Flow rate ranges for spherical metallic powders for additive manufacturing

Powder spreadability, and thus flowability, is widely considered a critical parameter for metal additive manufacturing (AM) outcome, that is for a stable, repeatable, and viable process. The flowability of metal powders for additive manufacturing can be measured by a variety of methods, with funnels being the simplest ones, thus widely accepted in the AM industry and supported by international standards (ISO and ASTM). What is lacking is a good understanding of what is an acceptable flowability value for a given alloy. It is thus important to understand the theoretical limits (range) on the funnel measurement outcome as prescribed by a standard method for a given metal alloy powder. Herein, we studied different metal alloy powders, including titanium, nickel and aluminum alloys, and their flowability in a funnel as a function of their density. We fitted the experimental data with Beverloo and Johanson models for upper and lower flowability limits, hinting at possible ranges for a funnel flow measurement.