Impact of inkjet printing parameters and environmental conditions on formation of 2D and 3D binder jetting geometries

Abstract

While Binder Jet Additive Manufacturing (BJAM) has great potential, its implementation is limited by defects in the finished parts. An improved understanding of how printing parameters impact the quality of the printed parts is needed. Prior work on the droplet/powder interactions in BJAM printing focused on individual lines, this work shows that successful layer formation favors larger droplet spacing than is viable in individual lines. When printing layers, the first printed layer was significantly rougher than the spread bed indicating significant powder ejection. However, this difference was eliminated after printing 1–4 additional layers. These results show that prior printed layers have a strong impact on droplet impact and imbibition and that simple droplet or line geometries are not effective for testing printing parameters. The roughness of the first layer may contribute to large pores observed between layers. This paper further examines the impact of key printing parameters including layer thickness, droplet/line spacing, and droplet inter-arrival time on the effective saturation and surface roughness of 2D and 3D parts. The droplet inter-arrival time (print frequency) had negligible impact on surface roughness and saturation under the conditions tested. Printed layers behaved similarly at droplet spacing values comparable to the droplet diameter (44 μm). In contrast, droplet spacing of 60 μm, produced substantially lower saturation. Effective saturation generally increases with increased number of layers. Ambient humidity exposure during printing is shown to have a negligible impact on printing outcomes though higher moisture levels from steam exposure dramatically alter saturation. Drying powder before spreading reduced variation in the printed parts. All tests were based on gas atomized −22 μm 316 SS powder.