Topology optimization of multi-phase shell-infill composite structure for additive manufacturing

This paper presents a topology optimization method for a multi-phase shell-infill composite, accounting for the coated shell and graded multi-phase microstructural infill. The method builds upon extended multi-phase density-based topology optimization approaches, and it consists of two major steps: (1) general structural configuration design of the shell-base composite structure and (2) detailed design of the graded multi-phase infill architecture. An erosion-based interface identification method is adopted to evolve the general structural configuration with a coated shell. Then the maximum and minimum length scale control constraints are simultaneously imposed on each phase material to generate graded multi-phase porous structures in the base region. The whole design process is performed on a full-size finite element analysis and only involves standard filtering operations. It avoids the separation of scales and guarantees the connectivity of microstructures. Several numerical examples for minimum compliance are presented, and a post-processing method is proposed to smooth the design boundaries when extracting CAD models for additive manufacturing. Eventually, the manufacturability of the post-processed prototype is verified with a multi-material 3D printer, which further illustrates the applicability of the proposed method.