1,721,128 research outputs found
Powder bed fusion with electron beam: The interplay of sintering, porosity, and coordination number in modelling the powder thermal conductivity through a novel tortuosity formulation
Full text linkFor the powder bed fusion with electron beam (PBF-EB) additive manufacturing, properties such as the thermal conductivity of the material surrounding the melting area are critical. Thermal conductivity is influenced by the extremely high temperature reached in a short time and distributed in the building area. This fast temperature growth produces sintering phenomena and the creation of a neck between the particles. Because of this sintering, measuring the thermal conductivity at the process conditions is challenging. This paper proposes an analytical formulation for estimating the effective powder bed thermal conductivity at the PBF-EB conditions, introducing a novel modelling strategy for the tortuosity factor. In a changing net of sintered powder particles, the proposed model for the tortuosity factor considers the neck evolution and the complexity of the heat transfer due to the several heat paths possible through the particle net. To show the effectiveness of the proposed model, the thermal conductivity is evaluated for three 3D structures characterised by an increasing number of powder particles and heat path complexity: a simple cubic, a body centred cubic and a portion of a powder bed. It is shown that thermal conductivity strongly depends on the arrangement of the particles in 3D space, the structure density and the complexity of the heat diffusion path (tortuosity). Also, the numerical results from the proposed model show good agreement when compared with finite element analysis and experimental literature data
Phase-field simulation of particles rigid body motion at the early stage of sintering in powder bed fusion with electron beam: A proposal for computational efficiency
Full text linkThe sintering of powder particles prior to full melting is a defining feature of the powder bed fusion with electron beam (PBF-EB) process, distinguishing it from other metal additive manufacturing techniques. Sintering involves the movement of atoms toward contact points between adjacent particles, leading to neck formation and growth. This atomic movement is driven by the high working temperatures of PBF-EB, which activate diffusion mechanisms and induce rigid body motion (RBM) of particles. While research on the numerical analysis of diffusion is growing, the motion of the particles occurring during the PBF-EB and its relevance are still unexplored. This work uses a phase field model to capture the physics of early-stage sintering in PBF-EB, incorporating both diffusion and RBM driven by vacancy migration. The influence of RBM parameters on neck formation and growth during the sintering of Ti6Al4V particles under PBF-EB conditions is investigated. Simulations encompass different process phases and durations (from seconds to hours), including the preheating of the layer and the cooling of the build. In addition, this work addresses the computational challenges of modelling RBM and proposes a novel approach to enhancing diffusion coefficients to emulate RBM effects, significantly reducing simulation times. Results indicate that incorporating RBM accelerates sintering and leads to larger neck formation compared to diffusion alone, although computational time increases by 30 %. Consequently, RBM should be prioritised in scenarios where its impact is critical, such as the preheating phase of PBF-EB. In contrast, during the process, the neck growth can be analysed by the novel proposed approach which significantly enhances computational efficiency while effectively capturing the influence of RBM on neck growth
A multiscale framework for the evaluation of thermal conductivity of sintered powder at the powder bed fusion with electron beam conditions
Full text linkThe thermal conductivity of the powder bed during the electron beam powder bed fusion (PBF-EB) process strongly influences the process conduction and the quality of the components produced. The evaluation of this property is challenging. The models currently available in the literature cannot provide values of the thermal conductivity that consider the temperature evolution typical of the preheating step. This work presents a novel computational framework to evaluate the thermal conductivity of a powder bed for the PBF-EB process. The framework combines the thermal conditions of the PBF-EB process with information on the geometrical features of the powder bed and an analytic method to calculate the thermal conductivity and its variation with temperature and time. The proposed numerical framework is applied to the body centred structure (BCC), a typical arrangement that can emulate the PBF-EB conditions. The numerical framework is multiscale by nature, providing information about the whole powder bed starting from geometrical information about the neck among the powder particles
Effect of 3D grading thickness on mechanical and deformation behaviour of gyroid structures produced via powder bed fusion with electron beam
Full text linkThe production of complex geometries with geometrical tuned features is made possible by Additive manufacturing (AM) processes. Powder Bed Fusion using Electron Beam (PBF-EB) is one of the AM techniques for metallic components, which stands out for its ability to fabricate intricate structures with high-performance materials. One example is surface-based architectures known as Triply Periodic Minimal Surfaces (TPMS), where structural walls are defined by a specific thickness. The mechanical behaviour and deformation mechanisms of TPMS are governed by both the geometry and the wall thickness of the structure. Conventional TPMS designs typically employ a uniform or one-dimensional thickness gradient, which constrains their performance under varied loading conditions. This study explores a novel approach involving three-dimensional thickness gradation, aiming to enhance structural integrity, improve load-bearing capacity, and enable functional optimisation. The gyroid surface, a widely studied TPMS for applications ranging from lightweight aerospace components to biomedical implants, is used as a reference geometry. Three types of initiator surface (diagonal plane, cross-shape, and sphere) are employed to create spatial variations in wall thickness between predefined minimum and maximum values. Samples are fabricated using the PBF-EB process, and the resulting structures are characterised via X-ray computed tomography to assess morphometric parameters. These parameters are then correlated with mechanical properties and deformation mechanisms and compared against gyroid TPMS with uniform thickness. The results reveal a significant influence of 3D thickness variation on performance, offering new insights for the design and additive manufacturing of next-generation TPMS structures with tailored mechanical responses
Simulating the sintering of powder particles during the preheating step of Electron Beam Melting process: Review, challenges and a proposal
Full text linkThe powder bed preheating before melting is a distinctive manufacturing step of the Electron Beam Melting (EBM) process. During preheating slight sintering occurs and small necks are formed between neighbouring particles. The necks improve the heat transfer and the powder bed strength allowing a reduction of supports structures and the neutralisation of the so-called smoke. However, preheating may represent over 50% of the total production time. This work investigates the major strategies in literature for preheating phase optimisation and proposes a numerical simulation approach to evaluate the neck growth and the corresponding sintering level
A phase-field study of neck growth in electron beam powder bed fusion (EB-PBF) process of Ti6Al4V powders under different processing conditions
Full text linkTraditional sintering processes are carried out to achieve complete material densification. In an electron beam powder bed fusion (EB-PBF) process, the same sintering mechanisms occur but only with the aim to form small connections between the particles (necks). A proper neck formation is central for the EB-PBF process because, among other effects, ensures the thermal stability of the process and helps to avoid smoke phenomena. This work presents a numerical study of neck formation under the EB-PBF processing conditions. A new type of modelling is introduced for the temperature sintering load and included in a phase-field model, which simulates the neck growth during the EB-PBF process of Ti6Al4V powders. The model was validated with an ad-hoc experiment, which provided a deviation with respect to the estimated neck diameter of about 9%. The deviation was investigated by reasonably varying the processing conditions. The results showed that the thermal history, the process time scale (including also the cooling phase), and the geometrical characteristics of the particles significantly affected the sintering rate and neck radius
Sintering during Electron Beam-Powder Bed Fusion (EB-PBF) of Ti6Al4V Alloy
No full textThe partial sinter between the powder particles during the electron beam – powder bed fusion (EB-PBF) process is fundamental to guarantee adequate thermal and electrical conductivities and conduct the process safely. The sintering degree is tuned by using the process parameters that, at the present day, are mainly optimised with an experimental trial and error approach. Simulation has proven the capability to reduce costs and time related to parameter optimisation. In the current work, a phase field model was developed to simulate sintering during the EB-PBF process. The novelty lies in simulating the sintering process under non isothermal conditions which emulate the heating of the powder due to the preheating and subsequent temperature decrease due to the layer additions. The results show a strong influence of the thermal history on the neck growth and dimension, which differ significantly with respect to the traditional approach to the sintering simulation which considers only constant temperature
Characterization and Finite Element Analyses of Tensile and Bending Behavior of Nylon Reinforced with Continuous Carbon Fiber Produced by Additive Manufacturing
Full text linkLeveraging advancements in extrusion technology, continuous filament fabrication (CFF) offers a cutting-edge approach to producing composite components layer by layer. What sets this technique apart is its ability to apply reinforcements precisely where needed, optimizing both performance and sustainability. The adopted approach to depositing the fiber using a reinforced filament is critical in determining the final characteristics. Despite its potential, there is limited understanding of mechanical performance, particularly under bending conditions and when only a few reinforced layers are used. This study investigates the mechanical behavior of CFF-produced composite materials under tensile and bending loads. Reinforced samples were fabricated and tested under varying conditions, such as fiber orientation, number of reinforcement layers, and placement along the build direction. The localized reinforcement capability of CFF highlights the importance of numerical modeling in virtually testing structures before production. To this end, the experimental results were replicated in a numerical environment, enabling precise calibration of a finite element model to predict the mechanical behavior of reinforced components
Roughness data of internal and external surfaces produced through EBM technique
No full textThis dataset is referred to the paper "Surface roughness model for Electron Beam Melting (EBM) processing Ti6Al4V" by Galati M., Rizza G., Delfanti S. and Denti L. It contains an STL file with the geometry of the artefact and an Excel file with all the roughness data collected. The artefact is produced through an EBM machine. Roughness data were collected through a profilometer and a confocal profilometer for internal and external surfaces. All the collected data are reported in the Excel file. These roughness data are adopted to develop the regression models capable to to describe upskin and downskin surfaces.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV
La ragione del dubbio
No full textLibro pubblicato per la Retrospettiva di Francesco Rosi del Premio internazionale Maestri del Cinema di Fiesole 200
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