Screw-assisted 3D printing with granulated materials: a systematic review

Abstract

This paper presents a systematic review on extrusion additive manufacturing (EAM), with focus on the technological development of screw-assisted systems that can be fed directly with granulated materials. Screw-assisted EAM has gained importance as an enabling technology to expand the range of 3D printing materials, reduce costs associated with feedstock fabrication, and increase the material deposition rate compared to traditional fused filament fabrication (FFF). Many experimental printheads and commercial systems that use some screw-processing mechanism can be found in the literature, but the design diversity and lack of standard terminology make it difficult to determine the most suitable solutions for a given material or application field. Besides, the few previous reviews have offered only a glimpse into the topic, without an in-depth analysis about the design of the extruders and associated capabilities. A systematic procedure was devised to identify the screw-assisted EAM systems that can print directly from granulated materials, resulting in 61 articles describing different pieces of equipment that were categorized as experimental printheads and commercial systems, for small- and large-scale applications. After describing their main characteristics, the most significant extruder modifications were discussed with reference to the materials processed and performance requirements. In the end, a general workflow for the development of 3D printers based on screw extrusion was proposed. This review intends to provide information about the state-of-the-art screw-assisted EAM and help the academy to identify further research opportunities in the field.

Material Extrusion Additive Manufacturing with Polyethylene Vitrimers

“…The reaction was conducted via a single-step process in a screw-assisted 3D printer at 220 °C. Pellet-fed screw-assisted 3D printers are increasingly being used to bypass the need for filaments, reducing the associated cost of filament production, while also increasing the deposition rate and expanding the range of 3D-printing materials [ 31 ]. For example, modified 3D printers have enabled the use of recycled polymer flakes from polyethylene terephthalate (PET) water bottles [ 32 ], polymer composites that are too brittle to be spooled into filaments [ 33 ], and recycled selective laser sintering (SLS) powder [ 34 ].…”

A Novel Manufacturing Concept of LCP Fiber-Reinforced GPET-Based Sandwich Structures with an FDM 3D-Printed Core

“…It is worth mentioning that the FDM melting process is not supported by the screw unit system, which limits the effectiveness of material plasticization. In selected cases, the use of screw plasticizing systems occurs only for large-size machines with the required high flow rate [ 22 , 23 , 24 , 25 ]. Therefore, the traditional FDM method cannot process composite materials with a high degree of filler content; therefore, new methods are constantly being developed to increase the effectiveness of the reinforcement.…”

Functionally Graded Multilayer Composites Based on Poly(D,L lactide)/Bioactive Fillers Fabricated by a 3D Direct Pellet Printing Multi-Extrusion Process

“…3D Direct Pellet multi-Extrusion (DPPmE) is a Fused Deposition Modeling (FDM) technique based on an extrusion system using polymer pellets as the starting material and thus avoiding the filament preparation required for Fused Filament Fabrication (FFF). This technique democratizes the access to additive manufacturing techniques since it expands the applicability of FDM to non-commercial materials in the filament form. − In former studies, it has already been demonstrated that well-designed structures can be manufactured with thermal unstable polymers and mechanical properties comparable to those of injection-molded parts . Besides, it is necessary to pay special attention to control the rheological properties of molten materials (like viscosity modulus, zero-shear viscosity, or relaxation time/elasticity) during extrusion through the nozzle and after deposition in order to ensure good interlayer welding and the mechanical robustness of 3D-printed parts. , Further, some DPPmE systems present an extrusion system with multiple screws, resulting in FGM-printed parts with different material composition and architecture.…”