Binder Jetting Additive Manufacturing: Fundamental Studies on Powder Spreading

Abstract

Powder spreading is a critical step of binder jetting additive manufacturing and has a determinative effect on the quality of the final product. The objective of this research is to improve the fundamental knowledge of powder spreading. A literature review on powder spreading was conducted. The effects of three groups of influencing factors (i.e., spreaders, spreading parameters, and feedstock powder properties) on quality of the powder bed were summarized. Layer thickness, roller traverse speed, and roller rotation speed were identified as factors that worth further study. The effects of layer thickness were studied by spreading powder of different flowabilities at different layer thicknesses in two different scenarios. The results indicated that powder flowability and measurement scenario are two factors that could confound the effect of layer thickness and should be considered in future studies on the effect of layer thickness on powder bed density. The effects of roller traverse and rotation speeds were investigated by comparing samples printed at different roller traverse and rotation speeds. The results showed that roller traverse speed had more significant effects than roller rotation speed. A high roller traverse speed can result in more interlayer defects and more binder-induced defects, and thus, lead to low density and low flexural strength.

Besides tuning the spreading parameters, two novel approaches to tailoring powder spreading, i.e., powder granulation and shell printing, were also investigated in this research. The effects of granulation were studied by comparing the flowability and printability of the raw nanopowder and the granulated powder. The results indicated that granulation is efficient in improving the flowability and printability of nanopowder, and at the same time, could maintain the high sinterability of nanopowder. The effects of shell printing were investigated by comparing the density and microstructure of samples printed through normal printing and shell printing. The results suggested that shell printing could be a useful method to tailor the density and microstructure of a part.