Thermo-mechanical model development and validation of directed energy deposition additive manufacturing of Ti-6Al-4V

A thermo-mechanical model of directed energy deposition additive manufacturing of Ti-6Al-4V is developed using measurements of the surface convection generated by gasses flowing during the deposition. In directed energy deposition, material is injected into a melt pool that is traversed to fill in a cross-section of a part, building it layer-by-layer. This creates large thermal gradients that generate plastic deformation and residual stresses. Finite element analysis (FEA) is often used to study these phenomena using simple assumptions of the surface convection. This work proposes that a detailed knowledge of the surface heat transfer is required to produce more accurate FEA results. The surface convection generated by the deposition process is measured and implemented in the thermo-mechanical model. Three depositions with different geometries and dwell times are used to validate the model using in situ measurements of the temperature and deflection as well as post-process measurements of the residual stress. An additional model is developed using the assumption of free convection on all surfaces. The results show that a measurement-based convection model is required to produce accurate simulation results.