The importance of lightweight design of mechanical parts is increasing rapidly due to material and energy savings. As additive manufacturing (AM) technology advances, the lattice structures, which are extremely difficult shapes to fabricate using conventional manufacturing processes, has attracted great interest due to their intrinsic characteristics such as high strength and lightweight. We propose an effective global-local design approach of gradient lattice structures with the selection of a lattice type in a zone and optimizing its strut diameter considering the whole loading conditions of a mechanical part, in order to obtain higher specific strength than other corresponding designs. In this work, two basic types of a lattice named as BCC and OTC, was utilized to design diverse local lattices based on optimizing a strut-diameter. To evaluate the usefulness of this approach, we designed a three-point bending test specimen with topology-optimized multi-lattice wire model, and strut-based topometry optimization on the wire model. The experimental test results show that the optimized specimen had more than 67% higher strength per weight compared to other multi-lattice ones. Through this work, we believe that this method is a promising way to effectively design high strength mechanical parts with lightweight for use in high-valuable industrial applications.
