Finite Element Modelling of Thermal Problems in Shape Metal Deposition

ANDRÉS ANCA; VICTOR FACHINOTTI; NÉSTOR CALVO; ALBERTO CARDONA

Córdoba, Argentina

Congreso; XVI Congreso sobre Métodos Numéricos y sus Aplicaciones ( ENIEF 2007); 2007

AMCA - Octubre 2007

Shape Metal Deposition (SMD) is a novel process for rapid prototyping that employs cold wire Tungsten inert gas (TIG) welding. The state of the art can be enhanced through modelling and control. Accuracy in the part depends on the thermal stresses induced during the welding process. Controlling the heat transfer during deposition would reduce residual stress and hence the distortion. Factors such as the way that temperature changes with the changing deposition geometry will be considered. Wall thickness is controlled by the current, travel speed and wire feed rate and also to some extent by the wire thickness. Travel speed is the resultant of the rotation and tilt of the table and the movement of the TIG welder robot. The faster the travel speed, the thinner the wall thickness, but the speed is limited to values where a consistent arc is produced. If the correct parameters are used, the deposited components will be fully dense. Therefore, care must be taken over the choice of weld parameters to prevent porosity due to poor choice of wire feed rate, excessive speed, etc. In this work, the finite element thermal modelling of SMD is presented. We use linear tetrahedral finite elements together with the discontinuous integration technique to account for the steep variation of properties during melting. The domain of analysis contains the weld and the substrate, while the welding arc is introduced as an ellipsoidal heat source depending on welding parameters. Special remeshing strategies are developed to follow the evolution of the piece during SMD. Finally, the application of a model to a real SMD case is discussed.