Isotropic Ti-6Al-4V lattice via topology optimization and electron-beam melting

Electron-beam melting (EBM) exhibits advantages over other metal-additive manufacturing techniques owing to its low residual stress, rapid fabrication speed, and high energy efficiency. However, in EBM, metal powder is preheated and sintered to stabilize the temperature gradient and powder position during melting with a high-power electron beam. When making a lattice structure by EBM, a certain size of the powder-removing hole is required to remove the sintered remaining metal powder from the lattice. However, a large powder-removing hole can reduce the lattice mechanical performance. We conducted topology optimization to derive an optimal lattice structure shape with high isotropic stiffness assuming fabrication by EBM and minimizing the performance reduction owing to fixed large powder-removing holes. The optimized structure was fabricated via the EBM of a Ti-6Al-4V alloy. The optimal lattice structure achieved 83% of the performance of the Hashin-Shtrikman upper bound in numerical simulations, but an approximate 20% stiffness reduction was observed in the experiments. The isotropy was high with an error in Young's modulus and a strength of less than 9% and 6%, respectively. These results are discussed based on numerical and experimental results.