The International Journal of Advanced Manufacturing Technology
Traditional sintering processes are carried out to achieve complete material densification. In an... more Traditional 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...
Lattice structures are 3D open topologically ordered geometries that repeat an elementary cell in... more Lattice structures are 3D open topologically ordered geometries that repeat an elementary cell in a predefined 3D space. Struts connected in specific nodes define the cell. Lattice structures are typical geometries that represent the design freedom unlocked by additive manufacturing (AM) and are unachievable with traditional processes. By tuning the morphometric parameters of the cell, its mechanical response can be significantly altered. Because of that, an accurate understanding of the process capabilities is crucial for achieving the nominally designed properties. Considering an electron beam powder bed fusion process, in this work, the same nominal lattice structure is produced under different processing conditions to determine the relationship between the process parameters, the actual cell morphometric parameters, and its mechanical response. Strut dimension, relative density and cross-section are measured using advanced X-ray computed tomography scanning analyses. Uniaxial co...
Stereolithography is known as one of the best Additive Manufacturing technologies in terms of geo... more Stereolithography is known as one of the best Additive Manufacturing technologies in terms of geometrical and dimensional precision for polymeric materials. In recent years, a lot of studies have shown that the creation of ceramic resins, through a particular combination of monomeric components and ceramic powders, allows to obtain complex shape geometries thanks to the photopolymerization process. This review highlights the characteristics and properties of ceramic resins, peculiarities of the ceramic stereolithography processes, up to the relationship between the composition of the ceramic resin and the complexity of the post-processing phases. The comparison of different studies allows outlining the most common steps for the production of ceramic resins, as well as the physical and chemical compatibility of the different compounds that must be studied for the good feasibility of the process.
IOP Conference Series: Materials Science and Engineering, 2021
In many industrial sectors, laser powder bed fusion (L-PBF) is the main additive manufacturing te... more In many industrial sectors, laser powder bed fusion (L-PBF) is the main additive manufacturing technology for producing end-usable metal parts. Although L-PBF technique has been developed in the last twenty years, ensuring process feasibility and achieving maximum product quality at the first building session is still a difficult goal to pursue. Simulation software packages are available in the market for the prediction of induced stresses and deformation in L-PBF products to help the user getting the part right at the first time. In this paper, Amphyon software by Additive Works is tested and experimentally validated for the production of Ti6Al4V parts in an EOSINT M270 Dual Mode machine. First, the sensitivity of the software is evaluated by changing the main process parameters by +/- 20% with respect to Ti64 reference values. After calibration, the software is validated by comparison of the predicted deformed shape of a reference part with the real geometry using 3D scanning. Exp...
Intermetallic γ‐TiAl based alloys offer outstanding creep properties, high specific strength and ... more Intermetallic γ‐TiAl based alloys offer outstanding creep properties, high specific strength and sufficient oxidation resistance at application temperature in the range from 600 to 800 °C. These properties make them prosperous candidatesto substitute heavy Ni‐based alloys offering weightsavings up to 50%. Drawbacksinclude their inherent brittleness as well as reactive melts, which complicate processing and drive costs. In this regard, electron beam melting (EBM), a powder bed additive manufacturing technology, offers low impurity pickup due to the vacuum environment and elevated processing temperature, enabling the manufacturing of TiAl components with increased geometrical complexity. Still, microstructures of electron beam melted titanium aluminides often show a banded character and suffer from Al loss due to process related evaporation decreasing room temperature ductility. As the formation mechanism of banded microstructures in electron beam melted Ti‐48Al‐2Cr‐2Nb (in at. % unle...
Continuous Filament Fabrication (CFF) is the additive manufacturing process for producing materia... more Continuous Filament Fabrication (CFF) is the additive manufacturing process for producing material reinforced with long fibres. Differently from other processes, CFF allows producing components in composite materials without using tools, moulds or post-processing operations and with a strengthened area only where it is strictly required. This innovative way of producing composites makes a new design approach necessary for better exploitation of the material. This work presents a preliminary study based on 3D Finite Element (FE) method to predict the mechanical behaviour of composite materials fabricated by CFF. With this aim, a FE model is developed to determine the actual material properties in terms of longitudinal, transverse and shear modulus. Comparisons between experimental and numerical tensile results at different fibre orientations validate the model. The robustness of the proposed approach is confirmed by the comparison with the experimental characterisation of composites produced with two different fibre reinforcements, Carbon and Kevlar®.
Abstract Electron beam powder-bed fusion (EB-PBF) is the most commonly named electron beam meltin... more Abstract Electron beam powder-bed fusion (EB-PBF) is the most commonly named electron beam melting (EBM) process. Unlike the other additive manufacturing (AM) for metal components, EBM is today applied for mass production in aerospace and medical because of the high temperature and the possibility to nest parts easily. The aim of this chapter is to provide a general overview that will be helpful to understand the EBM process and the physical phenomena that occur during the EBM process. It majorly covers introduction, mechanism, process parameters, and applications of EBM process; features of EBM parts and influence of process parameters on them. Lastly, the chapter covers in-situ monitoring system and simulation tools for EBM process.
Abstract Electron Beam Melting (EBM) is an Additive Manufacturing technique to produce functional... more Abstract Electron Beam Melting (EBM) is an Additive Manufacturing technique to produce functional components. Because of the high temperature during the EBM process, the surface texture of the as-built parts is extremely complex and unique. This distinctiveness of the surface depends on many factors and needs to be well understood to predict final surface properties accurately. Chief among these factors is the surface design. A proper surface design makes it possible to tailor a surface with specific properties such as biomimetics. However, predictive models are difficult to determine especially for downskin surfaces. To properly tailor a surface, a full factorial Design Of Experiment (DOE) was designed, and 2D and 3D roughness profiles were collected on an ad-hoc artefact using a profilometer and a confocal profilometer. This reference part comprises several surfaces to investigate the effect on surface roughness of different sloping angles, including upskin and downskin surfaces and cavities. The data are analysed using descriptive and inferential statistical tools, also by distinguishing the role of roughness and waviness in the overall surface texture. A deep investigation of the causes of surface roughness made it possible to obtain analytical predictive models. These models are robust and consistent with respect to the experimental observations. Finally, the accurate design of the artefact allows highlighting the relationship between the roughness and the surface slope.
End-usable metal parts can be produced by Electron Beam Melting process. In this process a high p... more End-usable metal parts can be produced by Electron Beam Melting process. In this process a high power electron beam generates the energy needed to melt metal powders and components are built up layer-by-layer. Today, an empirical trial and error approach is adopted to identify a suitable combination of process parameters for a given metal powder. This study proposes a three-dimensional FE thermal model to simulate the transient heat transfer during EBM process to enhance the knowledge in this field. Several specific subroutines are developed to take into account beam position during scan and material state change from powder to liquid in the melting phase and from liquid to solid during cooling. The model is validated against literature data. The developed thermal model is able to forecast the evolution of the temperature inside the layers in the EBM process. Moreover, FE model properly predicts the geometry of melt pool and scan line
At the design stage of a component, manufacturing constraints, related to the geometry, have to b... more At the design stage of a component, manufacturing constraints, related to the geometry, have to be applied in order to reduce manufacturing costs and the lead-time. Consequently, the final design for manufacturability could be very different from the optimal design, in terms of technical performances. Currently, classical manufacturing constraints can be removed and complex functional parts can be built cost-effectively through the use of metal additive manufacturing (AM) processes. The design freedom offered by AM can be exploited through certain techniques, such as topology optimization (TO). Thus, the performances of end-usable components that are currently produced through traditional manufacturing processes can be improved significantly. One of the main applications is that pertaining to the lightening of components through structural optimization. This study presents an industrial case in which the advantages of free- constraint TO and AM are exploited to increase the stiffnes...
The comprehensive approach to the development of a product should analysis all of the phases, fro... more The comprehensive approach to the development of a product should analysis all of the phases, from the design to the manufacturing for the selection of a good combination of materials, designs and manufacturing processes. Due to the complexity of addressing an all-inclusive problem, the decision is usually entrusted to the manufacturing engineers for which products that have producible features easily and simple geometries are desirable, even if sacrificing the component performances. However, today, Additive Manufacturing (AM) processes offer a wide degree of design freedom that allows overcoming the traditional manufacturing limitations.
The International Journal of Advanced Manufacturing Technology
Traditional sintering processes are carried out to achieve complete material densification. In an... more Traditional 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...
Lattice structures are 3D open topologically ordered geometries that repeat an elementary cell in... more Lattice structures are 3D open topologically ordered geometries that repeat an elementary cell in a predefined 3D space. Struts connected in specific nodes define the cell. Lattice structures are typical geometries that represent the design freedom unlocked by additive manufacturing (AM) and are unachievable with traditional processes. By tuning the morphometric parameters of the cell, its mechanical response can be significantly altered. Because of that, an accurate understanding of the process capabilities is crucial for achieving the nominally designed properties. Considering an electron beam powder bed fusion process, in this work, the same nominal lattice structure is produced under different processing conditions to determine the relationship between the process parameters, the actual cell morphometric parameters, and its mechanical response. Strut dimension, relative density and cross-section are measured using advanced X-ray computed tomography scanning analyses. Uniaxial co...
Stereolithography is known as one of the best Additive Manufacturing technologies in terms of geo... more Stereolithography is known as one of the best Additive Manufacturing technologies in terms of geometrical and dimensional precision for polymeric materials. In recent years, a lot of studies have shown that the creation of ceramic resins, through a particular combination of monomeric components and ceramic powders, allows to obtain complex shape geometries thanks to the photopolymerization process. This review highlights the characteristics and properties of ceramic resins, peculiarities of the ceramic stereolithography processes, up to the relationship between the composition of the ceramic resin and the complexity of the post-processing phases. The comparison of different studies allows outlining the most common steps for the production of ceramic resins, as well as the physical and chemical compatibility of the different compounds that must be studied for the good feasibility of the process.
IOP Conference Series: Materials Science and Engineering, 2021
In many industrial sectors, laser powder bed fusion (L-PBF) is the main additive manufacturing te... more In many industrial sectors, laser powder bed fusion (L-PBF) is the main additive manufacturing technology for producing end-usable metal parts. Although L-PBF technique has been developed in the last twenty years, ensuring process feasibility and achieving maximum product quality at the first building session is still a difficult goal to pursue. Simulation software packages are available in the market for the prediction of induced stresses and deformation in L-PBF products to help the user getting the part right at the first time. In this paper, Amphyon software by Additive Works is tested and experimentally validated for the production of Ti6Al4V parts in an EOSINT M270 Dual Mode machine. First, the sensitivity of the software is evaluated by changing the main process parameters by +/- 20% with respect to Ti64 reference values. After calibration, the software is validated by comparison of the predicted deformed shape of a reference part with the real geometry using 3D scanning. Exp...
Intermetallic γ‐TiAl based alloys offer outstanding creep properties, high specific strength and ... more Intermetallic γ‐TiAl based alloys offer outstanding creep properties, high specific strength and sufficient oxidation resistance at application temperature in the range from 600 to 800 °C. These properties make them prosperous candidatesto substitute heavy Ni‐based alloys offering weightsavings up to 50%. Drawbacksinclude their inherent brittleness as well as reactive melts, which complicate processing and drive costs. In this regard, electron beam melting (EBM), a powder bed additive manufacturing technology, offers low impurity pickup due to the vacuum environment and elevated processing temperature, enabling the manufacturing of TiAl components with increased geometrical complexity. Still, microstructures of electron beam melted titanium aluminides often show a banded character and suffer from Al loss due to process related evaporation decreasing room temperature ductility. As the formation mechanism of banded microstructures in electron beam melted Ti‐48Al‐2Cr‐2Nb (in at. % unle...
Continuous Filament Fabrication (CFF) is the additive manufacturing process for producing materia... more Continuous Filament Fabrication (CFF) is the additive manufacturing process for producing material reinforced with long fibres. Differently from other processes, CFF allows producing components in composite materials without using tools, moulds or post-processing operations and with a strengthened area only where it is strictly required. This innovative way of producing composites makes a new design approach necessary for better exploitation of the material. This work presents a preliminary study based on 3D Finite Element (FE) method to predict the mechanical behaviour of composite materials fabricated by CFF. With this aim, a FE model is developed to determine the actual material properties in terms of longitudinal, transverse and shear modulus. Comparisons between experimental and numerical tensile results at different fibre orientations validate the model. The robustness of the proposed approach is confirmed by the comparison with the experimental characterisation of composites produced with two different fibre reinforcements, Carbon and Kevlar®.
Abstract Electron beam powder-bed fusion (EB-PBF) is the most commonly named electron beam meltin... more Abstract Electron beam powder-bed fusion (EB-PBF) is the most commonly named electron beam melting (EBM) process. Unlike the other additive manufacturing (AM) for metal components, EBM is today applied for mass production in aerospace and medical because of the high temperature and the possibility to nest parts easily. The aim of this chapter is to provide a general overview that will be helpful to understand the EBM process and the physical phenomena that occur during the EBM process. It majorly covers introduction, mechanism, process parameters, and applications of EBM process; features of EBM parts and influence of process parameters on them. Lastly, the chapter covers in-situ monitoring system and simulation tools for EBM process.
Abstract Electron Beam Melting (EBM) is an Additive Manufacturing technique to produce functional... more Abstract Electron Beam Melting (EBM) is an Additive Manufacturing technique to produce functional components. Because of the high temperature during the EBM process, the surface texture of the as-built parts is extremely complex and unique. This distinctiveness of the surface depends on many factors and needs to be well understood to predict final surface properties accurately. Chief among these factors is the surface design. A proper surface design makes it possible to tailor a surface with specific properties such as biomimetics. However, predictive models are difficult to determine especially for downskin surfaces. To properly tailor a surface, a full factorial Design Of Experiment (DOE) was designed, and 2D and 3D roughness profiles were collected on an ad-hoc artefact using a profilometer and a confocal profilometer. This reference part comprises several surfaces to investigate the effect on surface roughness of different sloping angles, including upskin and downskin surfaces and cavities. The data are analysed using descriptive and inferential statistical tools, also by distinguishing the role of roughness and waviness in the overall surface texture. A deep investigation of the causes of surface roughness made it possible to obtain analytical predictive models. These models are robust and consistent with respect to the experimental observations. Finally, the accurate design of the artefact allows highlighting the relationship between the roughness and the surface slope.
End-usable metal parts can be produced by Electron Beam Melting process. In this process a high p... more End-usable metal parts can be produced by Electron Beam Melting process. In this process a high power electron beam generates the energy needed to melt metal powders and components are built up layer-by-layer. Today, an empirical trial and error approach is adopted to identify a suitable combination of process parameters for a given metal powder. This study proposes a three-dimensional FE thermal model to simulate the transient heat transfer during EBM process to enhance the knowledge in this field. Several specific subroutines are developed to take into account beam position during scan and material state change from powder to liquid in the melting phase and from liquid to solid during cooling. The model is validated against literature data. The developed thermal model is able to forecast the evolution of the temperature inside the layers in the EBM process. Moreover, FE model properly predicts the geometry of melt pool and scan line
At the design stage of a component, manufacturing constraints, related to the geometry, have to b... more At the design stage of a component, manufacturing constraints, related to the geometry, have to be applied in order to reduce manufacturing costs and the lead-time. Consequently, the final design for manufacturability could be very different from the optimal design, in terms of technical performances. Currently, classical manufacturing constraints can be removed and complex functional parts can be built cost-effectively through the use of metal additive manufacturing (AM) processes. The design freedom offered by AM can be exploited through certain techniques, such as topology optimization (TO). Thus, the performances of end-usable components that are currently produced through traditional manufacturing processes can be improved significantly. One of the main applications is that pertaining to the lightening of components through structural optimization. This study presents an industrial case in which the advantages of free- constraint TO and AM are exploited to increase the stiffnes...
The comprehensive approach to the development of a product should analysis all of the phases, fro... more The comprehensive approach to the development of a product should analysis all of the phases, from the design to the manufacturing for the selection of a good combination of materials, designs and manufacturing processes. Due to the complexity of addressing an all-inclusive problem, the decision is usually entrusted to the manufacturing engineers for which products that have producible features easily and simple geometries are desirable, even if sacrificing the component performances. However, today, Additive Manufacturing (AM) processes offer a wide degree of design freedom that allows overcoming the traditional manufacturing limitations.
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Papers by Manuela Galati