Investigations on Binder Jetting Additive Manufacturing: Process Physics and Innovative Approaches

Abstract

This study investigated several aspects of binder jetting additive manufacturing, including the effects of particle size, printing orientation, powder bed compaction, and texturing on the density, microstructure, and mechanical behavior of the fabricated parts.

The effects of particle size on flowability and sinterability of the feedstock powder and resultant properties of fabricated parts were studied. The results showed that flowability increased, but sinterability decreased as particle size increased. The highest density was achieved by the medium powder due to the balance between flowability and sinterability. The results demonstrated that the compressive strength was dominated by sinterability, as the highest strength was achieved by the fine powder. Additionally, the effect of printing orientation on the flexural strength of the parts from binder jetting was investigated. Despite no noticeable difference in density among various printing orientations, significant change in flexural strength was observed. Analysis of the microstructure revealed that printing orientation played a crucial role in determining the defect distributions, which was attributed to the difference observed in the flexural strength.

In addition, a novel approach of combining powder bed compaction and nanopowders was introduced to improve the density of parts fabricated through binder jetting. The study revealed that at the same layer thickness, higher compaction thickness resulted in higher powder bed density, higher sintered density, and smaller number and size of pores in sintered samples. Finally, this work demonstrated, for the first time, the successful fabrication of textured ceramics using binder jetting. This was achieved using two different binder jetting machines: a lab-designed press-compaction-assisted binder jetting machine, and a commercially available roller-compaction-assisted binder jetting machine. A mixture of alumina nanoplatelets and nanoparticles was used as the feedstock powder (the nanoplatelets served as templates for epitaxial grain growth during sintering, while the nanoparticles were consumed by the grain growth). Varying the nanoplatelet fraction in the feedstock powder revealed that the sintered density decreased as the nanoplatelet fraction increased, while the degree of texture increased. Texture evaluation indicated that the development of texture mostly occurred during sintering. Interestingly, the flexural strength of the sintered samples with nanoplatelets was higher than those without nanoplatelets, suggesting the increased degree of texture has a stronger effect on the flexural strength than the reduced sintered density under these conditions.