Topology optimization of self-supporting infill structures

This paper presents a density-based topology optimization approach to design self-supporting and lightweight infill structures with efficient mechanical properties for enclosed structural shells. A new overhang constraint is developed based on the additive manufacturing (AM) filter to ensure that the infills are not only self-supporting in a specified manufacturing direction but can also provide necessary supports to the external shell for successful manufacturing. Two-field-based parametrization and topology optimization formulations are used to impose minimum length scales and to avoid the impractical design solutions that exhibit one-node connection structural members. Besides, a localized volume constraint is utilized to achieve a porous infill pattern. By solving the optimization problem, a shell-infill design can be obtained with very few overhang elements that can be easily post-processed without affecting the mechanical properties of the overall structure. As a result, the optimized design contains no overhang elements and exhibits a better mechanical property than that with predefined periodic infill patterns of the same weight. Numerical examples are given to demonstrate the effectiveness and applicability of the proposed approach.