Добірка наукової літератури з теми "Fabrication additive indirecte"

Purpose – The purpose of this paper is to review the current status of additive manufacturing (AM) used for tissue engineering (TE) scaffold. AM processes are identified as an effective method for fabricating geometrically complex objects directly from computer models or three-dimensional digital representations. The use of AM technologies in the field of TE has grown rapidly in the past 10 years. Design/methodology/approach – The processes, materials, precision, applications of different AM technologies and their modified versions used for TE scaffold are presented. Additionally, future directions of AM used for TE scaffold are also discussed. Findings – There are two principal routes for the fabrication of scaffolds by AM: direct and indirect routes. According to the working principle, the AM technologies used for TE scaffold can be generally classified into: laser-based; nozzle-based; and hybrid. Although a number of materials and fabrication techniques have been developed, each AM technique is a process based on the unique property of the raw materials applied. The fabrication of TE scaffolds faces a variety of challenges, such as expanding the range of materials, improving precision and adapting to complex scaffold structures. Originality/value – This review presents the latest research regarding AM used for TE scaffold. The information available in this paper helps researchers, scholars and graduate students to get a quick overview on the recent research of AM used for TE scaffold and identify new research directions for AM in TE.

This paper presents a comprehensive review of the literature for fabricating PDMS microfluidic devices by employing additive manufacturing (AM) processes. AM processes for PDMS microfluidic devices are first classified into (i) the direct printing approach and (ii) the indirect printing approach. The scope of the review covers both approaches, though the focus is on the printed mold approach, which is a kind of the so-called replica mold approach or soft lithography approach. This approach is, in essence, casting PDMS materials with the mold which is printed. The paper also includes our on-going effort on the printed mold approach. The main contribution of this paper is the identification of knowledge gaps and elaboration of future work toward closing the knowledge gaps in fabrication of PDMS microfluidic devices. The second contribution is the development of a novel classification of AM processes from design thinking. There is also a contribution in clarifying confusion in the literature regarding the soft lithography technique; this classification has provided a consistent ontology in the sub-field of the fabrication of microfluidic devices involving AM processes.

This work explores the use of additive manufacturing (AM) to reprocess recycled glass and carbon fibers in the automotive sector. It aims to foster exploitation of recycled Glass Fiber Reinforced Polymers (rGFRPs) and recycled Carbon Fiber Reinforced Polymers (rCFRPs) through two manufacturing workflows: indirect Fused Filament Fabrication (FFF) and UV-assisted Direct Ink Writing (UV-DIW). An industrial case study on vehicle components has been considered by prototyping one real component. After the tensile tests, some molds were fabricated with a FFF 3D printer for the indirect 3D printing process to cast an epoxy-based thermosetting resin with rGFs and rCFs. The second technology consisted in fabricating the parts by hardening in-situ a photo- and thermal-curable thermosetting acrylic liquid resin with rGFs. These results validate the use of AM and recycled composites for applications in the automotive sector. These approaches may be implemented for customizable components for batches below 100 vehicles as the first step for their exploitation.

Bone replacements for congenital defects, cancer resections, and traumas are typically performed using bone grafting. However, due to scarcity of the source material, synthetic materials for bone replacements are sometimes used instead. Unfortunately, the ability to engineer anatomically correct pieces of viable and functional human bone are difficult and time-consuming through conventional manufacturing methods. This paper proposes an alternative route which incorporates the use of AM technology for fabricating patient-specific implants. The implants were computer-aided design (CAD) from a stereolithography (STL) file of a mandible. AM method was combined with lost wax casting (LWC) technology to produce the customised A-W glass-ceramic implants. An initial study of sintered A-W was performed on cylindrical samples show on average 19.8% porous with on average 75% of the porosity being open and an average flexural strength of 82.6 MPa. The A-W scaffolds display a degree of macro-and micro porosity. The geometrical shape of the A-W implants shows a close resemblance to the required implant. Additive manufacturing assisted fabrication of A-W glass-ceramic provides a promising method for manufacturing customised medical implants.

The additive manufacturing of products promises exciting possibilities. Measurement methodologies, which measure an in-process dataset of these products and interpret the results, are essential. However, before developing such a level of quality assurance several in-process measurands must be realized. One of these is the material flow rate, or rate of adding material during the additive manufacturing process. Yet, measuring this rate directly in material extrusion additive manufacturing presents challenges. This work presents two indirect methods to estimate the volumetric flow rate at the liquefier exit in material extrusion, specifically in Fused Deposition Modeling or Fused Filament Fabrication. The methods are cost effective and may be applied in future sensor integration. The first method is an optical filament feed rate and width measurement and the second is based on the liquefier pressure. Both are used to indirectly estimate the volumetric flow rate. The work also includes a description of linking the G-code command to the final print result, which may be used to create a per extrusion command model of the part.

This preliminary investigation explored additive manufacturing to fabricate cobalt-chromium onlay restorations without the use of digital design. Extracted molars were prepared for four-surface onlays followed by the conventional approach for the fabrication of provisionals. The provisionals were digitized with an intraoral scanner, and stereolithography (STL) files were fabricated with additive manufacturing in cobalt-chromium, utilizing selective laser melting (SLM). Onlays were bonded to the corresponding tooth. Restorations were polished after cementation and assessed with photography, radiography, and a clinical post-cementation checklist. Cementation was unremarkable; marginal adaption and surface finish were generally acceptable. A simple, efficient, and inexpensive alternative workflow for the fabrication of indirect restorations without using the digital design is proposed.

AbstractSilicon carbide (SiC) ceramic and related materials are widely used in various military and engineering fields. The emergence of additive manufacturing (AM) technologies provides a new approach for the fabrication of SiC ceramic products. This article systematically reviews the additive manufacturing technologies of SiC ceramic developed in recent years, including Indirect Additive Manufacturing (Indirect AM) and Direct Additive Manufacturing (Direct AM) technologies. This review also summarizes the key scientific and technological challenges for the additive manufacturing of SiC ceramic, and also forecasts its possible future opportunities. This paper aims to provide a helpful guidance for the additive manufacturing of SiC ceramic and other structural ceramics.

The research and development of biomaterials have brought about new treatments in regenerative medicine. The research work presented in this paper focus on the use of Poly-Lactide-co-glycolide (PLGA) in the fabrication of patient specific fracture fixation plate by indirect additive manufacturing method. The use of biopolymers such as PLGA has been seen as a solution to the problems of stress shield and post-surgery inherent in biometal fixation plates. This paper discusses the consequence of this processing method on characteristics and properties of the PLGA. PLGA of ratio 50:50, 65:35 and 85:15 was processed and compared. The granules of PLGA were positioned in the cavity of the stereolithography (SLA) mould and heated under constant pressure with sintering temperature of 73°C for 2.0hours. Both the variation in samples fabricated from this process with the designed model and the changes in material characteristics are below 10%. The flexural strength for PLGA of ratio 50:50, 65:35 and 85:15 is 73.8±2.3MPa, 75.0±2.8, 60.0±11.7, respectively. The characteristics and mechanical tests indicate that the results were comparable with conventional processing of PLGA.

Additive manufacturing (AM) is a production process for the fabrication of three-dimensional items characterized by complex geometries. Several technologies employ a localized melting of metal dust through the application of focused energy sources, such as lasers or electron beams, on a powder bed. Despite the high potential of AM, numerous burdens afflict this production technology; for example, the few materials available, thermal stress due to the focused thermal source, low surface finishing, anisotropic properties, and the high cost of raw materials and the manufacturing process. In this paper, the combination by AM of meltable resins with metal casting for an indirect additive manufacturing (I-AM) is proposed. The process is applied to the production of open cells metal foams, similar in shape to the products available in commerce. However, their cellular structure features were designed and optimized by graphical editor Grasshopper®. The metal foams produced by AM were cast with a lost wax process and compared with commercial metal foams by means of compression tests.

Ce mémoire de thèse découle d’une recherche collaborative initiée en octobre 2020, dont le thème s’articule autour de l’élaboration de pièces céramiques techniques à géométrie complexe par des procédés innovants. Associant les compétences du CERAMATHS de Maubeuge-France et du BCRC de Mons-Belgique, cette thèse appliquée a été co-financée par l’agglomération de Maubeuge-Val-de-Sambre (CAMVS) et le BCRC et s’inscrit dans une démarche d’Éco-conception visant notamment la fabrication de couronnes dentaires en ZrO2. La stratégie établie consiste à associer des techniques additives aux procédés de gel-casting, par moulage de gels polymériques biosourcées minéralisables après traitement thermique conventionnel. Il s’agit de lever des problèmes récurrents propres aux opérations d’usinage de pièces à géométrie complexe (production de déchets, apparition de microfissures …). De nombreux essais et mesures expérimentales sont présentées, ainsi que des calculs de modélisations moléculaires, afin de comprendre les mécanismes chimiques mis en jeu au cours des étapes de transformation et de corréler mesures physico-chimiques et calculs prévisionnels.Le mémoire de thèse s’articule donc en quatre chapitres principaux :Le chapitre II présente les prothèses dentaires d’une manière générale et une description des diverses techniques de fabrication issues de la littérature. Se focalisant principalement sur la confection de pièces céramiques, ce chapitre bibliographique permet de comparer et de classer les procédés entre eux, en précisant les techniques de mise forme additive directe et indirecte, soustractive et formative. Un focus sur le procédé de gel casting permet d’aborder les avantages potentiels d’une voie exploitant un gel chargé en poudres céramiques. En justifiant la démarche expérimentale retenue, cette bibliographie permettra de confronter les difficultés actuelles de mise en œuvre de pièces céramiques complexes avec les exigences du domaine dentaire.Nous verrons dans le chapitre III que l’Agarose est utilisable en tant que matrice polymérique sacrificielle apte à disperser des poudres céramiques avant traitement thermique et densification. Ce chapitre est ainsi consacré à la caractérisation des matières premières, puis à la confection de pièces céramiques combinant une méthode additive (conception de moules) et une méthode Gel Casting exploitant l’Agarose. D’une part, l’agarose en solution y est présentée d’un point de vue préparatoire, comportemental et physico-chimique. D’autre part, la fabrication des moules par stéréolithographie est également décrite. Le chapitre IV précise les stratégies et les travaux entrepris pour modifier les propriétés générales de l’agarose. Divers succinates d’agarose ont été synthétisés et caractérisés expérimentalement dans ce sens. Des résultats sont présentés pour qualifier le comportement rhéologique, avec des interprétations confortées par des calculs de modélisation macromoléculaire. Le chapitre V concerne la mise en œuvre d’une gélification chimiquement activée afin d’exploiter les propriétés de l’alginate de sodium plutôt que celles de l’agarose. Dans ce chapitre, deux voies différentes sont étudiées sur la base de variations stœchiométriques du milieu réactionnel initial, ainsi que des résultats prometteurs de mise en forme.La conclusion générale précise un bilan qualitatif et des perspectives sur notre procédé qui associe des moules obtenus par stéréolithographie et une matrice visqueuse à base de polymères naturels tels que l’agarose et l’alginate de sodium
This thesis results from collaborative research initiated in October 2020, the theme of which revolves around the development of technical ceramic pieces with complex geometry using innovative processes. Combining the skills of CERAMATHS of Maubeuge-France and the BCRC of Mons-Belgium, this applied thesis was co-financed by the agglomeration of Maubeuge-Val-de-Sambre (CAMVS) and the BCRC and is part of an approach of Eco-design aimed in particular at the manufacture of dental crowns in ZrO2. The established strategy consists of combining additive techniques with gel-casting processes, by molding biosourced polymer gels that can be mineralized after conventional heat treatment. This involves addressing recurring problems specific to machining operations on parts with complex geometry (production of waste, appearance of microcracks, etc.). Numerous tests and experimental measurements are presented, as well as molecular modeling calculations, in order to understand the chemical mechanisms involved during the transformation stages and correlate physicochemical measurements and forecast calculations. The thesis is therefore divided into four main chapters: Chapter II presents dental prostheses in general and a description of the various manufacturing techniques taken from the literature. Focusing mainly on the making of ceramic pieces, this bibliographical chapter allows us to compare and classify the processes between them, specifying the techniques of direct and indirect additive, subtractive and formative shaping. A focus on the gel casting process allows us to address the potential advantages of a route using a gel loaded with ceramic powders. By justifying the experimental approach adopted, this bibliography will make it possible to confront the current difficulties of implementing complex ceramic parts with the requirements of the dental field. We will see in the chapter III that Agarose can be used as a sacrificial polymer matrix capable of dispersing ceramic powders before heat treatment and densification. This chapter is thus devoted to the characterization of raw materials, then to the manufacture of ceramic parts combining an additive method (mold design) and a Gel Casting method using Agarose. On the one hand, agarose in solution is presented from a preparatory, behavioral and physicochemical point of view. Furthermore, the manufacturing of molds by stereolithography is also described. Chapter IV specifies the strategies and work undertaken to modify the general properties of agarose. Various agarose succinates have been synthesized and experimentally characterized in this direction. Results are presented to qualify the rheological behavior, with interpretations supported by macromolecular modeling calculations. Chapter V concerns the implementation work of chemically activated gelation in order to exploit the properties of sodium alginate rather than those of agarose. In this chapter, two different pathways are studied based on stoichiometric variations of the initial reaction medium, as well as promising shaping results. The general conclusion specifies a qualitative assessment and perspectives on our process which combines molds obtained by stereolithography and a viscous matrix based on natural polymers such as agarose and sodium alginate

La fabrication additive (Impression 3D) consiste à fabriquer des objets couche par couche en utilisant un modèle 3D, un matériau approprié et une machine dédiée. Pour la construction, c’est un nouveau mode constructif qui se profile. Depuis 2010, la fabrication additive a fait un saut technique et médiatique dans ce secteur. Les projets d’impression 3D se sont multipliés et diversifiés avec les premières maisons construites entièrement au moyen de cette technologie (Winsun, D-Shape, Contour Crafting, Apis Cor…etc). Ce travail s’inscrit dans le cadre d’une thèse CIFRE démarrée en 2015 entre le laboratoire de génie civil de l’Ecole Centrale de Lille et l’entreprise Bouygues Construction. L’objectif de ce travail est d’étudier le potentiel de la fabrication additive pour la construction et plus précisément de proposer une formulation à matrice cimentaire qui sera mise en œuvre par impression 3D.La thèse est organisée en trois grandes parties.La première partie est consacrée à la définition de l’impression 3D et des matériaux cimentaires pour définir leurs interactions. La deuxième partie est dédiée à la formulation d’un matériau cimentaire imprimable. L’imprimabilité a été définie par trois indicateurs : l’extrudabilité, la buildabilté et l’adhérence. La troisième partie est destinée à la validation de la formulation proposée. Ce travail peut être considéré comme une première approche pour définir un protocole d’évaluation de l’imprimabilité des matériaux cimentaires à l’échelle du laboratoire ainsi qu’une première étape pour la conception d’une imprimante 3D destinée et adaptée à la construction
Additive Manufacturing (3D printing) consists in building an object layer by layer following a 3D model. For this purpose an appropriate material, machine and model are needed. From Construction industry point of view, 3D printing is considered as a new building method. Since 2010, the use of 3D printing for construction has known a large evolution. More and more real construction projects are using this new technology. Some of these examples are Winsun in China, D-Shape in Italy, Contour Crafting in California or Apis Cor in Russia…etc.The work presented in this manuscript was conducted through an industrial PhD thesis (CIFRE) which was launched between “Ecole Centrale de Lille” and “Bouygues Construction” in 2015. The objective of this work was to study the potential of large scale 3D printing integration in the construction process and more precisely the development of a printable cement based mix design.The work is organized in three main parts.The first part was dedicated to 3D printing and cement based material as general concepts. Then their interactions were analyzed. The second part was devoted to the printable mix design. The printability was defined using three indicators: Extrudability, Buildability and layers adhesion. The third part was dedicated to check the printability of the proposed mix design. This work may be considered as a first approach to define a laboratory scale methodology for cement based materials printability testing. It is also a step to contribute to the development of construction 3D printers

Unlike traditional stochastic scaffold fabrication techniques, additive manufacturing (AM) can be used to create tissue-specific three-dimensional scaffolds with controlled porosity and pore geometry (meso-structure). However, due to the relatively few biocompatible materials available for processing in AM machines, direct fabrication of tissue scaffolds is limited. To alleviate material limitations and improve feature resolution, a new indirect scaffold fabrication method is developed. A four step fabrication process is explored: Fused Deposition Modeling (FDM) is used to fabricate scaffold patterns of varied pore size and geometry. Next, scaffold patterns are surface treated, and then mineralized via simulated body fluid (SBF); forming a bone-like ceramic throughout the scaffold pattern. Finally, mineralized patterns are heat treated to pyrolyze the pattern and sinter the minerals. Two scaffold meso-structures are tested: â tubeâ and â backfill.â Two pattern materials are tested [acrylonitrile butadiene styrene (ABS) and investment cast wax (ICW)] to determine which material is the most appropriate for mineralization and sintering. Mineralization is improved through plasma surface treatment and dynamic flow conditions. Appropriate burnout and sintering temperatures to remove pattern material are determined experimentally. While the â tube scaffoldsâ were found to fail structurally, â backfill scaffoldsâ were successfully created using the new fabrication process. The â backfill scaffoldâ meso-structure had wall thicknesses of 470 â 530 µm and internal channel diameters of 280 â 340 µm, which is in the range of appropriate pore size for bone tissue engineering. â Backfill scaffoldsâ alleviated material limitations, and had improved feature resolution compared to current indirect scaffold fabrication processes.
Master of Science

The photoluminescence (PL) in crystalline silicon (c-Si) has been investigated during the last decades. Recent interest has focused on the visible PL that is observed in Si nanoclusters and in porous Si (PSi), the infrared PL in silicon-germanium superlattices, and the subgap PL due to impurities in c-Si [1]. Band edge PL in bulk Si is inefficient and usually observed only at low temperatures because c-Si has an indirect bandgap. The electroluminescence (EL) is as inefficient as the photoluminescence (PL) and, in addition, the EL is quenched by an electric field E ≥ 104 V/cm due to field-induced dissociation of the exciton. In this work we report a significant increase of the Si band edge photoluminescence and electroluminescence and its unexpectedly weak temperature dependence in large Si nanocrystals produced by the recrystallization of oxidized porous Si.

The photoluminescence (PL) in crystalline silicon (c-Si) has been investigated during the last decades. Interest has focused on the visible PL that is observed in Si nanoclusters and in porous Si (PSi), the infrared PL in silicon-germanium superlattices, and the subgap PL due to impurities in c-Si [1]. Whereas strong room-temperature PL has been demonstrated in the visible with porous silicon, band edge PL in bulk Si is inefficient and usually observed only at low temperatures. The electroluminescence (EL) is as inefficient as the PL, and, in addition, the EL is quenched by an electric field E ≥ 104V/cm due to field-induced dissociation of the exciton [2]. A result of the indirect bandgap of Si, bandgap luminescence is extremely weakly reabsorbed by Si. It follows that the light generated, propagated, and detected at the Si bandgap would not disturb the Si microelectronic circuitry with which it shares a chip, a situation that is very desirable for systems applications.

Abstract Electromechanical impedance allows for a quick assessment of the mechanical integrity of the part under test by providing insights into its dynamic response. In previous studies, it has been shown that electromechanical impedance signatures obtained via directly bonded piezoelectric transducers can successfully be used for non-destructive evaluation of manufactured parts. Indirect electromechanical impedance measurements, through an instrumented fixture or testbed, has also been introduced as a promising solution for quick evaluation of manufactured parts. While such indirect impedance measurements alleviate the need for individual parts to be instrumented, they increase the complexity of the measurement system. Factors such as fixture design, part-fixture interface, and clamping force are found to impact measurement sensitivity to manufacturing defects and anomalies. In this paper, the effects of instrumented fixture material on indirect electromechanical impedance measurements are investigated. Three geometrically-identical fixtures are considered in this study. Two are commercially available clamps made of aluminum and steel, while the third is an additively manufactured replica made of PLA through a fused filament fabrication process. The fixtures are instrumented with monolithic piezoelectric transducers for electromechanical impedance measurement. Strain gauges are used to measure the clamping force exerted by the fixture on the part under test. Test specimens are made of machined steel blocks including defect-free (control) parts along with others featuring manufacturing defects. The impact of fixture’s material properties, as compared to the part under test, on the defect-detection capabilities of indirect impedance-based NDE is evaluated.

Industrial development releases plenty of oil/dyes wastes to water making unsafe the environment to live in. This project aims to solve the problems associated with environmental pollution and discharge of industrial effluents to water bodies. This is very important in the global scenario as water is the basis of life. The problem of leaking oil and dyes in water bodies is one of the biggest problems that cause instability in the ecosystem since, it has a negative impact on marine creatures that live in these water bodies. In addition, this damage is transmitted to humans in an indirect way. The current project aims to develop ZnO/PVDF composite nanofibers using electrospun technique. The fabricated nanofibers were analyzed mainly for their morphology by using scanning electron microscope, X-Ray diffraction, mechanical tensile strength, UV light spectroscope and oil separation experiments was mainly targeted for the proposed research and photocatalytic performance. Using these nanoparticles oil absorption was done for the water contaminated with oil and dye. The novelty of this particular proposal is defined by the nontoxic material fabrication method in the form of membrane, the fabricated membrane can be used for both absorbing oil & separating dyes from water. We have successfully synthesized the flower-like ZnO architectures by hydrothermal method, developing oil and dye absorbing membrane using electrospinning techniques. It can absorb oil and dyes from water wastes, can be reused many times. The observed results suggest that the fabricated flexible electrospun nanofibers are suitable for the wastewater treatment. Our future recommendations to test different types of dyes not mentioned in this research involve, mixing two dyes together and check testing by the fabricated membrane, testing mixture of both oil and dye wastes together and develope the membrane to be as a sponge, which can hold the oil then collecting this oil and reusing it again.

Abstract The utilization of suction pile as a foundation for subsea structures is a modern alternative to the traditional foundation types. Suction pile foundation is widely used nowadays due to the benefits and advantages relevant to the design and installation of such a foundation. Throughout this paper, A review of three types of load-bearing suction pile foundation is introduced based on a cost efficiency as well as design and construction aspects study. The aim of this review is to explore and critically assess the pros and cons of each type of the studied types to outline a guidance or a selection criterion for the different circumstances. The approach adopted for the achievement of the above objective is based on a numerical analysis of the suction pile foundation types under certain loading combination, in which, both geotechnical and structural aspects are fulfilled to reach a sound design and optimum dimensions of the three said suction pile foundation types satisfying a prefdefined acceptance criterion. The resulted design of the three types is then used in a cost-based comparison to conclude the most cost-effective type, in addition to a critical assessment and review of the suction pile foundation design and construction challenges to figure out the pros and cons of each type. The said comparison has concluded that the single pile should be the basic and the most preferable choice. This is due to its’ high direct and indirect cost efficiency and the simplicity and easiness of fabrication and installation. Double-piled type has also shown positive outcomes with regard the cost efficiency as well as the construction performance, which raises a question mark on its’ rare use in the industry. Four-piled suction pile foundation type, and despite being frequently used in the industry, has shown a negative cost efficiency along with high construction precautions. The review has shown that the four-piled type foundation is advantageous only when needed to support an extra-size structure with large footprint area or when used in a highly sloped seabed surface to get the benefit from its’ high levelling capability.