An investigation into the effect of gradients on the manufacturing fidelity of triply periodic minimal surface structures with graded density fabricated by selective laser melting

Triply periodic minimal surfaces (TPMSs) have attracted increasing attention for their high manufacturability, biocompatibility, and mechanical properties. In this work, graded Gyroid cellular structures (GCSs) with varying gradient directions were mathematically designed and manufactured via selective laser melting (SLM). The effect of gradients on manufacturing fidelity, i.e. degree of conformity between the manufactured part and engineering design, of these structures was investigated using X-ray computed tomography (CT). The results indicate that relative density and volume fraction of as-built GCSs are higher than those specified in the engineering design due to strut diameters being larger than specification and the presence of bonded powder particles. Manufacturing fidelity is shown to depend on the geometry of the struts in these structures, including inclination angle of struts, relative density, and density gradient direction. Bonded powder particles were particularly present at the upper inner walls of sphere-like pores, where inclination angles are low and as a result there is a lack of support and non-ideal transfer of heat from the melt pool. Decreasing density along the building direction reduces the occurrence of bonded powder particles and increases manufacturing fidelity. The empirical findings in this study provide insight into the effects of part geometry on the quality of its manufacture by SLM. Results are used to establish guidelines for optimal design of cellular structures.