Paper Number
AM3 

Session
Additive Manufacturing

Title
Rheological and heat transfer effects in thermoplastic extrusion additive manufacturing

Presentation Date and Time
October 15, 2018 (Monday) 10:40

Track / Room
Track 3 / Bellaire

Authors (Click on name to view author profile)

1. Phan, David D. (University of Delaware, Department of Chemical and Biomolecular Engineering)
2. Swain, Zachary R. (University of Delaware, Department of Materials Science and Engineering)
3. Mackay, Michael E. (University of Delaware, Materials Science & Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
David D. Phan¹, Zachary R. Swain², and Michael E. Mackay^3
1Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE; ²Department of Materials Science and Engineering, University of Delaware, Newark, DE; ³Materials Science & Chemical and Biomolecular Engineering, University of Delaware, Newark, DE

Speaker / Presenter 
Phan, David D.

Text of Abstract
Additive manufacturing, commonly known as 3D printing, provides unlimited design freedom and access to more complex geometries compared to other contemporary manufacturing techniques. Recent advances in this technique have contributed to a diverse palette of printable materials, some of which include: metals, hydrogels, ceramics, and polymers. Complementary to this is a wide variety of printing methods, such as the laser sintering of powders and the controlled extrusion of thermoplastic materials. The latter is often referred to as fused filament fabrication (FFF) or material extrusion (ME) and is the most commercially widespread. In ME, filament of thermoplastic material is conveyed towards a melting zone before being pushed through a computer-controlled nozzle and deposited onto a build plate, with the process being repeated until the desired product is formed. The strength of the final product relies heavily on how well individually laid tracks of molten material “weld” together due to intermolecular diffusion of polymer chains. This diffusion process therefore depends on the temperature the material achieves within the melting zone, making this a heat transfer problem. The complex flow geometry also presents itself as a rheological problem, requiring a unified rheology-heat transfer analysis to understand the ME mechanism. Firstly, we present a modified Cogswell model, which we use to relate extrudate temperatures to entry pressures formed by the flow field. Entry pressure measurements and calculations reveal unintuitive flow behavior, which we believe is attributable to heat transfer limitations within the melt zone. We then present a dimensionless Nusselt-Graetz number analysis using the temperatures obtained from our rheological model and indeed find that heat transfer is a significant bottleneck in manufacturing the strongest printed parts. Future work will focus on applying our models to inform the redesign of ME-based 3D printers.