Design of spatially-varying orthotropic infill structures using multiscale topology optimization and explicit de-homogenization

This paper presents a systematic design procedure of shell-infill structures for additive manufacturing (AM). Specifically, multiscale topology optimization based on the homogenization design method is employed for the design of a structure composed of coated exterior and spatially-varying orthotropic interior. The proposed procedure consists of five sequential steps including homogenization, topology optimization, and de-homogenization processes. Through the homogenization step, the effective elasticity tensor of the orthotropic infill microstructure is prepared as a function of microstructure design variables. In the topology optimization step, microstructure design variables are optimized together with the density design variable, for the simultaneous design of the infill microstructure and coated macrostructure. Finally, a spatially-varying infill microstructure is restored using a de-homogenization process. This study proposes a practical de-homogenization scheme that restores a designed infill microstructure using the explicit geometry representation of rectangular void holes. The proposed scheme is suitable to generate a result in a Computer-Aided Design (CAD) format for AM. The effectiveness of the proposed design procedure is validated through two design examples for compliance minimization problem. In addition, designed shell-infill structures are fabricated using a multi-jet printing machine.