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1. Analytical Study and Experimental Verification of Shear-Thinning Ink Flow in Direct Ink Writing Process

   https://doi.org/10.1115/1.4056926  

   Guo, Zipeng ; Fei, Fan ; Song, Xuan ; Zhou, Chi ( July 2023 , Journal of Manufacturing Science and Engineering)

   Direct ink writing (DIW) process is a facile additive manufacturing technology to fabricate three-dimensional (3D) objects with various materials. Its versatility has attracted considerable interest in academia and industry in recent years. As such, upsurging endeavors are invested in advancing the ink flow behaviors in order to optimize the process resolution and the printing quality. However, so far, the physical phenomena during the DIW process are not revealed in detail, leaving a research gap between the physical experiments and its underlying theories. Here, we present a comprehensive analytical study of non-Newtonian ink flow behavior during the DIW process. Different syringe-nozzle geometries are modeled for the comparative case studies. By using the computational fluid dynamics (CFD) simulation method, we reveal the shear-thinning property during the ink extrusion process. Besides, we study the viscosity, shear stress, and velocity fields, and analyze the advantages and drawbacks of each syringe-nozzle model. On the basis of these investigations and analyses, we propose an improved syringe-nozzle geometry for stable extrusion and high printing quality. A set of DIW printing experiments and rheological characterizations are carried out to verify the simulation studies. The results developed in this work offer an in-depth understanding of the ink flow behavior in the DIW process, providing valuable guidelines for optimizing the physical DIW configuration toward high-resolution printing and, consequently, improving the performance of DIW-printed objects.

    

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2. Rubber ink formulations with high solid content for direct-ink write process

   https://doi.org/10.1016/j.addma.2021.102023  

   Kim, Myoeum ; Choi, Jae-Won ( August 2021 , Additive Manufacturing)
3. Complex ink flow mechanisms in micro-direct-ink-writing and their implications on flow rate control

   https://doi.org/10.1016/j.addma.2022.103183  

   Estelle, Kevin T. ; Gozen, B. Arda ( November 2022 , Additive Manufacturing)
4. 3D printing of synthetic rubber ink via direct ink writing process

   Kamath, S.S. ( January 2021 , Rubber world)
5. High through-thickness thermal conductivity of 3D-printed composites via rotational direct ink writing

   https://doi.org/10.1016/j.addlet.2023.100167  

   Wilt, Jackson K. ; Hmeidat, Nadim S. ; Bohling, John W. ; Compton, Brett G. ( December 2023 , Additive Manufacturing Letters)

   Composites printed using material extrusion additive manufacturing (AM) typically exhibit alignment of high- aspect-ratio reinforcements parallel to the print direction. This alignment leads to highly anisotropic stiffness, strength, and transport properties. In many cases, it would be desirable to increase mechanical and transport properties transverse to the print direction, for example, in 3D-printed heat sinks or heat exchangers where heat must be moved efficiently between printed roads or layers. Rotational direct ink writing (RDIW), where the deposition nozzle simultaneously rotates and translates during deposition, provides a method to reorient fibers transverse to the print direction during the printing process. In the present work, carbon fiber-reinforced epoxy composites were printed by RDIW with a range of nozzle rotation rates and the in-plane and through-thickness thermal conductivity was measured. In addition, the orientation of carbon fiber (CF) in the composites was measured using optical microscopy and image analysis, from which second-order fiber orientation tensors were calculated. These results showed that the orientation of CF became less anisotropic as nozzle rotation rate increased, leading to increased through-thickness thermal conductivity, which increased by 40% at the highest rotation rate. The orientation tensors also showed that RDIW was more effective at reorienting fibers within the in-plane transverse direction compared to the through-thickness transverse direction. The results presented here demonstrate that a current weakness of material extrusion AM composites—poor thermal conductivity in the through-thickness direction—can be significantly improved with RDIW. 

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