Technical paper
Double-electrode arc welding process: Principle, variants, control and developments

https://doi.org/10.1016/j.jmapro.2013.08.003Get rights and content

Abstract

Double-electrode gas metal arc welding (DE-GMAW) is a novel welding process in which a second electrode, non-consumable or consumable, is added to bypass part of the wire current. The bypass current reduces the heat input in non-consumable DE-GMAW or increases the deposition rate in consumable DE-GMAW. The fixed correlation of the heat input with the deposition in conventional GMAW and its variants is thus changed and becomes controllable. At the University of Kentucky, DE-GMAW has been tested/developed by adding a plasma arc welding torch, a GTAW (gas tungsten arc welding) torch, a pair of GTAW torches, and a GMAW torch. Steels and aluminum alloys are welded and the system is powered by one or multiple power supplies with appropriate control methods. The metal transfer has been studied at the University of Kentucky and Shandong University resulting in the desirable spray transfer be obtained with less than 100 A base current for 1.2 mm diameter steel wire. At Lanzhou University of Technology, pulsed DE-GMAW has been successfully developed to join aluminum/magnesium to steel. At the Adaptive Intelligent Systems LLC, DE-GMAW principle has been applied to the submerged arc welding (SAW) and the embedded control systems needed for industrial applications have been developed. The DE-SAW resulted in 1/3 reduction in heat input for a shipbuilding application and the weld penetration depth was successfully feedback controlled. In addition, the bypass concept is extended to the GTAW resulting in the arcing-wire GTAW which adds a second arc established between the tungsten and filler to the existing gas tungsten arc. The DE-GMAW is extended to double-electrode arc welding (DE-AW) where the main electrode may not necessarily to be consumable. Recently, the Beijing University of Technology systematically studied the metal transfer in the arcing-wire GTAW and found that the desired metal transfer modes may always be obtained from the given wire feed speed by adjusting the wire current and wire position/orientation appropriately. A variety of DE-AW processes are thus available to suit for different applications, using existing arc welding equipment.

Introduction

Two technologies have been developed to modify GMAW for faster deposition: Tandem GMAW [1], [2] and Variable-Polarity GMAW (VP-GMAW) [3], [4], [5], [6], [7]. In Tandem GMAW, two torches have been integrated into one bigger torch, and two close arcs are independently established between their own wire and work-piece in parallel and are adjusted by their own GMAW power supply. In essence, Tandem GMAW is still considered two parallel conventional GMAW processes. It allows the deposition rate be doubled without increasing the arc pressure. For VP-GMAW, liquid droplets are still detached during the reverse polarity (wire positive) period, but the welding wire can be melted faster during the straight polarity (wire negative) period [3], [8]. It was found that to melt the welding wire at the same rate, the base metal heat input could be “up to 47 percent less” than the conventional pulsed GMAW [8]. Thus, when the allowed base metal heat input is given, VP-GMAW may also double the deposition rate. Modifications by adding a laser to form hybrid laser-arc processes [9], [10], [11], [12], [13], [14], [15], [16] can penetrate deeper to reduce the needed deposition. However, the resultant process is no longer a pure arc welding process and many advantages associated with arc welding may be compromised.

The double-electrode GMAW [17], [18] and its variants are introduced to increase the deposition rate without increasing the heat input, reduce the heat input without compromising the deposition rate, or freely provide the needed heat input and deposition rate as desired by different applications which typically use GMAW or its variants. For conventional GMAW and its variants, the base metal current is exactly the same as the wire current, i.e., the current flows through the wire. This is the fundamental principle not only for GMAW but also for all other conventional arc welding processes in which an arc must be established between an electrode and the work-piece. Because of this fundamental principle, while the wire current needs to be increased to increase the deposition rate, the base metal current increases exactly the same regardless of the actual need of the work-piece. The DE-GMAW changes this principle by introducing a bypass channel such that the deposition rate no longer needs to be proportional to the heat input applied into the work-piece.

In this tutorial, the principle, developments and extension of the DE-GMAW are discussed and outlined to help further develop/extend this process for manufacturing applications.

Section snippets

Double-electrode GMAW principle

Fig. 1 demonstrates the principle of the DE-GMAW process and its variants where the main electrode is a consumable wire. The main power supply, main torch/electrode and work-piece form the conventional GMAW process and the main loop. The bypass torch added provides an additional electrode to form an additional arc, i.e., the bypass arc, with the main electrode and closes the bypass loop. In Fig. 1, the bypass arc is powered by an added second power supply but it may also be powered by the same

Non-consumable DE-GMAW using constrained bypass arc

A non-consumable DE-GMAW uses a non-consumable bypass electrode to realize the general DE-GMAW system in Fig. 1. Its feasibility was first verified using a PAW torch to provide the non-consumable second electrode in 2004 at the University of Kentucky [17], [18] as shown in Fig. 2. The use of PAW torch was to ease the establishment of the bypass arc because the pilot arc can easily provide a reliable channel to bridge the main arc with the tungsten second electrode. In fact, the constrained

Non-consumable DE-GMAW using unconstrained bypass arc

While the pre-existence of a constrained pilot arc can ease the ignition of the bypass arc after the main arc has been established, its associated high cost for the equipment and the inconvenient large size of the bypass torch are all unwanted. In the non-consumable DE-GMAW system shown in Fig. 4, the PAW torch in Fig. 2 is replaced by a GTAW torch. The bypass power supply is replaced by a bypass control circuit which controls the passing bypass current at the desired level. The main GMAW power

Metal transfer in non-consumable DE-GMAW using unconstrained bypass arc

The American Welding Society (AWS) classifies the metal transfer into three primary modes: spray transfer, globular transfer, and short-circuiting transfer. In the spray transfer, the liquid metal droplets transfer into the weld pool across the arc gap with diameters similar to or smaller than that of the wire. The International Institute of Welding (IIW) further classifieds the spray transfer mode into the projected spray (or drop spray), streaming spray, and rotating spray. In the globular

Consumable DE-GMAW and analysis [23,24]

In non-consumable DE-GMAW, although extra heat input and arc force have been reduced, the energy absorbed by the bypass electrode is wasted. If the bypass electrode is a consumable wire, the waste can be eliminated while still providing the advantages associated with DE-GMAW. The resultant process is the consumable DE-GMAW shown in Fig. 10 and its heat input controllability as represented by the range of the deposition efficiency p has been discussed earlier in Section 2 and especially

Control of consumable DE-GMAW

A method to produce desired welds is to control the base metal current and bypass current at desired levels such that the heat input determined by the total current (their sum) and penetration capability determined by the base metal current and heat input are accurately controlled. When CV power supplies are used, these two currents may be adjusted by their corresponding wire feed speeds in large ranges. The adjustments on the wire feed speeds affect the total mass input but it may be

Double-electrode submerged arc welding (DE-SAW) [27]

Submerged arc welding (SAW) is a variant of GMAW which allows the use of extra high currents to deposit metals at high speeds. The major issue associated with high currents and high deposition rates is the associated large heat input which causes large distortion whose correction is highly costly. An extension of the DE-GMAW into SAW may result in desirable heat input and distortion reductions. The resultant variant is referred to as DE-SAW.

Fig. 12 shows a DE-GMAW system developed at the

Penetration depth control [27]

A number of studies have been devoted to modeling the SAW process [31], [32], [33], [34], [35]. Based on these studies, a comprehensive model has been proposed to correlate the depth of the weld penetration to a number of welding parameters as the regression variables:P=f(Ibm,Wt,G,CTWD,S)

Here P is the depth of partial penetration weld (in.), Ibm the base metal current (A), Wt the total deposition rate (lb/h), G the gap of the joint (in.), CTWD the contact-tip-to-work distance (in.), and S the

Pulsed DE-GMAW for aluminum and galvanized steel welding

Aluminum alloy and galvanized steel hybrid structures can effectively reduce vehicle weights. However, aluminum and steel have very different physical characteristics including the melting temperature and thermal expansion that make the corresponding dissimilar metal joining to be challenging. Laser and cold metal transfer (CMT) welding are few fusion welding methods that have found success for this type of dissimilar metals joining due to their low heat input [36], [37]. Since the DE-GMAW

Other variants of DE-GMAW and double-electrode arc welding

A few variants have been proposed to extend the DE-GMAW concept or beyond the exact definition of DE-GMAW. The indirect arc method [43] has been independently proposed and developed at Shandong University, which establishes an arc between two consumable rods without the work-piece to be a part of the arc, either anode or cathode, will not be discussed below. It reduces the heat input to a minimum and shares a certain similarity with DE-DMAW but lacks the mechanism to adjust the heat input as

Summary and future work

  • Double-electrode GMAW changes the principle of conventional arc welding where the arc is established between the electrode and work-piece, and the electrode current equals the base metal current.

  • Double-electrode GMAW reduces the base metal current from the main wire melting current by means of a bypass loop.

  • Both non-consumable and consumable DE-GMAW, including their variants, increase and adjust/control the deposition efficiency from that of the conventional GMAW, resulting in a reduced and

Acknowledgements

The Adaptive Intelligent Systems LLC thanks the support from the Navy under contracts N00024-09-C-4140, N65538-08-M-0049, and N65538-10-M-0110 and Kentucky Cabinet for Economic Development (CED) Office of Commercialization and Innovation through Kentucky Science and Engineering Corp. under agreements KSTC-184-512-08-038 and KSTC-184-512-09-067. The Adaptive Intelligent Systems LLC also thanks the approvals for public release from the Navy (5720/00DT 2013-0033, 5720/00DT 2012-0854, 5720/00DT

References (54)

  • D.D. Harwig et al.

    Arc behavior and melting rate in the VP-GMAW process

    Welding Journal

    (2006)
  • D.D. Harwig

    Arc Behavior and Melting Rate in the VP-GMAW Process

    (2003)
  • A. Mahrle et al.

    Hybrid laser beam welding-classification, characteristics, and applications

    Journal of Laser Applications

    (2006)
  • L. Liu et al.

    A new laser-arc hybrid welding technique based on energy conservation

    Materials Transactions

    (2006)
  • P. Seyffarth et al.

    Laser-arc processes and their applications in welding and materials treatment

    (2002)
  • C. Bagger et al.

    Review of laser hybrid welding

    Journal of Laser Applications

    (2005)
  • W.M. Steen et al.

    Arc augmented laser welding

    Metal Construction

    (1979)
  • R.P. Walduck et al.

    Plasma arc augmented laser welding

    Welding and Metal Fabrication

    (1994)
  • E.W. Reutzel et al.

    Joining pipe with the hybrid laser-GMAW process: weld test results and cost analysis

    Welding Journal (Miami, Fla)

    (2006)
  • M. Sullivan

    Laser pipe welding project, in National Shipbuilding Research Program Welding Panel Meeting, Provo, UT

    (2006)
  • Y.M. Zhang et al.

    Double electrodes improve GMAW heat input control

    Welding Journal (Miami, Fla)

    (2004)
  • K.H. Li et al.

    Double-electrode GMAW process and control

    Welding Journal (Miami, Fla)

    (2007)
  • M. Amin

    Pulse current parameters for arc stability and controlled metal transfer in arc welding

    Metal Construction

    (1983)
  • K.H. Li et al.

    Metal transfer in double-electrode gas metal arc welding

    Journal of Manufacturing Science and Engineering, Transactions of the ASME

    (2007)
  • K.H. Li et al.

    Mechanism of metal transfer in DE-GMAW

    Journal of Materials Science and Technology

    (2009)
  • K.H. Li et al.

    Consumable double-electrode GMAW – Part 1: the process

    Welding Journal (Miami, Fla)

    (2008)
  • K.H. Li et al.

    Consumable double-electrode GMAW part II: monitoring, modeling, and control

    Welding Journal

    (2008)
  • Cited by (81)

    • An investigation on droplet transfer for bypass-current wire-heating PAW

      2021, Journal of Manufacturing Processes
      Citation Excerpt :

      The deposition efficiency was no longer proportional to the heat input applied to the base metal. A variety of traditional arc welding processes have been improved and significant results have been achieved on the basis of the bypass current theory [21–27]. Researchers have shown an increase in the process of bypass current technology research, the influence of bypass current on the droplet transfer behavior was also studied [28–32].

    • Hybrid welding technologies

      2021, Advanced Welding and Deforming
    • Advancements in Intelligent Gas Metal Arc Welding Systems: Fundamentals and Applications

      2021, Advancements in Intelligent Gas Metal Arc Welding Systems: Fundamentals and Applications
    View all citing articles on Scopus
    View full text