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Review
. 2021 Sep 18;13(18):3160.
doi: 10.3390/polym13183160.

Analytical and Numerical Models of Thermoplastics: A Review Aimed to Pellet Extrusion-Based Additive Manufacturing

Alessio Pricci  1 , Marco D de Tullio  1 , Gianluca Percoco  1
Affiliations
Review

Analytical and Numerical Models of Thermoplastics: A Review Aimed to Pellet Extrusion-Based Additive Manufacturing

Alessio Pricci et al. Polymers (Basel). .

Abstract

Recent developments in additive manufacturing have moved towards a new trend in material extrusion processes (ISO/ASTM 52910:2018), dealing with the direct extrusion of thermoplastic and composite material from pellets. This growing interest is driven by the reduction of costs, environmental impact, energy consumption, and the possibility to increase the range of printable materials. Pellet additive manufacturing (PAM) can cover the same applications as fused filament fabrication (FFF), and in addition, can lead to scale towards larger workspaces that cannot be covered by FFF, due to the limited diameters of standard filaments. In the first case, the process is known as micro- or mini-extrusion (MiE) in the literature, in the second case the expression big area additive manufacturing (BAAM) is very common. Several models are available in literature regarding filament extrusion, while there is a lack of modeling of the extrusion dynamics in PAM. Physical and chemical phenomena involved in PAM have high overlap with those characterizing injection molding (IM). Therefore, a systematic study of IM literature can lead to a selection of the most promising models for PAM, both for lower (MiE) and larger (BAAM) extruder dimensions. The models concerning the IM process have been reviewed with this aim: the extraction of information useful for the development of codes able to predict thermo-fluid dynamics performances of PAM extruders.

Keywords: additive manufacturing; industry 4.0; pellet extrusion; polymer melting modeling; single-screw extrusion.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
(a) Perspective view of FFF process; (b) front view of the complete extrusion system in PAM.
Figure 2
Figure 2
Energy requested for different manufacturing processes—reprinted from [5].
Figure 3
Figure 3
Scheme of the extrusion process in IM.
Figure 4
Figure 4
Solid conveying kinematics and geometry; W1—channel width at mean diameter, S—screw lead, e—flight width, φ—helix angle, Δsc—computational step in downstream direction, Vb—barrel velocity, Vsz—solid body velocity.
Figure 5
Figure 5
Overview of a DEM simulation of spherical particles—reprinted with permission from [22], with the permission of AIP Publishing.
Figure 6
Figure 6
Polynomial regression of data—reprinted with permission from [23].
Figure 7
Figure 7
Maddock melting mechanism: W—channel width, H—channel height, hgap—radial clearance between screw flights and barrel, hmolten—local molten layer thickness, X—local solid bed width.
Figure 8
Figure 8
Brinkman number (Br) along screw channel direction for both the standard extruder used in the IM process (SE) and the mini-extruder (ME) used in the pellet extrusion-based process—reprinted from [7].
Figure 9
Figure 9
(a) Klenk; (b) Maddock; (c) Lindt melting mechanism.
Figure 10
Figure 10
Experimental, CFD, and analytical predictions of the solid content in screw vanes of an IM extruder—reprinted with permission from [10].
Figure 11
Figure 11
Correction factors for rectangular channels for a given aspect ratio (width to height ratio).
See this image and copyright information in PMC

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