Behaviour of the iron vapour core in the arc of a controlled short-arc GMAW process with different shielding gases

Abstract

The controlled metal transfer process (CMT) is a variation of the gas metal arc welding (GMAW) process which periodically varies wire feeding speed. Using a short-arc burning phase to melt the wire tip before the short circuit, heat input to the workpiece is reduced. Using a steel wire and a steel workpiece, iron vapour is produced in the arc, its maximum concentration lying centrally. The interaction of metal vapour and welding gas considerably impacts the arc profile and, consequently, the heat transfer to the weldpool. Optical emission spectroscopy has been applied to determine the radial profiles of the plasma temperature and iron vapour concentration, as well as their temporal behaviour in the arc period for different mixtures of Ar, O2 and CO2 as shielding gases. Both the absolute iron vapour density and the temporal expansion of the iron core differ considerably for the gases Ar + 8%O2, Ar + 18% CO2 and 100% CO2 respectively. Pronounced minimum in the radial temperature profile is found in the arc centre in gas mixtures with high Ar content under the presence of metal vapour. This minimum disappears in pure CO2 gas. Consequently, the temperature and electrical and thermal conductivity in the arc when CO2 is used as a shielding gas are considerably lower.

Influence of the CO2 Content in Shielding Gas on the Temperature of the Shielding Gas Nozzle during GMAW Welding

“…Values under argon determined in [12] for an arc 1040 ms after the start of the high current phase and 1.7 mm above the workpiece. Values for 82% argon/18% CO 2 and CO 2 determined in [13] for an arc 980 ms after the start of the high current phase approximately 1.5 mm above the workpiece. The welding current at the time of measurement was about 420 A for argon, about 250 A for 82% argon/18% CO 2 , and about 330 A for CO 2 .…”

“…The arc temperatures and thus the radiated heat also differ between the shielding gases. Corresponding temperatures were published in [12,13] and are shown in Figure 2. In [12], temperatures of approximately 9000-10,000 K in the metal-vapor dominated arc core were determined for an arc in an argon shielding gas; see Figure 2.…”

“…In [12], temperatures of approximately 9000-10,000 K in the metal-vapor dominated arc core were determined for an arc in an argon shielding gas; see Figure 2. Outside this range, the temperatures in the plasma were approximately 12,000 K. In [13], shielding gas mixtures of CO 2 with high argon content and pure CO 2 were investigated. It is shown that the minimum temperature in the arc core is more pronounced for argon-rich shielding gas mixtures than under pure CO 2 ; see Figure 2.…”

“…the plasma were approximately 12,000 K. In [13], shielding gas mixtures of CO2 with high argon content and pure CO2 were investigated. It is shown that the minimum temperature in the arc core is more pronounced for argon-rich shielding gas mixtures than under pure CO2; see Figure 2.…”

The influence of arc plasma parameters on the form of a welding pool

“…The protective gas was argon of special purity grade. Spectroscopic diagnostics of the plasma temperature was performed by measuring the absolute intensities [7][8][9] of the argon spectral line at 696.54 nm in three arc regions (1 mm below the cath ode, the arc middle, and 1 mm above the anode). The temperatures in three regions of the welding arc obtained experimentally and calculated in the ANSYS CFX package are shown in Figs.…”