AbstractThe friction stir weld (FSW) method was developed in 1991 by The Welding Institute (TWI) and is very useful for manufacturing components with low fusion weldability. The success of this relatively new technique is due, in part, to an appropriate combination of some parameters. In order to understand the influence of the parameters such as rotation speed, axial force, and welding velocity, simulations were carried out using the AISI 304L stainless steel. In this work, the process was considered to be a 3D non-Newtonian fluid and the heat input was calculated from the friction between the tool and the plate and from the plastic deformation. The thermal results were compared with the experimental results from the thermocouple measurements. Furthermore, the material flow was related to the formation of defects observed in the experimental welds. The results of the simulation were able to determine the temperature distribution and heat flow, as well as to predict defects in the welding. The simulated viscosity values enabled the prediction of the parameters most likely to cause the formation of flashes. In addition, the injection of inert particles into the model made it possible to predict the formation of wormholes.