Fundamental consolidation mechanisms during selective beam melting of powders

Abstract

During powder based additive manufacturing processes, a component is realized layer upon layer by the selective melting of powder layers with a laser or an electron beam. The density of the consolidated material, the minimal spatial resolution as well as the surface roughness of the resulting components are complex functions of the material and process parameters. So far, the interplay between these parameters is only partially understood. In this paper, the successive assembling in layers is investigated with a recently described 2D-lattice Boltzmann model, which considers individual powder particles. This numerical approach makes several physical phenomena accessible, which cannot be described in a standard continuum picture, e.g. the interplay between capillary effects, wetting conditions and the local stochastic powder configuration. In addition, the model takes into account the influence of the surface topology of the previous consolidated layer on the subsequent powder layer. The influence of the beam power, beam velocity and layer thickness on the formation and quality of simple walls is investigated. The simulation results are compared with experimental findings during selective electron beam melting. The comparison shows that our model, although 2D, is able to predict the main characteristics of the experimental observations. In addition, the numerical simulation elucidates the fundamental mechanisms responsible for the phenomena that are observed during selective beam melting.

Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

“…Körner uses the multi-distribution function approach to reduce these limitations under the assumption that the fluid density is not strongly dependent on temperature. The method has been applied in 2D to study single layer [11] and layer upon layer consolidation [12], and shows the importance that the powder packing has on the melt characteristics. Their observation of the undesirable balling effect was attributed to the local powder arrangement [11].…”

Modeling of Ti-W Solidification Microstructures Under Additive Manufacturing Conditions

“…The thermal Lattice Boltzmann method for coupled heat and incompressible fluid flow fields has been used previously to simulate convection problems [29,[82][83][84] and been coupled to cellular automata (CA) to simulate the solidliquid phase change for pure materials. [7,31,32,36,79] If it is assumed that the fluid is incompressible, viscous heat dissipation is negligible, and no work is done by the external pressure, an additional set of distribution functions can be introduced to the model for heat transport. These are analogous to those for solute (the heat is advected as a passive scalar), but include a heat diffusivity, internal energy density, and a heat source term in place of solute diffusivity, concentration, and the solute source term, respectively.…”

“…[7,31,33] Additionally, the method is computationally efficient and easily parallelized. [34,35] Ko¨rner et al [7,36] used a thermal Lattice Boltzmann model for the combined heat transport, fluid flow, and phase change problem, for Ti-6Al-4V in a powder bed-based AM process.…”

Nanoparticle improved metal materials for additive manufacturing

“…Presumably, the temperature in the generated melt pool is not high enough to cause sufficient material flow and to wet adjacent material areas. Melt pool evolution is strongly dependent on a complex interaction of different physical processes, as laser beam absorption, evaporation, wetting of powder particles, heat conduction, capillary effects, surface tension, melt viscosity and melt pool dynamics [23][24][25]. For this reason, one possible explanation is that the Al 2 O 3 nanoparticles influence the wetting behavior and/or affect the melt convection current, so that no ideal welding line can be formed.…”