Article
A Combined Experimental and Modeling Study for Pellet-Fed
Extrusion-Based Additive Manufacturing to Evaluate the
Impact of the Melting Efficiency
Andrea La Gala
1
, Rudinei Fiorio
1
, Daniel V. A. Ceretti
1
, Mustafa Erkoç
1
, Ludwig Cardon
1
and Dagmar R. D’hooge
2,3,
*
Citation: La Gala, A.; Fiorio, R.;
Ceretti, D.V.A.; Erkoç, M.; Cardon, L.;
D’hooge, D.R. A Combined
Experimental and Modeling Study for
Pellet-Fed Extrusion-Based Additive
Manufacturing to Evaluate the
Impact of the Melting Efficiency.
Materials 2021, 14, 5566. https://
doi.org/10.3390/ma14195566
Academic Editors: Loic Hilliou and
A. Javier Sanchez-Herencia
Received: 18 August 2021
Accepted: 21 September 2021
Published: 25 September 2021
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4.0/).
1
Centre for Polymer and Material Technologies (CPMT), Department of Materials, Textiles and Chemical
Engineering, Ghent University, Technologiepark, 130, Zwijnaarde 9052, 9000 Ghent, Belgium;
Andrea.LaGala@UGent.be (A.L.G.); rudinei.fiorio@UGent.be (R.F.); daniel.ceretti@ugent.be (D.V.A.C.);
mustafa.erkoc@ugent.be (M.E.); ludwig.cardon@ugent.be (L.C.)
2
Centre for Textiles Science and Engineering (CTSE), Department of Materials, Textiles and Chemical
Engineering, Ghent University, Technologiepark, 70A, Zwijnaarde 9052, 9000 Ghent, Belgium
3
Laboratory for Chemical Technology (LCT), Department of Materials, Textiles and Chemical Engineering,
Ghent University, Technologiepark, 125, Zwijnaarde 9052, 9000 Ghent, Belgium
* Correspondence: dagmar.dhooge@ugent.be
Abstract:
To improve the product quality of polymeric parts realized through extrusion-based addi-
tive manufacturing (EAM) utilizing pellets, a good control of the melting is required. In the present
work, we demonstrate the strength of a previously developed melt removal using a drag framework
to support such improvement. This model, downscaled from conventional extrusion, is successfully
validated for pellet-based EAM—hence, micro-extrusion—employing three material types with differ-
ent measured rheological behavior, i.e., acrylonitrile-butadiene-styrene (ABS), polylactic acid (PLA)
and styrene-ethylene-butylene-styrene polymer (SEBS). The model’s validation is made possible by
conducting for the first time dedicated EAM screw-freezing experiments combined with appropriate
image/data analysis and inputting rheological data. It is showcased that the (overall) processing
temperature is crucial to enable similar melting efficiencies. The melting mechanism can vary with
the material type. For ABS, an initially large contribution of viscous heat dissipation is observed,
while for PLA and SEBS thermal conduction is always more relevant. It is highlighted based on
scanning electron microscopy (SEM) analysis that upon properly tuning the finalization of the melting
point within the envisaged melting zone, better final material properties are achieved. The model can
be further used to find an optimal balance between processing time (e.g., by variation of the screw
frequency) and material product performance (e.g., strength of the printed polymeric part).
Keywords: rapid prototyping; 3D printing; melting single screw extrusion; material design
1. Introduction
Over the past few years, the use of additive manufacturing (AM) has significantly
increased in the production of polymeric products and material shapes [
1
–
10
]. Most
polymeric AM applications start with a filament [
9
–
12
], which is forced through a heated
nozzle, promoting its melting to then deposit consecutive material layers. This is performed
according to geometric and process parameters that can have a strong influence on the
properties of the final parts [
13
–
16
]. In recent years, however, a growing number of
AM applications introduced the use of single-screw extruders (SSEs) fed with polymer
pellets [
17
–
21
]. The global term for such AM modifications is extrusion-based AM (EAM),
complementary with conventional large-scale extrusion [22–26].
EAM allows us to overcome several limitations of filament-based AM, which is also
known as fused filament fabrication (FFF). Specifically, soft polymers can be manufactured
that are difficult to process through traditional 3D printing [
19
,
20
]. Printing employing
Materials 2021, 14, 5566. https://doi.org/10.3390/ma14195566 https://www.mdpi.com/journal/materials
