Thermal and metal transfer behaviours in pulsed current gas metal arc weld deposition of Al–Mg alloy

Abstract

The control of pulsed current gas metal arc (GMA) welding is highly critical owing to the simultaneous influence of the pulse parameters on thermal and metal transfer behaviours of the process. An analytical model has been developed to provide a theoretical understanding of the influence of pulse parameters on the behaviour of metal transfer and thermal characteristics in pulsed current GMA welding using Al-Mg filler wire. The variations in thermal and metal transfer behaviours with changes in pulse parameters have been satisfactorily analysed considering a summarised influence of pulse parameters defined by a dimensionless factor w5(I b /I p )ft b , proposed previously. A large number of process parameters have been considered, as a result of using four different GMA welding power sources. The hypothesis has been verified using some previously reported experimental results. The theoretical model may be useful in the control of pulse parameters to achieve desired behaviours of thermal and metal transfer under different conditions of weld fabrication, thereby facilitating more universal application of GMA welding. List of symbolsa acceleration of droplet due to plasma aerodynamic drag force, m s 22 A s total surface area of molten metal transferred per pulse, m 2 A w cross-sectional area of filler wire, m 2 C p specific heat of argon plasma510 4 J kg 21 K 21 C p(l) specific heat of liquid filler metal5 1130 J kg 21 K 21 C p(s) specific heat of solid filler metal5 1049 J kg 21 K 21 D diameter of droplets, m E w electrode extension520610 23 m f pulse frequency H A heat input due to arc heating, J s 21 H cv convective heat loss per unit mass of filler metal during flight from tip of filler wire to weld pool, J kg 21 H de heat content per unit mass of droplet at time of deposition, J kg 21 H dp heat content of total weld metal deposited per pulse, kJ H i heat content per unit mass of molten metal during its detachment from electrode, J kg 21 H O heat generated at tip of electrode per unit time, J s 21 H r radiative heat loss per unit mass of filler metal during flight from tip of filler wire to weld pool, J kg 21 H R heat input due to resistive heating, J s 21 H tl total heat loss during flight of molten metal transferred per pulse, kJ H w heat absorbed by filler wire per unit time, J s 21 I b base current, A I eff effective current, A I m mean current, A I p peak current, A j eff effective current density at tip of electrode, A m 22 j g current density of plasma in arc column, A m 22 j m mean current density at tip of electrode, A m 22 l arc length50 . 01 m L latent heat of filler wire53 . 97610 5 J kg 21 M t mass of filler wire transferred per pulse, kg N d number of molten filler metal droplets transferred per pulse N u Nusselt number P r Prandtl number r effective radius, m R resistance of electrode extension, V R e Reynolds number R O resistivity of filler wire50 . 25610 26 V m Science and Technology of Welding and Joining 2006 VOL 11 NO 2232 R w radius of filler wire50 . 8610 23 m t total pulse time t b base cur...

Pulsed Current GMAW for Superior Weld Quality of Austenitic Stainless Steel Sheet

“…Thus, it may facilitate a thorough study concerning the influence of thermal behaviour on the characteristics of weld joint with respect to varying heat input and f in the cases of GMAW and P-GMAW respectively. Besides heat input the variation in f more precisely controls the thermal behaviour of weld joint through regulation of heat built up in weld pool due to its significant influence on energy distribution in the welding process dictated by the interactive pulse parameters [8][9][10]13) …”

“…[5][6][7][8][9][10] However, the involvement of large number of simultaneously interactive pulse current parameters in P-GMAW, that includes pulsed current (I p ), base current (I b ), pulse time (t p ), pulse off time (t b ) and pulse frequency (f), introduces certain degree of complexity in controlling the process for desired welding. [5][6][7][8][9][10] It is reported with ample justification that the complexity of the process primarily arising due to criticality in selection of pulse parameters can be largely solved with the help of correlation of the weld characteristics with a summarized influence of pulse parameters defined by a dimensionless hypothetical factor fϭ[(I b /I p )ft b ] derived from the energy balance concept of the process, where t b is expressed as [(1/f)Ϫt p ]. [8][9][10] In spite of its great potentialities hardly any systematic work has been reported so far on the joining of stainless steel sheet by controlled use of P-GMAW process in consideration of a summarized influence of pulse parameters.…”

“…[5][6][7][8][9][10] It is reported with ample justification that the complexity of the process primarily arising due to criticality in selection of pulse parameters can be largely solved with the help of correlation of the weld characteristics with a summarized influence of pulse parameters defined by a dimensionless hypothetical factor fϭ[(I b /I p )ft b ] derived from the energy balance concept of the process, where t b is expressed as [(1/f)Ϫt p ]. [8][9][10] In spite of its great potentialities hardly any systematic work has been reported so far on the joining of stainless steel sheet by controlled use of P-GMAW process in consideration of a summarized influence of pulse parameters.…”

“…11,12) The pulsed current welding, as it is schematically shown in Fig. 2, was performed at a low heat input with a variation in f from 0.12 to 0.41 to further favourably manipulate thermal behaviour [8][9][10] of the weld producing a sound joint. The low heat input of the P-GMAW process was decided in reference to the successfully tried lowest heat input of the conventional GMAW to produce flawless sound weld joint.…”

Análise da oscilação da poça de solda em P-GMAW por meio de processamento de imagens obtidas por perfilografia

“…Mas o controle das características do arco e do comportamento da transferência de metal pela seleção apropriada dos parâmetros do pulso é bastante difícil devido à infl uência simultânea de um número relativamente grande de parâmetros durante a soldagem [8]. Isso envolve os parâmetros de pulso como corrente média (I m ), corrente de pico (I p ), corrente de base (I b ), tempo de pico (t p ), tempo de base (t b ), frequência de pulso (f), assim como a tensão do arco (V).…”