A method to determine the depowdered height in lattices manufactured by electron beam melting

After completing a part in electron beam melting (EBM), a depowdering operation is required to separate the sintered but unmelted powder from the manufactured part. Depowdering lattice structures can be difficult or even impossible due to their intrinsic shape. The aim of this paper is to propose a criterion to ensure that a lattice structure manufactured by EBM can be depowdered. The objective is to use this criterion during the design phase of lattice structures to make them manufacturable and depowderable. Experiments are conducted on depowdering octet-truss lattice structures with variable bars thickness and mesh sizes. Different criteria are introduced, among them the criterion “hydraulic diameter” of a lattice structure, inspired by the Darcy-Weisbach hydraulic law used to calculate the pressure drop in a pipe. This criterion can be determined using only geometrical characteristics of lattices available in the CAD model of the part. Results show that the levels of depowdering for lattice structures are proportional to this hydraulic diameter. As a validation, a bike stem has been manufactured following the criterion and has demonstrated its efficiency.