1,720,985 research outputs found
A comprehensive review of extrusion-based additive manufacturing processes for rapid production of metallic and ceramic parts
Full text linkThe extrusion-based additive manufacturing (EAM) technique is recently being employed for rapid production of metals and ceramic components. This technique involves extruding the metal or ceramic material in solid powder form mixed with a binder (i.e., an expendable viscous fluid), which is removed from the part after 3D printing. These technologies rely on the large design freedom allowed and the cost efficiency advantage over alternative metal additive manufacturing processes that are based on high energy beams, such as laser or electron beams. The EAM of metals and ceramics is not yet widespread, but published scientific and technical literature on it is rapidly growing. However, this literature is still less extensive than that on the fused deposition modeling (FDM) of plastics or the selective laser melting (SLM) of metals. This paper aims at filling this gap. FDM and powder injection molding are identified as preceding or enabling technologies for EAM. This paper systematically reviews all aspects of the feedstock EAM processes used for production of complex-shaped parts. The unique characteristics and advantages of these processes are also discussed with respect to materials and process steps. In addition, the key process parameters are explained to illustrate the suitability of the EAM process for diverse application domains
Freeform 3D deposition of small diameter copper tubes using a powder-binder feedstock
Full text linkCopper is an interesting material for many applications including thermal management devices, which make often use of copper piping. This study proposes a method for the freeform deposition of a copper-binder feedstock, extruded through an additive manufacturing machine. Several tubes have been printed using a special nozzle and varying process parameters. The dimensional results of the deposited specimens at the green state and the physical properties of the tubes after debinding and sintering have been measured. The results demonstrate that piping in serpentine layout can be deposited by extrusion and sintered, even with sharp bends without significant ovalization of the cross-section
Rapid surface quality assessment of green 3D printed metal-binder parts
No full textMixtures made of a solid metal powder and a viscous polymeric binder are increasingly used in material Extrusion Additive Manufacturing (EAM) processes. The EAM process adopts the relative movement of an extruder head to a build table, to deposit thin strands of the mixture and build a 3D object layer by layer. In this study, EAM process was applied to produce 3D printed square plate-shaped parts of stainless steel 316 L at the green state, i.e. before debinding and sintering. The 3D printing experiments were designed by considering various independent process parameters: extrusion velocity v e , table velocity v t , layer height h and hatch spacing D a . The surface characteristics of as printed (green) square plate-shaped parts were investigated by a rapid, high-resolution optical imaging technique. The obtained images were analyzed to model the effect of the process parameters on the surface uniformity Ui and space filling Fi. The proposed methodology can be also used as a process monitoring technique. The study has demonstrated that the layer height h has the most relevant effect on the infill quality and should be set at a low value for good quality. However, a combination of the other parameters can be found that yields a compromise between infill surface quality and build up rate
Manufacturing and performance of 3D printed plastic tools for air bending applications
Full text linkIn the sheet metal forming industry, rapid tools, especially those made of polymeric materials, are increasingly used for small to medium volume productions, to compress the times and costs of tooling. The present work is aimed at evaluating the performance of 3D printed tools for sheet metal V-die air bending process. Samples made of polycarbonate and polylactide were characterized through compression tests, using different printing strategies, to verify the effect of the printing parameters on the strength of the materials. FEA simulations of air bending were performed in order to predict the state of stress and strain of the plastic tools. Polymeric dies were then produced and used for repeated V-bending tests of metal sheets. The endurance and performance of the 3D printed tools were evaluated by analysing the changes in their surface and the repeatability of the bending angle after springback. The results show how the polymeric materials and their printing parameters influence the performance of the polymeric tools. Among the various tested configurations, the PLA dies, printed with a printing pattern of 45-90-45 degrees exhibit the best performance
Determination of process induced dimensional variations of ceramic parts, 3d printed by extrusion of a powder-binder feedstock
Full text linkThis paper aims at presenting a methodology for compensation of dimensional variation during production of ceramic parts via extrusion based additive manufacturing process. A systematic geometric deviation is measured in as printed (green) and as sintered parts. In the present study, a specially developed CNC extrusion unit is used for 3d printing onto a 3 degrees of freedom parallel kinematics table. Two ceramic feedstocks, alumina and zirconia, are procured and their processing route is illustrated. The generated, corrected and modified G codes are directly fed to the controller of the table and extrusion unit. Validation of the performance is carried out by multiple samples and repeated measurements. Experimental results exhibit effective compensation and significant improvement in the dimensional accuracy. The calculation of geometric deviations and the proposed parametric determination through optimization allow the reduction in global dimensional variation, which decreases all sort of systematic errors concurrently. The proposed procedure is easily transferable to other rapid prototyping machines and allows scalability based on achieved surface quality, manufacturing time, mass and dimensional measurement
Effect of printing parameters on mechanical properties of extrusion-based additively manufactured ceramic parts
Full text linkThe purpose of this study is to investigate the effect of printing parameters on the physical and mechanical properties of additively manufactured ceramics (alumina and zirconia). Sample parts were obtained by extrusion-based additive manufacturing of a ceramic-binder mixture and subsequent post-processing (debinding and sintering). Their mechanical properties (microhardness, flexural strength, toughness) were measured and correlated with the printing parameters. Part orientation is the most significant factor for microhardness and flexural strength in both ceramic materials. Parts with vertical orientation show higher hardness while horizontal samples show higher flexural strength compared to their respective counterparts. Extrusion velocity was found to be insignificant for hardness and flexural strength. However, a marginal increase in fracture toughness with the increase in the extrusion velocity was observed. The fracture toughness of additively manufactured ceramics shows an increasing trend with elastic modulus and flexural strength and a decreasing trend with hardness and sintered density
Extrusion of metal powder-polymer mixtures: Melt rheology and process stability
Full text linkThe mixture of metal powder and a viscous polymeric binder (often referred to as feedstock) is commonly used for Metal Injection Moulding (MIM) applications. Recently, the interest towards the extrudability of metal/binder feedstocks is increasing, especially because of the growth of additive manufacturing techniques based on the vertical extrusion and layered deposition of filaments. In this experimental work, a feedstock prepared as a mixture of stainless steel 316 L powder with water-soluble binder was tested. The rheological behaviour of different mixtures (with powder loading between 50 and 63% in volume) was assessed using a capillary rheometer. The theoretical window of optimal extrudability was determined, in terms of temperature, shear rate and powder loading. Then, a specially designed CNC controlled extrusion system was used for performing vertical extrusion tests. The analysis of extrusion pressure profiles and the dimensional variability of the filaments was used to correlate the theoretical extrudability predicted by the rheological model with the actual extrusion tests. All results indicate that the conditions which yield better stability of the extrusion process are those that allow higher viscosity of the mixtures
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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