Technical paperThe controlled short circuit GMAW process: A tutorial
Introduction
Short arc, short circuit or dip transfer is a variant of the GMAW process. It has been used for many years particularly for the fabrication of plain carbon and low alloy steels. It operates at low current and produces a fast freezing weld pool which is particularly suitable for joining thin sheet steel and for all positional welding of thicker sections. It also has good root run filling capabilities and tolerance to variable root gaps when used by skilled manual operators or appropriately designed automatic systems. Like most process modes it does have limitations but before exploring these and the developments which allow them to be overcome it is necessary to understand the principles of the conventional dip transfer process.
Section snippets
Conventional dip transfer
The wire is fed at a constant speed towards the workpiece at a rate which slightly exceeds the rate at which the combined effect of resistive heating in the wire extension and arc heating can melt it. As a result the gap between the electrode tip and the weld pool gradually decreases and ultimately the solid wire bridges the arc, dips into the weld pool and creates a short circuit. Conventional GMAW power sources have a nominally constant voltage output (Fig. 1) which results in a very high
Limitations
The original transformer rectifier power supplies used for GMA welding had fixed static current–voltage characteristics and inductively controlled dynamic response. These features enable the basic process requirements to be met and were adjusted by the operator to provide stable operation. In practice most welders choose a high dip frequency since this is easily tuned by ear and appears more stable. Unfortunately effective heating of the workpiece only occurs during the arcing period [3] and as
Overcoming the limitations
Whilst the dip transfer GMAW process is extremely useful the potential for lack of fusion and excessive spatter generation have in the past restricted its use. It was recognized that these limitations were partly due to the conventional power source design which made it difficult to decouple the heating effect of the arcing period from the conditions which produced stable, low spatter operation. Smith [4] attempted to improve the process by using two power sources connected in parallel – a low
Controlled dip transfer
The ability to modify the power source output dynamically improved significantly with the introduction of electronic power control for welding systems. In the early 70s, Boughton and MacGregor [6] working at TWI in the UK developed a control system for dip transfer GMAW using a transistor series regulator power source to electronically control the short circuit waveform. The principle is illustrated in Fig. 5.
At the onset of the short circuit (detected by the voltage waveform minimum) the
Summary
There are now around 10 variants of the controlled dip process. All of these systems not only offer stable low spatter short circuit transfer but they allow this to be achieved at lower dip frequencies which addresses the arc heating limitation of conventional dip transfer discussed above. All of these techniques retain the inherent characteristics of short circuiting transfer – they give good positional performance and are applicable to thin sheet with mean currents from around 40 to 180 amps.
Conclusion
Controlled short circuit transfer GMAW is a development of conventional short circuit transfer process which retains all of the advantages and overcomes the previous limitations of this important process mode. The use of controlled short circuiting also has the unanticipated advantage of much improved root run gap tolerance on thicker sections. Choice of the appropriate system should be based on the features described above and the overall flexibility or simplicity of operation.
Acknowledgements
The authors would like to thank colleagues at the University of Wollongong and elsewhere who have contributed to the advancement of this process and our understanding of it. In particular we are grateful to the late Peter Boughton for his pioneering work in this field in the 1970s and more recently Dr. Gary Dean who pursued further research on this topic in Australia.
References (14)
Developments in the MIG welding of sheet steel and strip, sheet metal industries
Control of short circuit gas metal arc welding process using instantaneous current regulation
(2000)Optimisation of metal transfer and fusion using current control in dip transfer GMAW
(2003)Features of short circuiting CO2 arc welding with a duplex power source
British Welding Journal
(1966)Advanced welding processes, book, first published by IOP 1992, revised ed. 2006 published by Woodhead Publishing Limited 1992
(1992)- et al.
Control of short circuiting in MIG welding
Welding Research International
(1974) A new, low spatter arc welding machine
Welding Journal
(1993)
Cited by (41)
Influence of controlled and conventional short circuit waveforms on mechanical and microstructural effects in the gas metal arc welding processes
2024, Case Studies in Thermal EngineeringEnhancing tensile properties of pulsed CMT–MIG welded high strength AA2014-T6 alloy joints: Effect of post weld heat treatment
2024, International Journal of Lightweight Materials and ManufactureDeepening the understanding of arc characteristics and metal properties in GMAW-based WAAM with wire retraction via a multi-physics model
2023, Journal of Manufacturing ProcessesImproving arc stability during wire arc additive manufacturing of thin-walled titanium components
2021, Journal of Manufacturing ProcessesCitation Excerpt :Norish et al. demonstrated this mode of transfer using a microprocessor-controlled powder source system which allowed retracting the wire instantaneously when the wire comes in contact with the weld pool [20,18]. The current and dynamic wire feed controlled dip short-circuit transfer was commercialised by Fronius as Cold Metal Transfer welding system [18]. Similarly, current-controlled dip short circuit transfer without dynamic wire feed was commercialised by Lincoln in the name of surface tension transfer (STT) [21].
Fabrication of metallic parts with overhanging structures using the robotic wire arc additive manufacturing
2021, Journal of Manufacturing ProcessesCitation Excerpt :From the preceding analysis and section 2.1, it is clear that the short circuit mode of operation is most suitable for multi-directional WAAM. In addition, Norrish and Cuiuri [28] explain that the controlled short circuit process offers improved stability, lower spatter and better process tolerance. Most commonly, these controlled short circuit processes rely on transient current control to prepare a droplet on the wire tip during the arcing period and minimise short circuit rupture current [29].
Wire feed pulsation as a means of inducing surface tension metal transfer in Gas Metal Arc Welding
2021, Journal of Manufacturing Processes