Simulation based build up strategies for additive manufacturing of Ti6Al4V alloy by Laser Beam Wire-Directed Energy Deposition (W-DED-LB) process
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Laser Beam Wire- Directed Energy Deposition (W-DED-LB) is a strategic additive manufacturing technology very suitable for industrial applications demanding medium-large structural part with high deposition rates. However, thermal gradients generated by repeated melting and cooling often cause significant residual stresses and distortion in the workpiece. To reduce this effect, manufacturing alternately on both sides of the substrate is a key strategy for those components with symmetry plane, considering that the substrate will be part of the component. On the other hand, modelling and simulation of DED processes is a powerful tool to assess the part distortion but is challenging due to the multi-physics and multiscale nature of the process. Therefore, complex numerical models must be used. From simulation perspective, this requires differentiation between three types of models according to the time scale and size of the domain to be analysed. Specifically, macro models are used to analyse how the distortion affect the global behaviour of the part, but there is currently no standardized calculation method available for large component manufactured by DED processes. The aim of this work is to apply simulation models to mitigate the final distortion of Ti6Al4V parts manufactured by W-DED-LB process. The simulation has been used to evaluate the best manufactured sequence to distortion compensation. For this purpose thermomechanical model available in the commercial software as Simufact Welding and a simplification of a shrinkage method driven by experimental fitting in ABAQUS software have been used. For the shrinkage purpose a nonlinear elastoplastic model applying the inherent ɛih deformations as ɛth thermal deformations has been considered. This model has been used to evaluate the distortion accumulation trends under different manufacturing strategies: one side and both sides build-up with different sequences. The results of the finite element model, as well as the experimental data, show that alternately side deposition on the base plate balances the build-up distortion during the manufacturing process and the sequence of deposited material significantly affects the success of the distortion mitigation strategy.