<p>Metal sandwich structures are highly valued in the aerospace industry because of their temperature resistance and high specific flexural strength. However, conventional manufacturing techniques for joining face sheets to a core structure (e.g., brazing) severely limit the shapes that can be economically produced and are fraught with defects that limit the structural performance. The purpose of this article is to investigate the capability of electron beam powder bed fusion additive manufacturing to produce a novel topology optimized core for Ti-6Al-4V sandwich structures. A uniform triply periodic minimal surface diamond lattice was applied to the sandwich core, and then the thickness was functionally graded using a compliance (density-based) minimization strategy, and a stress minimization strategy, based on a four-point bend load case. The flexural properties of the functionally graded sandwich structures were compared with a uniform lattice in static four-point bend experiments defined by ASTM C393. Postfracture analysis by scanning electron microscopy and optical microstructural analysis revealed a superior monolithic sandwich structure, but with orthotropic properties with respect to the build direction. It is important to any materials and process engineer or designer to consider this work for future advanced manufacturing metal sandwich applications.</p>