Additive manufacturing of intricate lattice materials: Ensuring robust strut additive continuity to realize the design potential

Additive manufacturing (AM) has enabled the emergence of intricate lattice materials with controlled structural or functional properties unfeasible for conventional materials. A striking feature of these novel materials is the substantial number of constituent strut elements contained in them, e.g., more than 5 × 105 struts (diameter: 0.5 mm; length: 5.0 mm) in a common tetrahedron lattice with dimensions of 200 × 200 × 200 mm3. A prerequisite for realizing the full design potential of these structures is to ensure the robust additive continuity of each constituent strut, which refers to geometric continuity between two successive layers of a strut, in order to achieve high lattice structural integrity. This critical issue has, however, remained unanswered. Herein we formulate a design-and-manufacture interlocked strut additive continuity model for powder bed fusion (PBF) and apply it to the entire design gamut of Ti-6Al-4 V struts. On this basis, a strut additive continuity threshold value (φ = 0.9) is proposed and validated with 23,100 inclined struts in Ti-6Al-4 V lattices manufactured by electron beam PBF (EB-PBF). Design maps are then constructed for EB-PBF of lattice materials. Furthermore, a minimum powder-bed density (0.6ρTD) for powder selection and a powder-specific initial layer thickness (0.6Dv(90)) are recommended. This work establishes a necessary basis for the design and manufacture of robust lattice materials by EB-PBF including graded lattices.