Design of conformal lattice metamaterials for additive manufacturing

Conformal lattice materials (cell sizes ranging from nanometres to millimetres), including conformal metal lattice metamaterials, are cellular materials or structures that conform to all or part of the physical space of a product with topologically complete boundary cells. Enabled by powder bed fusion (PBF) additive manufacturing (AM), conformal metal lattice metamaterials provide an innovative solution for lightweight engineering or integration of structure and function. A key step in their fabrication is to generate a conformal lattice model suitable for PBF AM. This research reviews their design methods and evaluates each method using seven criteria. These include (i) the sequence of geometric modelling and lattice topology generation (sequential or simultaneous), (ii) integrity of lattice cell topology at boundaries, (iii) compatibility with lattice cell types, (iv) applicability to complex geometry, (v) ease of coding, (vi) accessibility via common software tools, and (vii) ability to define strut inclination angles in a complex conformal design space. On this basis, various laser PBF (LPBF) manufacturability issues of conformal metal lattices are considered, and two Ti-6Al-4V conformal lattices are fabricated using LPBF and evaluated. This review provides a necessary foundation for future research and applications of conformal lattice metamaterials in various engineering fields.