This paper studied the influences of shielding gas compositions on the transport phenomena in the metal domain during gas metal arc welding (GMAW). A comprehensive model was developed to simulate the time-dependent processes of the electrode melting; the droplet formation, detachment, transfer and impingement onto the workpiece; the weld pool dynamics and bead formation and their transient coupling with the arc plasma. The transient melt-flow velocity and temperature distributions in the metal shielded by pure argon and argon-helium mixtures with various mixing ratios are presented. It is predicted that the increase of helium content and the resulting arc contraction induce an upward electromagnetic force at the bottom of the droplet to sustain the droplet at the electrode tip. As a result, the more oblate droplet and the longer droplet formation time are produced. The behaviors of the predicted droplet shape and detachment frequency are in agreement with the published results. It is also found that, under the identical energy input, the weld bead has a shallower penetration depth and broader bead width when helium content increases.

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