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

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.

Fused Deposition Modelling (FDM) of Thermoplastic-Based Filaments: Process and Rheological Properties—An Overview

“…The BAAM process allows several of the limitations of the FDM process to be overcome, such as the use of more expensive filaments in comparison to polymers in pellets form and the buckling effect during the feeding. However, this method has significant drawbacks, such as the elimination of support structures with adequate post processing, reduced printable resolution due to larger bead size, poor surface finish, and slow cooling due to quick deposition [122].…”

Pellet Production from Pruning and Alternative Forest Biomass: A Review of the Most Recent Research Findings

“…Using biomass in the form of pellets results in biofuel that is more affordable than when using biomass waste directly for energy generation. Pellet production takes place by extrusion, which involves passing semi-dry biomass that has been previously processed into dust, sawdust, or shavings through a hole that is a few millimeters in size to create small cylinders that are cut to the necessary length and then cooled [ 27 , 28 ]. This procedure lowers the cost of handling, transport, and storage by increasing the bulk density of the biomass [ 29 , 30 , 31 ].…”

Comparing pellet‐ and filament‐based additive manufacturing with conventional processing for ABS and PLA parts

“…In PBAM, polymers in the form of granules instead of filaments are fed in small single-screw extruders (SSEs) to allow for material deposition and solidification. 1,2,[13][14][15][16][17][18][19][20][21] Such extrusion-based AM (EAM) overcomes limitations of filament-based AM, allowing applications for soft and brittle polymers that can be more challenging to 3D print. 22,23 The cost of the pellet feedstock material is also lower compared to the filament counterpart 23 and EAM allows to bypass the filament production extrusion process so that less degradation of the material is expected.…”

“…A competitive less mature additive manufacturing (AM) technique, as mainly developed in the last two decades, is(PBAM). In PBAM, polymers in the form of granules instead of filaments are fed in small single‐screw extruders (SSEs) to allow for material deposition and solidification 1,2,13–21 . Such extrusion‐based AM (EAM) overcomes limitations of filament‐based AM, allowing applications for soft and brittle polymers that can be more challenging to 3D print 22,23 .…”