1,720,971 research outputs found
Performance Analysis of Electro-chemical Machining of Ti-48Al-2Nb-2Cr Produced by Electron Beam Melting
Full text linkTi-48Al-2Nb-2Cr is a challenging and difficult-to-cut titanium aluminide (TiAl) alloy with several manufacturing issues because of the high sensitivity to crack formation and oxygen picking up. Electron beam powder bed fusion (EB-PBF) made feasible TiAl near net shape components, but the surfaces are particularly rough and present complex surface topographies. In this present investigation, experimental analysis and optimization are proposed for electro-chemical machining (ECM) on as-built Ti-48Al-2Nb-2Cr surfaces manufactured using EB-PBF. Experimental runs are performed under pulsed machining conditions and varying specific process metrics to understand the machining effects on the process efficiency and removal phenomena. In particular, the morphology and isotropy of the surface are studied before and after the machining by scanning electron and confocal microscopies. The results establish the optimal machining conditions and a range for the active machining time that produce, compared to the as-built surface, an extremely smooth and isotropy surface without any detrimental effect on the surface integrity and microstructure
High-temperature tensile behavior of AlSi7Mg parts built by LPBF under high-productivity conditions
No full textAs additive manufacturing of metals gains traction for demanding applications, more comprehensive material cards covering mechanical response across a broader spectrum of operating conditions are needed. The integration of additive manufacturing into industries that rely on aluminum alloys, notably automotive and aerospace, underscores the imperative of a profound comprehension of how these materials respond to mechanical loading at elevated temperatures. Such insights are not only important for powertrain components but also for parts that combine structural and functional purposes, such as heat exchangers. At the same time, automotive applications need to target the production of large parts with sufficiently high productivity. This study addresses the intricate interplay between microstructural evolution, plastic deformation and mechanical response of AlSi7Mg parts fabricated by laser powder bed fusion under high-productivity conditions, spanning a testing temperature range of 25-300 degrees C. Above 150 degrees C, a significant decrease in proof and tensile strength is measured, accompanied by localized necking and the formation of dimples on the rupture surfaces. At 300 degrees C, the pronounced plasticization leads to yielding and failure at stress values 30-40% lower than at room temperature, with triple ductility. Work-hardening coefficients were calculated to describe the plastic regime. Furthermore, an investigation into density, hardness, microstructure, and fracture surfaces was conducted to corroborate the mechanical response. The outcomes enabled the quantification of mechanical property variations across the 6 temperature intervals, thereby constructing a map that empowers industry to unlock the full potential of additive manufacturing aluminum alloys
Repeatability of the fatigue performance of additively manufactured A357.0 under different thermal treatment conditions
Full text linkA357.0 parts were produced by laser-based powder bed fusion. An in-situ annealing strategy was applied by pre-heating the build platform, in order to relieve residual stresses and reduce anisotropic effects upon processing. The mean value and standard deviation for the fatigue strength at the given life time of 1 × 107 cycles were determined according to the staircase method, before and after T6 heat treatment. Samples parallel to the build platform and parallel to the growth direction were analysed separately and compared. The fatigue behaviour was substantially insensitive to post-processing heat treatment, since fracture initiation was governed by sub-surface lack-of-fusion defects that remained unchanged in the T6 conditions. The heat treatment caused an increase in porosity, yet without significant detriment to the fatigue resistance. The build orientation was not found to affect the average value of the fatigue strength, but it caused variations of the repeatability
Preliminary assessment of electro-chemical machining for aluminum parts produced by laser-based powder bed fusion
No full textElectro-chemical machining (ECM) is a nonconventional machining process based on the anodic dissolution of the workpiece. The peculiar features of this process make it suitable for application in the aerospace, automotive, or medical fields where laser-based powder bed fusion (L-PBF) is consolidating as a manufacturing solution for high-performance components. The roughness of as-built L-PBF parts often requires surface finishing before usage in order to enable a correct operation as well as to prevent early fatigue failure. The viability of ECM on L-PBF components is still scarcely investigated in the literature. In this article, the process was applied to AlSi10Mg parts produced by L-PBF. An experimental plan was designed to select the process parameters and to study their effect on the surface roughness and morphology. Process variables including feed rate, time, voltage, and water pressure were investigated. As a result, it was observed that the ECM performance was different for parts produced by traditional processes or by L-PBF, even for comparable composition. Owing to the presence of satellite particles on L-PBF surfaces, ECM was only effective in the pulsed mode
An Asymmetrical Additively Manufactured Hairpin Winding for increased efficiency and sustainability
No full textTechnological Feasibility of Lattice Materials by Laser-Based Powder Bed Fusion of A357.0
Full text linkLattice materials represent one of the utmost applications of additive manufacturing. The promising synergy between additive processes and topology optimization finds full development in achieving components that comprise bulky and hollow areas, as well as intermediate zones. Yet, the potential to design innovative shapes can be hindered by technological limits. The article tackles the manufacturability by laser-based powder bed fusion (L-PBF) of aluminum-based lattice materials by varying the beam diameter and thus the relative density. The printing accuracy is evaluated against the distinctive building phenomena in L-PBF of metals. The main finding consists in identification of a feasibility window that can be used for development of lightweight industrial components. A relative density of 20% compared with fully solid material (aluminum alloy A357.0) is found as the lowest boundary for a 3-mm cell dimension for a body-centered cubic structure with struts along the cube edges (BCCXYZ) and built with the vertical edges parallel to the growth direction to account for the worst-case scenario. Lighter structures of this kind, even if theoretically compliant with technical specifications of the machine, result in unstable frameworks
Disclosing the build-up mechanisms of multi jet fusion: Experimental insight into the characteristics of starting materials and finished parts
No full textMulti Jet Fusion (MJF) is an emerging additive manufacturing (AM) technique that enables the production of prototypes and functional parts starting from a thermoplastic-based powder, mainly polyamide 12 (PA12). Layer upon layer, the polymeric particles are selectively impregnated with two different inks and then fused and consolidated by an infrared (IR) lamp. Much faster than other AM techniques for polymers, MJF has shown exciting potentialities. However, little is known about the consolidation mechanisms acting in MJF and about the effect on the properties of the finished parts of the quality of the materials, powder and inks, and of the printing conditions. The present contribution investigates these issues. The study also compares virgin PA12 powder with pure PA12, recycled PA12 for MJF and PA12 for in selective laser sintering (SLS). The powders showed slight differences. The two inks have the same composition, except for the presence of graphitic carbon. Tensile tests showed that the printed parts are isotropic. However, the deformation at break is affected by building direction of the sample. Occasionally, poor inter-layer adhesion is observed and the tensile strength and the deformation at break collapse. Printed tensile specimens are found to be representative of the material behaviour of a printed component, apart from the deformation at break which is systematically overestimated
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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