Direct metal deposition (DMD) allows to generate complex structures by the direct interaction betweena projected powder and a laser beam, with or without using a coaxial device. One of the main issues to address concerns the prediction of layer widths and heights from the laser and powder parameters, in order to allow thermal or thermo-mechanical modelling in a second step. Indeed, most of the thermalor thermo-mechanical simulations of DMD considered a-priori wall geometries, which strongly limits their predictive aspect.
For this purpose, a simplified finite element-aided analytical modelling was developed and successfully tested on two aeronautical materials : Ti6Al4V titanium alloy and Inconel 718 Nickel - based superalloy.
Our analytical model first considered on a spatially discretized surface the local interaction between the FE simulated melt-pool (in steady state condition) and the local powder feed rate Dm (g/min) distribution, then provided us with average values for the to layers widths wi and heights Δhi on growing wall-like structures. By an incremental approach, this allowed us to predict the entire geometry of a growing wall on a substrate, considering separately each manufactured layer. A thermal limitation to layer growth was alsoimplemented in the model to address specific conditions for which thermal energy contained into the melt-pool does not melt all the incident powder.
A comparison with experimental data was shown to be satisfactory on a large range of experimental conditions.
In a second step, rather simple thermal simulations carried out on COMSOLTM FE software, and using a specific function for the thermal conductivity κ (t,T,x,z) to address additive layers, allowed to reproduce with a good accuracy thermal cycles and melt pool dimensions during the construction of Ti6Al4V and Inconel 718 walls. This was confirmed by comparisons between numerical simulations and experimental T=f(t). It was concluded that our dual simulation-aided morphological + thermal model is an efficient and useful method for predicting geometries and heat cycling of manufactured walls.