Development and validation of a fully coupled thermo-mechanical model for in-situ micro-rolling in laser-directed energy deposition: Single-track multi-layer case

Abstract

Directed Energy Deposition (DED) has recently been hybridised with in-situ rolling, providing elevated temperature deformations and enhancing build quality. Analysing the thermo-mechanical aspects of deformations with sufficient fidelity can not be achieved experimentally. So, a fully coupled thermo-mechanical model for a multi-layer case using the finite element method has been developed to capture the thermal and mechanical facets of the deposition and rolling processes. Modelling features a hybrid active and quiet element activation strategy that mitigates convergence issues from activating a newly deposited layer over previously rolled ones. The model's predictions have been validated with reasonable accuracy against temperature history and rolling load measurements in an experimental case study using IN718. These predictions provide insights into the in-situ rolling effects with their quantification, including the impact on the thermal and stress-strain fields and histories. For instance, the temperature at the rolling location and the local temperature drop increase with the number of layers. The thermal stress induced by deposition overshadows the influence of in-situ rolling. The rolling deformation penetrates till the third preceding layer, and deposition leads to above the recrystallisation temperature reheating till the fourth layer. These predictions can be used for parametric optimisation with metallurgical criteria.