Effects of fumed silica flow aids on flowability and packing of metal powders used in Binder-Jetting additive manufacturing process

Abstract

Binder-Jetting is a fairly new sinter-based additive manufacturing technology for metals. Due to sintering, small particle size distributions are favorable, yet they are limiting the printing process due to bad flowability and compaction. This paper aims to resolve this contradiction by adding flow aids to powders used in Binder-Jetting. Therefore 5 different powders with successively decreasing particle size distributions ranging from 32 µm (D90) to 5 µm (D90) are combined with 2 different fumed silica (aerosil) flow aids. Improvements are measured by the use of apparent and tap density as well as hausner ratio. Results show that the mixing process for flow aids and powders has significant influence on the improvements. Moreover, the amount of aerosil is a key criterion for optimized flow behavior. Improvements up to 42 % for apparent and 11 % for tap density are achieved. Hausner ratio can be improved up to 34 %. Preliminary printing results indicate that increased flowability and packing behavior also increases powder bed density and green density. The results are in line with existing theories regarding the use of flow aids in powders used in other industries and can be now be adopted for metal powders as well.