Computational modelling of shaped metal deposition

Shaped metal deposition (SMD) is a novel process for rapid prototyping that employs tungsten inert gas (TIG) welding controlled by a robot inside an inert gas chamber to build parts by successive layer deposition. This process can be enhanced through modelling and control. Industries are interested in developing systematized models to explain observed phenomena and to predict processing conditions for process planning and optimization. In this work, thermal and mechanical finite element (FE) modelling of SMD is presented. The thermal problem is solved with linear tetrahedral finite FEs that take into account the liquid/solid phase change phenomenon. The mechanical problem is solved with hexahedral elements with tri-linear interpolation of displacements and constant interpolation of mean stresses (Q1-P0). Special techniques to account for material addition were developed, based on activation/deactivation of FEs. Numerical tests were conducted to determine the heat source model parameters. An experiment using Ti-6Al-4V material was developed to validate the formulation. The test consisted of a TIG-wash procedure (arc passing without wire feeding to preheat the plate) followed by a single welding layer. The results, including temperatures and residual displacements, are compared with those obtained with the finite element method (FEM) code. Finally, a multilayer SMD numerical example is presented. Copyright (C) 2010 John Wiley & Sons, Ltd.