A novel numerical method to predict the transient track geometry and thermomechanical effects through in-situ modification of the process parameters in Direct Energy Deposition

摘要

Direct Energy Deposition (DED) is being widely used to repair damaged components to increase service life and economical operation. Process parameters including laser power, traverse speed and the mass flowrate of the feedstock material may be adapted in-situ. This allows bespoke repair strategies to be devised to match the variability in the condition of the parts supplied that require repair; however, there are limited modelling techniques that allow the adaptive control within the DED process to be represented. In this study, a novel modelling strategy is presented which allows the DED process to be modelled in a transient state. This allows varying process parameters to be included in the model, to predict the transient track geometry and the associated thermomechanical effects of the process. Here, a single-track deposition of IN718 with a varying cross section has been modelled utilising the proposed approach. The modelling methodology was validated with a corresponding experimental study on a deposition made using a Nd:YAG laser source with a coaxial nozzle. An in-situ modification was generated by variation of the laser power. The track profile was compared against focus variation microscopy images and the thermomechanical portion of the model was validated through in-situ temperature measurements, micrographs and residual stress, obtained from neutron diffraction measurements. A good agreement between the predicted and experimental findings were observed. The track height and width were predicted with a maximum error of 6.5% and 7.6% respectively. The peak temperature and residual stress were predicted within 6.2% and 11.4% respectively. Overall, the modelling method presented will allow complex and bespoke multi parameter repair strategies to be rapidly developed.