Binder jetting of sand molds and cores for metal casting provides a scalable and efficient means of producing metal components with complex geometric features made possible only by Additive Manufacturing. Topology optimization software that can mathematically determine the optimum placement of material for a given set of design requirements has been available for quite some time. However, the optimized designs are often not manufacturable using standard metal casting processes due to undercuts, backdraft and other issues. With the advent of binder-based 3D printing technology, sand molds and cores can be produced to make these optimized designs as metal castings. However, mold parting surfaces must be carefully designed to insure that unbonded sand can be completely removed from the printed mold and, to effectively use 3D printed sand molding technology, up-front casting simulation should be used to develop gating and risering systems that are likely to produce good castings on the very first pour. This paper contains examples of the development of complex castings produced using 3D printed sand molds and cores.