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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

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

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

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


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]


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]


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]


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]


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]


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]


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]


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]


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]


& 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]


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]


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


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


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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