PSI - Issue 25

S. Valvez et al. / Procedia Structural Integrity 25 (2020) 394–399

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S.Valvez et al./ Structural Integrity Procedia 00 (2019) 000 – 000

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bulk material are removed by machining or cutting. SM allows the production of precision components, but with limited level of complexity (Newman et al. 2015). On the other hand, additive manufacturing is a process that adds successive layers of material to create a 3D model. It allows the production of complex geometries, with some drawbacks associated to the quality of surface finish and geometry tolerance (Newman et al. 2015). Comparing this technique with some traditional subtractive processes, AM allows a significant reduction in the amount of raw material, leading to more economical models (Plymill et al. 2016). 3D Printing (3DP) is a subdivision of additive manufacturing, which is highly flexible processing technique that can be applied to different materials, like polymers, metals, ceramics and other materials (Liu et al. 2019; Araya-Calvo et al. 2018; Stansbury and Idacavage 2016). This technique was first used in the 1980s and is currently being used for prototyping and producing more complex components (Goh et al. 2019). It is possible to produce physical models at lower costs, faster and with complex geometries (Carneiro et al. 2015; Ivey et al. 2017; Richter et al. 2016), but one of its main advantages is the possibility of combining different materials (Stansbury and Idacavage 2016). Related with the fourth industrial revolution (or industry 4.0), additive manufacturing emerges as a very promising global production technology, because it allows for "mass customization" rather than "mass production". 3D printing is expected to be the main responsible for printing high performance structures (Liu et al. 2019; Goh et al. 2019). However, the use of neat polymers is not a viable option for printing structures with certain characteristics, such as electrical conductivity and enhanced mechanical properties. This limitation is solved by combining polymeric matrices with reinforcements, achieving a printed model with better structural stability and functional properties not attainable by any single constituent. Therefore, this is only possible when particles, fibres or nano-reinforcements are added to the polymers (Wang et al. 2017). In this context, this paper aims to review the studies available in the literature on carbon fibre reinforced polymer composites printed by fused deposition modelling. Special focus will be given to continuous carbon fibres reinforced PLA composites. Additive manufacturing techniques have been developing the polymer industry leading to an improvement of the commercial manufacturing sector (Wendel et al. 2008; Wang et al. 2017). In these processes, 3D structures are printed by adding layer by layer of material according to a CAD model. It offers the ability to print parts with geometric complexities and materials that could not be produced by subtractive manufacturing processes (Guo and Leu 2013). The rapid prototype is one of the main advantages of AM processes, because it is possible to print mock-ups models or even the final products in limited series (Carneiro et al. 2015; Ivey et al. 2017). The model will be designed in a 3D software (CAD), converted to a printer compatible format and transmitted to the machine for printing (Richter et al. 2016). Nowadays we have different additive manufacturing techniques, such as Stereolithography (SLA), Selective Laser Sintering (SLS), Laminated Object Manufacturing (LOM) and Fused Deposition Modelling (FDM) among the most popular (Stansbury and Idacavage 2016). The ability to manufacture complex parts, mass customization and low cost are the main reasons why the fused deposition modelling is one of the most widely used techniques (Carneiro et al. 2015; Kruth et al. 1998). Basically, this printing method consists on depositing fused material (bulk filament) on a drop-down platform (Dudek 2013). The printhead moves in the XY plane and deposits the material, layer by layer, according to the predefined geometry and where the most recently deposited material merges with the older layers. After finishing a layer, the nozzle moves vertically to start a new layer on top of the previous one and the process repeats successively until the printed model matches the 3D CAD model. Post-printing hardening of the 3D model is not required. Some printers have a second nozzle on their head that can be used to print models with different materials (Dudek 2013; Parandoush and Lin 2017). Finally, this technique is limited to thermoplastic polymers, but due to the softness of the filament that does not support the compression stress during the feeding process (the filament bends causing misfeeding), highly flexible thermoplastics are not recommended (Wang et al. 2017). 2. Techniques