1,721,011 research outputs found
THE INFLUENCE OF LASER POWER AND SCAN SPEED ON THE MICROSTRUCTURE, DISTORTIONS, AND MECHANICAL PROPERTIES IN THE L-PBF OF Ti-6Al-4V
Full text linkLaser powder bed fusion (L-PBF) has gained a lot of interest for its ability to build complex geometries with freedom of design. The wrong choice of process parameters like laser power (P) and scan speed (v) can result in parts with low ductility, pores, and distortion. In the literature, the influence of P and v on the quality of the printed part in terms of porosity defects, distortion, and mechanical properties has been widely explored. However, to obtain functional parts without defects it is crucial to consider different aspects simultaneously. This paper aimed to fill the lack of knowledge in the literature about the combined effect of laser power and scan speed on microstructure and distortions and their influence on mechanical properties. In this frame, tensile tests, microstructural, density, and distortion measurements were carried out to study the effect of P and v on mechanical strength, ductility, density, and distortion for Ti-6Al-4V parts produced with L-PBF. Three levels of P and v were analyzed in a range of 340-380 W and 1400-1600 mm/s, respectively. From the experimental analysis, a big influence of P on the ultimate tensile strength (UTS) and density was observed. Ductility, instead, was more affected by the v. Overall, high P and v resulted in significant distortions due to the increase in thermal gradient and cooling rate. Furthermore, porosity acted as a stress-relieving factor, and as a consequence, samples with high porosity showed less distortion
Selective Laser Melting of Ti6Al4V: Effects of Heat Accumulation Phenomena Due to Building Orientation
Full text linkTitanium alloy Ti6Al4V is one of the most utilized alloys in the field of additive manufacturing due to the excellent combination of mechanical properties, density and good corrosion behavior. These characteristics make the use of this material particularly attractive for additively manufacturing components with complex geometry in sectors such as aeronautics and biomedical. Selective Laser Melting (SLM), by which a component is fabricated by selectively melting of stacked layers of powder using a laser beam, is the one of most promising additive manufacturing technologies for Ti6Al4V alloy. Although this technique offers numerous advantages, it has some critical issues related to the high thermal gradients, associated with the process, promoting the formation of a metastable martensitic microstructure resulting in high tensile strength but poor ductility of the produced parts. The formation of microstructural defects such as balling and porosity can occur together with the presence of residual stresses that may significantly affect the mechanical characteristics of the component. Specific process parameters and geometries can determine heat accumulation phenomena that result in a progressive decrease in thermal gradients between layers. These heat accumulation phenomena are influenced by the number of layers deposited, but also by the building orientation that, for a given geometry, determines a variation of the deposited surface for each layer. © 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland
The Effect of Building Direction on Microstructure and Microhardness during Selective Laser Melting of Ti6Al4V Titanium Alloy
Full text linkDuring the last few years, additive manufacturing has been more and more extensively used in several industries, especially in the aerospace and medical device fields, to produce Ti6Al4V titanium alloy parts. During the Selective Laser Melting (SLM) process, the heterogeneity of finished product is strictly connected to the scan strategies and the building direction. An optimal managing of the latter parameters allows to better control and defines the final mechanical and metallurgical properties of parts. Acting on the building direction it is also possible to optimize the critical support structure. In particular, more support structures are needed for the sample at 0°, while very low support are required for the sample at 90°. To study the effects of build direction on microstructure heterogeneity evolution and mechanical performances of selective laser melted Ti6Al4V parts, two build direction samples (0°, 90°) were manufactured and analyzed using optical metallographic microscope (OM) and scanning electron microscopy (SEM). Isometric microstructure reconstruction and microhardness tests were carried out in order to analyze the specimens. The obtained results indicate that the build direction has to be considered a key geometrical parameter affecting the overall quality of the obtained products
A numerical model to study the temperature and residual stress profiles in hybrid additive manufacturing
Full text linkRecently, there has been an increasing interest in hybrid additive manufacturing (HAM) technologies to overcome the limits of conventional and additive manufacturing (AM) technologies. In the case of metals, HAM can be used to combine AM with forming operations. This concept can be applied in both the production of bulk and sheet metal parts. When sheet metal parts are taken into consideration, usually AM technology such as laser powder bed fusion (LPBF) and direct energy deposition (DED) can be combined with traditional forming operations.
L-PBF is preferred when small details have to be applied to the metal sheet before undergoing the forming process. Thus, mass customization can be achieved by using the flexibility of the AM process, its ability to print complex geometries, and the speed of the sheet metal forming process. In this study, a numerical model was developed in order to analyze the influence of the L-PBF process on the metal sheet. The results show how the metal sheet is strongly influenced by the
thermal input due to the deposition of the AM part. Moreover, the presence of residual stress can be observed within the metal sheet, which can result in distortion and create problems in the following forming step. The numerical model highlights also the more critical area, in which highstress concentration is observed
Influence of Line Energy Density on the Ductility of Ti6Al4V L-PBF Parts for Hybrid Metal Forming Applications
No full textIn the last decade have been developed many hybrid metal forming
processes that foresee the integration of commonly used sheet metal forming processes,
such as bending, deep drawing, spinning, and incremental forming, with
the metal additive manufacturing process as the Powder Bed Fusion technology
Selective Laser Melting. These integrations have been developed more in the productive
sectors characterized by the request of components with complex geometries
in small numbers such as, for example, the aerospace sector. Hybrid additive
manufacturing overcomes the typical limitations of additive manufacturing
related to low productivity, metallurgical defects, and low dimensional accuracy
and promotes new applications with traditional manufacturing processes. In this
perspective, obtaining parts characterized by high strength and ductility becomes
a key aspect in the development of hybrid processes. In the present work samples
of Ti6Al4V alloy were printed using the SLM additive manufacturing technology
and the influence of process parameters, such as the Linear Energy Density
on the ductility of material was studied. The characterization of the samples was
performed through tensile tests to determine the mechanical characteristics of the
material and by OM analysis of the fracture surface of tensile tested specimens.
Further density analysis, using the principle of Archimedes, allowed quantifying
the porosity defects
Finite element modeling (FEM) as a design tool to produce thin wall structures in laser powder bed fusion (L-PBF)
Full text linkLaser Powder Bed Fusion (LPBF) has been widely adopted in many industrial sectors such as biomedical, automotive, and aerospace thanks to the possibility to produce objects with complex shapes and meet customers' needs. Despite all the advantages that LPBF can offer, the rise of residual stress due to the high thermal gradients generated during the process can limit its application. This is the case with thin-wall structures where the build-up of residual stress can compromise the success of the printing process. Being able to print this structure can be useful in fuel cell applications where the implementation of cooling channels in bipolar plates can improve their performance. This paper aims to provide guidelines for designing thin-wall structures produced by LPBF processes through numerical simulations by understanding the effect of residual stress on part distortion
Sample building orientation effect on porosity and mechanical properties in Selective Laser Melting of Ti6Al4V titanium alloy
No full textIn recent decades, the focus of research has shifted towards new production technologies with the aim of optimizing production and reducing costs. These innovative technologies include additive manufacturing processes as Selective Laser Melting (SLM). The analysis of the literature on the identification of optimal building orientation to maximize the mechanical properties and minimize porosity of the final products highlights contrasting results, denoting that the thermomechanical complexity of the process, as associated with the variation of the building orientation, has not been fully clarified. A study in which the building orientation effect was evaluated together with the geometry of the sample and characterized as a function of the preferentially active heat exchange phenomena was carried out with the aim to provide guidelines for the choice of the orientation angle. Heat accumulation phenomena observed in SLM were taken into account to define three geometrical parameters able to identify the causes of the decrease of mechanical properties due to incorrect choice of the orientation angle
Ductility and linear energy density of Ti6Al4V parts produced with additive powder bed fusion technology
Full text linkHybrid metal forming processes involve the integration of commonly used sheet metal
forming processes, as bending, deep drawing and incremental forming, with additive
manufacturing processes as Powder Bed Fusion. In recent ybears, these integrations have been more developed for manufacturing sectors characterized by components with complex geometries in low numbers, as the aerospace sector. Hybrid additive manufacturing overcomes the typical limitations of additive manufacturing related to low productivity, metallurgical defects and low dimensional accuracy. In this perspective, a key aspect of hybrid processes is the production of parts characterized by high strength and ductility. In the present work, a study was carried out on
the influence of process parameters, such as laser power and scanning speed, on material ductility for Ti6Al4V alloy samples produced by Selective Laser Melting. In particular, the material strength and ductility were related to the process linear energy density (LED)
Residual stress and part distortion prediction in L-PBF of Ti-6Al-4V using layer-by-layer FEM simulation
Full text linkDue to its ability to accommodate customer demands and produce objects with complex shapes, Laser Powder Bed Fusion (LPBF) has been widely adopted in numerous industry areas, including biomedical, automotive, and aerospace. Even with all the benefits that LPBF has to offer, its use may be limited by the development of residual stress according to the strong thermal gradients produced throughout the process. Residual stresses within the samples can result in part distortion after the removal from the built platform or even in part failure during the process if the residual stresses are excessive. In order to save time and costs, numerical simulation can be an effective tool to predict residual stress and part distortion in opposition to the trial-and-error approach which involves an expansive and time-consuming experimental campaign. To this aim a finite element method (FEM) together with a layer-by-layer approach was used in this study. Numerical simulations were performed on the commercial software DEFORM-3DTM with which different values of laser power were investigated. Moreover, the influence of the voxel mesh on the FEM model accuracy was also investigated
Effect of build and unit cell orientation on the tensile, compressive, and torsional behavior of Ti-6Al-4V gyroid sheet-based structures
No full textLaser powder bed fusion (LPBF) enables the fabrication of intricate porous metallic structures, such as the sheet-based gyroid, recently used in orthopedic implants. Many implants are subjected to a complex stress environment, making strength verification across different loading modes imperative. This study investigates the effect of both unit cell and build orientation on gyroid structures. Build orientation and unit cell orientation were varied from 0 degrees to 90 degrees in 15 degrees increments to determine the degree of anisotropy of Ti-6Al-4V samples in tension, compression, and torsion. For the relatively isotropic gyroid structure, build orientation was the most influential factor on anisotropy in tension and compression. The samples with 30 degrees build orientation (B30) showed the highest strength across all three loading modes due to the overall print quality and orientation of layers withstanding the applied forces. These results guide the design optimization of 3D printed orthopedic implants with varying build and unit cell orientation
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