DOI: 10.1615/ICHMT.2015.IntSympAdvComputHeatTransf
ISBN Print: 978-1-56700-429-8
ISSN: 2578-5486
COMPUTATION OF EFFECTIVE THERMAL CONDUCTIVITY OF POWDERS FOR SELECTIVE LASER SINTERING SIMULATIONS
RESUMO
Selective laser sintering (SLS) is an additive manufacturing technique for rapidly
creating parts directly from a CAD model by using a laser to fuse successive layers of powder.
However, careful selection of processing parameters is important to ensure high quality produced parts.
Currently no technique exists to use new materials and designs without experimentation to determine
optimum processing parameters. Continuum models of the process show promise in reducing
experimentation by predicting the properties of SLS parts produced using given parameters, but they
require bulk powder material properties such as effective thermal conductivity which are often not
known. In this paper, we develop a model to determine this quantity computationally and, unlike in
previous works, use it to examine the effects of finite bed depth and temperatures near the material
melting point.
In this work, a Discrete Element Model (DEM) is developed and implemented in the open source
solver MFiX. An empty domain is initialized and randomly filled with spherical particles falling under
the influence of gravity. Two opposing walls of the domain are then set to a fixed temperature and
resulting heat sources in all particles are calculated using models developed in previous works for
particle-particle contact conduction, particle-fluid-particle conduction, and a view factor model for
radiation. A non-linear solver is used to calculate the steady-state particle temperatures. Total heat flux
from the walls is then calculated and effective thermal conductivity determined using Fourier's law.
Results are compared against previous computational and experimental measurements for powder beds
and good agreement is obtained. Results for effective thermal conductivity of finite sized beds and
beds with a wide range of temperatures are obtained with quantified uncertainties. These results may
be used in SLS continuum models to accurately characterize of thermal properties of finite-thickness
beds and bed with temperatures near the material melting point.