In the context of additive manufacturing the group “Numerical Simulation” focuses on beam-based technologies using a powder bed. Different materials from metals and metal alloys (Ti64, TiAl, IN718) to polymers (PA12) can be applied to the software. The scientific research focuses, in close cooperation with the experimental group “Additive Manufacturing”, on the understanding of the fundamental mechanism during powder melting and material consolidation as well as on the prediction of innovative process strategies regarding porosity, microstructure and alloy concentration.
A predictive software relies on exact physical and numerical models. The most important aspect is the correct modelling of the thermal conditions. Almost all modifications of process parameters have a direct influence on heat conduction, the coupling of the energy source or heat sinks by e.g. heat radiation or evaporation. Furthermore, many material parameters are temperature dependent and sensitive to a correct model. During melting a melt pool evolves, which dynamics is mainly covered by capillarity, wetting, Marangoni convection and gravity. The temperature gradient and the solidification velocity mainly influence the final microstructure after solidification.
The 2D simulation of selective electron beam melting bases on the software for modelling of foam formation. The base software is extended by certain modules comprising the electron beam absorption, phase transitions, selective evaporation or grain structure evolution. After a careful experimental validation, the aim of this software is to predict process windows and explain process phenomena. Most process phenomena during selective electron beam melting are covered by a 2D simulation. A more realistic modelling of the melt pool dynamics and the grain structure evolution is reached by 3D simulations. Therefore, two different simulation tools for these purposes are developed at WTM. The 3D hydrodynamics software requires a massively parallel implementation, which has been developed in cooperation with the Chair of System Simulation. The melt pool dynamics and the material consolidation are investigated in full spatial dimension. Using this software, process windows for dense parts as well as innovative process strategy modifications are predicted. The grain structure evolution is modelled by a separate software, which enables the grains to grow in all possible directions during processing. Here, a macroscopic approach is used, where the powder particles are approximated by a continuum. Additionally, only the thermodynamics is modelled. With these simplifications, domains on the scale of whole parts are possible to simulate.
Besides funding from industry and DFG/EU projects, the development of the simulation software is mainly funded by the collaborative research centre SFB 814 “Additive Manufacturing” (http://www.sfb814.forschung.uni-erlangen.de/).