In this paper we present a numerical model for the simulation of Friction Stir Welding (FSW) processes. FSW is a solid-state
welding process based upon the mixing provoked by a rotating pin that is forced to move between the pieces to join (usually plates). The model employs the Natural Element Method (NEM), a member of the vast family of meshless methods, to perform simulations in an updated Lagrangian approach. This avoids the burden associated with remeshing in traditional Eulerian or Arbitrary Lagrangian-Eulerian (ALE) approaches to this same problem. The method allows to understand the flow patterns that lead to the formation of layers during the welding. Experimental results that confirm the presence of chaotic flow will also presented.