Finite-element modelling of heat transfer in shaped metal deposition and experimental validation

Shaped metal deposition (SMD) is a novel technology for building near-net-shaped components by successive layer deposition using a welding machine. The SMD rig consists of a robot with a tungsten inert gas welding torch and manipulator, both of which are housed inside a sealed chamber. A series of walls were made from Ti–6Al–4V alloy by SMD and the heat transfer problem during layer deposition was analysed in all cases. The specimens were built using a wide range of process parameters (number of layers, layer height, wire feed rate, travel speed, heat input, etc.) and wall dimensions. During the fabrication process, the SMD built part is subjected repeatedly to high temperature gradients and high heating and cooling rates, resulting in a unique morphology and microstructures usually not observed in conventional fabrication techniques. A finite-element model for the thermal analysis of this deposition process was constructed. The aims of this study are, firstly, to correlate the predicted temperature field to experimental observations to validate the numerical model of this complex process; and secondly, to explain on the basis of the computed temperature and temperature rate the appearance of characteristic microstructures on the top of the walls, and in the substrate and intermediate region.