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Shell printing is an advantageous binder jetting technique that prints only a thin shell of the intended object to enclose the loose powder in the core. In this study, powder packing in the shell and core was investigated for the first time. By examining the density and microstructure of the printed samples, powder packing was found to be different between the shell and core. In addition, the powder particle size and layer thickness were found to affect the powder packing in the shell and core differently. At a 200 µm layer thickness, for the 10 µm and 20 µm powders, the core was less dense than the shell and had a layered microstructure. At a 200 µm layer thickness, for the 70 µm powder, the core was denser and had a homogeneous microstructure. For the 20 µm powder, by reducing the layer thickness from 200 µm to 70 µm, the core became denser than the shell, and the microstructure of the core became homogeneous. The different results could be attributed to the different scenarios of particle rearrangement between the shell and core for powders of different particle sizes and at different layer thicknesses. Considering that the core was denser and more homogeneous than the shell when the proper layer thickness and powder particle size were selected, shell printing could be a promising method to tailor density and reduce anisotropy.

 

Abstract Feedstock powders used in binder jetting additive manufacturing include nanopowder, micropowder, and granulated powder. Two important characteristics of the feedstock powders are flowability and sinterability. This paper aims to compare the flowability and sinterability of different feedstock powders. Three powders were compared: nanopowder (with a particle size of ∼100 nm), micropowder (with a particle size of 70 μm), and granulated powder (with a granule size of ∼70 μm) made from the nanopowder by spray freeze drying. Flowability metrics employed included apparent density (AD), tap density (TD), volumetric flow rate (VFR), mass flow rate (MFR), Hausner ratio (HR), Carr index (CI), and repose angle (RA). Sinterability metrics employed included sintered bulk density (SBD), volumetric shrinkage (VS), and densification ratio (DR). Results show that the granulated powder has a higher flowability than the nanopowder and a higher sinterability than the micropowder. Moreover, different flowability metric values of the granulated powder are close to those of the micropowder, indicating that these two powers have a comparably high flowability. Similarly, different sinterability metric values of the granulated powder are close to those of the nanopowder, indicating that these two powders have a comparably high sinterability. 

Abstract Nanocomposites have been widely used to improve material properties. Nanoscale reinforcement materials in vat photopolymerization resins improve the hardness, tensile strength, impact strength, elongation, and electrical conductivity of the printed products. This paper presents a literature review on the effects of reinforcement materials on nanocomposite properties. Additionally, preprocessing techniques, printing processes, and postprocessing techniques of nanocomposites are discussed. The nanocomposite properties are summarized based on their applications in the mechanical, electrical and magnetic, and biomedical industries. Future research directions are proposed to improve the material properties of printed nanocomposites.