Repeatability of a Topology Optimized Tapered Box Beam Additively Manufactured With Electron Beam Melted Ti-6Al-4V

The aerospace industry has been investing in metal additive manufacturing for the benefit of being able to print parts that are lighter weight and more capable than those manufactured with traditional methods.  High quality serial production is important in this industry as it directly impacts product safety; therefore, the manufacturing repeatability of additively manufactured components has to be proven before wide implementation.  Electron Beam Melting (EBM) is a powder bed fusion (PBF) form of additive manufacturing capable of producing fully dense titanium components where an electron beam is used as the energy source to selectively melt Ti-6Al-4V powder within a build chamber to produce a 3-dimensional part.  This technology promises designers the freedom from the design constraints imposed by traditional manufacturing techniques (e.g. machining, casting, etc.) with the capability to print complex structures that could not be manufactured any other way, like those generated by topology optimization codes.  While topology optimization algorithms have been used previously to optimize the weight of metallic structures, they often generate complex organic like shapes that cannot be manufactured with traditional methods, or at least in a cost-effective way.  Therefore, traditional manufacturing has limited the optimization applications due to various rules and restrictions of the fabrication methods.

In this study, the application of a traditional cantilevered tapered box beam was used as a use case for an organically shaped topology optimized cantilevered beam structure.  The design space was scaled down to a reasonable volume, but not such that the structure could fit in the chamber of an Arcam A2X EBM additive machine as a single piece.  The required size meant that it must to be printed in two pieces that required assembly.  A 3D topology optimized, organically shaped, asymmetric solution was generated, which was followed by a CAD design and finite element stress analysis to ensure the result would meet the design requirements.  An experiment was conducted in order to test the manufacturing repeatability of the design for additive manufacturing (DfAM) structure, where multiples of beam parts were printed out of gas atomized Ti-6-4 powder using default Arcam optimized process parameters.  The beams were assembled and then tested for ultimate load in both bending and torsion.  The work flow of the optimization process, design strategy, manufacturing, assembly, and strength testing will be presented.  This serves as vital information for any additive manufacturing designer who must design for the additive EBM process and understand how repeatable the process is at manufacturing capable products.