An integrated comprehensive 3D model has been developed to study the transport phenomena in gas metal arc welding (GMAW). This includes the arc plasma, droplet generation, transfer and impingement onto the weld pool, and weld pool dynamics. The continuum formulation is used for the conservation equations of mass, momentum, and energy in the metal zone. The free surface is tracked using the volume-of-fluid (VOF) technique. The 3D plasma arc model is solved for the electric and magnetic fields in the entire domain. The interaction and coupling between the metal zone and the plasma zone is considered. The distributions of velocity, pressure, temperature, and free surface for the metal zone and the velocity, pressure, and temperature for the plasma zone are all calculated as a function of time. The numerical results show the time-dependant distributions of arc pressure, current density, and heat transfer at the workpiece surface are different from presumed Gaussian distributions in previous models. It is also observed that these distributions for a moving arc are non-axisymmetric and the peaks shift to the arc moving direction. (C) 2008 Elsevier Ltd. All rights reserved.