Fused Deposition Modeling (FDM) is a widely used additive manufacturing technology for fabrication of complex geometric parts using thermoplastic polymers. The quality issues and inferior properties ...of fabricated parts limited this process to manufacture parts for industrial level applications. Reinforcing the polymer with nanoparticles, short fibers or continuous fibers improve mechanical, thermal and electrical properties compared to the neat polymer. Several works have been carried out since last two decades to print quality products through FDM by using composite materials. The success of expanding this technique to industrial applications depends on the preparation of printable composite feedstock filament and printing without defects. This article reviews the challenges involved in the preparation of composite feedstock filaments and printing issues during the printing of nano composites, short and continuous fiber composites. The printing process of various thermoplastic composites ranging from amorphous to crystalline polymers is discussed. Also, detailed explanation is given about the analytical and numerical models used for simulating the FDM printing process and for estimating the mechanical properties of the printed parts. This critical review mainly helps the young researchers working in the area of processing of composite materials via 3D printing.
Additive Manufacturing (AM), and more specifically Fused Filament Fabrication (FFF), allow the production of highly customized parts, provide enormous freedom-of-design and can lead to material ...savings due to the layer-by-layer material deposition that is inherent to this family of production processes. FFF utilizes both amorphous and semi-crystalline thermoplastic filaments as feedstock materials, offering a wider range of materials compared to some other polymer-based additive manufacturing techniques. However, the current trend where FFF, and AM in general, are changing from a technique for rapid prototyping to the production of fully functional parts designed for high-end applications creates the inevitable need to incorporate more engineering and high-performance thermoplastics, which are most often semi-crystalline polymers, into the material palette. Crystallization provides semi-crystalline polymers with some distinct features that set them apart from their amorphous counterparts, yet it also can present difficulties regarding their processing. Understanding of the behavior of semicrystalline polymers during FFF processing is thus a prerequisite to exploit their full potential. This review provides a broad overview of FFF processing of semicrystalline polymers. Particular focus lies on the impact of processing conditions and feedstock modifications, such as the incorporation of fillers or the formation of blends, on crystallinity as well as the microstructure of printed parts, the impact of microstructure on the mechanical performance, and general part quality. Furthermore, attention is given to some specific phenomena that can occur during printing of semi-crystalline feedstock filaments which have shown to strongly impact the printing process. Examples are self-nucleation in the case of insufficient heat transfer and melting, flow-induced crystallization due to high shear deformations upon extrusion, and the negative impact of crystallization on chain mobility which is relevant for the development of interlayer strength and on dimensional accuracy due to excessive shrinkage. Finally, this review is concluded with a critical outlook on perspectives for future research to address the current challenges that are still faced when employing semi-crystalline polymers as FFF feedstock.
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Fused deposition modelling (FDM) is the most commonly investigated 3D printing technology for the manufacture of personalized medicines, however, the high temperatures used in the ...process limit its wider application. The objective of this study was to print low-melting and thermolabile drugs by reducing the FDM printing temperature. Two immediate release polymers, Kollidon VA64 and Kollidon 12PF were investigated as potential candidates for low-temperature FDM printing. Ramipril was used as the model low melting temperature drug (109 °C); to the authors’ knowledge this is the lowest melting point drug investigated to date by FDM printing. Filaments loaded with 3% drug were obtained by hot melt extrusion at 70 °C and ramipril printlets with a dose equivalent of 8.8 mg were printed at 90 °C. HPLC analysis confirmed that the drug was stable with no signs of degradation and dissolution studies revealed that drug release from the printlets reached 100% within 20–30 min. Variable temperature Raman and solid state nuclear magnetic resonance (SSNMR) spectroscopy techniques were used to evaluate drug stability over the processing temperature range. These data indicated that ramipril did not undergo degradation below its melting point (which is above the processing temperature range: 70–90 °C) but it was transformed into the impurity diketopiperazine upon exposure to temperatures higher than its melting point. The use of the excipients Kollidon VA64 and Kollidon 12PF in FDM was further validated by printing with the drug 4-aminosalicylic acid (4-ASA), which in previous work was reported to undergo degradation in FDM printing, but here it was found to be stable. This work demonstrates that the selection and use of new excipients can overcome one of the major disadvantages in FDM printing, drug degradation due to thermal heating, making this technology suitable for drugs with lower melting temperatures.
Predicting the influence of material composition on the printability of highly filled metal powder-polymer systems present a significant challenge in metal fused filament fabrication (MF3). The ...current work presents an approach to evaluate new material compositions used to fabricate filaments for their printability. In this study, filaments with 59 vol.% (87 wt.%) of Ti-6Al-4V powder with two particle size distributions {fine (D50 = 13 μm) and coarse (D50 = 30 μm)} dispersed in a polymer matrix were examined. The respective forces to overcome the pressure drop, for successful printing, were found to increase with an increase in the feed rate, and were also dependent on the feedstock viscosity. In addition, shear forces estimated from the filament shear strength were found to be limiting conditions for successful printing. Based on these observations, a criterion has been proposed to evaluate filament printability from the predicted limiting force for filament failure and the required force to achieve continuous material flow for successful printing. Under present experimental conditions, successful printing was achieved up to 2 mm/s and 8 mm/s for fine and coarse powder filaments, in good agreement with the model predictions. The model was experimentally tested and found to be applicable for other compositions. The results demonstrate a new printability criterion to design novel materials for MF3.
•Printability of Ti64 alloy powder-polymer filaments for fused filament fabrication.•Filament viscosity and feed rate influences the pressure drop at the nozzle exit.•Filament strength dictates successful material extrusion and printing.•Powder attributes influences printability and print speed.•Predictive process models allow materials development in fused filament fabrication.
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Three-dimensional printing (3DP) is a highly disruptive technology with the potential to change the way pharmaceuticals are designed, prescribed and produced. Owing to its low cost, ...diversity, portability and simplicity, fused deposition modeling (FDM) is well suited to a multitude of pharmaceutical applications in digital health. Favourably, through the combination of digital and genomic technologies, FDM enables the remote fabrication of drug delivery systems from 3D models having unique shapes, sizes and dosages, enabling greater control over the release characteristics and hence bioavailability of medications. In turn, this system could accelerate the digital healthcare revolution, enabling medicines to be tailored to the individual needs of each patient on demand. To date, a variety of FDM 3D printed medical products (e.g. implants) have been commercialised for clinical use. However, within pharmaceuticals, certain regulatory hurdles still remain. This article reviews the current state-of-the-art in FDM technology for medical and pharmaceutical research, including its use for personalised treatments and interconnection within digital health networks. The outstanding challenges are also discussed, with a focus on the future developments that are required to facilitate its integration within pharmacies and hospitals.
The study is focused on multifunctional performance of carbon nanotubes (CNT) and Graphene nanoplatelets (GNP) reinforced PEEK composites enabled via fused filament fabrication (FFF) additive ...manufacturing (AM) utilizing in-house nanoengineered filaments. Thermo-physical, mechanical and wear characteristics of electro-conductive PEEK nanocomposites are reported. The coefficient of thermal expansion (CTE) is found to decrease by 26% and 18% with the incorporation of 5 wt% GNP and 3 wt% CNT into PEEK polymer, respectively. The decrease in CTE provides better dimensional stability to resulting nanocomposite structures. Due to uniform dispersion of CNT and GNP in the PEEK matrix, the crystallization temperature and degree of crystallinity are both increased. The 3D printed PEEK nanocomposites reveal interfacial voids between the beads and intra-bead pores and thus exhibit lower density compared to that of the 3D printed neat PEEK. Young's and storage moduli are found to increase by 20% and 66% for 3 wt% CNT loading and by 23% and 72% for 5 wt% GNP loading respectively. However, the PEEK nanocomposites exhibit similar tensile strength to that of neat PEEK. The coefficient of friction obtained from fretting wear tests is found to decrease by 67% and 56% for 1 wt% CNT and 3 wt% GNP loaded PEEK nanocomposites, respectively and the decrease is attributed to reduced hardness and increased porosity. Multifunctional performance of carbon nanostructures reinforced AM-enabled PEEK composites demonstrated here makes them suitable for a range of applications such as orthopedics, oil and gas, automotive, electronics and space.
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•The crystallization temperature and degree of crystallinity of AM-PEEK increase with the addition of carbon nanostructures.•The CTE of PEEK nanocomposites decreases by 26% and 18% with the addition of 5wt.% GNP and 3wt.% CNT, respectively.•Young’s modulus of PEEK increases by 20% and 23% by the addition of 3wt.% CNT and 5wt.% GNP respectively.•The PEEK/GNP exhibits ductile fracture with concomitant increase in strain at break and toughness relative to neat PEEK.•The coefficient of friction decreases by 67% for 1wt% CNT and 56% for 3wt% GNP due to reduced hardness & increased porosity.
In this study, the tensile, flexural and fracture behavior of PEEK processed by fused filament fabrication (FFF) is reported. Three different configurations, viz., specimens built horizontally with a ...raster angle of 0° (H-0°) and 90° (H-90°), and vertically with a raster angle of 90° (V-90°) are examined. The best performing specimen in terms of its tensile, flexural and fracture toughness properties is H-0°, followed by H-90° and V-90°. The H-0° and H-90° specimens exhibit 85% and 75% of tensile and flexural strengths of molded bulk PEEK, respectively. The fracture toughnesses of the H-0° and H-90° specimens are 78% and 70% of molded bulk PEEK, respectively. However, V-90° specimens show lower tensile, flexural and fracture toughness properties compared to those of H-0°, H-90° and molded PEEK. The fracture surface and microtomography analyses indicate that the degree of interfacial bonding between beads during layer-by-layer buildup, is affected by the thermal gradient across the beads. The PEEK specimen configurations examined here have different thermal gradient in the build directions and such variations manifest themselves in their macroscopic mechanical behavior. The findings of this study provide guidelines for FFF of PEEK to enable its realization in applications such as orthopedic implants.
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•Horizontally 3D printed PEEK with raster angles of 0o and 90o exhibits tensile flexural and fracture properties comparable to those of molded PEEK•Specimens built vertically are prone to delamination, exhibiting poorer mechanical performance due to high thermal gradient in the build-direction•Stick-slip fracture and lower Poisson’s ratio are observed for specimens built vertically, due to the presence of interfacial voids.•Minimizing thermal gradients across beads is the key to producing parts with excellent macroscopic properties
The fused filament fabrication (FFF) process is characterized by fast local temperature decrease. Such characteristic usually leads to lower crystallinity degree in final printed parts when ...semi-crystalline polymers are used. By melt-compounding poly(lactic acid) (PLA) with its nucleating agent Talc, filaments of PLA/Talc composite were produced and used in FFF. Through investigations in static/dynamic mechanical and thermal properties, and morphology, the influence of Talc on the PLA based composite in FFF are revealed: after melt compounding with Talc, PLA matrix can crystallize considerably during fast cooling in FFF; as a consequence, final parts exhibited higher degree of crystallinity than the case of neat PLA; furthermore, melt crystallization process releases heat, promoting coalescence between adjacent layers, and ultimately contributes to higher parts stiffness and better mechanical integrity. This paper presents a first example in which in-situ melt crystallization is recovered for semi-crystalline polymers during FFF via composition modification. With this example, an increase in crystallinity from 3.6% to 12% can lead to 15% increase in flexural modulus for FFF printed parts. Research results also provide insights in material property reinforcement, heat treatment on finished parts, and explorations in other semi-crystalline materials in FFF.
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•Talc promotes PLA melt-crystallization in FFF.•Polymer melt-crystallization releases heat and delays printed parts cooling in FFF.•Heat treatment on semi-crystalline polymers at Tcc increases the crystallinity degrees significantly.
Fused filament fabrication (FFF), one of the most promising additive manufacturing (AM) methods has attracted considerable attention to date. Although FFF is evolving into a manufacturing tool with ...significant technological and material advancements, there remains a challenge to transfer FFF-printed parts into functional objects for practical applications. Polymer components fabricated by FFF technique exhibit weak and anisotropic mechanical properties compared to their counterparts by conventional processing. The limited mechanical property for the FFF-printed parts is a result of weak interlayer bond interface that develops during the layer-wise deposition process. This review documents recent advances on the bond interface in FFF-printed parts in aspects of its mechanisms, characterization and enhancement methods. The main objective is to provide a comprehensive understanding of the process-structure-properties of interlayer bond in FFF technique.
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•The mechanical anisotropy in FFF-printed parts is a result of poor interlayer bond, varying with polymer materials.•The time for interlayer bond formation provided by the FFF process depends on the characteristic timescale of the polymer.•Complete molecular diffusion and entanglement rather than neck growth is required to achieve strong bond interface.•Both process control and material modification can facilitate the formation of strong interlayer bond in FFF-printed parts.
Fused filament fabrication (FFF), a much-appreciated three-dimensional printing (3DP) technology, has triggered the industrial innovations by providing viable and cost-effective solutions for design ...validations, product prototyping, and the production of high-performance functional components. Indeed, the main credit of its successful career goes to material and printing flexibilities. However, the technology still faces various downsides, including poor finish, geometrical fits and tolerances, anisotropy, in-printing errors, and limited mechanical strength, that cannot be easily outweighed as these suppress its practical implications. As of utmost necessity, this review paper discusses the various abilities and inabilities of this technology to generate a roadmap of futuristic tasks for better outcomes. The review paper will act as a first-hand reference, through the well-defined possible directions, to the young researchers and senior scientist.
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