Design, testing, and simulation of additively manufactured open porous structures

Abstract

One strength of additive manufacturing lies in its potential to realize functionality-optimized applications, often based on complex designs. This thesis comprehensively investigates the additive manufacturing of open porous structures, which contain interconnected pores that are accessible from the outer surface. A comprehensive guideline is presented, including the design, manufacturing, and property characterisation, yielding a holistic overview of the development from concept to industrial application. It is explained how open porous structures can be achieved by adjusting the manufacturing parameters for laser beam powder bed fusion, without a detailed predefined CAD model of the pores. This approach enables the creation of a wide variety of porosities without having to change the underlying geometry. Samples are manufactured in a nickel-based superalloy and pure copper. The flow resistance and thermal diffusivity of the open porous structures are evaluated by laboratory testing and multiphysics CFD simulation. Generally, representative geometries are required for the simulations. Without a predefined CAD model, the geometry of the open porous structure for the simulation must be derived from a physical sample, which is done by micro-computed tomography imaging (μ-CT imaging). The processing of the μ-CT data for characterising structural features and their use in multiphysics CFD simulation is evaluated. A voxel-based 3D reconstruction of the open porous structures is introduced, and the influence of downsampling the voxel models on the 3D reconstructed geometry is studied. The setup of a volume mesh, i.e. polyhedral mesh, for multiphysics CFD simulation is discussed in detail. Different mesh settings are proposed and tested to minimize the deviation between the multiphysics CFD simulation results and the laboratory test results. As an outlook for industrial applications, a pure copper wick heat pipe prototype is designed, manufactured, and characterised by laboratory testing and multiphysics CFD simulation. The additive manufacturing process for the open porous pure copper material is successfully developed in a parameter study. A simulation approach of a homogenized representation of the open porous structure is discussed. The general functionality and performance benefits of the heat pipe prototype are confirmed. The results indicate the complexity of the industrial use of additively manufactured open porous structures.