Analysing thermo-mechanical effects of in-situ micro-rolling in single-bead laser-directed energy deposition via finite element modelling

In-situ rolling in directed energy deposition has shown improvements in deposited part quality. These improvements are driven by high-temperature material deformation. Experimentally capturing high-temperature deformation aspects is challenging. The modelling approach requires simultaneous consideration of rolling and deposition aspects. Therefore, a fully coupled thermo-mechanical model is developed for single-bead cases. It combines the frameworks of heat source motion, corresponding element activations, and thermo-mechanical rolling deformations in a single analysis. Johnson–Cook plasticity model is incorporated for yield stress evolutions with thermo-mechanical deformations. Experimental validations are done using temperature and rolling load measurements in laser deposition with 90% and 84% respective accuracies. Thermal predictions of the offset-dependent rolling temperatures are made, and the chilling effects of rolling are identified to be spatially and temporally confined on the deposited bead. The induced plastic strains on the bead for given compressions are quantified, and corresponding rolling loads are predicted. Plane strain condition with triaxial stress formation at the rolling location offers new insights on the relief in longitudinal stress, even with compressive load in the build direction, due to restriction in the plastic flow of material in the longitudinal direction with Poisson’s effects. Thus, this work comprehensively understands the hot deformation effects of in-situ rolling and its parameters through finite element analyses in single bead cases.