1,721,129 research outputs found
Defining a new process window for LPBF of Ti-6Al-4V based on micro-warping phenomena
Full text linkDespite the many advantages that additive technologies have over subtractive ones, low porosity levels, good mechanical properties, and low residual stresses remain the most pressing issues that need further research. In particular, the latter can cause a mismatch between the desired geometry and the geometry that can be achieved.
In this work, a process window for the Laser Powder Bed Fusion (LPBF) process of Ti-6Al-4V alloys, has been identified. The micro-warping phenomenon, which causes the deformation of the printed part during the printing job and the failure of the process, was taken into account together with the parts’ strength, ductility, and porosity. The occurrence of micro-warping phenomena was assessed by the new Warping Alert (WA) parameter,
which depends on the parameters P and v. It was found that, before balling, micro-warping limits the process window in the laser power (P) – laser velocity (v) plane. However, optimal mechanical performances can be found in the proximity of the micro-warping zone, thus making it extremely important to determine the WA threshold value to the process design
Numerical Investigation on Dissimilar Titanium-Aluminum T-joints Produced by Friction Stir Welding: Process Mechanics and Material Flow
No full textFriction stir welding (FSW) is a renowned joining technology for creating difficult-to-be-welded or non-weldable dissimilar material joints engendering viscoplastic material flow at the interface. The present work compares the evolution of the material flow and properties during FSW of extremely different materials, viz., Aluminum alloy 6156 and commercially pure Ti Grade 2 with the help of numerical simulation and practical. The necessity of the appropriate heat flux to be achieved through balancing parameters was realized through simulation and experimental outcomes. In the paper, a numerical model is presented to predict the main field variables distribution and the resultant material flow during FSW of dissimilar Al-Ti skin stringer joints. Valuable insights relating to material flow patterns observed while altering the mutual skin stringer positions have been elaborated. Macrostructural and microstructural characterizations were carried out to understand the localized material microstructural evolution comprising grain refinement, intermetallic, defects, etc. The parametric influence on grain morphologies, intermittent phases, joint strengths, and hardness are discussed in depth. Interestingly, the joint strength values recorded for prepared T-joints are comparable with the ones found for butt joint configurations reported in the literature
The role of thermal contribution in the design of AA2024 friction stir welded butt and lap joints: mechanical properties and energy demand
Full text linkAlthough in recent times the use of solid-state welding processes as friction stir welding (FSW) has become increasingly
widespread, for some joint morphologies, as lap joints, there are still signifcantly less data available on both process parameters optimization and energy consumption. In the present paper, the authors investigated the possibility of enhancing the
joint quality in two diferent confgurations, i.e. lap and butt joints, taking into account specifc thermal contribution (STC)
conferred to the weld. Strength, micro-hardness and microstructure were evaluated on the produced AA2024 aluminum alloys
butt and lap joints. The surface response method (RSM) was used to investigate the efects of the main process parameters
and to identify optimal technological parameters in terms of joint resistance, while the specifc energy consumption (SEC) of
the entire process was acquired with the aim to provide design guidelines taking into account, at the same time, mechanical
performance and environmental impact. It was found that the same optimal range of revolutionary pitch can be identifed for
both the confgurations. Additionally, maximizing welding speed, for a given revolutionary pitch, contributes to signifcantly
reduce the environmental impact of the process with no detrimental effect on the joint performance
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
Single block 3D numerical model for linear friction welding of titanium alloy
No full textA two-stage approach for the simulation of Linear Friction Welding is presented. The proposed model, developed using the commercial simulation package DEFORM, is 3D Lagrangian, thermo-mechanically coupled. The first phase of the process was modelled with two distinct workpieces, while the remaining phases were simulated using a single-block model. The Piwnik–Plata criterion was set up and used to determine the shifting from the dual object to the single-block model. The model, validated against experimental temperature measurements, is able to predict the main field variables distributions with varying process parameters. Titanium alpha and beta phases evolution during the whole process has been predicted and the obtained results have been correlated to the experimentally measured micro-mechanical properties of the joints
Energy-driven decision support tool for friction stir additive manufacturing operations
Full text linkFriction Stir Additive Manufacturing (FSAM) allows the production of components by stacking and joining sheets via friction stir welding. FSAM's energy efficiency depends on the number of passes needed to achieve a specified build width. This study introduces a single-pass, pinless FSAM method for producing AA5754-H22 components. Mechanical tests showed performance comparable to traditional FSAM, with bonding efficiency between 91 % and 94 % of the base material. Energy evaluations for two industrial scenarios revealed that a pinless approach should be preferred over FSAM when a single-thickness approach is used with sheets of thicknesses lower than 4 mm. When a sheet thickness of 5 mm is considered, lower electrical energy consumption is obtained for build heights of 11 mm and higher. In a multi-thickness approach, the proposed approach is energetically effective with build height lower than 16 mm. Life Cycle Assessment (LCA) examined the environmental impact, including material considerations. The single-thickness pinless method (4 mm, 5 mm, and 1 mm cases) was analyzed using Cumulative Energy Demand (CED). For heights up to 18 mm, the pinless approach minimized or matched CED. However, for heights that are multiples of 5 mm, traditional FSAM showed advantages. At 17 mm, energy savings of 16 % and 9 % were achieved for 4 mm and 5 mm cases, respectively. In terms of Global Warming Potential, the pinless approach matched the single-thickness 4 mm case with an impact of 7.704 kgCO2,eq. Overall, the pinless method is preferable for most target heights
Solid State Joining of Thin Hybrid Sandwiches Made of Steel and Polymer: a Feasibility Study
No full textThe growing demand for more environmentally friendly vehicles has led to an increased use of light materials in the transportation industry with the aim to reduce structural weight, fuel consumption, and gas emissions, thereby boosting cost-effectiveness and recyclable properties. Complex multi-material steel-based components would allow to improve mechanical properties and minimize weight even further. In particular, new sandwich materials made by steel outer skins and a polymeric internal layer seems very promising for obtaining mechanical performance and lightness at the same time. Unfortunately, traditional welding techniques, like arc welding, laser welding, and resistance spot welding, usually used to join steels and aluminum alloys, cannot be applied for these materials due to their peculiar nature. In this paper, the feasibility of Friction Stir Welding to join thin sandwich components made of two steel outer layers and an internal polymeric layer was assessed. Both a pin and a pinless tool were used to weld the upper and the lower surface of the joint in order to obtain solid state bonding of the metal and fusion welding of the polymer at the same time
Experimental and Numerical Analysis on Post Welding Formability of FSWed AZ31 Magnesium Alloy Thin Joints obtained using a “Pinless” Tool Configuration
No full textThe post welding formability of friction stir welded AZ31 magnesium alloy thin sheets (1.5 mm thick), obtained using a “pinless” tool configuration, was widely investigated by means of the hemispherical punch method at 350°C, with a constant crosshead speed of 0.1 mm/s. The results were compared with those obtained on the base material. It has shown that formability of the joints is lower than the one of the base material. The experimental work was supported by a numerical investigation based on FEM in order to highlight the material flow occurring during the welding process. Additionally, hemispherical punch tests were simulated starting from the calculated conditions, in terms of accumulated strain, derived from the simulation of the welding process. Good agreement was found between the experimental and the numerical results, both for the welding and post welding forming
A new control parameter to predict micro‐warping‐induced job failure in LPBF of TI6AL4V titanium alloy
Full text linkLaser powder bed fusion (LPBF) includes a few printing techniques widely used, in recent years, concerning the additive
manufacturing of Ti6Al4V alloys. These produced parts, typically utilized in sectors such as aerospace and biomedical, are
characterized by very high added value. It is therefore fundamental to identify the influence of process parameters typical
of LPBF technology on the occurrence of warping leading to process failure. This study deals with the characterization of
single-track and “micro-scale” level warping phenomena which may lead to protrusion of material over the powder bed and
process failure before normal termination. This phenomenon was investigated as a function of process parameters, referring
also to the strength and ductility characteristics of the manufactured samples. With this purpose, several samples were
printed using variable process parameters both in terms of line energy density (LED) values and in terms of laser power and
speed combinations such as to guarantee constant LED values. For the samples that did not show significant micro-warping
phenomena, in addition to the transversal and longitudinal geometric characterization of the single track, tensile tests were
performed to determine both the resistance of the material and the ductility characteristics. The single tracks, for given process
parameters, were printed on a homogeneous material substrate. For every single track, a microstructural and morphological
transverse and longitudinal characterization has been carried out and the measured geometrical features were correlated to
the process parameters. The obtained results allowed the identification of a new threshold parameter, indicating the limit
operating conditions beyond which significant warping phenomena and process failure occur
An insight into the electrical energy demand of friction stir welding processes: the role of process parameters, material and machine tool architecture
No full textThe manufacturing sector accounts for a high share of global electrical energy consumption and CO 2 emissions, and therefore, the environmental impact of production processes is being more and more investigated. An analysis of power and energy consumption in friction stir welding processes can contribute to the characterization of the process from a new point of view and also provide useful information about the environmental impact of the process. An in-depth analysis of electrical energy demand of friction stir welding is here proposed. Different machine tool architectures, including an industrial dedicated machine, have been used to weld aluminum and steel sheets under different process conditions. The influence of tool rotation and feed rate was investigated. A power study, with breakdown analysis, was carried out to identify the contribution of the main sub-units and to determine the total demand. Different setups have been analyzed in order to identify the conditions resulting in the highest energy and mechanical efficiency. Potential control strategies for energy consumption reduction of FSW process are proposed
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