Additive manufacturing of the high-performance thermoplastic : Experimental study and numerical simulation of the Fused Filament Fabrication

Additive manufacturing (AM) refers to a wide variety of manufacturing processes for rapid prototyping and production of final and semi-final products. In opposite to conventional orsubtractive processes, in additive manufacturing, the material is gradually added layer by layer to form the parts. AM enables the fabrication of complex parts which were impossible or not costeffective to manufacture with the traditional processes. Fused Filament Fabrication (FFF) is basedon the melting of a polymeric filament in an extruder; the filament is then deposited layer by layerto manufacture the final parts. Despite growing interest from industries and a large audience inrecent years, these manufacturing processes are still not well mastered, especially for not mass produced polymers. In this thesis, we will take an insight into the printability of PEEK(Polyetheretherketone). The aim is to find the printing conditions to obtain the best quality of theprinted parts by FFF process. In the first step, we have determined the polymer properties influencing the quality of the printed parts by FFF. The rheological properties, the surface tension,the thermal conductivity and thermal expansion have been determined experimentally. Then, thecoalescence phenomenon of the polymeric filaments has been studied by experimental, analyticaland numerical simulation. Furthermore, the stability of the filament and its flow properties when itexits from the extruder in the FFF process has been determined by experimental, analytical andnumerical simulation. Then, we have focused on the determination of the die swelling of PEEKextrudate. Lastly, the kinetics of isothermal and non-isothermal crystallization of PEEK has beenstudied by experimental study. The kinetics of crystallization has been applied to FFF process bynumerical simulation in order to determine the optimum environment temperature to control thecrystallization of printed parts. The crystallization of PEEK reaches its maximum value (about22%) of crystallization during the deposition

Toward improvement of the properties of parts manufactured by FFF ( Fused Filament Fabrication) through understanding the influence of temperature and rheological behaviour on the coalescence phenomenon

In this paper, the printing temperature ranges of PLA and PEEK, two semi-crystalline thermoplastics, have been investigated for the Fused Filament Fabrication (FFF) process. The printing range, comprised between the melting temperature and the degradation of each polymer, is 160°C to 190°C for PLA and 350°C to 390°C for PEEK. The complex viscosity has been measured for both polymers within the printing range. The kinetics of coalescence has been registered by measuring the bonding length between two filaments of the same polymer according to the temperature. At 167°C, the filaments of PLA reached the maximum value of bonding length. For PEEK, the filaments reached the maximum value of bonding length at 380°C. For the both materials, the final height of the filament is 80% of the initial diameter. The comparison of the obtained results with experimental study and predictive model shows a good agreement when the polymer is totally in fusion state

Influence of parameters controlling the extrusion step in fused filament fabrication (FFF) process applied to polymers using numerical simulation

Extrusion is one of the oldest manufacturing processes; it is widely used for manufacturing finished and semi- finished products. Moreover, extrusion is also the main process in additive manufacturing technologies such as Fused Filament Fabrication (FFF). In FFF process, the parts are manufactured layer by layer using thermoplastic material. The latter in form of filament, is melted in the liquefier and then it is extruded and deposited on the previous layer. The mechanical properties of the printed parts rely on the coalescence of each extrudate with another one. The coalescence phenomenon is driven by the flow properties of the melted polymer when it comes out the nozzle just before the deposition step. This study aims to master the quality of the printed parts by controlling the effect of the parameters of the extruder on the flow properties in the FFF process. In the current study, numerical simulation of the polymer coming out of the extruder was carried out using Computational Fluid Dynamics (CFD) and two phase flow (TPF) simulation Level Set (LS) method by 2D axisymmetric module of COMSOL Multiphysics software. In order to pair the heat transfer with the flow simulation, an advection-diffusion equation was used. Advection-diffusion equation was implemented as a Partial Differential Equation (PDE) in the software. In order to define the variation of viscosity of the polymer with temperature, the rheological behaviors of two thermoplastics were measured by extensional rheometer and using a parallel-plate configuration of an oscillatory rheometer. The results highlight the influence of the environment temperature and the cooling rate on the temperature and viscosity of the extrudate exiting from the nozzle. Moreover, the temperature and its corresponding viscosity at different times have been determined using numerical simulation. At highest shear rates, the extrudate undergoes deformation from typical cylindrical shape. These results are required to predict the coalescence of filaments, a step towards understanding the mechanical properties of the printed parts

Processes and materials used for direct writing technologies:A review

Direct Writing (DW), also known as Robocasting, is an extrusion-based layer-by-layer manufacturing technique suitable for manufacturing complex geometries. Different types of materials such as metals, composites, ceramics, biomaterials, and shape memory alloys can be used for DW. The simplicity and cost-efficiency of DW makes it convenient for different applications, from biomedical to optics. Recent studies on DW show a tendency towards the development of new materials and applications. This represents the necessity of a deep understanding of the principles and parameters of each technique, material, and process challenge. This review highlights the principles of many DW techniques, the recent advancements in material development, applications, process parameters, and challenges in each DW process. Since the quality of the printed parts by DW highly depend on the material extrusion, the focus of this review is mainly on the ceramic extrusion process and its challenges from rheological and material development point of view. This review delivers an insight into DW processes and the challenges to overcome for development of new materials and applications. The main objective of the review is to deliver necessary information for non-specialist and interdisciplinary researchers

Influence of the printing parameters on the stability of the deposited beads in fused filament fabrication of poly(lactic) acid

Fused Filament Fabrication (FFF) is one among a wide variety of processes of Additive Manufacturing. Similar to the others, FFF enables freeform fabrication and optimized structures, from. The aim of this work is to optimize the printing conditions in the FFF process based on reliable properties: printing parameters and physical properties of the polymer. The chosen polymer is poly(lactic) acid (PLA), a biodegradable thermoplastic polyester derived from corn starch and, as one of the most common polymers in the FFF process. the maximum inlet velocity of the filament in the liquefier is empirically determined according to process parameters such as the feed rate, the nozzle diameter and the dimensions of the deposited segment. Then, the rheological behavior of poly(lactic) acid including the velocity field, the shear rate and the viscosity distribution in the nozzle are determined by analytical study and numerical simulation. Our results show the variation of the shear rate according to the diameter of the nozzle and the inlet velocity. The shear rate reaches its maximum value for high inlet velocity and smaller diameters, near the internal wall. The distribution of the viscosity is obtained along the radius of the nozzle. For high inlet velocity, some defects appear at the surface of the extrudates. At highest shear rates, the extrudates undergo severe deformation microscopy. These results are valuable for choosing the printing parameters ( in order to improve the quality of the manufactured parts

Impression 3D des thermoplastiques hautes performances : Étude expérimentale et modélisation numérique du procédé par dépôt de filament

Additive manufacturing (AM) refers to a wide variety of manufacturing processes for rapid prototyping and production of final and semi-final products. In opposite to conventional or subtractive processes, in additive manufacturing, the material is gradually added layer by layer to form the parts. AM enables the fabrication of complex parts which were impossible or not cost-effective to manufacture with the traditional processes. Fused Filament Fabrication (FFF) is based on the melting of a polymeric filament in an extruder; the filament is then deposited layer by layer to manufacture the final parts. Despite growing interest from industries and a large audience in recent years, these manufacturing processes are still not well mastered, especially for not mass-produced polymers. In this thesis, we will take an insight into the printability of PEEK (Polyetheretherketone). The aim is to find the printing conditions to obtain the best quality of the printed parts by FFF process.In the first step, we have determined the polymer properties influencing the quality of the printed parts by FFF. The rheological properties, the surface tension, the thermal conductivity and thermal expansion have been determined experimentally. Then, the coalescence phenomenon of the polymeric filaments has been studied by experimental, analytical and numerical simulation. Furthermore, the stability of the filament and its flow properties when it exits from the extruder in the FFF process has been determined by experimental, analytical and numerical simulation. Then, we have focused on the determination of the die swelling of PEEK extrudate. Lastly, the kinetics of isothermal and non-isothermal crystallization of PEEK has been studied by experimental study. The kinetics of crystallization has been applied to FFF process by numerical simulation in order to determine the optimum environment temperature to control the crystallization of printed parts. The crystallization of PEEK reaches its maximum value (about 22%) of crystallization during the deposition. Furthermore, the crystallization releases heat in the system that increases the temperature of the deposited bead gradually up to 20 ℃.La fabrication additive (FA) fait référence à une grande variété de procédés de fabrication pour le prototypage rapide et la production de produits finis et semi-finis. Contrairement aux procédés classiques ou soustractifs, en fabrication additive, le matériau est ajouté progressivement couche par couche pour former les pièces. La fabrication additive permet la fabrication de pièces complexes impossibles ou peu rentables à fabriquer avec les procédés traditionnels. Le procédé FFF (Fused Filament Fabrication) est basé sur la fusion d'un filament polymère ; le filament est ensuite déposé couche par couche pour fabriquer les pièces finales. Malgré l'intérêt croissant des industries et du grand public ces dernières années, ces procédés de fabrication ne sont toujours pas bien maîtrisés, en particulier pour les polymères qui ne sont pas de grande consommation. Dans cette thèse, nous allons nous intéresser à l’imprimabilité du PEEK (Polyétheréthercétone). Dans un premier temps, nous avons déterminé les propriétés du polymère influençant la qualité des pièces imprimées par FFF. Les propriétés rhéologiques, la tension superficielle, la conductivité thermique et la dilatation thermique ont été déterminées expérimentalement. Ensuite, le phénomène de coalescence des filaments polymères a été étudié par des mesures expérimentales, un modèle analytique et par simulation numérique. De plus, la stabilité du filament et ses propriétés d’écoulement lorsqu’il sort de l’extrudeuse dans le procédé FFF ont été déterminées expérimentalement puis par analytique et simulation numérique. Ensuite, nous nous sommes concentrés sur la détermination du gonflement des filaments de PEEK. Enfin, la cinétique de la cristallisation isotherme et non isotherme du PEEK a été étudiée expérimentalement. La cinétique de cristallisation a été appliquée au procédé FFF par simulation numérique afin de déterminer la température d’environnement optimale pour contrôler la cristallisation des pièces imprimées. La cristallisation du PEEK atteint sa valeur maximale (environ 22%) de cristallisation pendant le dépôt. En outre, la cristallisation libère de la chaleur dans le système, ce qui augmente progressivement la température du filament déposé jusqu'à 20 ℃

Influence of printing parameters on the stability of deposited beads in fused filament fabrication of poly(lactic) acid

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An Investigation of the Influence of Viscosity and Printing Parameters on the Extrudate Geometry in the Material Extrusion Process

The material extrusion process is one of the most popular additive manufacturing processes. The presence of porosity in the MEX printed parts, which ultimately deteriorates the mechanical properties, is one of the main drawbacks of the MEX process. The porosity in the structure is related to the shape of the adjacent beads and overlapping during the material deposition. Due to the deposition nature of the MEX process, the porosity cannot be entirely removed from the printed parts. Understanding the influence of process parameters on material deposition and the rheological properties is crucial to improving the quality of the final product. In this study, the two-phase-flow numerical approach with the level-set equations has been used for the first time to model the material deposition on the moving platform in 3D. The influence of the viscosity and printing parameters, including travel speed, inlet velocity, viscosity, nozzle diameter, and layer height, on the width of the deposited bead has been investigated. The simulation results are validated against experimental measurements with an average error of 5.92%. The width measured by the experimental study shows good agreement with the results of the numerical simulation. The comparison between the results of the 3D numerical simulation and 2D simulation reveals that the 2D simulation is not appropriate and accurate enough to predict the geometry of the deposited bead with the given set of parameter settings. The key novelty of this research paper is the application of the level-set method in a 3D context for material deposition on a moving substrate

Toward improvement of the properties of parts manufactured by FFF ( Fused Filament Fabrication) through understanding the influence of temperature and rheological behaviour on the coalescence phenomenon

International audienceIn this paper, the printing temperature ranges of PLA and PEEK, two semi-crystalline thermoplastics, have been investigated for the Fused Filament Fabrication (FFF) process. The printing range, comprised between the melting temperature and the degradation of each polymer, is 160°C to 190°C for PLA and 350°C to 390°C for PEEK. The complex viscosity has been measured for both polymers within the printing range. The kinetics of coalescence has been registered by measuring the bonding length between two filaments of the same polymer according to the temperature. At 167°C, the filaments of PLA reached the maximum value of bonding length. For PEEK, the filaments reached the maximum value of bonding length at 380°C. For the both materials, the final height of the filament is 80% of the initial diameter. The comparison of the obtained results with experimental study and predictive model shows a good agreement when the polymer is totally in fusion state