controlled electrically, the CMT
process controlsmaterial transfer via both the initiation and
duration of theshort circuit and mechanically assisted methods. The
maininnovation is the reverse of the wire by a specialised
alter-native current (AC) servomotor incorporated into the gunthat
can oscillate the wire at frequencies up to 70 Hz at themoment of
the short circuit occurrence to assist with dropletdetachment. The
metal can then be transferred to the moltenpool with the retraction
force and the electromagnetic forceof the welding pool [41]. Figure
10a and b show the current
and voltage waveform of the CMT process and the principleof the
droplet and electrode motion sequence. The dropletdetachment occurs
at almost zero current input. The twomain steps are arc phasing and
short arc, described as follows[39, 4143]:
Arcing phase: The arcing phase is distinguished by aconstant arc
voltage corresponding to an initial highpulse of current which
ignites the welding arc and heatsboth the workpiece and the wire
electrode. The currentis then reduced to ensure that droplet
detachment is notinitiated but that a molten globule remains
attached tothe end of the electrode and a weld pool is
created.Short circuit phase: In the short circuit phase,
theelectrode is fed into the weld pool, initiating an elec-trical
short circuit, marked by a reduction in arc voltage.In conventional
dip transfer, arcing results in a rapidrise in current which melts
the end of the electrode andbreaks the contact with the work
surface [38, 44]. Thepoint of short circuit is sensed and the
welding currentis reduced to a minimum, extinguishing the welding
arcand limiting the thermal energy transferred to the workpiece.
After a defined duration, the electrode is retractedpinching the
molten droplet into the weld pool andbreaking the short circuit.
The arc is then reignited andthe cycle repeats.
FORNIUS has continued to develop the CMT conceptand an enhanced
CMT version, called CMTAdvanced, waspresented in 2009. The process
integrated the retraction ofthe electrode, measurement and control
of the arc length,and control of the polarity of the welding
current. Thechange of polarity occurs during the short circuit
phaseand prevents possible negative effects as the circuit
arcburns, for instance, instabilities related to the arc break
ofthe process. The deposition rate can be adjusted by
Table 8 Example welding parameters with the Intelligent Arc
Control process
References Material Groove Wire Shielding gas Welding speed
Current Volt
[33] Mild steel Gap 510 mm, 1.6 mm thickness 1.2 mm solid
Ar80%/CO2 20 % 38 A 16.8 V
Fig. 8 a Current and voltage ofMAG and SPMAG methodand b
corresponding droplettransfer sequence [34]
Int J Adv Manuf Technol (2013) 67:655674 663
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alternating the positive and negative process cycle. CMTAdvanced
is said to decrease heat input, minimise distor-tion, emit few
fumes and be easy to perform. The process isoffered in two
variants; the first is characterised by a flowwith two positive and
negative cycles of CMT, and thesecond is a combination of a
negative phase and CMT of thepositive impulse phase [41, 45].
A variant of CMT is pulsed CMTAdvanced, the principleof which is
shown in Figs. 11 and 12, where the processflows with negative CMT
phase and positive pulse phase.Compared with the conventional AC
process, CMTAdvanced separates the pulse arc from the negative
currentphase. The process is characterised by a pulse cycle
withcontinuous feeding wire and a negatively pulsed CMT cyclewith a
reversing electrode and an impulse arc phase withcontinuous wire
feeding (Fig. 12). The metal transfer effectsof the pulsed cycle
(positive electrode) after the negativephase of the current found
in the conventional AC processdo not apply because the molten metal
formed during thenegative CMT cycle is smoothly transferred in the
followingshort circuit. Furthermore, the molten metal is
transferred inthe pulsed cycle without a short circuit. Therefore,
theinitialisation is of importance in controlling the
transitionbetween two different cycles [41, 45, 46].
Table 11 presents example data for some cases of weldingof
different material grades using CMT. The result showedgood
weldability o from 0.3 mm thickness and successfultests were also
made with dissimilar materials such as alu-minium and steel. The
results demonstrate the flexibility ofthe process and acceptable
results were obtained for steel,stainless steel and aluminium.
Dissimilar metal joining ofaluminium to zinc-coated steel sheet
without cracking by theCMT process in a lap joint is possible. The
compound layerat the interface between steel and weld metal main
consistsof Fe2Al5 and FeAl3 phase [40, 42, 4749].
3.2 MicroMIG process
The MicroMIG process is developed by the SKS WeldingSystem
Company and was launched at the Essen weldingand cutting 2009 expo.
The process is characterised by asupported mechanical molten metal
transfer located betweenthe pulsed waveform. The manufacturer
claims a high de-position rate without increasing the frequency,
which resultsin less spatter and lower heat input. Figure 13 shows
atypical waveform of the MicroMIG process [50]:
& Pulse sequence: A pulse sequence (3) (specific numberof
pulse) is used to create the weld pool and set indi-rectly the wire
feed speed (deposition rate). The lastpulse creates a drop of
molten wire at the wire end.
& Droplet transfer: (2) The wire is fed with low
currentuntil contact with workpiece.
& Mechanically assisted droplet transfer: When the
elec-trode is in contact with the weld pool (5) the direction ofthe
wire feeder changes and the wire is retracted for apre-determined
time (4).
& After re-ignition: The direction of the wire feeder
isagain reversed (forward) and a new pulse sequence startsafter a
short waiting time (1).
The MicroMIG process was realised with standardcomponents. These
components are already in industrialuse worldwide. The torch system
works with only onemain wire feeding unit, therefore,
synchronisation prob-lems, as in pushpull systems, are completely
elimina-ted. In addition, no wire buffer is required. The
relatedconsumables (liner, driver rolls, centre guides) are
avail-able for aluminium wires with a diameter ranging from
Table 9 Effect of robot MAGprocess welding parameters [37] Upper
sheet Low sheet
Joint date (lap joint) Material S355 steel Material S355
steel
Thickness (mm) 1.3 Thickness (mm) 1.2
Weld data Current (A) 70 Stick out (mm) 9
Voltage (V) 17.4 Speed (m/min) 0.5
Fig. 9 Current waveform of metal transfer stabilisation welding
pro-cess [34, 42]
664 Int J Adv Manuf Technol (2013) 67:655674
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0.8 to 1.6 mm. The process is designed for robotapplications
[50].
Table 12 presents example parameters for an experimentwith
X5CrNi18-10. The MicroMIG process was able toachieve acceptable
mechanical properties and visual appear-ance, with few defects
[51].
4 Variable polarity GMAW or AC-MIG transfer process
Variable polarity (VP)-GMAW or AC GMAW is a recentpulse welding
process [52, 53]. The electrode positive back-ground period current
switches to maintain the arc at a lowcurrent. The electrode
positive peak period is used to trans-fer the droplets by using a
high-current pulse that squeezesthe droplet off the electrode tip.
The drops transfer acrossthe arc into the weld pool. The VP-GMAW
waveform can
be designed to provide a range of heat inputs for a givenwire
feed speed, thus allowing optimization of the travelspeed for
different weld deposit size applications [52, 54].
Steel and aluminium alloy are the most widely used metalsin
various industries. When joining steel to an aluminiumalloy, it is
not easy to obtain good welding quality becausetheir physical
characteristics greatly differ. In particular, theintermetallic
compound layer that appears between the dis-similar welding parts
makes them brittle, thereby resulting insignificantly low strength
and deformation. In order to mini-mise the brittleness of the
intermetallic compound layer, itsthickness must be 10 m or less
[55, 56].
In a study conducted by JP Hyoung et al., steel (SPRC 440)was
weld brazed to aluminium alloy (6 K21) using AC-pulsedMIG welding,
which alternates between DC electrode-positive and DC
electrode-negative based on the EN ratio.The resulting weld
characteristics were evaluated [57].
The study drew the conclusions from experiments on thejoining of
SPRC 440 steel and 6 K21 aluminium alloy byAC pulse MIG welding
that based on the SEM and EDSanalyses, a thin intermetallic
compound layer was obtaineddue to lower heat input to the base
metal as the EN ratioincreased. In addition, the analysis of the
tensile strength testin relation to changes in the EN ratio, it was
observed that asthe EN ratio increased, the tensile strength value
improvedwith good gap bridging ability [57].
Table 10 Example welding parameters with the metal transfer
stabilisation process
References Material Groove Wire Shielding gas Wire
speed(cm/min)
Welding speed(cm/min)
Current Volt Gas flowrate
[39] AISI304L 2.0 mm ER308; 1.0 mm 98 % Ar+2 % O2 450 70 100 A
15.0 V 15 l/min
AISI304L 1.0 mm Lap joint ER308; 1.0 mm 98 % Ar+2 % O2 410 100
100 A 14.0 V /
AISI304L 0.6 mm Lap joint ER308; 1.0 mm 98 % Ar+2 % O2 530 300
115 A 14.0 V /
Fig. 10 a Cold metal transfer tension and current wave curve and
bCMT droplet and electrode motion sequence [40]
Fig. 11 Variation of welding current (IS), welding voltage (US),
andwire feed speed (Wfs) in CMT for dependence pulse CMTAdvanced
inthe EP and EN phases [41]
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The polarity switches from electrode positive (EP) to ENjust
after the pulse peak current and a cathode spot is formedon the
surface of the retained molten metal near the slenderwire tip.
Under the effects of the randommotions and reactionforces of the
cathode spot, the retained molten metal is pulv-erised to form tiny
spatters flying out of the arc area [58].
4.1 AC-MIG (OTC-Daihen) process
The AC MIG welding process from OTC-Daihen JapaneseCompany,
presented in 2008, uses the digital AC/MIG PulseInverter DW300 to
perform welding operations with lowheat input. The new version is a
completely digitally con-trolled process based on the previous
AC-MIG200, whichwas limited in its application. The innovation
extends the
performance from robotic to manual application by improv-ing the
stability of the arc at low values of welding current.The previous
version was limited to aluminium, mild steelbut new welding
equipment has included structural steel[53, 59]. The increase of
the welding current and the load(P0300 A at 80 %) gives additional
advantages [54, 60].
The EN polarity ratio has a significant effect on wiremelting
speed in AC-pulsed MIG welding. It has been foundthat at 150 A of
mean welding current, the melting speed ofa wire with 40 % EN ratio
is 60 % higher than that with a0 % EN ratio (DCEP) in DC-pulsed
welding. In addition tothe high deposition rate, it was observed
that low amperageresults in a decrease in heat input as the EN
ratio grows. DW300 comprises software with an algorithm capable of
vary-ing the EN ratio up to 80 % [61].
Figure 14 is an illustration of a typical AC MIG/MAGwaveform.
The first waveform (a) is characterised with aconventional EN ratio
limited to 30 %, adequate for alumi-nium welding. In the second AC
waveform (b), the ENcomponent is divided in two areas: the base
current and
Fig. 12 Process course, two positive (EP) and negative (EN)
CMTAdvanced cycles [39, 41]
Table 11 Example welding parameters with the CMT process
References Material Groove Wire Shielding gas Wirespeed
Weldingspeed
PeakCurrent
Volt (V) Gas flowrate
[42] Zinc-coatedsteel (0.6 mm)
Dissimilar lapjoint
Al-Si 1.2 mm Argon 15 l/min
Al 1060(1 mm)
[47] AA 6111 Bead on aplate 3 mm
12 mm 4043 Pure argon 1.0 m/min Mix CMT
[40] NiCr Butt joint0.32 mm
4316 1.0 mm 97.5 % Ar+2.5 %CO2
Stainlesssteel
AlMg3 Butt joint AlSi5; 1.2 mm Pure argon 2.0 m/min 1.0 mm
[48] Hot-dipgalvanisedsteel and Al1060
Lap joint;1 mm
Al-Si 1.2 mm Argon 3.9 m/min 762 mm/min 66 A 11.8 15 l/min5.4
m/min 913 mm/min
[49] DC 0.4 Lap joint;0.8 mm
Autrod 1251;1 mm
Ar 80 % +CO2 20 %
/ 1530 mm/s / 8189 ACTWD01018 mm
Fig. 13 Current waveform of the MicroMIG SKS Welding System[48,
50]
666 Int J Adv Manuf Technol (2013) 67:655674
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the pulse current. The base current is applied to sustain thearc
at the time of the changing of voltage polarity and thepulse part
is to control the penetration [58].
The results of two experiments are presented in Table 13.The
materials are Japan low alloy steel (SPCC) and alumi-nium alloy
(A5052). Welds joints were performed on a beadon plate of 3.2 and 3
mm to evaluate the penetration relativeto the EN ratio. The results
showed lower penetration as theratio increases and less risk of
burn through [57, 58].
4.2 Cold process
The German company, Cloos, in 2002, successfully devel-oped the
first variable polarity MIG/MAG welding GLC353 QUINTO cold process
(CP) [58, 62]. The DC positivepolarity of the electrode in pulse
MIG/MAG provides astable arc and better penetration; however, it is
likely togenerate undercut, burn-through on sheet metal and
otherdefects. On the other hand, negative DC MIG/MAG weld-ing
generates an unstable arc, difficult droplet transfer, andshallow
penetration. The AC GMAW that Cloos developedintegrates the
advantages of both previous applications [62].
GLC 353 QUINTO CP uses a unique current waveform.By adjusting
the parameters of the negative base value of theheat input, the
welding process is carefully controlled toensure the best welding
results. In the actual welding,increasing the base value of
negative time can significantlyimprove the deposition rate of the
wire, improve weldingspeed, and reduce the heat input [62].
CP consists of a special current waveform designed to fillthe
gap and ensure good coverage and excellent weldingresults. The
positive polarity ensures the cleaning stage andthe heat input of
the base metal by control of the pulse phaseto release the droplet
to the base metal. The arc surrounds
the tip of the electrode during the negative phase that
directsheat into the wire and cools the weld pool [62].
The CP process consists of two different concepts. Thefirst,
presented in Fig. 15, combines the current and voltagewaveform and
can be described as follows [62, 63]:
& Arc burning period (1): The current and voltage are inthe
required negative pulse for a certain period time. Thewire is
moving toward the workpiece
& Short circuiting period (2) and (3): The current
andvoltage are suddenly increased to a level required tostart the
droplet transfer
& Pinching period (4): The wire short with the work pieceand
the current is increases sharply to allow the pincheffect and
necking for the droplet transfer into the weldpool. The voltage is
reduced to about zero, just as inshort circuiting transfer mode
& Droplet transfer period (5): There is a sudden decreasein
the current and voltage to permit smooth separation ofthe molten
metal to the weld pool and re-ignition of thearc
It can be observed that the CP process combines theadvantages of
the AC pulse and dip transfer modes. Theburning arc occurs in EN
polarity, which results in anincrease in the melting rate. In
addition, the short arc periodconsiderably reduces heat input in
the workpiece comparedto the conventional short arc process.
The second concept is a variable polarity GMAW pro-cess. Figure
16 presents a typical current and voltage wave-form of the process.
The concept is an innovation in thedomain of AC MIG/MAG pulse
welding. The curve bene-fits from the latest research into possible
improvements inthe shape of the variable polarity waveform and can
bedescribed as follows:
Table 12 Example welding parameters with MicroMIG
References Material Groove Wire Shielding gas Welding
speed(cm/min)
Gas flow rate(l/min)
[51] 1,4301 (X5CrNi18-10) Lap joint; 0.8 mm 1,4370; 1.0 mm 98 %
Ar, 2 % CO2 100 14
1,4301 (X5CrNi18-10) T joint; 1.5 mm 1,4370; 1.0 mm 98 % Ar, 2 %
CO2 95 14
Fig. 14 Modified currentwaveforms in DW 300 with ENratio up to
30 % (a) andabove 30 % (b) [58]
Int J Adv Manuf Technol (2013) 67:655674 667
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& Transition from EP to EN (1): the EP is kept at lowcurrent
level to ensure smooth transition to the ENpolarity and avoid tiny
spatter
& Arc burning period at EN (2) and (3): the arc
shapeincrease the melting of the electrode, the penetrationand
maintain EN period to keep a constant arc length
& Pinching period (4): Peak positive pulse for pinch
effectand start necking for droplet transfer
& Droplet transfer period (5): the current is reduced
atrequired level to prepare the alternative change to EN
Table 14 presents examples of welding parameters withthe CP
process. In a manual test on DC01 steel (2 mm thicklow alloy
steel), the welding process was found to be fasterthan the same
weld with the semi-automatic conventionalprocess. A 0.7-mm thick
stainless steel was welded with CPand completion of the weld was
faster than the same welddone with a conventional semi-automatic
process and aboutas fast as the same semi-automatic pulse welding
process.The welding tests for 4-mm thick S700MC and 4-mm
thickAISI304L were not successful showing that CP is not suit-able
for this thickness [63, 64].
5 Pulse spray/short circuit metal transfer
An alternative transfer technique, GMAW-P, was inventedin the
mid-1960s. This mode of metal transfer overcomesthe drawbacks of
the globular mode while achieving the
benefits of spray transfer. GMAW-P is characterised bypulsing of
the current between the low-level backgroundcurrent and the
high-level peak current in such a way thatthe mean current is
always below the threshold level ofspray transfer. The purpose of
the background current is tomaintain the arc, whereas the peak
currents are long enoughto ensure detachment of the molten droplet
[65].
The transition current zone between the globular and thespray
mode is of great importance in the GMAW-P process.It limits the
highest current for globular transfer and thelowest for spray
transfer and thus determines the workingconditions of the process
[66, 67]. The GMAW-P processadvances the concept of combined or
hybrid metal transfermode. In normal transfer mode the dissimilar
modes, e.g.free flight transfer and bridging transfer modes occur
ran-domly, however in combined or hybrid metal transfer therelevant
mode is attained intentionally and in a controlledmanner using
features of advanced power sources [68]. Theemphasised is in
combination of pulse spray and short arcmetal transfer mode.
The classic methods of arc welding (TIG, MIG), used tojoin
aluminium alloy parts of small thickness, do not pro-vide the
required quality of weld joints, mainly because ofthe difficulties
in maintaining a stable process with lowwelding current, and cause
welding unconformities, suchas decreased mechanical properties in
the joint and a rela-tively large heat-affected zone (HAZ),
melting, partial
Table 13 Example welding parameters with the AC-MIG process
References Material Groove Wire (in) Shielding gas Wire
speed(cm/min)
Current (A) Volt Gas flow rate(l/min)
[58] SPCC Bead on plate; 3.2 mm ER70s-G; 1.2 mm 80 % Ar+20 %CO2
700 165210 24.526.5 V 20
A5052 Bead on plate; 3 mm ER5356; 1.2 mm 100 % Ar 600 6598
15.617.6 V 20
Fig. 15 Metal transfer process and current and voltage waveforms
ofnon-pulsed cold welding [79]
Fig. 16 Pulse droplet transition and current and voltage
waveforms ofthe cold-welding process [79]
668 Int J Adv Manuf Technol (2013) 67:655674
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melting, hot cracks in high-strength aluminium alloys with ahigh
content of alloying elements, oxide inclusions andporosity, as well
as weld shape inconsistencies (especiallyfor the MIG method)
[69].
An investigation comparing the effects of the GMAWand the GMAW-P
welding processes on microstructure,hardness, tensile and impact
strength of AISI 1030 steeljoints fabricated by ASP316L austenitic
stainless steel fillermetal showed that the GMAW-P joints of AISI
1030 steelcouples exhibit less grain growth when compared toGMAW
joints in the HAZ. The highest impact strengthvalue was measured in
the sample performed with theGMAW-P technique. The grain growth
because of the highheat input occurring in the GMAW technique
causes adecrease in the impact strength values of the joint. Thelow
heat input in the GMAW-P and the fine grains occurringin the weld
metal due to the rapid solidification and shapedas small and
slender structured, increased the hardness value[70].
The GMAW of thin aluminium was complicated by thefact that short
circuiting arc transfer (short arc) is not rec-ommended for the
GMAW of aluminium alloys. Spraytransfer is always recommended for
welding aluminium. Inthe past, it was impossible to weld thin
aluminium of1.6 mm thickness because even with the smallest
diameteraluminium wire available for the GMAW, 0.8 mm, thewelding
current had to be above 85 A to get spray transfer.This was just
too much current to weld thin materials, and sothe GMAW of thin
aluminium simply was not performed inproduction. Pulsed GMAW was
developed and made it
possible to control the welding process much more preciselyand
to change the welding current very quickly. However, itis very
different today [71].
5.1 Pulse/pulse arc process
The company ESAB developed an enhancement of GMAW-P in 2003. The
technology is an improvement permittingmore accurate control of the
waveform and thus enabled thecompanys engineers to design a
multi-process powersource called ARISTO Superpulse. The concept,
knownas pulse/pulse (double pulse) and pulse/spray, was
alreadyavailable from other manufacturers but the innovation byESAB
is a pulse/short arc, which aims is to completelycontrol the heat
input and arc for sheet thin metal. Thepulse/pulse arc mode is used
for welding medium thicknessand thin materials. Aristo Superpulse
is fundamentally asoftware solution included in the operator
pendant [72].
Figure 17a illustrates the pulse/pulse process technology.A
motivation behind the approach was to provide a GMAWsolution for
aluminium welding that made the process lessdifficult than standard
pulse and therefore required lessoperational skill. Unlike standard
pulse welding, pulse/pulseuses a sequence of varying pulse wave
shapes to create abead shape and appearance similar to the GTAW
process. Itutilises low amperage in the primary phase for heat
reduc-tion and higher amperage in the second phase for
enhancedpenetration [7375].
Figure 17b presents the spray arc/pulse arc process,which was
initially developed for positional welding of
Table 14 Example welding parameters with the cold process
References Material Groove Wire Wire speed(m/min)
Welding speed(cm/min)
Current (A) Volt
[64] DC01 2 mm
AISI 304 L 0.7 mm
Low alloy steel Lap joint 1.5 and 4.17 mm 2.25
Al Lap joint (gap 1.5 mm) AlSi5; 1.6 mm 9.0 15
[63] CuSi3 Lap joint; 1.0 mm 1.2 mm 4.5 80 132135 16.016.5 V
Fig. 17 ESAB AristoSuperPulse waveforms: a pulse/pulse, b
spray/pulse, c pulse/short arc [73]
Int J Adv Manuf Technol (2013) 67:655674 669
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thick materials. The welding speed and even penetration
areprovided during the spray arc phase, whereas heat input
isreduced during pulse phase. This arc welding process modeenables
vertical-up welding of aluminium without any wav-ing motion. It
utilises spray arc transfer in the primary phasefor enhanced
penetration and pulse arc in the secondaryphase, which serves to
cool the weld pool for less heattransfer to the base material and
less distortion. Pulsing inthe second phase also allows spray type
transfer to beachieved in all positions of welding [7375].
Figure 17c depicts the pulse arc/short arc process, whichwas
developed for very thin aluminium and stainless steel. Itutilises
pulse in the primary phase and a short arc in thesecond phase with
very low heat input and a GTAW beadappearance. It can be used in
all positions of welding andhas low sensitivity to variations in
root gap. The process canalso be used for root runs from one side
in thicker materialswithout the need for backing.
Tables 15 and 16 present welding parameters of stainlesssteel
and AlMg, respectively, as given by the manufacturerfor the
combined pulse and dip or spray transfer modeprocess. An analysis
by [74] of welding process speed withcombined pulse investigated
the distortion resulting whenwelding aluminium. The results showed
that the processreduces heat input without compromising
productivity.
6 Comparisons of new arc welding processesand conventional
welding processes
Table 17 presents a comparison of some key features of newarc
welding and conventional processes. The new processeslisted in this
table belong to the GMAW welding processgroup. It should also be
noted that the comparison does notdistinguish between manual,
semi-automatic and robotisedprocesses, and focuses on the waveform
ability to increasethe droplet transfer with low heat input. The
comparison isbased on the results of both academic studies and
informa-tion provided by the suppliers of the power sources. It
canbe seen that a significant amount of the information is
frommanufacturers. This is because limited research has
beenpublished presenting comparisons of new welding applica-tions;
the main raison being the investment required toconduct such
comparative research.
A variety of arc welding process concepts has beensuggested
during the last decades but interest in scientificresearch of such
processes is still low, although some ofthem, such as WiseRoot,
STT, and CMT, have been studiedand scientific publications are
available. These weldingprocesses have demonstrated improvements in
terms of heatinput reduction, improved speed and productivity, and
anincreased range of material weldability [39, 42, 47, 76].
Table 15 Example weldingparameters with the pulse/dipor spray
process [78]
Material type Stainless steel Travel speed
Material thickness 0.8 mm Primary wire feed speed (WFS) 2.0
m/min
Joint type V. Butt Secondary wire feed speed (WFS) 1.2
m/minWelding position PA
Wire type 16.32 (316 LSi) Primary voltage 21.8 VWire diameter
1.0 mm
Gas Type 97.5 Ar; 2.5CO2 Secondary voltage 14.8 (+0.8) VPrimary
phase Pulse
Secondary phase Dip/spray Primary time 0.30 sPr. phase synrgic
On
Sec phase Synrgic On Secondary time 0.10 s
Table 16 Example weldingparameters with the pulse/dip orspray
process [78]
Material type AlMg Travel speed
Material thickness 1.5 mm Primary wire feed speed (WFS) 3.0
m/min
Joint type Butt Secondary wire feed speed (WFS) 1.1 m/minWelding
position PA, PC
Wire type 18.15(5356) Primary voltage 22.8 (+10)VWire diameter
1.2 mm
Gas type Ar Secondary voltage 12.0 (+3.6)VPrimary phase
Pulse
Secondary phase Dip/spray Primary time 0.2 sPr. phase synrgic
On
Sec phase synrgic On Secondary time 0.1 s
670 Int J Adv Manuf Technol (2013) 67:655674
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Table17
Com
parisonof
lowheatinputwelding
processesforthin
sheetmetal[1379]
Group
Features
processes
Welding
speedvs
MIG
/MAG
Therm
alinput
Materialandthickness
Gap
-bridgingand
positio
n(m
m)
Productivity
Steel(mm)
Stainless
steel
(mm)
Al(mm)
Mixed
joint
Advanced
controlled
WiseR
oot
10%
faster
1015
%less
0.6
Yes
No
6GoodDifferent
positio
n
STT
Highwelding
speed
Low
erthan
TIG
0.9
Yes
0.9
Possible
5aHighproductiv
ity
RMD
Increase
2or
3tim
esfastera
Reduceheatinputa
3.17
orless
Yes
3.1or
less
b
4.7
Highproductiv
ityforroot
pass
ColdArc
Can
improve
Minim
ised
0.3
Yes
1.3
Yes
+Possiblea
Allpositio
na
ColdMIG
Increase
Minim
ised
0.6
Yes
0.6
Yes
aCan+
Allpositio
n,
IAC
15%
faster
Reduceheatinputa
0.6a
Program
me
include
0.6a
b
+Possiblea
Increase
productiv
itya
SP-M
AG
Faster
Low
erTestedon
1.2
Yes
b
a
Possible
Increase
productiv
ity
CBT
Faster
Reduce
0.8
Yes
No
No
1.4
++
Mechanically
assisted
CMT
50%
Slig
htly
twice
fastera
30%
0.3
Yes
0.3
Yes
2.5
++
CMTAdvanced
50%
Slig
htly
twice
fastera
30%
0.3
Yes
0.3
Yes
2.5
+++
Micro
MIG
Sam
eas
Lessa
0.6
Yes
0.6
b
Noexp
++
AC-M
IGmodified
AC-M
IG+Increased
Reductio
n30
40
%a
Thinner
Yes
Lessthan
0.8a
Noexpb
2+++Goodbecauseof
meltin
grate
CP
++Increased
Reductio
n
0.5
Yes
0.8
No
2+++
Hybridmetal
transfer
Pulse/shortarc
++Increased
Reduce
0.6
Yes
0.6
Yes
Nob
Highproductiv
ityroot
pass
Conventional
MIG
/MAG
Shortcircuit
Slower
Moderatelyhigher
0.6
No
Difficult
Thinsheetallpositio
n
pulse
Moderatelyslow
erHigher
0.6
Yes
Yes
No
Difficult
Thinandmedium
Decreaseof
feature,+increase
infeature
aIndicatio
nfrom
themanufacture
bNoinform
ation
Int J Adv Manuf Technol (2013) 67:655674 671
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7 Conclusions and summary
The aim of this study was to investigate new innovations interms
of novel concepts and significant improvements. Theinvestigation
leads to the following conclusions.
Arc welding processes have developed considerably withnew
techniques and applications being implemented.Principal aims have
been to reduce the heat input, suppressthe harmful spatter
phenomenon, and increase the flexibilityof welding processes.
Usability of the processes discussed inthis study is an important
issue, conventional GMAW, forexample, is limited to thin thick
(0.65 mm) material forshort arcs. Moreover, it requires high skill
and causes burn-through and spatter when welding thinner sheet
material.New modified short arc welding processes are suitable
forthinner sheet metals, gap bridging, root pass and materialssuch
as stainless steel, and heat-sensitive and coated sheetmetal. Some
modified short arc processes have dissimilarmaterial joining
capability.
Although the arc welding process consists of about 12groups,
particular interest has been directed to GMAW overthe last decade.
The new arc welding processes in this studyfocus on the control of
short-circuiting, pulse spray,mechanically assisted droplet
transfer, and the combinedmode in the GMAW.
The design of the power source has been a main target
ofinnovation and modern power sources have high speedswitching with
new advanced inverter and electronic devi-ces for digitalised
feedback control. Use of an inverter isincreasingly common in
industrial applications. As thespeed of the inverter increases, it
enables faster higher speedresponses during feedback control.
The control of droplet detachment by the reversal of wirefeeder
motion has been improving, thus mechanical retrac-tion of the
electrode has been integrated into the weldingprocess. The approach
is still limited to small manufac-turers. Control through voltage
and current is the main partof droplet transfer, since it affects
the shape of the currentand voltage waveform. New welding devices
have consid-erable flexibility in terms of adjustment of waveforms.
Awaveform designer would be useful to provide the welderwith more
options.
Mechanically assisted droplet transfer has led to thecreation of
a new welding torches and wire feeders. Theconcept initially
affected the size of the gun; a current trendis to focus on
developing a convenient size of welding gun.
The external parameters such as CTWD and shieldinggases can
affect the voltage and current waveform.Shielding gases controlled
devices can be improved andthey can benefit from intelligent
optimization of the followrate.
The voltage and current waveform provided by the man-ufacturer
are different from those obtained by independent
laboratories with the same settings. New transfer modessuch as
the combined pulse, short-circuiting and mechaniseddroplet transfer
implemented by innovative arc weldingconcepts should be introduced
in new classification of metaltransfer modes. This work can be used
to further studyindustrial development and application of new
weldingprocedures.
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