Effect of topological characteristics on manufacturability and mechanical performance of multiscale graded structures fabricated by laser powder bed fusion

Abstract

Complex multiscale structures emerge as a current focal point due to the controllability of physical, mechanical and geometrical properties spatially. However, the multiscale structures often modify the topological characteristics of structures, primarily including scale and geometry variation, thereby adding complexity of the laser powder bed fusion process. To investigate the effects of topological characteristics on manufacturability and mechanical properties, we fabricated uniform Gyroid structures with different unit cell size to evaluate scale variation and unit cell size graded Gyroid structure with different graded magnitude to evaluate structural geometry variation. As the unit cell size of uniform structures decreased, the structural thickness increased and dross defects diminished, while the relative density deviation was insensitive to unit cell size. The correspondence between relative density and mechanical properties of uniform Gyroid structures was established based on Gibson-Ashby equation. Unit cell size grading led to structural distortion. As the graded magnitude increased, the mean structure thickness and relative density of graded structures increased, and the mechanical properties decreased. The mechanism by how unit cell distortion affects manufacturability and mechanical performances was revealed. Furthermore, we present a performance-driven strategy for designing multiscale Gyroid structures, in which the topologically optimized density distribution is mapped onto the unit cell sizes. A three-point bending beam was constructed by the multiscale optimization method, which showing a ∼9.6 % increase in bending strength and a ∼46.8 % improvement in bending displacement compared to uniform beam. This study could offer guidance for the design and manufacturing of multiscale structures.