Title: Qualitative Chemorheological Considerations for Continuous Reactive Additive Manufacturing

Authors: Aynslie J. Fritz, Jeffrey S. Wiggins

DOI: 10.33599/nasampe/c.22.0059

Abstract: An emerging additive manufacturing (AM) method, Continuous Reactive Additive Manufacturing (CRAM), has the potential to overcome traditional AM limitations such as slow fabrication time, material processing limitations and/or cost, part size, and insufficient material properties resulting from anisotropy. CRAM operates through the individual metering of reactive monomers to a static mixer mounted on a print gantry. Upon mixing, polymerization is initiated and continues throughout the print, thus yielding isotropic (equally distributed) properties throughout the printed specimen. While the use of liquid monomers permits reductions in print time and energy consumption, the isotropic (equally distributed) properties have the potential to revolutionize industrial use of AM for high mechanical integrity, end-use products. Nevertheless, for CRAM printing to be successful, the material utilized must adhere to strict chemorheological requirements; namely, polymerization must occur rapidly upon deposition and the deposited material must have sufficient viscosity (to prevent flow) and high modulus (to support subsequent layers). However, degree of polymerization must be minimized to allow interlayer polymerization for enhanced mechanical isotropy. Consequently, a narrow window of acceptable chemorheological properties exist. Moreover, obtaining accurate and reproducible rheological data is extremely difficult and requires the use of a dual-channel syringe pump or hand-mixing gun. This research explores a qualitative screening method to compliment the printability criteria already established in literature. Using various amounts of fumed silica (FS) in polyurethanes, a qualitative flip test is correlated with the rheological results. The rheological results are then compared to literature precedent to establish if they meet the printability criteria. Of the four samples tested, the sample containing 5.0 wt% FS met one of the criteria, while the 7.5 wt% FS met two of the four. Using the 5.0 wt% FS sample, a specimen measuring 191.4 mm long, 70.7 mm wide, and 3.6 mm thick was printed to examine the print quality while considering the qualitative and rheological results. Reasonable resolution of the print specimen was demonstrated, thus yielding a foundation for further optimization of print parameters and expansion to other reactive chemistries.

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Conference: CAMX 2022

Publication Date: 2022/10/17

SKU: TP22-0000000059

Pages: 9

Price: $18.00