Probing Ink–Powder Interactions during 3D Binder Jet Printing Using Time-Resolved X-ray Imaging

Abstract

Capillary-driven ink infiltration through a porous powder bed in three-dimensional (3D) binder jet printing (inkjet printing onto a powder bed) controls the printing resolution and as-printed “green” strength of the resulting object. However, a full understanding of the factors controlling the kinetics of the infiltration remains incomplete. Here, high-resolution in situ synchrotron radiography provides time-resolved imaging of the penetration of an aqueous solution of eythylene glycol through a porous alumina powder bed, used as a model system. A static drop-on-demand inkjet printer was used to dispense liquid droplets onto a powder surface. The subsequent migration of the liquid front and its interactions with powder particles were tracked using fast synchrotron X-radiography in the Diamond Synchrotron, with phase-contrast imaging at a frame rate of 500 Hz. Image processing and analysis reveal that both the time-dependent increment in the wetting area and the propagation of the “interface leading edge” exhibit heterogeneous behavior in both temporal and spatial domains. However, mean infiltration kinetics are shown to be consistent with existing infiltration models based on the Washburn equation modified to account for the spreading of the liquid drop on the powder surface and using a modified term for the bed porosity.

X-ray Imaging of Alloy Solidification: Crystal Formation, Growth, Instability and Defects

“…Unlike LPBF and DED, which are characterised by a scanning heat source, AM by binder jetting uses an iterative ink-jet printing method, where alternating layers of build material and binding material are deposited to build up components [55,56]. Parab et al investigated this process in situ using a commercial binder jetting system with a droplet-ondemand ink-jet print-head.…”

“…The focus of solidification research on Al alloys derives from the relatively easy-to-achieve melting temperatures of around 660 °C, and excellent absorption contrast between Al and typical alloying elements such as Cu and Zn. Further, the high temporal resolution now afforded also allows new insights to be gained on transient phenomena during non-equilibrium, rapid solidification processes, such as the effect of processing parameters on melt pool morphology and melt pool defects in additive manufacturing (AM) [48][49][50][51][52][53][54], and has also made a contribution to the development and validation of new AM processes [55,56].…”

Removal of Stair-Step Effects in Binder Jetting Additive Manufacturing Using Grayscale and Dithering-Based Droplet Distribution

“…The literature describes fluid infiltration in porous media due to capillary pressure. For example, Barui investigated the ink infiltration of powdered materials similar to a binder jetting process [ 24 ]. It is concluded that the “infiltration proceeds in a highly non-uniform manner with dramatic differences in fluid penetration rate” [ 24 ] and that the Washburn/Denesuk [ 25 ] model can be applied successfully.…”

Absorption and Spreading of a Liquid Droplet Over a Thick Porous Substrate

“…Liu et al noticed that imbibition in a compressed bed predominantly occurs at the constant contact area and provided a universal dimensionless relation for the imbibed liquid volume versus time. Barui et al investigated the dynamics of ethylene glycol–water solution penetration in alumina powder bed using X-ray imaging. Washburn-based models were found consistent with experimental data using a semi-empirically determined porosity correction factor …”