In arc welding based additive manufacturing, the surface topographies of deposited layer are more complex than conventional welding, therefore, the distribution of the electromagnetic force in molten pool, arc pressure, plasma shear stress and heat flux on molten pool surface are not the same as the conventional welding. A three-dimensional weak coupling modeling method of the arc and metal transport is developed to simulate the arc, molten pool dynamic and droplet impingement in arc welding based additive manufacturing. In the arc model, the molten pool is simplified to be solid state on the basis of experimentally observed results. The arc is simulated firstly, and then the electromagnetic force, arc pressure, plasma shear stress and heat flux are extracted and transmitted to metal transport model. The volume of fluid (VOF) method is employed to track free surface of molten pool and droplet, and the continuum surface force (CSF) method is applied to transform all the surface forces on free surface as localized body forces. This weak coupling model has better accuracy than empirical model and decreases computational consumption. The molten pool morphology and cross-sectional profile of simulated results accord well with experimental results in both single-bead deposition and overlapping deposition, which indicates that this weak coupling modeling method is capable of simulating the complex heat and mass transfer phenomena in arc welding based additive manufacturing. (C) 2016 Elsevier Ltd. All rights reserved.