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Modelling flow-enhanced crystallisation during fused filament fabrication of semi-crystalline polymer melts

McIlroy, C.; Graham, R.S.

Authors

C. McIlroy

RICHARD GRAHAM richard.graham@nottingham.ac.uk
Professor of Applied Mathematics



Abstract

Achieving better control in fused filament fabrication (FFF) relies on a molecular understanding of how thermoplastic printing materials behave during the printing process. For semi-crystalline polymers, the ultimate crystal morphology and how it develops during cooling is crucial to determining part properties. Here crystallisation kinetics are added to a previously-developed model, which contains a molecularly-aware constitutive equation to describe polymer stretch and orientation during typical non-isothermal FFF ow, and conditions under which ow-enhanced nucleation occurs due to residual stretch are revealed. Flow-enhanced nucleation leads to accelerated crystallisation times at the surface of a deposited filament, whilst the bulk of the filament is governed by slower quiescent kinetics. The predicted time to 10% crystallinity, t10, is in quantitative agreement with in-situ Raman spectroscopy measurements of polycaprolactone (PCL). The model highlights important features not captured by a single measurement of t10. In particular, the crystal morphology varies cross-sectionally, with smaller spherulites forming in an outer skin layer, explaining features observed in full transient crystallisation measurements. Finally, exploitation of ow-enhanced crystallisation is proposed as a mechanism to increase weld strength at the interface between deposited filaments.

Citation

McIlroy, C., & Graham, R. (2018). Modelling flow-enhanced crystallisation during fused filament fabrication of semi-crystalline polymer melts. Additive Manufacturing, 24, (323-340). doi:10.1016/j.addma.2018.10.018. ISSN 2214-7810

Journal Article Type Article
Acceptance Date Oct 6, 2018
Online Publication Date Oct 10, 2018
Publication Date 2018-12
Deposit Date Oct 8, 2018
Publicly Available Date Oct 11, 2019
Print ISSN 2214-7810
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 24
Pages 323-340
DOI https://doi.org/10.1016/j.addma.2018.10.018
Keywords Fused filament fabrication; semi-crystalline polymer melt; flow-enhanced crystallisation; polycaprolactone
Public URL https://nottingham-repository.worktribe.com/output/1150698
Publisher URL https://www.sciencedirect.com/science/article/pii/S2214860418305554

Files

McIlroyAM2018 Finalversion (1.3 Mb)
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Publisher Licence URL
http://creativecommons.org/licenses/by-nc-nd/4.0/





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