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Polymers
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Extrusion Based Additive Manufacturing
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Extrusion Based Additive Manufacturing

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Processing and Engineering".

Deadline for manuscript submissions: closed (30 November 2021) | Viewed by 20205

Special Issue Editors

Prof. Dr. Gianluca Cicala

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Guest Editor
Department of Civil Engineering and Architecture, University of Catania, Viale Andrea Doria 6, 95125 Catania, Italy
Interests: additive manufacturing; polymers; composites; recycling
Special Issues, Collections and Topics in MDPI journals
Prof. Marco Cavallaro

E-Mail Website
Guest Editor
Institute of Materials and Manufacturing, Brunel University London, Uxbridge UB8 3PH, UK
Interests: additive manufacturing; material extrusion; powder bed fusion; computational design; personalised manufacturing
Dr. Ian Major

E-Mail Website
Guest Editor
Materials Research Institute, Athlone Institute of Technology, Dublin Road, N37 HD68 Athlone, Ireland
Interests: homopolysaccharide; naturally-occurring polymers; polysaccharide; immunotherapies; bioactives; immune priming; cancer therapies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Extrusion Based Additive Manufacturing, also referred as FFF (Fused Filament Fabrication), is a widely used additive manufacturing technique in various fields ranging from simple prototyping to functional parts production. FDM (Fused Deposition Modelling) was patented by Scott Crump back in 1989 and then the company Stratasys was founded. The availability of open desktop machines followed Crump first patents expire and let FDM technique to be easily available with the result of pushing further the research on materials for FDM. Nowadays, relevant developments resulted from FDM spreading. For example, FDM is today used to produce full metal parts starting from formulations of polymers filled with very high content of metal powder similarly to Metal Injection Moulding. Two companies are the forefront in this technology: Desktop Metal and MarkForged. Both companies received multimillion investments from leading companies like BMW, Google etc. MarkForged developed also an FDM machine to print Nylon parts reinforced with continuous reinforcement fibres. The company Anisoprint exploited similar concept allowing to print reinforced parts with a wider selection of matrix types. FDM approach was also extended from simple layer by layer building to a 3D layer deposition using a 6 axis robot systems as demonstrated by the Robotic Composite 3D Demonstrator.

Despite all these developments the research and the possibility of new outcomes are still to come. The market response to the introduction of machine like those from Roboze, Apium and Intamsys producing PEEK parts demonstrate that Extrusion Based Additive Manufacturing techniques are still not to its limits. The use of tailored materials for Extrusion Based Additive Manufacturing is not fully exploited and also the lack of standards for this technology, even if there are some general for AM like ISO/ASTM 52900 and more specific to Material Extrusion, for example ISO/ASTM 52903-1, is an open field needing for contributions by industry and academia. The present special issues is aimed to collect contributions ranging from novel materials development to the characterization of mechanical and functional properties of FDM printed parts. Papers focusing on the development of standards for FDM or on the use of FDM for functional applications are also welcome.

Prof. Gianluca Cicala
Prof. Marco Cavallaro
Prof. Ian Major
Guest Editors

Keywords

  • Additive Manufacturing
  • Extrusion Based
  • Fused Deposition Modelling
  • Fused Filament Forming
  • Polymer Blends
  • Composites
  • Nanocomposites
  • Mechanical Properties
  • Thermal Properties
  • Rheology
  • Functional properties

Published Papers (5 papers)

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Research

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35 pages, 6217 KiB  
Article
The Extent of Interlayer Bond Strength during Fused Filament Fabrication of Nylon Copolymers: An Interplay between Thermal History and Crystalline Morphology
by Dries Vaes, Margot Coppens, Bart Goderis, Wim Zoetelief and Peter Van Puyvelde
Polymers 2021, 13(16), 2677; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13162677 - 11 Aug 2021
Cited by 14 | Viewed by 2904
Abstract
One of the main drawbacks of Fused Filament Fabrication is the often-inadequate mechanical performance of printed parts due to a lack of sufficient interlayer bonding between successively deposited layers. The phenomenon of interlayer bonding becomes especially complex for semi-crystalline polymers, as, besides the [...] Read more.
One of the main drawbacks of Fused Filament Fabrication is the often-inadequate mechanical performance of printed parts due to a lack of sufficient interlayer bonding between successively deposited layers. The phenomenon of interlayer bonding becomes especially complex for semi-crystalline polymers, as, besides the extremely non-isothermal temperature history experienced by the extruded layers, the ongoing crystallization process will greatly complicate its analysis. This work attempts to elucidate a possible relation between the degree of crystallinity attained during printing by mimicking the experienced thermal history with Fast Scanning Chip Calorimetry, the extent of interlayer bonding by performing trouser tear fracture tests on printed specimens, and the resulting crystalline morphology at the weld interface through visualization with polarized light microscopy. Different printing conditions are defined, which all vary in terms of processing parameters or feedstock molecular weight. The concept of an equivalent isothermal weld time is utilized to validate whether an amorphous healing theory is capable of explaining the observed trends in weld strength. Interlayer bond strength was found to be positively impacted by an increased liquefier temperature and reduced feedstock molecular weight as predicted by the weld time. An increase in liquefier temperature of 40 °C brings about a tear energy value that is three to four times higher. The print speed was found to have a negligible effect. An elevated build plate temperature will lead to an increased degree of crystallinity, generally resulting in about a 1.5 times larger crystalline fraction compared to when printing occurs at a lower build plate temperature, as well as larger spherulites attained during printing, as it allows crystallization to occur at higher temperatures. Due to slower crystal growth, a lower tie chain density in the amorphous interlamellar regions is believed to be created, which will negatively impact interlayer bond strength. Full article
(This article belongs to the Special Issue Extrusion Based Additive Manufacturing)
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19 pages, 11974 KiB  
Article
A Comparison of Miniature Lattice Structures Produced by Material Extrusion and Vat Photopolymerization Additive Manufacturing
by Rafael Guerra Silva, María Josefina Torres and Jorge Zahr Viñuela
Polymers 2021, 13(13), 2163; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13132163 - 30 Jun 2021
Cited by 10 | Viewed by 2406
Abstract
In this paper, we study the capabilities of two additive manufacturing technologies for the production of lattice structures, namely material extrusion and vat photopolymerization additive manufacturing. A set of polymer lattice structures with diverse unit cell types were built using these additive manufacturing [...] Read more.
In this paper, we study the capabilities of two additive manufacturing technologies for the production of lattice structures, namely material extrusion and vat photopolymerization additive manufacturing. A set of polymer lattice structures with diverse unit cell types were built using these additive manufacturing methods and tested under compression. Lattice structures built using material extrusion had lower accuracy and a lower relative density caused by the air gaps between layers, but had higher elastic moduli and larger energy absorption capacities, as a consequence of both the thicker struts and the relatively larger strength of the feedstock material. Additionally, the deformation process in lattices was analyzed using sequential photographs taken during the compression tests, evidencing larger differences according to the manufacturing process and unit-cell type. Both additive manufacturing methods produced miniature lattice structures with similar mechanical properties, but vat polymerization should be the preferred option when high geometrical accuracy is required. Nevertheless, as the solid material determines the compressive response of the lattice structure, the broader availability of feedstock materials gives an advantage to material extrusion in applications requiring stiffer structures or with higher energy absorption capabilities. Full article
(This article belongs to the Special Issue Extrusion Based Additive Manufacturing)
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11 pages, 3437 KiB  
Article
Interlayer Bonding Capability of Additively Manufactured Polymer Structures under High Strain Rate Tensile and Shear Loading
by Patrick Striemann, Lars Gerdes, Daniel Huelsbusch, Michael Niedermeier and Frank Walther
Polymers 2021, 13(8), 1301; https://0-doi-org.brum.beds.ac.uk/10.3390/polym13081301 - 15 Apr 2021
Cited by 4 | Viewed by 1810
Abstract
Additive manufacturing of polymers via material extrusion and its future applications are gaining interest. Supporting the evolution from prototype to serial applications, additional testing conditions are needed. The additively manufactured and anisotropic polymers often show a weak point in the interlayer contact area [...] Read more.
Additive manufacturing of polymers via material extrusion and its future applications are gaining interest. Supporting the evolution from prototype to serial applications, additional testing conditions are needed. The additively manufactured and anisotropic polymers often show a weak point in the interlayer contact area in the manufacturing direction. Different process parameters, such as layer height, play a key role for generating the interlayer contact area. Since the manufacturing productivity depends on the layer height as well, a special focus is placed on this process parameter. A small layer height has the objective of achieving better material performance, whereas a larger layer height is characterized by better economy. Therefore, the capability- and economy-oriented variation was investigated for strain rates between 2.5 and 250 s−1 under tensile and shear load conditions. The test series with dynamic loadings were designed monitoring future applications. The interlayer tensile tests were performed with a special specimen geometry, which enables a correction of the force measurement. By using a small specimen geometry with a force measurement directly on the specimen, the influence of travelling stress waves, which occur due to the impact at high strain rates, is reduced. The interlayer tensile tests indicate a strain rate dependency of additively manufactured polymers. The capability-oriented variation achieves a higher ultimate tensile and shear strength compared to the economy-oriented variation. The external and internal quality assessment indicates an increasing primary surface profile and void volume content for increasing the layer height. Full article
(This article belongs to the Special Issue Extrusion Based Additive Manufacturing)
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13 pages, 1704 KiB  
Article
Basic Research for Additive Manufacturing of Rubber
by Welf-Guntram Drossel, Jörn Ihlemann, Ralf Landgraf, Erik Oelsch and Marek Schmidt
Polymers 2020, 12(10), 2266; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12102266 - 01 Oct 2020
Cited by 11 | Viewed by 3572
Abstract
The dissemination and use of additive processes are growing rapidly. Nevertheless, for the material class of elastomers made of vulcanizable rubber, there is still no technical solution for producing them using 3D printing. Therefore, this paper deals with the basic investigations to develop [...] Read more.
The dissemination and use of additive processes are growing rapidly. Nevertheless, for the material class of elastomers made of vulcanizable rubber, there is still no technical solution for producing them using 3D printing. Therefore, this paper deals with the basic investigations to develop an approach for rubber printing. For this purpose, a fused deposition modeling (FDM) 3D printer is modified with a screw extruder. Tests are carried out to identify the optimal printing parameters. Afterwards, test prints are performed for the deposition of rubber strands on top of each other and for the fabrication of simple two-dimensional geometries. The material behavior during printing, the printing quality as well as occurrences of deviations in the geometries are evaluated. The results show that the realization of 3D rubber printing is possible. However, there is still a need for research to stabilize the layers during the printing process. Additionally, further studies are necessary to determine the optimum parameters for traverse speed and material discharge, especially on contours. Full article
(This article belongs to the Special Issue Extrusion Based Additive Manufacturing)
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Review

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29 pages, 11826 KiB  
Review
Fused Filament Fabrication of PEEK: A Review of Process-Structure-Property Relationships
by Ali Reza Zanjanijam, Ian Major, John G. Lyons, Ugo Lafont and Declan M. Devine
Polymers 2020, 12(8), 1665; https://0-doi-org.brum.beds.ac.uk/10.3390/polym12081665 - 27 Jul 2020
Cited by 125 | Viewed by 8154
Abstract
Poly (ether ether ketone) (PEEK) is a high-performance engineering thermoplastic polymer with potential for use in a variety of metal replacement applications due to its high strength to weight ratio. This combination of properties makes it an ideal material for use in the [...] Read more.
Poly (ether ether ketone) (PEEK) is a high-performance engineering thermoplastic polymer with potential for use in a variety of metal replacement applications due to its high strength to weight ratio. This combination of properties makes it an ideal material for use in the production of bespoke replacement parts for out-of-earth manufacturing purposes, in particular on the International Space Station (ISS). Additive manufacturing (AM) may be employed for the production of these parts, as it has enabled new fabrication pathways for articles with complex design considerations. However, AM of PEEK via fused filament fabrication (FFF) encounters significant challenges, mostly stemming from the semi crystalline nature of PEEK and its associated high melting temperature. This makes PEEK highly susceptible to changes in processing conditions which leads to a large reported variation in the literature on the final performance of PEEK. This has limited the adaption of FFF printing of PEEK in space applications where quality assurance and reproducibility are paramount. In recent years, several research studies have examined the effect of printing parameters on the performance of the 3D-printed PEEK parts. The aim of the current review is to provide comprehensive information in relation to the process-structure-property relationships in FFF 3D-printing of PEEK to provide a clear baseline to the research community and assesses its potential for space applications, including out-of-earth manufacturing. Full article
(This article belongs to the Special Issue Extrusion Based Additive Manufacturing)
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