Dynamic analysis of droplet transfer in gas–metal arc welding: modelling and experiments

Abstract

In this work, a pulsed welding process is investigated to highlight how a time-varying profile of current impacts the metal transfer dynamics. First, the process is recorded using a high-speed camera, allowing us to qualitatively evaluate the effectiveness of metal transfer and the synchronization of droplet detachment with current peaks. Second, a time-dependent axisymmetric 2D model is developed to take into account both the droplet detachment using a volume-of-fluid model and the production and diffusion of metal vapour through a simplified diffusion model (neglecting demixing effects). We report a comparison between experimental and simulative results of a pulsed transfer mode for a steel wire (φ = 1 mm) and Ar shielding gas.

On the Visualization of Gas Metal Arc Welding Plasma and the Relationship Between Arc Length and Voltage

“…As the current increases to the peak phase, the amount of vapor emitted from the wire tip increases due to the increase in wire tip temperature. This evolution of metal vapor region has been repeatedly predicted by numerical simulations [8,9,13] and reported in studies utilizing high-speed imaging [25]. Additionally, in Figure 1 for the exposure time of 3.91 and 6.25 µs, one can see that the metal vapor around the secondary droplet is pushed downward away from the molten pool as the pulse current increases to a peak value, owing to the increase in plasma flow velocity as a consequence of the current increase [10].…”

“…Additionally, in Figure 1 for the exposure time of 3.91 and 6.25 µs, one can see that the metal vapor around the secondary droplet is pushed downward away from the molten pool as the pulse current increases to a peak value, owing to the increase in plasma flow velocity as a consequence of the current increase [10]. This metal vapor pushed to lower temperature regions of the arc will allow the nucleation and growth of nanoparticles by condensation, leading to fume formation [13,31] (see Supplemental Video S1 for details).…”

“…In Figure 1 at the times of 123.0 and 79.8 ms for the exposure time of 3.91 and 6.25 µs, respectively, the light captured by the camera sensor is being emitted from the wire tip, weld pool, and the small droplet being transferred. Those regions are the main sources of iron vapor, owing to their high surface temperatures [11,13]. As the current increases to the peak phase, the amount of vapor emitted from the wire tip increases due to the increase in wire tip temperature.…”

“…This definition, along with being more general, is physically more consistent, and agrees with the results of Hertel et al [8,9] which show that depending on the amount of iron metal vapor present in the arc, less than 20% of the instantaneous current is flowing through the electrode tip. This is due to the shift in arc attachment position to the tapered region caused by the presence of a high concentration of iron vapor at the wire tip [10][11][12][13][14]. Therefore, the definition that the electric arc comprises the region between the electrode tip and the surface of the weld pool is not quite physically accurate.…”

“…According to the literature, the structure of the electric arc in GMAW assumes a conical shape, and is divided in two distinct regions: an outer cone composed mostly of the ionized shielding gas, and an inner cone, which presents a high concentration of electrode metal vapor [8][9][10][11][12][13][18][19][20][21][22]. This arc structure has been reported via spectroscopy measurements [18][19][20][21]23], numerical simulations [8,9,24], and high-speed imaging experiments [25].…”