A finite difference method for thermal behaviour and stress analysis during laser directed energy deposition considering airflow convection effects

Thermal behaviour in directed energy deposition (DED) governs both the microstructural evolution of deposited layers and the distribution of residual stresses. However, the effect of airflow field at the nozzle on the thermal history is unclear at present. Here, a temperature field predicted model was developed to investigate the thermal changes in additively manufactured IN718 alloy, incorporating airflow effects and heat exchange. To improve the calculation accuracy and efficiency, a finite difference solution method based on multi-scale discretization and hybrid Newton iteration is proposed. Meanwhile, the effectiveness of the theoretical model was verified by the built temperature acquisition system, with 8.01% in average error. Subsequently, the influence of thermal history on the residual stress distribution in the deposited layer and substrate is analyzed in deposition process. Results indicate that the residual von Mises stress is greater at locations closer to the severe heat-affected zone. As the distance from the severe heat-affected zone increases, the residual von Mises stress decreases. The residual von Mises stress is slightly greater at the middle edge compared to both ends of the deposited layer. This study provides insights for optimising forming quality during metal 3D printing.