Indirect Additive Manufacturing Based Casting (I AM Casting) of a Lattice Structure

Abstract

Direct-metal additive manufacturing (AM) processes such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM) methods are being used to fabricate complex metallic cellular structures with a laser or electron beam over a metal powder bed. Even though these processes have excellent capabilities to fabricate parts with cellular mesostructures, there exist several constraints in the processes and applications: limited selection of materials, high thermal stress by the high local energy source, poor surface finish, and anisotropic properties of parts caused by combined effects of one-dimensional (1D) energy based patterning mechanism, the deposition layer thickness, powder size, power and travel speed of laser or electron beam. In addition, manufacturing cost is still high with the Direct-metal AM processes. As an alternative for manufacturing metallic 3D cellular structures, which can overcome the disadvantages of direct-metal AM techniques, polymer AM methods may be combined with metal casting. We may call this “Indirect AM based Casting (I AM casting)”. The objective of this study is to explore the potential of I AM Casting associated with development of a novel manufacturing process — Indirect 3D Printing based centrifugal casting which is capable of producing multifunctional metallic cellular structures with internal cooling channels having a 2mm inner diameter and 0.5mm wall thickness. We characterize polymers by making expendable patterns with a polyjet type 3D printer; e.g., modulus, strength, melting and glass transition temperatures and thermal expansion coefficients. A transient flow and heat-transfer analysis of molten metal through 3D cellular network mold will be conducted. Solidification of molten metal through cellular mold during casting will be simulated with temperature dependent properties of molten metal and mold over a range of running temperatures. The volume of fluid (VOF) method will be implemented to simulate the solidification of molten metal together with a user defined function (UDF) of ANSYS/FLUENT. Finally, experimental validation will be conducted.