Numerical simulation of arc and droplet transfer in pulsed GMAW of mild steel in argon

Abstract

The process capability of gas metal arc welding (GMAW) processes is mainly determined by the arc properties and the material transfer. In recent years, numerical methods are being used increasingly in order to understand the complex interactions between the arc and material transfer in gas metal arc welding. In this paper, we summarize a procedure to describe the interaction between an arc and a melting and vaporizing electrode. Thereafter, the presented numerical model is used to investigate the arc properties and the metal transfer for a pulsed GMAW process of mild steel in argon. The results of the numerical simulation are compared with OES measurements as well as high-speed images at different times in the pulse cycle and show excellent agreement. The results illustrate the high influence of the changing vaporization rate on the arc attachment at the wire electrode in the high current phase. It could be shown that a substantial part of the current does not participate in the constriction of the wire electrode via the resulting lorentz force which explains the nearly spatter-free droplet detachment in pulsed GMAW processes of mild steel in argon shielding gas.

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

“…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].…”

“…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].…”

“…Hertel et al [8,9] observed a shift in the arc attachment at the wire electrode tapering region, rather than the wire tip, and attributed this phenomenon to the decrease of electrical conductivity of the plasma at the tip of the wire electrode. This is caused by the high vaporization rate of the electrode tip, which cools down the plasma at this region decreasing its electrical conductivity, and subsequently increases the actual arc length, contributing to the increase in arc voltage.…”

“…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]. This last technique requires appropriate apparatus and settings to be employed in order to reveal the details of the different arc regions, metal transfer, and fume formation, in order to provide useful information regarding the welding process and metal transfer phenomenon.…”

“…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].…”