WELDING RESEARCH Metal Transfer with Force … free metal transfer with low welding current (Refs. 16–20). The droplet size and trajectory were well controlled by the laser power

Introduction Gas metal arc welding (GMAW) iscurrently one of the most widely usedwelding methods due to its productivi-ty (Refs. 1, 2) and convenience for au-tomatic and semiautomatic weldingapplications. The transfer of the melt-ed wire (electrode) onto the base metalforms a process referred to as metaltransfer. Metal transfer plays an es-sential role in determining the processstability, welding productivity, and soon, plus it has been an active field ofresearch and application in the weld-ing community (Refs. 3–6). The metaltransfer depends significantly on thewelding current levels. To obtain a free

droplet transfer process, a certain levelof welding current should be used.However, higher welding current willapply higher heat input into the work-piece, which may be unnecessary orundesirable in certain applications.Hence, research has been conducted toexplore welding methods to reducewelding current and achieve stable freemetal transfer at the same time. Pulsed gas metal arc welding(GMAW-P) has been proved as an ef-fective method to achieve the desirablefree transfer/spray transfer at a need-ed heat input determined by the aver-age current, but the peak current mustbe higher than the transition current,which may blow the liquid metal away

from the weld pool and cause melt-through (in complete joint penetrationapplications) (Refs. 7, 8). Cold metaltransfer (CMT), developed at andpatented by Fronius, Inc., is a processthat utilizes a fast mechanical move-ment to draw the welding wire backsuch that the liquid metal can be sepa-rated from the wire to transfer themetal at a current much lower thanthe transition current. As a result,both the total heat input and currentlevels can be much reduced (Refs. 9,10). However, the complicated devicefor the mechanical movement intro-duces disadvantages affecting its wideracceptance. The patented surface tension trans-fer (STT) (Refs. 11–13) process is an-other effective method to reduce spat-ter to a minimum with low heat inputand arc pressure, but its effectiverange for the average current is re-stricted by the mandatory need for theparticular current waveform/rangeneeded to reduce spatter and may notalways be most desirable for certainapplications. Zhang et al. proposed a patentedmethod (Refs. 14, 15) to use a peakcurrent much lower than the transi-tion current to produce the desiredspray transfer by taking advantage ofthe momentum of a downward (awayfrom the gun) droplet. Recently, laser-enhanced GMAW,which utilizes a low-power laser toprovide an additional detaching forceto transfer droplet, was developed to

WELDING RESEARCH

KEYWORDS • Metal Transfer • Force Analysis • Indirect Arc Welding

NOVEMBER 2014 / WELDING JOURNAL 431-s

Metal Transfer with Force Analysis in Consumableand Nonconsumable Indirect Arc Welding Process

At a certain welding current level, there was an optimized wire feed speedto achieve a higher metal transfer rate and smaller droplet size

BY J. WANG, Y. HUANG, J. XIAO, J. FENG, C. Y. TIAN, AND J. WANG

ABSTRACT This paper proposes an indirect arc welding process that uses a consumable and nonconsumable electrode to establish an arc. Because there is no welding current passingthrough the workpiece, the heat input is reduced. The consumable electrode is a welding wire and the nonconsumable is a tungsten electrode. The wire feed speed and welding current are two main parameters determining the metal transfer in the process, andtheir effects are experimentally examined in this paper. It was found that at a certainwelding current level, there was an optimized wire feed speed to achieve a higher metaltransfer rate and smaller droplet size. When the current increases, the transfer with theoptimized feed speed would change from globular to spray transfer. Forces acting on thedroplet were analyzed to explain phenomena experimentally observed from the metaltransfer process. The arc behavior was also analyzed to better understand this weldingprocess and its metal transfer.

J. WANG ([email protected]), J. XIAO, and J. FENG are with the National Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin, China. Y. HUANG is with the Center for Sustaining Manufacturing and Department of Electrical Engineering,University of Kentucky, Lexington, Ky. In addition, WANG, C. Y. TIAN, and J. WANG are with the School of Materials Science and Engineering, Jiamusi University, Jiamusi, China.

achieve free metal transfer with lowwelding current (Refs. 16–20). Thedroplet size and trajectory were wellcontrolled by the laser power intensi-ty. Pulsing current was also combinedwith this method to reduce the heatinput, and the patented droplet oscil-lating method was also introduced tothis process to further control the be-havior of the metal transfer (Ref. 21). Double electrode GMAW (DE-GMAW) and double bypass GMAW(DB-GMAW) are arc welding processesthat adopted one or two bypass gunsto reduce the total heat input to theworkpieces (Refs. 4, 5, 22). The currentthrough the main gun was decoupledto two or three parts with only one ofthem to be passed through the basemetal. Pulsing current can be used tofurther reduce heat input. Development for various low-heat-input arc welding methods suitable forvarious applications has been a majorcontinuous effort in the welding re-search community. To contribute tothis effort, the consumable and non-consumable electrodes indirect arcwelding (CNC-IAW) was developed toprovide an alternative way to reduceheat input in the arc welding process(Refs. 23–26). In the CNC-IAWprocess, the welding current throughthe conventional GMAW gun will di-rectly pass to another tungsten torch,considered as a nonconsumable gastungsten arc (GTA) electrode, back tothe power supply. Instead, the currentwill no longer pass through the base

material as in conventional arc weld-ing. The main heat input to the work-piece would be only from the moltendroplets. Unfortunately, while thisprocess provides unique and distin-guished properties, it lacks under-standing at fundamental levels. This paper denotes to enhance un-derstanding the CNC-IAW processfrom its metal transfer, which funda-mentally affects any arc weldingprocess with a consumable electrode.

Experimental Setup andConditions In the CNC-IAW process, comparedto the conventional GMAW process,the welding current through the weld-ing wire will not pass into the base ma-terial back to the power supply. In-stead, a secondary tungsten torch isadopted as the negative terminal thatis directly connected to the negativeterminal of the power supply. In thiscase, no welding current would passthrough the base material, and theheat input into the workpiece is main-ly from the molten droplet whose heatshould be relatively small. The totalheat input to the workpiece in CNC-IAW will be reduced. Figure 1 shows the schematic con-figuration of the proposed system forCNC-IAW. The tungsten nonconsum-able electrode and welding wire areconnected to the power supply’s nega-tive and positive terminals, respective-ly. The indirect arc generated between

the two electrodes produces continu-ously transferred molten droplets. Thebase metal is independent of the indi-rect arc and not connected to the weld-ing power supply. The welding currentflows from the positive terminal to thewelding wire and then to the indirectarc ignited between the two dissimilarelectrodes. Through the tungsten electrode, thewelding current flows back into the neg-ative terminal of the welding powersource. The heat input can be controlledby adjusting the distance between thewelding torches and base metal, whichis none of polarities of the arc. With thesynchronous forward movement of thetwo torches or movement of the work-piece, the deposited metal solidifies intoa weld joining the two members of theworkpiece being joined. The metaltransfer is imaged using a high-speedcamera and backlighting, as can be seenin Fig. 1. Figure 2 shows the main importantparameters needed to set up the experi-mental system to conduct the CNC-IAWprocess as expected. In this study, theGMAW gun and tungsten torch stayedstationary while the workpiece movedat a constant speed. The high-speedcamera was placed at a distance about1.0 m from the welding torches. Thecontact tube-to-workpiece distance d1,which plays an important role in deter-mining process stability, was set at 20mm. Both torches were set about 30 degwith the perpendicular line such thatthe angle between the two torches wasabout 60 deg. The wire extension lengthwas hard to set exactly as it would varydepending on the current level in rela-tion to the wire feed speed. However, the approximate value ofd2 from the cross point, where the wireand tungsten extension intersect asshown in Fig. 2, to the contact tubewas about 15 mm. The horizontal dis-tance between the welding wire andtungsten electrode d3 defined in Fig. 2was the most important parameter todetermine arc stability. From the ex-perimental results, 1–2 mm was foundto be the acceptable value for this dis-tance, which ensured arc stability. The welding power source used inthis study was a Fronius MW2200,and it was operated in constant cur-rent (CC) mode. Pure argon was usedas the shielding gas for the weldingwire as well as for the tungsten elec-

WELDING RESEARCH

WELDING JOURNAL / NOVEMBER 2014, VOL. 93432-s

Fig. 1 — Schematic diagram of the experimental configuration.

WANG ET AL SUPP NOV 2014_Layout 1 10/15/14 9:25 AM Page 432

trode. The flow rate was about 15L/min for both torches. The filler met-al was 1.0-mm-diameter CuSi3 weld-ing wire, and the base metal was 3.0-mm-thick 30CrMnSi steel. The high-speed camera recorded the weldingprocess for the later analysis at 1000f/s. When observing the metal trans-fer, the droplet could not be clearly ob-served for the influence of the arclight. A continuous xenon lamp couldproduce the high-intensity white lightcreated by the ionized xenon gas arc.Its intensity is bright enough that thelight could penetrate the indirect arc. However, it could not penetrate thedroplet. When recording the metaltransfer, the xenon lamp was used asthe backlighting source to shine on thedroplet. The camera could clearlyrecord the projector of the droplet inthe arc. When recording the arc behav-ior, the xenon lamp was not used to fil-ter the disturbance of the arc. The real-time welding voltages and currentswere acquired by the data acquisitionsystem shown in Fig. 1. The wire feedspeeds and welding current settingvalues used in the experiments arelisted in Table 1.

Results and Discussions

Effect of VoltageAmpereCharacteristic

The power supply’s voltage-amperecharacteristic has a significant effecton the stability of the welding processand metal transfer, and should be dis-cussed first. Hence, the constant volt-age (CV) and constant current (CC)modes were compared in the prelimi-nary study for selection of furtherstudy. By comparing the welding cur-rent and arc voltage waveforms duringwelding with the two voltage-amperecharacteristics, the power supply’s ef-fect on this process could be obtained. In particular, when the CV modewas adopted, as shown in Fig. 3A, B,the standard deviations (square rootsof the variances) for the welding volt-age and current were about 2.2 V and37.5 A, respectively, for the lower wirefeed speed (4.0 m/min). Increasing thewire feed to a higher level (9.0 m/min)resulted in similar results. This resultcould be explained by the CV mode arclength self-regulation mechanism. In

CV mode, the welding current can au-tomatically change with the variationof the arc length. When the arc lengthincreases, the welding current woulddecrease, and vice versa. Furthermore, the arc will distinguishfor the large decreasing welding currentas shown in Fig. 3A. When the CC modewas used, as shown in Fig. 3C, D, thestandard deviation for the welding volt-age was around 0.6 V for lower wire feedspeed (5.0 m/min). The fluctuation inthe welding current was not significant.When the wire feed speed was increased(also increasing the current level accord-ingly), similar results were obtained.Hence, to reduce fluctuations in thewelding voltage and current during thewelding process that directly affect arcstability, the CC mode was chosen toconduct CNC-IAW.

Effect of Wire Feed Speed onMetal Transfer

Metal transfer plays an essentialrole in determing the process stabilityand weld bead formation. The wirefeed speed and welding current wereidentified as two main parameters toaffect metal transfer. To explore thesetwo parameters’ influences, one pa-rameter was set as constant and an-other to be changed. To this end, thewelding current was first set as con-stant at 110 A. Experiments were con-ducted with different wire feed speedsat the same welding current to investi-gate their effect on metal transfercharacteristics. Figure 4 shows the typical metaltransfer processes under different wirefeed speeds for the same welding cur-rent of 110 A. Each image series in Fig.4 shows a complete transfer cycle withdifferent interval times between im-ages. As shown in Fig. 4, different met-al transfer phenomena were observed

WELDING RESEARCH


Fig. 2 — System installation parameters.

Table 1 — Welding Parameters in CNC-IAW Experiments

WFS (m/min)

4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10

Welding Current (A)

90 √ √ √ √110 √ √ √ √130 √ √ √ √ √150 √ √ √ √ √ √170 √ √ √ √ √


with different wire feed speeds. When the wire feed speed was at 5.0m/min, as shown in Fig. 4A, the dropletwas usually detached at the positionwhen the wire was above the crosspoint of the welding wire and tungsten.The metal transfer frequency was about8 Hz. When the wire feed speed in-creased to 6.0 m/min, as shown in Fig.4C, the droplet would be detached be-low the cross, but the metal transferrate was still about 8 Hz. However,when the wire feed speed was set at 5.5m/min, as shown in Fig. 4B, the detach-ing position was just at the cross posi-tion. The metal transfer frequency in-creased to about 16 Hz. The droplet waseasy to detach the tip of the wire com-pared with the metal transfer in Fig.4A, C. The main heat input to the work-piece in this process was mainly fromthe heat in the droplet. This is the maindifference between this process and thetraditional one. The metal transfer fre-quency changes as the wire extensionlength changes such that the wire tipchanges its position in the arc zone. Itappears that the cross point provides acondition to favor detachment. The sta-bility of the metal transfer was im-proved. When the metal transfer fre-quency increases, the droplet size willalso be reduced. It will benefit theprocess stability. To understand the peak phenome-non observed on the metal transfer fre-quency, forces acting on the dropletneed to be analyzed. It is well knownthat in conventional GMAW, the majorforces acting on the droplet include thegravitational force, electromagneticforce (Lorentz force), aerodynamic dragforce, surface tension, and momentum

force (Refs. 27–29).To be simple, the dy-namic-force balance theory (DFBM)(Ref. 30) is used in this paper to conductpreliminary analysis on the forces in theCNC-IAW process. The force due to the gravity can beexpressed as

where md is the mass of the droplet, rdis the droplet radius, is the dropletdensity, and g is the acceleration of thegravity. The surface tension is given as

where rw is the electrode radius while is the surface tension coefficient. The aerodynamic drag force can beexpressed as

where Cd is the aerodynamic drag coef-ficient, Ad is the area of the drop seenfrom above, and p and vp are the den-sity and fluid velocity of the plasma.

The momentum force can be ex-pressed as

where ve is the wire feed speed and mdis the change of the droplet mass.The electromagnetic force, Fem, is given by

where 0 is the magnetic permittivity,I is the welding current, and is thehalf-angle subtended by the arc root atthe center of the droplet. The increaseof Fem accelerates and the detachmentis completed rapidly. In the conven-tional GMAW process, the droplet isnot detached when the retaining forceF is still sufficient to balance the de-taching force Ft

In Ref. 19, all these forces were ap-proximately calculated and estimated.The results show that the aerodynamicdrag force and momentum force wererelatively small compared to otherforces. In this case, they would be neg-lected in the later analysis. The maindetaching forces, gravitational andelectromagnetic, are shown in Fig. 5.The surface tension force is the mainretaining force. The aerodynamic dragforce and momentum force are not in-cluded in Fig. 5 as aforementioned. For the constant current in theCNC-IAW process shown in Fig. 4,when the wire feed speed is low orhigh, the arc shape would be elongat-ed. In these cases, the main part ofelectromagnetic force as one of de-taching force, Fem,H, is not largeenough to balance out the main partof the retaining surface tension. Thedroplet would grow to a larger size toachieve a larger gravitational force todetach from the solid wire. The metaltransfer frequency would be lowerthan the one with the droplet right de-

43

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WELDING RESEARCH


Fig. 3 — Effect of welding power voltageampere characteristicwith different wire feed speeds. A — 4.0 m/min, 18 V, CV mode; B — 9.0 m/min, 18 V, CV mode; C — 5.0 m/min, 90 A, CC mode; D — 8.5 m/min, 150 A, CC mode.

A

B

C

D

.


taching from the crossing point of thewelding wire and tungsten shown inFig. 4B. The stability of the metal transferwith different wire feed speeds couldalso be illustrated by the welding cur-rent and arc voltage waveform as shownin Fig. 6. The welding current and volt-age significantly reflect stability of themetal transfer and arc behavior. Thefluctuations in the current and voltagecontain important information aboutthe stability of the metal transfer. In theCNC-IAW process with CC mode, the

wire feed speed affects the welding volt-age to a certain degree. When the wire feed speed was 5.0m/min, the average voltage was about25 V, and a relatively large fluctuationin the voltage waveform could be ob-served. The reason was obvious. As thelarger size droplet was needed to in-crease the gravitational detachingforce, and there was an elongated arc,there would be a great opening for thedroplet to grow and detach. The rootof the indirect arc did not enwrap thewhole droplet, which would lead to thelarger fluctuation of the arc voltage. When the wire feed speed was in-creased to 5.5 m/min, the opening be-tween the wire tip and tungsten tipdecreased. So, the average weldingvoltage decreased to about 20 V, andthe fluctuation in the voltage wave-

form also decreased. As the dropletwas detached just beside the tungstentip, the arc was not so long that it en-wrapped the whole droplet althoughthe arc shape was asymmetric. Therewas no need for a larger gravitationaldetaching force, and in this case, thedroplet was detached at a relativelysmall size. It would, in turn, reduce theopening and time interval of the volt-age variation. The metal transfer wasrelatively stable. When the wire feed speed increasedto about 6.0 m/min, the average voltageincreased again. As the arc was elongat-ed again, the arc could not enwrap thewhole droplet. As aforementioned, thedroplet would grow to a larger size toobtain a larger detaching force. As such, for a fixed welding currentlevel, there was an optimal wire feedspeed range to minimize the length ofthe indirect arc and achieve a stablemetal transfer process. By selectingthe optimized one, the droplet couldbe detached at a small size that maybenefit the stability of the metal trans-fer and arc as well as the formation ofthe weld bead.

Effect of Welding Current onMetal Transfer

After selecting the optimized wirefeed speed for each welding currentlevel, the welding current effect onmetal transfer could be conducted. Asshown in Fig. 7, it was found that thewelding current had a significant influ-ence on the metal transfer modes, fre-quency, and droplet size. When the wire feed speed and weld-

WELDING RESEARCH


Fig. 4 — Effect of wire feed speed on metal transfer. A — 5.0 m/min; B — 5.5 m/min; C — 6.0 m/min.

Fig. 5 — The main forces acting on thedroplet.

Fig. 6 — Welding current and arc voltagewaveforms of different wire feed speeds.

A

A

B

B

C

C


ing current were low, as shown in Fig.7A, the diameter of the droplet wasmuch larger than that of the weldingwire diameter. The correspondingtransfer could be considered the globu-lar metal transfer. The transfer fre-quency was low, which was usually 5–6Hz. For these experimental conditions,the electromagnetic force, one of themain detaching forces, was small be-cause of low welding current, thedroplet would grow to a larger size togain a large enough gravitational forceto balance out the surface tension. Asit needed some time interval to achievea larger-sized droplet, the metal trans-fer frequency was relatively low. Increasing the wire feed speed andwelding current to a higher level(5.5–10.0 m/min and 110–170 A), asshown in Fig. 7B–E, the droplet sizewas reduced. The diameter of thedroplet size was almost the same asthat of the welding wire, and the metaltransfer could be considered as spraymode. As the welding current was

higher than previous ones, and itreached a certain level, the electro-magnetic force was large enough toprovide a detaching force combinedwith the effect of the gravitationalforce. A larger droplet size to obtain alarge gravitational force was not need-ed any more. As the time to form adroplet was reduced, the metal trans-fer frequency also increased. The metal transfer frequency anddroplet size are shown in Figs. 8 and 9.In this case, a conclusion could bereached that when increasing wire feedspeed and the corresponding weldingcurrent, the metal transfer modewould be changed from the globularmetal transfer to the projected spraytransfer, and then to the stream sprayone. The metal transfer frequency alsoincreased with the droplet diameterdecrease. When the wire feed speed and cor-responding welding current increased,the droplet trajectory also changedgradually. As shown in Fig. 7A, B, the

trajectory of the detached droplet wasnot along with the axis of the weldingwire. When the wire feed speed andcorresponding current increased, asshown in Fig. 7C–E, the droplet wastransferred to the weld pool almostalong with the feed direction of thewelding wire. In fact, as shown in Fig.5, the gravitational force can be de-composed to two parts: one along theaxis of welding wire Fg,H, which woulddetach the droplet, and another verti-cal to the wire filling direction Fg,V,which would cause the oscillation ofthe droplet. The electromagnetic forcecould also be decomposed into twoparts similarly as the gravitationalforce, Fem,H and Fem,V, which tend tocause the droplet to detach and oscil-late, respectively. As the direction ofaerodynamic drag force and momen-tum force along with the welding wirefeeding direction, the main forces toaffect the droplet trajectory would begravitational force vertical componentFg,V and electromagnetic force verticalcomponent Fem,V. When the wire feed speed and corre-sponding welding current were low, alarger-sized droplet was obtained. Thegravitational force’s vertical componentFg,V was larger than the electromagneticforce’s vertical component Fem,V. In thiscase, the droplet detaching directionwould not be along the wire feed direc-tion, and that tends toward the gravita-tional force direction. When increasingthe welding current, the electromagnet-ic force’s vertical component Fem,Vwould also increase, and it could balanceout the gravitational force vertical com-ponent Fg,V. The droplet would be de-tached at the direction of the wire axle.

Arc Behavior

When the droplet formed, de-tached, and transferred into the weldpool, the arc would be changed corre-spondingly. Analysis of the arc behav-ior would benefit the understanding ofthe metal transfer phenomenon in theCNC-IAW process. As discussed previously, the arcshape has a significant effect on themagnitude of the electromagnetic force.The arc shape changes with the weldingcurrent and would influence the dropletdetachment position. With the lowerwire feed speed, the droplet is detachedabove the tungsten electrode tip. When

WELDING RESEARCH


Fig. 7 — The effect of different welding currents on metal transfer. A — 90 A, 4.5 m/min; B — 110 A, 5.5 m/min; C — 130 A, 7.0 m/min; D — 150 A, 8.0 m/min; E — 170 A, 10 m/min.

A

B

C

D

E


increasing the wire feed speed to a high-er level, the droplet is detached underthe tungsten electrode tip. When usingthe medium and optimized wire feedspeed, the droplet is detached in thevicinity of the tungsten electrode tip, asillustrated in Fig. 10. When the detach-ment occurs above the tungsten tip, asshown in Fig. 10A, the arc shape is char-acterized as a Y shape, and the arc size islarge and its brightness is not intensiveenough. The distance between the twoelectrodes is large, and the arc looks tobe elongated. As analyzed in the previ-ous section, the electromagnetic forcewas not large in this situation. When the droplet was detached un-der the tungsten tip as shown in Fig.10C, the arc shape was characterizedas a pencil shape. The elongated arcmay be the reason for the reduced arcbrightness. When the detachment oc-curred in the vicinity of the tungstentip as shown in Fig. 10B, the arc shapewas considered a heart shape. The dis-tance between the welding wire tipand tungsten tip was approximatelyminimized. This position is consideredto be optimal. The arc shape gradually changed inthe metal transfer process, as shownin Fig. 11. The periodic change of thearc shape was just correlated with dif-ferent stages of droplet detachment.During the initial period (0–9 ms),the droplet began to form at the tipof the welding wire, and the arc evi-dently did not change. When thedroplet grew (9–21 ms), since the arcalways searched for the shortestchannel for the minimal energy con-sumption, the position of the arc rooton the droplet changed gradually.When the droplet grew to a certainsize (21–30 ms), the arc was squeezedbetween the consumable and noncon-

sumable electrode. The elongated arccould be observed. In the last stageafter the droplet detached (30–33ms), the elongated arc went back toits original shape. The arc had an intrinsic self-regula-tion mechanism when the arc lengthwas short (Ref. 31). The arc intrinsicregulation was closely related to theinstantaneous wire melting rate,which would fluctuate depending onthe different heating positions of thearc (Ref. 32). In the CNC-IAW process,the instantaneous wire feed speedcould fluctuate within a small rangebecause of the characteristics of thewire feeder. It could lead to arc lengthfluctuations. When the instantaneous wire feedspeed was lower than the setting one,the arc length would increase, asshown in Fig. 12A. The indirect arccould not enwrap the whole pendingdroplet before detaching, and the in-stantaneous melting rate of weldingwire decreased a little. In this case,more solid wire would appear in thearc zone to maintain a stable arclength. If the instantaneous wire feedwas higher than the setting one, asshown in Fig. 12C, the melting speedwould increase and then the length ofthe solid wire would reduce. The arcwould go back to the previous balanc-ing position, as shown in Fig. 12B. As mentioned previously, the dis-

tance between the consumable andnonconsumable electrodes was only 1–2mm. The arc length in CNC-IAW wasmuch shorter than that in conventionalGMAW. In this case, the arc intrinsicself-regulation ability would be obviousand important to maintaining a certainarc length. It could benefit the stabilityof the metal transfer process, and thusof the welding process.

Conclusions

• An indirect arc welding processwith consumable and nonconsumableelectrodes was proposed, and parame-ters that determine a stable processwere identified; • For a given welding current, therewas an optimal wire feed speed thatcould maintain a stable metal transferprocess for higher metal transferfrequency and smaller droplet size; • The welding current mainly deter-mines the metal transfer mode,droplet size, and metal transfer fre-quency; • The forces acting on the droplet inthe proposed CNC-IAW were analyzedto explain and understand the metaltransfer phenomena observed; • The arc shape had a significant ef-fect on the droplet transfer, and it wasrelated to the wire feed speed andwelding current.

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Fig. 8 — Metal transfer frequency in CNCIAW.

Fig. 10 — Arc shape in CNCIAW. A — Y shape; B — heart shape; C — pencil shape.

Fig. 9 — Droplet size in CNCIAW.

A B C


This work was supported by theNational Natural Science Foundationof China (51005101), Jiamusi Univer-sity Talent Cultivation Project(RC2010-028), and State Key Labora-tory of Advanced Welding ProductionTechnology Project (AWJ-M13-04).

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WELDING RESEARCH


Fig. 11 — Periodic change in the indirect arc shape (150 A, 8.0 m/min).

Fig. 12 — The schematic of an arc intrinsic selfregulation mechanism. A — Lower instantaneous welding wire; B — normal instantaneous welding wire; C — higher instantaneous welding wire.

References

Acknowledgments

A B C


Documents

WELDING RESEARCH Metal Transfer with Force … free metal transfer with low welding current (Refs. 16–20). The droplet size and trajectory were well controlled by the laser power