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Binder jetting is a subset of additive manufacturing and is a suitable technique for the construction of metallic, ceramic and polymeric composite materials. In this rapid prototyping method, a binder is selectively deposited onto the powder bed, bonding these areas together to form a solid part one layer at a time usually based on a CAD model. Selection of appropriate parameters in order to obtain the final product with desired quality and proper construction time is a challenge, which is due to high influences of binder jetting process parameters on the quality of fabricated objects. Powder characteristics such as particle packing, green strength, particle size distribution, and also wettability and flow ability of powder, as well as binder characteristics and device parameters are effective factors on the binder jetting process. In this 3D printing technique, there are possible defects that are divided to two groups of before and after sintering defects that should be controlled to achieve a printed part with minimum deviation from the designed model.

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The purpose of this study was to prepare a 3D printable powder composed of hydroxyapatite and biocompatible polymers such as chitosan, dextrin, and polyvinylpyrrolidone for the binder jetting process. The relationship between powder properties such as flowability and particle size distribution, as well as printing quality were investigated in the binder jetting process. For this purpose, 3D printable powder and an appropriate solvent were designed and demonstrated by hydroxyapatite and water-soluble polymers such as carboxymethyl chitosan, dextrin, and PVP. Results showed that a combination of 60%wt. hydroxyapatite, 28%wt. carboxymethyl chitosan, 10% wt. dextrin, and 2% wt. PVP, with controlled particle size distribution according to the Dinger-Funk equation led to the best print quality. Finally, flash dipping of the 3D printed parts in chitosan solution resulted in increases of compressive and Young's modulus from 1.3 and 10 MPa to 7.4 and 125 MPa, respectively.

Additive manufacturing of ceramics through the direct ink writing method becomes possible when the effective parameters on rheology are optimized accurately. Successful manufacturing first requires the easy flowing of the ink through the nozzle and then a suitable viscoelastic response for the shape retention of the 3D printed structure. In the present study, fused silica pastes with different particle size distributions varying from D90 of 5–50 µm were prepared for direct ink writing of porous structures. The rheological properties of the pastes, including flow behavior and the viscoelastic moduli variations, were investigated to study the influence of particle size and its distribution on fabricating complex structures. Through investigations, it was found that the narrower size distributions were more appropriate for direct ink writing of fused silica pastes. As the distribution became narrow, the shear thinning behavior was intensified, and the pastes showed high elasticity. The sintering procedure was performed using microwave radiation to suggest a fast process for manufacturing fused silica complex parts containing partially crystallized cristobalite phase and providing porosity of about 10% and a relative density of 90%.