Fused Filament Fabrication (FFF) is widely used in Additive Manufacturing (AM) due to its low cost and ability to produce complex thermoplastic parts. Advances in high-performance materials, such as carbon fibre-reinforced PEKK, along with improved printer resolution have expanded its suitability for functional components. However, achieving high geometric precision remains challenging. Additive and Subtractive Hybrid Manufacturing (ASHM) offers a potential solution by combining 3D printing with subtractive post-processing, while a NURBS-based workflow can address geometric inaccuracies inherent to STL models. This study evaluates a NURBS-based Additive and Subtractive Hybrid Manufacturing (NURBS-ASHM) framework to fabricate cylindrical parts with high precision. Three methodologies were compared: conventional STL-based AM, precise AM using NURBS trajectories, and hybrid manufacturing integrating post-process milling. The results show that NURBS-based AM improves roundness and cylindricity by up to 49

Fused Deposition Modeling (FDM) is among the most widely used Additive Manufacturing (AM) technologies, valued for its capacity to produce complex thermoplastic parts at relatively low cost. Although initially limited to prototyping due to the poor mechanical performance of unreinforced polymers, recent advances in high-performance materials, particularly carbon fibre-reinforced Polyetherketoneketone (PEKK), have significantly broadened its industrial applications. These composite thermoplastics offer enhanced mechanical, thermal, and chemical properties, enabling the production of functional load-bearing components. Moreover, improvements in printer resolution and process control have increased the geometric accuracy and repeatability of FDM outputs.Nonetheless, meeting the stringent precision requirements of certain applications remains a challenge. Additive and Subtractive Hybrid Manufacturing (ASHM) has emerged as a promising solution by combining 3D printing with subtractive post-processing to enhance geometric accuracy and surface finish, albeit at a higher cost. Furthermore, the limitations of traditional AM workflows based on STL polygonal representations that inherently reduce geometric fidelity can be overcome by adopting a NURBS-based approach, which enhances direct and more accurate G-code generation.This study assessed the combined use of ASHM and a NURBS-based workflow to manufacture cylindrical components with enhanced precision. Three methodologies were compared: conventional STL-based AM, precise AM using NURBS trajectories, and hybrid manufacturing integrating post-process milling. Experimental results revealed substantial improvements in geometric quality. NURBS-based AM achieved up to 49% and 43% enhancement in roundness and cylindricity, respectively, over traditional STL-based printing. The incorporation of ASHM further improved these metrics, reaching up to 73% and 78% geometric accuracy. These findings underline the effectiveness of combining advanced modelling and hybrid manufacturing for producing high-precision parts in cost-sensitive contexts.

Fused filament fabrication (FFF) is one of the most widely used additive manufacturing (AM) techniques, which has enabled a simpler, more flexible, and low-cost processing procedure for obtaining functional fibre reinforced composite products. However, one of the shortcomings of AM processing is its poor geometric and dimensional behaviour that hinders the manufacture of high-quality functional parts. Though this limitation can be overcome with surface post-processing machining, the machining of composites is complex due to their non-homogeneous microstructure producing delamination, splintering, and fractures. In this study, the machinability of short carbon fibre reinforced glycol-modified polyethylene terephthalate (CF-PETG) processed by FFF additive manufacturing was assessed in face milling and edging peripheral milling operations by analysing the AM process parameters layer thickness (Lt) and build orientation (Bo). This machinability analysis was based on energy consumption and geometric properties. The former was assessed by measuring cutting forces, and the latter involved examining dimensional accuracy, flatness and surface roughness measurements, combined with 3D-topography and SEM microscope images. PETG processed by FFF showed good machinability in both machining operations with acceptable energy consumption and surface texture, with no significant effect of Lt or Bo. The addition of carbon fibre reinforcement to PETG improved energy consumption in both operations, and enhanced the surface texture in face milling. However, machinability worsened in terms of geometric properties for peripheral milling with the addition of carbon fibre and increased Lt, exhibiting substantial surface defects such as tearing and burrs.

Purpose Non-uniform rational B-splines (NURBSs) are the de facto standard for representing objects in computer-aided design (CAD). The purpose of this paper is to discuss how to stick to this standard in all phases of the additive manufacturing (AM) workflow, from the CAD object to the final G-code, bypassing unnecessary polygonal approximations. Design/methodology/approach The authors use a commercial CAD system (Rhino3D along with its programming environment Grasshopper) for direct slicing of the model, offset generation and trimming. Circular arcs are represented as quadratic NURBSs and free-form geometry as quadratic or cubic polynomial B-splines. Therefore, circular arcs are directly expressible as G2/G3 G-code commands, whereas free-form paths are rewritten as a succession of cubic Bézier curves, thereby admitting exact translation into G5 commands, available in firmware for AM controllers, such as Marlin. Findings Experimental results of this paper confirm a considerable improvement in quality over the standard AM workflow, consisting of an initial polygonization of the object (e.g. via standard tessellation language), slicing this polygonal approximation, offsetting the polygonal sections and, finally, generating G-code made up of polyline trajectories (G1 commands). Originality/value A streamlined AM workflow is obtained, with a seamless transfer from the initial CAD description to the final G-code. By adhering to the NURBS standard at all steps, the authors avoid multiple representations and associated errors resulting from approximations.

Historia del artículo: Recibido 5 de Mayo 2017 En la versión revisada 5 de Mayo 2017 Aceptado 31 de Mayo 2017 Accesible online 21 de Junio 2017 La impresión 3D o prototipado rápido es un método de fabricación aditiva que se emplea para la generación de prototipos y piezas funcionales. FDM (Fused Deposition Modelling) es la más popular debido a su uso extensivo en impresoras 3D para la fabricación de piezas con geometrías complejas, con las ventajas de un bajo coste y sin necesidad de mecanizados. La calidad de las partes fabricadas (acabado superficial, precisión dimensional o propiedades mecánicas) dependen de diversas variables del proceso. El estudio de la influencia de estos parámetros es de gran importancia para entender el funcionamiento de materiales de impresión 3D, y para determinar los desarrollos futuros.

Biomedical fracture fixation implants have complex sculp-tured geometries to adapt perfectly to fractured bones,making them difficult and expensive to manufacture with conventional machining methods.Fused filament fabrication(FFF)is a very popular Additive Manufacturing technology that simplifies the manufacture of parts with complex geome-tries,making it ideal for the manufacture of customized medical implants.

Purpose The extrusion-based additive manufacturing method followed by debinding and sintering steps can produce metal parts efficiently at a relatively low cost and material wastage. In this study, 316L stainless-steel metal filled filaments were used to print metal parts using the extrusion-based fused filament fabrication (FFF) approach. The purpose of this study is to assess the effects of common FFF printing parameters on the geometric and mechanical performance of FFF manufactured 316L stainless-steel components. Design/methodology/approach The microstructural characteristics of the metal filled filament, three-dimensional (3D) printed green parts and final sintered parts were analysed. In addition, the dimensional accuracy of the green parts was evaluated, as well as the hardness, tensile properties, relative density, part shrinkage and the porosity of the sintered samples. Moreover, surface quality in terms of surface roughness after sintering was assessed. Predictive models based on artificial neural networks (ANNs) were used for characterizing dimensional accuracy, shrinkage, surface roughness and density. Additionally, the response surface method based on ANNs was applied to represent the behaviour of these parameters and to identify the optimum 3D printing conditions. Findings The effects of the FFF process parameters such as build orientation and nozzle diameter were significant. The pore distribution was strongly linked to the build orientation and printing strategy. Furthermore, porosity decreased with increased nozzle diameter, which increased mechanical performance. In contrast, lower nozzle diameters achieved lower roughness values and average deviations. Thus, it should be noted that the modification of process parameters to achieve greater geometrical accuracy weakened mechanical performance. Originality/value Near-dense 316L austenitic stainless-steel components using FFF technology were successfully manufactured. This study provides print guidelines and further information regarding the impact of FFF process parameters on the mechanical, microstructural and geometric performance of 3D printed 316L components.

Los compuestos termoplásticos reforzados con fibra continua (CFRTPCs) se están convirtiendo en materiales alternativos para reemplazar los polímeros y metales termoendurecibles convencionales debido a su excelente rendimiento mecánico, reciclaje y potencial utilizado en estructuras ligeras. El modelado de deposición fundida (FDM) es una tecnología de fabricación aditiva prometedora y una alternativa a los procesos convencionales para la fabricación de CFRTPC debido a su capacidad para construir piezas funcionales con geometrías complejas. Las propiedades mecánicas de una pieza construida dependen de varios parámetros del proceso. El objetivo de este estudio es caracterizar el efecto de la orientación de la construcción, el grosor de la capa y el contenido de volumen de fibra en el rendimiento mecánico de componentes compuestos reforzados con fibra continua impresos en 3D fabricados por una impresora 3D de escritorio. Se realizan ensayos de tracción y flexión en tres puntos para determinar la respuesta mecánica de las probetas impresas. Las imágenes SEM de superficies fracturadas se evalúan para determinar los efectos de los parámetros del proceso en los modos de falla. Se observa que el efecto del espesor de capa de las muestras de nailon sobre el rendimiento mecánico es marginalmente significativo. Además, las muestras continuas reforzadas con fibra muestran valores de resistencia y rigidez más altos que las no reforzadas. Los resultados muestran que los compuestos reforzados con fibra de carbono exhiben el mejor rendimiento mecánico con mayor rigidez y las muestras planas exhiben valores más altos de resistencia y rigidez que las muestras en el borde. Además, los resultados muestran que la resistencia y la rigidez aumentan a medida que aumenta el contenido de volumen de fibra en la mayoría de los casos, pero, a la inversa, el nivel de incremento en el rendimiento mecánico es moderado con un aumento continuo en el contenido de fibra, particularmente en el caso de Kevlar® y fibras de vidrio, debido a una unión débil entre las capas de fibra / nailon, así como a la presencia de mayores niveles de defectos.

3D printing is a promising additive manufacturing technology capable of producing functional parts of continuous fibre reinforced thermoplastic composites (CFRTPCs). Thus recyclable parts having complex geometries are obtained in a simple manner [1]. In addition, the use of thermoplastic polymers significantly reduces the manufacturing costs because, unlike thermoset polymers, autoclave is not required for curing purposes. This is one of the greatest opportunities for 3D printing as an alternative to conventional manufacturing processes [2, 3]. Pieces obtained from both, conventional manufacturing methods and 3D printing technology, consists on a sequence of stacked sheets. Although greater automation and the possibility to optimize the design of each sheet are advantages of 3D printing, the adhesion between the matrix and the reinforcement fibres is insufficient and consequently, parts with inferior mechanical properties are obtained. Some studies have been interested in the effect of different process parameters on the mechanical performance of the printed parts, however, further research is required. A fundamental challenge is to get good consolidation between the fibres and the polymer matrix, with control of the fibre orientation and low cost [4, 5]. The aim of this work was to evaluate the mechanical properties of multidirectional 3D printed continuous carbon, glass and Kevlar fibre reinforced nylon composites, manufactured by FDM technique. Special attention was paid to the impact damage resistance and tolerance. [1] L. Nickels, Strengthening the 3D printing composites field, Reinforced Plastics, 62 (2018) 298-301 [2] L.G. Blok, M. L. Longana, H. Yu and B. K. S. Woods, An investigation into 3D printing of fibre reinforced Thermoplastic composites, Additive Manufacturing, 22 (2018) 176-186 [3] T. Liu, X. Tian, M. Zhang, D. Abliz, D. Li and G. Ziegmann, Interfacial performance and fracture patterns of 3D printed continuous carbon fibre with sizing reinforced PA6 composites, Composites Part A: Applied Science and Manufacturing, 114 (2018) 368-376 [4] R. Velu, F. Raspall and S. Singamneni, 3D printing technologies and composite materials for structural applications, Green Composites for Automotive Applications, chapter 8 (2019) 171-196 [5] Q. Hu, Y. Duan, H. Zhang, D. Liu, B. Yan and F. Peng, Manufacturing and 3D printing of continuous carbon fiber prepreg filament, 53 (2018) 1887-1989

The increasing worldwide demand for high-quality on-demand products manufactured with flexible and efficient productions systems has led to the development additive manufacturing technologies (AM). One of the most popular AM technologies, is fused filament fabrication (FFF) due to its ability to manufacture complex parts using a broad range of thermoplastic polymers with low production costs. However, FFF still cannot compete with traditional manufacturing processes when it comes to producing high quality end-use products. To improve mechanical properties and geometric quality features of end-use products, researchers are developing new advanced filaments infused with nanoparticles, short and continuous fibres. In the search for enhanced materials, glycol-modified polyethylene terephthalate (PETG) filaments and PETG reinforced with carbon fibres (PETG-CF) have been developed for FFF, but the effects of the addition of these fibres on geometric properties have not been analysed. The main objective of this study is to evaluate the impact of fibre addition to PETG filaments on the geometric properties of FFF manufactured parts by analysing their dimensional accuracy, and surface roughness. The effect of the 3D printing parameter -speed, layer thickness, and build orientation - on the geometric behaviour were assessed. Artificial neural network based predictive models of geometric parameters of the two candidate PETG-based filaments were used to find optimal printing parameters. In general terms, the carbon fibre addition to PETG-based polymers negatively affected the dimensional accuracy, flatness, and surface roughness in most of the printing conditions, significantly reducing the printing parameter combinations where the optimal values were achieved.

3D printing is a promising additive manufacturing technology capable of producing functional parts of continuous fibre reinforced thermoplastic composites (CFRTPCs). Thus recyclable parts having complex geometries are obtained in a simple manner [1]. In addition, the use of thermoplastic polymers significantly reduces the manufacturing costs because, unlike thermoset polymers, autoclave is not required for curing purposes. This is one of the greatest opportunities for 3D printing as an alternative to conventional manufacturing processes [2, 3]. Pieces obtained from both, conventional manufacturing methods and 3D printing technology, consists on a sequence of stacked sheets. Although greater automation and the possibility to optimize the design of each sheet are advantages of 3D printing, the adhesion between the matrix and the reinforcement fibres is insufficient and consequently, parts with inferior mechanical properties are obtained. Some studies have been interested in the effect of different process parameters on the mechanical performance of the printed parts, however, further research is required. A fundamental challenge is to get good consolidation between the fibres and the polymer matrix, with control of the fibre orientation and low cost [4, 5]. The aim of this work was to evaluate the mechanical properties of multidirectional 3D printed continuous carbon, glass and Kevlar fibre reinforced nylon composites, manufactured by FDM technique. Special attention was paid to the impact damage resistance and tolerance. [1] L. Nickels, Strengthening the 3D printing composites field, Reinforced Plastics, 62 (2018) 298-301 [2] L.G. Blok, M. L. Longana, H. Yu and B. K. S. Woods, An investigation into 3D printing of fibre reinforced Thermoplastic composites, Additive Manufacturing, 22 (2018) 176-186 [3] T. Liu, X. Tian, M. Zhang, D. Abliz, D. Li and G. Ziegmann, Interfacial performance and fracture patterns of 3D printed continuous carbon fibre with sizing reinforced PA6 composites, Composites Part A: Applied Science and Manufacturing, 114 (2018) 368-376 [4] R. Velu, F. Raspall and S. Singamneni, 3D printing technologies and composite materials for structural applications, Green Composites for Automotive Applications, chapter 8 (2019) 171-196 [5] Q. Hu, Y. Duan, H. Zhang, D. Liu, B. Yan and F. Peng, Manufacturing and 3D printing of continuous carbon fiber prepreg filament, 53 (2018) 1887-1989

Purpose Fused filament fabrication (FFF) is one of the most popular additive manufacturing (AM) technologies due to its ability to build thermoplastic parts with complex geometries at low cost. The FFF technique has been mainly used for rapid prototyping owing to the poor mechanical and geometrical properties of pure thermoplastic parts. However, both the development of new fibre-reinforced filaments with improved mechanical properties, and more accurate composite 3D printers have broadened the scope of FFF applications to functional components. FFF is a complex process with a large number of parameters influencing product quality and mechanical properties, and the effects of the combined parameters are usually difficult to evaluate. An array of parameter combinations has been analysed for improving the mechanical performance of thermoplastic parts such as layer thickness, build orientation, raster angle, raster width, air gap, infill density and pattern, fibre volume fraction, fibre layer location, fibre orientation and feed rate. This study aims to assess the effects of nozzle diameter on the mechanical performance and the geometric properties of 3D printed short carbon fibre-reinforced composites processed by the FFF technique. Design methodology approach Tensile and three-point bending tests were performed to characterise the mechanical response of the 3D printed composite samples. The dimensional accuracy, the flatness error and surface roughness of the printed specimens were also evaluated. Moreover, manufacturing costs, which are related to printing time, were evaluated. Finally, scanning electron microscopy images of the printed samples were analysed to estimate the porosity as a function of the nozzle diameter and to justify the effect of nozzle diameter on dimensional accuracy and surface roughness. Findings The effect of nozzle diameter on the mechanical and geometric quality of 3D printed composite samples was significant. In addition, large nozzle diameters tended to increase mechanical performance and enhance surface roughness, with a reduction in manufacturing costs. In contrast, 3D printed composite samples with small nozzle diameter exhibited higher geometric accuracy. However, the effect of nozzle diameter on the flatness error and surface roughness was of slight significance. Finally, some print guidelines are included. Originality value The effect of nozzle diameter, which is directly related to product quality and manufacturing costs, has not been extensively studied. The presented study provides more information regarding the dependence of the mechanical, microstructural and geometric properties of short carbon fibre-reinforced nylon composite components on nozzle diameter.

Purpose Fused filament fabrication (FFF) technique using metal filled filaments in combination with debinding and sintering steps can be a cost-effective alternative for laser-based powder bed fusion processes. The mechanical behaviour of FFF-metal materials is highly dependent on the processing parameters, filament quality and adjusted post-processing steps. In addition, the microstructural material properties and geometric characteristics are inherent to the manufacturing process. The purpose of this study is to characterize the mechanical and geometric performance of three-dimensional (3-D) printed FFF 316 L metal components manufactured by a low-cost desktop 3-D printer. The debinding and sintering processes are carried out using the BASF catalytic debinding process in combination with the BASF 316LX Ultrafuse filament. Special attention is paid on the effects of build orientation and printing strategy of the FFF-based technology on the tensile and geometric performance of the 3-D printed 316 L metal specimens. Design/methodology/approach This study uses a toolset of experimental analysis techniques [metallography and scanning electron microcope (SEM)] to characterize the effect of microstructure and defects on the material properties under tensile testing. Shrinkage and the resulting porosity of the 3-D printed 316 L stainless steel sintered samples are also analysed. The deformation behaviour is investigated for three different build orientations. The tensile test curves are further correlated with the damage surface using SEM images and metallographic sections to present grain deformation during the loading progress. Mechanical properties are directly compared to other works in the field and similar additive manufacturing (AM) and Metal Injection Moulding (MIM) manufacturing alternatives from the literature. Findings It has been shown that the effect of build orientation was of particular significance on the mechanical and geometric performance of FFF-metal 3-D printed samples. In particular, Flat and On-edge samples showed an average increase in tensile performance of 21.7% for the tensile strength, 65.1% for the tensile stiffness and 118.3% for maximum elongation at fracture compared to the Upright samples. Furthermore, it has been able to manufacture near-dense 316 L austenitic stainless steel components using FFF. These properties are comparable to those obtained by other metal conventional processes such as MIM process. Originality/value 316L austenitic stainless steel components using FFF technology with a porosity lower than 2% were successfully manufactured. The presented study provides more information regarding the dependence of the mechanical, microstructural and geometric properties of FFF 316 L components on the build orientation and printing strategy.

In this work, the effect of short carbon fibre (CF) on the mechanical and geometric properties of 3D printed polylactic acid (PLA) composite parts processed using the Fused Filament Fabrication (FFF) technique have been analysed. Tensile, flexural and interlaminar shear strength (ILSS) tests were performed to obtain the mechanical performance of the different samples. The surface quality and geometric accuracy of the printed specimens were also evaluated. Finally, Scanning Electron Microscope (SEM) images of the printed samples are analysed. The results revealed that the addition of carbon fibres effectively improved all assessed mechanical properties of PLA-CF composites as compared to the neat PLA. In particular, Flat PLA-CF samples showed an average increase in tensile performance of 47.1% for the tensile strength and 179.9% for the tensile stiffness in comparison to the neat PLA. From the flexural behaviour point of view, Flat PLA-CF samples revealed an increase in average flexural strength and stiffness of 89.75% and 230.95%, respectively in comparison to the neat PLA. Furthermore, PLA-CF samples depicted the best ILSS performance. In general, the use of short carbon fibre as reinforcement did not affect the dimensional accuracy of the PLA-CF samples, and even improved the surface roughness in certain cases, particularly in Flat and On-edge orientations.

In recent years, significant advancements in Fused Filament Fabrication (FFF) have enabled this technology to become one of the most leading techniques of Additive Manufacturing (AM) for the production of functional products. The poor mechanical properties of manufactured parts have traditionally imposed considerable limitations on use of FFF processes. These shortcomings have been overcome using new advanced filaments with nanoparticle reinforced components, short-length and continuous fibres, and other composite material processing technologies. Polymers reinforced with graphene nanoplatelets (GNP) have been an effective solution for improving electrical, thermal, and mechanical properties. However, the geometric properties of functional products manufactured with GNP reinforced polymers have not been analysed in spite of being crucial for the manufacture, assembly, and service life of functional products. The aim of this study was to compare an improved PLA polymer (PLA-3D) with a GNP reinforced PLA composite (PLA-Graphene) by analysing the geometric properties of dimensional accuracy, flatness error, surface texture, and surface roughness. The effect of the 3D printing parameters - build orientation (Bo), layer thickness (Lt), and feed rate (Fr) - on the geometric properties of two PLA-based filaments were evaluated. The results showed dimensional accuracy was mainly affected by the build orientation, where an increase in the layer area on the X-Y plane showing the highest dimensional deviation owing to the longer displacements of the extruder accumulating positioning errors. The dimensional accuracy along the Z-axis was not affected by any of the printing parameters nor the accumulation of layers, with results close to nominal ones. The flatness error and surface roughness were strongly conditioned by building orientation, with the best results obtained in the flat orientation. Neither of the compared materials showed significant variations between them in geometric properties, with similar results in the tested printing conditions.

Advanced fiber reinforced composites have excellent specific strength and stiffness properties, but tend to be limited by linear elastic response and sudden, brittle failure. This lack of ductility greatly limits the structural efficiency of reinforced composite designs. Hence, achieving some non‐linear behavior is desirable and it can help composite structures to maintain functionality even when they are overloaded to improve safety and reduce the applied safety factors. The aim of this study is to characterize and assess the effect of laminate thickness and the type of scaling technique on the damage response of symmetric angle‐ply carbon fiber‐reinforced polymer (CFRP) composite laminates subjected to tensile and flexural loading. This study considers the different behavior of the composite material under tension and compression in order to evaluate their influence on the failure modes. Tensile and three‐point bending tests were carried out to determine the mechanical response in terms of strength and stiffness of the different CFRP laminates. Optical micrographs of failed samples were used to assess damage mechanisms of the different configurations. It was observed that non‐linear behavior and high strains to failure could be achieved with angle‐ply laminates. Furthermore, the maximum flexural strength increased and maximum flexural strain decreased as laminate thickness increased. Finally, the results obtained demonstrate that introducing ply clustering had a negative effect on the mechanical performance and pseudo‐ductility exhibited by angle‐ply laminates. POLYM. COMPOS., 40:3678–3690, 2019. © 2019 Society of Plastics Engineers

Fused filament fabrication (FFF) is a promising additive manufacturing (AM) technology due to its ability to build thermoplastics parts with advantages in the design and optimization of models with complex geometries, great design flexibility, recyclability and low material waste. This technique has been extensively used for the manufacturing of conceptual prototypes rather than functional components due to the limited mechanical properties of pure thermoplastics parts. In order to improve the mechanical performance of 3D printed parts based on polymeric materials, reinforcements including nanoparticles, short or continuous fibers and other additives have been adopted. The addition of graphene nanoplatelets (GNPs) to plastic and polymers is currently under investigation as a promising method to improve their working conditions due to the good mechanical, electrical and thermal performance exhibited by graphene. Although research shows particularly promising improvement in thermal and electrical conductivities of graphene-based nanocomposites, the aim of this study is to evaluate the effect of graphene nanoplatelet reinforcement on the mechanical properties, dimensional accuracy and surface texture of 3D printed polylactic acid (PLA) structures manufactured by a desktop 3D printer. The effect of build orientation was also analyzed. Scanning Electron Microscope (SEM) images of failure samples were evaluated to determine the effects of process parameters on failure modes. It was observed that PLA-Graphene composite samples showed, in general terms, the best performance in terms of tensile and flexural stress, particularly in the case of upright orientation (about 1.5 and 1.7 times higher than PLA and PLA 3D850 samples, respectively). In addition, PLA-Graphene composite samples showed the highest interlaminar shear strength (about 1.2 times higher than PLA and PLA 3D850 samples). However, the addition of GNPs tended to reduce the impact strength of the PLA-Graphene composite samples (PLA and PLA 3D850 samples exhibited an impact strength about 1.2-1.3 times higher than PLA-Graphene composites). Furthermore, the addition of graphene nanoplatelets did not affect, in general terms, the dimensional accuracy of the PLA-Graphene composite specimens. In addition, PLA-Graphene composite samples showed, in overall terms, the best performance in terms of surface texture, particularly when parts were printed in flat and on-edge orientations. The promising results in the present study prove the feasibility of 3D printed PLA-graphene composites for potential use in different applications such as biomedical engineering.

Continuous Fibre Reinforced Thermoplastic Composites (CFRTPCs) are becoming alternative materials to replace the conventional thermosetting polymers and metals due to excellent mechanical performance, recycling and potential used in lightweight structures. Fused deposition modelling (FDM) is a promising additive manufacturing technology and an alternative of conventional processes for the fabrication of CFRTPCs due to its ability to build functional parts having complex geometries. The mechanical properties of a built part depend on several process parameters. The aim of this study is to characterize the effect of build orientation, layer thickness and fibre volume content on the mechanical performance of 3D printed continuous fibre reinforced composites components manufactured by a desktop 3D printer. Tensile and three-point bending tests are carried out to determine the mechanical response of the printed specimens. SEM images of fractured surfaces are evaluated to determine the effects of process parameters on failure modes. It is observed that the effect of layer thickness of nylon samples on the mechanical performance is marginally significant. In addition, continuous fibre reinforced samples show higher strength and stiffness values than unreinforced ones. The results show that carbon fibre reinforced composites exhibit the best mechanical performance with higher stiffness and flat samples exhibit higher values of strength and stiffness than on-edge samples. Additionally, the results show that strength and stiffness increase as fibre volume content increases in most cases but, conversely, the level of increment in mechanical performance is moderate with continued rise in fibre content, particularly in the case of Kevlar (R) and glass fibres, due to weak bonding between the fibre/nylon layers as well as the presence of increased levels of defects. Finally, the practicality of the results is assessed by testing an evaluation structure.

The evolution of fused filament fabrication (FFF) technology, initially restricted to the manufacturing of prototypes, has led to its application in the manufacture of finished functional products with excellent mechanical properties. However, FFF technology entails drawbacks in aspects, such as dimensional and geometric precision, and surface finish. These aspects are crucial for the assembly and service life of functional parts, with geometric qualities lagging far behind the optimum levels obtained by conventional manufacturing processes. A further shortcoming is the proliferation of low cost FFF 3D printers with low quality mechanical components, and malfunctions that have a critical impact on the quality of finished products. FFF product quality is directly influenced by printer settings, material properties in terms of cured layers, and the functional mechanical efficiency of the 3D printer. This paper analyzes the effect of the build orientation (Bo), layer thickness (Lt), feed rate (Fr) parameters, and plate-extruder movements on the dimensional accuracy, flatness error, and surface texture of polylactic acid (PLA) using a low cost open-source FFF 3D printer. The mathematical modelling of geometric properties was performed using artificial neural networks (ANN). The results showed that thinner layer thickness generated lower dimensional deviations, and feed rate had a minor influence on dimensional accuracy. The flatness error and surface texture showed a quasi-linear behavior correlated to layer thickness and feed rate, with alterations produced by 3D printer malfunctions. The mathematical models provide a comprehensive analysis of the geometric behavior of PLA processing by FFF, in order to identify optimum print settings for the processing of functional components.

Advanced fiber reinforced composite materials have become relevant in aerospace, automotive, wind energy, marine, and civil engineering applications due to their high specific stiffness and strength, corrosion resistance, and fatigue performance. In addition, composite materials are subjected to complicated loading conditions, such as bending, tension, compression, and twisting. However, a significant characteristic of composite materials is their unequal compressive/tensile response. The aim of this work is to highlight the effects of laminate thickness and the type of scaling technique on the flexural response of symmetric cross-ply CFRP laminates, taking into account the unequal compressive/tensile response of these laminates. This different response has been analyzed in order to determine the failure mode exhibited by the laminates under flexural loading (flexural or interlaminar shear failure) and, additionally, where it was produced for design purposes. Three-point bending tests were carried out to determine the mechanical response in terms of strength and stiffness of the different CFRP laminates. Optical micrographs of fracture surfaces were used to assess failure mechanisms of the different configurations. It was observed that the effect of laminate thickness was significant. Thicker laminates show lower strength and strain to failure, but, conversely, higher bending stiffness. In addition, the results depict a significant change on the flexural damage performance with the stacking sequence and the type of scaling technique (sublaminate/ply-level) due to unequal compressive/tensile response. Finally, the results obtained demonstrate that introducing ply clustering had a negative effect on the [90/0] configuration, but, conversely, an improvement of the flexural damage performance on the [0/90] configuration.