Morphological and thermal modelling of direct metal deposition: Application to aeronautical alloys

Abstract

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.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 he...