Energy transfer including solid-liquid phase transformation aspects in modelling of additive layer manufacturing using Lattice Boltzmann-Cellular automata methods: ICCHMT 2018 International Conference on Computational Heat, Mass and Momentum Transfer

A new holistic numerical model based on Lattice Boltzmann and cellular automata methods (LBM-CA) is currently under development within a frame of an integrated modelling approach applied for studying the complex relationship between different physical mechanisms taking place during laser assisted additive layer manufacturing (ALM). The entire ALM process has been analysed and divided on several stages considering a powder bed deposition, laser energy absorption and heating of the powder bed by the moving highly concentrated energy source leading to powder melting, fluid flow in the melted pool and through partly or not melted material and solidification. The presented earlier results included the entire structure of the model consisting of different modules connected together demonstrating the homogeneity of the proposed holistic model. The modules, considering the mentioned above physical phenomena, were developed to different extent leaving many aspects of this integrated numerical approach for further consideration and analysis. The aim of this work is more detailed analysis of energy transfer including solid-liquid phase transformation during the ALM process. The presented results are mainly related to consideration of melting and solidification of the powder bed including of the free surface flow, wettability, surface tension and other relevant phenomena. Initially, the absorbed thermal energy spreads by heat diffusion. The solid-liquid phase transformation starts when the temperature in the affected zone exceeds the solidus temperature. After consuming latent heat, when the volume of liquid phase exceeds a threshold, the solid particulate material exhibit signs of liquid behaviour, where heat transport is described by diffusion or convection including radiation and convection heat transfer from the liquid surface. The excess heat in the area of the liquid phase is dissipated by heat conduction into the deeper layers of the powder bed leading to re-solidification of the melt pool. The different stages and fragments of LBM-CA model development are presented and discussed. The validation of the general aspects of the obtained modelling data showed that the developed numerical algorithm is in good agreement with available experimental results and theoretical predictions. For example, Fig. 1 illustrates predictive abilities of the algorithm in terms of melting, free surface flow, wettability and solidification of the droplets on the solid basement.