EFFECT OF SHIELDING GASES ON METAL TRANSFER AND WELD BEAD GEOMETRY IN SYNERGIC MIG WELDING OF ALUMINIUM ALLOY 6061

Abstract

This experimental study was carried out to analyze voltage transients associated with synergic MIG welding of aluminium alloy 6061 for various plate thicknesses using different shielding gases and relation between these transients and observations is used to analyze the mode of metal transfer and weld bead geometry. The quality, efficiency and overall operating acceptance of the welding operation are strongly dependent on the shielding gas, since it dominates the mode of metal transfer. The shielding gas not only affects the properties of the weld but also determines the shape and penetration pattern as well. The type of metal transfer depend on many welding parameters as welding wire feed rate, arc voltage, nozzle to plate distance and types of shielding gas used. Easy, convenient and popular method to observe the mode of metal transfer is digital storage oscilloscope, in which the voltage transients were recorded during welding and analyzed. The study of weld bead geometry is important, as it determine the stress carrying capacity of a weld. Fractional factorial technique of design of experiment was used to develop relationship for predicting weld bead geometry, which enables to quantify the direct and interaction effects. The response factors, namely bead penetration, weld width, reinforcement height as affected by arc voltage, wire feed rate, welding speed, gas flow rate and nozzle-to-plate distance for Argon, Helium and Argon+ 50% Helium mixture have been investigated and analyzed. The models developed have been checked for their adequacy and significance by using the F-test and the t-test, respectively. Main and interaction effects of the process variables on weld bead geometry are presented in graphical form. The developed models can be used for prediction of important weld bead dimensions and control of the weld bead quality by selecting appropriate process parameter values.