Defect generation and propagation mechanism during additive manufacturing by selective beam melting

During powder bed based additive manufacturing processes a component is fabricated by locally melting of powder layers with a laser or an electron beam. The fast melting process of the stochastic powder bed induces vigorous melt pool movements which sometimes lead to faults acting as starting points for larger defects such as channels bridging many layers. Since the formation of these defects cannot be understood in the framework of a homogenized numerical approach we have developed a mesoscopic numerical model based on the Lattice Boltzmann Method for the local melting process which considers individual powder particles. The model takes into account full hydrodynamics including capillary and wetting effects. It is shown that these effects combined with the stochastic powder layer are the origin of fault formation. The numerical results are compared with experiments in order to demonstrate the predictive value of our model.