74 results on '"Buffa G"'
Search Results
2. Solid State Bonding Mechanics In Extrusion And FSW: Experimental Tests And Numerical Analyses.
- Author
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Buffa, G., Donati, L., Fratini, L., and Tomesani, L.
- Subjects
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SOLIDS , *EXTRUSION process , *MECHANICS (Physics) , *ALUMINUM alloys , *FRICTION , *WELDING - Abstract
In the paper the authors compare the different solid state bonding mechanics for both the processes of hollow profiles extrusion and Friction Stir Welding (FSW), through the results obtained from a wide experimental campaign on AA6082-T6 aluminum alloys. Microstructure evaluation, tensile tests and micro-hardness measurements realized on specimens extracted by samples of the two processes are discussed also by means of the results obtained from coupled FEM simulation of the processes. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
3. New Materials Design Through Friction Stir Processing Techniques.
- Author
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Buffa, G., Fratini, L., and Shivpuri, R.
- Subjects
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FRICTION , *WELDING , *FORGING , *IRONWORK , *BEARINGS (Machinery) , *ALUMINUM alloys - Abstract
Friction Stir Welding (FSW) has reached a large interest in the scientific community and in the last years also in the industrial environment, due to the advantages of such solid state welding process with respect to the classic ones. The complex material flow occurring during the process plays a fundamental role in such solid state welding process, since it determines dramatic changes in the material microstructure of the so called weld nugget, which affects the effectiveness of the joints. What is more, Friction Stir Processing (FSP) is mainly being considered for producing high-strain-rate-superplastic (HSRS) microstructure in commercial aluminum alloys. The aim of the present research is the development of a locally composite material through the Friction Stir Processing (FSP) of two AA7075-T6 blanks and a different material insert. The results of a preliminary experimental campaign, carried out at the varying of the additional material placed at the sheets interface under different conditions, are presented. Micro and macro observation of the such obtained joints permitted to investigate the effects of such process on the overall joint performance. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
4. Friction Stir Welding Of AA6082-T6 Sheets: Numerical Analysis And Experimental Tests.
- Author
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Buffa, G., Fratini, L., Ghosh, S., Castro, J.C., and Lee, J.K.
- Subjects
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FRICTION welding , *PRESSURE welding , *WELDING , *MANUFACTURING processes , *PHYSICS - Abstract
3D numerical simulation of the Friction Stir Welding process is developed with the aim to highlight the process mechanics in terms of metal flux and temperature, strain and strain rate distributions. The numerical results have been validated though a set of experimental tests. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
5. On the FSW of AA2024-T4 and AA7075-T6 T-joints: an industrial case study.
- Author
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Acerra, F., Buffa, G., Fratini, Livan, and Troiano, G.
- Subjects
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WELDING , *JOINTS (Engineering) , *AERONAUTICS , *METALLURGIC chemistry , *MANUFACTURING processes - Abstract
In this paper, the authors present the results of a wide experimental campaign on aeronautical T-shaped parts of industrial interest characterized by dissimilar materials for the skin and stringer. The friction stir welding process engineering was developed with the aim to determine the specific process parameters determining the soundness on the obtained T-parts both from the metallurgical and mechanical point of view. Furthermore, the performance of the obtained T-joints was investigated. [ABSTRACT FROM AUTHOR]
- Published
- 2010
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- View/download PDF
6. Improved FE model for simulation of friction stir welding of different materials.
- Author
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Fratini, L., Buffa, G., and Monaco, L. Lo
- Subjects
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SIMULATION methods & models , *WELDING , *TRIBOLOGY , *FINITE element method , *SOLDER & soldering - Abstract
One of the most relevant aspects of friction stir welding is the possibility to weld different materials. In the present paper, the authors present an improved continuum finite element model for the simulation of friction stir welding processes aimed to obtain T joints, made of a stringer in AA7175-T73511 and of a skin in AA2024-T4. The model, taking into account the thermomechanical behaviours of the two different materials, is utilised to study the occurring material flow and residual stress state. Numerical results are compared with experimental observations: the model is able to predict the material flow, obtaining important information on the joint failure mode. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
7. In-process heat treatments to improve FS-welded butt joints.
- Author
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Fratini, L., Buffa, G., and Shivpuri, R.
- Subjects
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FRICTION stir welding , *HEAT treatment of metals , *WELDING , *METALWORK , *MANUFACTURING processes , *ALLOYS - Abstract
Friction-stir welding (FSW) is a relatively new but already well known solid-state welding process whose main advantage with respect to fusion welding processes is the possibility to successfully weld light alloys, traditionally considered difficult to weld or unweldable. Despite the good mechanical performances that can be obtained, there exists the possibility to further improve the joints’ effectiveness through post-welding heat treatments that are however time and cost-expensive and, therefore, not best suited for industrial applications. In the present paper, the authors report the results of an experimental campaign, developed on FSW of AA7075-T6 aluminum alloy, aimed to investigate the possibility to enhance the joint performances through in process heat treatments. Welded joints were developed under three different conditions, namely, free air, forced air, and with water flowing on the surface of the joint itself. The influence of the external refrigerants was investigated at the varying of the specific thermal contribution conferred to the joint. Both mechanical and metallurgical investigations were developed on the welded joints highlighting both improvements of mechanical performances of the joints and reductions in the softening of the material when external refrigerants are used. [ABSTRACT FROM AUTHOR]
- Published
- 2009
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8. Influence of material characteristics on plastomechanics of the FSW process for T-joints
- Author
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Fratini, L., Buffa, G., and Shivpuri, R.
- Subjects
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MECHANICAL behavior of materials , *FRICTION stir welding , *JOINTS (Engineering) , *WELDING , *ALUMINUM alloy welding , *STRENGTH of materials - Abstract
Abstract: The potential of friction stir welding (FSW) has thoroughly been investigated by several authors, however their focus has primarily been on butt joints. T-joints are of paramount interest for transportation industries especially due to their capacity to straighten panels. Welding of T-joints is very challenging due to thin walls, poor location of the rib–web interface and the requirements for corner-fillets. This paper investigates FSW of T-joints of two popular aluminum alloys, i.e. 2024-T4 and 6082-T6, and the role played by the material characteristics on joining. First, an experimental study is carried out with specially designed fixture to determine the effect of process conditions. Then, the joints are metallurgically and mechanically evaluated. Finally using a numerical model of the process previously developed by the authors, the thermal and plastic flow fields for the two alloys are calculated and compared. It is found that the material dependent thermal and plastic fields affect the state of TMAZ, HAZ and nugget-region in the joint and that the low-strength high-work hardening alloy 6082 provides a much better joint integrity than the higher-strength low-hardening 2024 primarily due to the greater penetration of the plastic zone in the former. [Copyright &y& Elsevier]
- Published
- 2009
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9. On the influence of tool path in friction stir spot welding of aluminum alloys
- Author
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Buffa, G., Fratini, L., and Piacentini, M.
- Subjects
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SOLDER & soldering , *MANUFACTURING processes , *ELECTRIC welding , *MICROMECHANICS - Abstract
Abstract: Friction stir spot welding (FSSW) has been proposed as an effective technology to spot weld the so-called “difficult to be welded” metal alloys. In the paper, a variation of the FSSW process has been considered. A tool path is given after the sinking phase nearby the initial penetration site; in this way a larger welding spot is obtained and more material is involved in the bonding process. The process mechanics of such modified FSSW process is highlighted and the joint strength undergoing tensile tests is considered at the varying both of the assigned tool path and of a few process parameters. Macro- and micro-analyses are made in order to analyze the local material microstructure evolution. It is found that improved performances, with respect to the “traditional” FSSW process, are obtained for all the considered case studies. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
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10. On the thermo-mechanical loads and the resultant residual stresses in friction stir processing operations.
- Author
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Buffa, G., Fratini, L., Pasta, S., and Shivpuri, R.
- Subjects
FRICTION ,MECHANICS (Physics) ,WELDING ,METALLURGY ,MICROMECHANICS ,MICROSTRUCTURE - Abstract
Abstract: In friction stir welding and processing both a thermal flux and a mechanical action are exerted on the material determining metallurgical evolutions, changes in the mechanical behaviour and a complex residual stress state. In the paper, the metallurgical changes are examined through numerical simulation and experiments to highlight and distinguish the effects of thermal and mechanical loadings. A particular focus is made on the residual stresses generated during the stir processing of AA7075-T6 aluminium blanks. The predictions of FE model are validated by experimental measurements. Lastly, this paper presents an in-process quenching of the processed blanks for improved mechanical properties and microstructure. [Copyright &y& Elsevier]
- Published
- 2008
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11. Finite element studies on friction stir welding processes of tailored blanks
- Author
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Buffa, G., Fratini, L., and Shivpuri, R.
- Subjects
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MANUFACTURING processes , *WELDING , *SEALING (Technology) , *BEARINGS (Machinery) , *FORGING - Abstract
Abstract: Although friction stir welding (FSW) has been successfully used to join materials that are difficult-to-weld or unweldable by fusion welding methods, it is still in its early development stage and, therefore, its potential has not been fully exploited yet. FSW appears to be a very promising process for tailor-welded blanks to overcome the difficulties encountered in traditional fusion welding processes for obtaining a sound welding with good nugget integrity. In this paper the friction stir welding process for tailored blanks of aluminum alloy is investigated through a FEM developed by the authors. In particular FSW for sheets with different thicknesses is studied. For each setup a different welding tool is designed, an extra nuting angle is considered, and numerical simulations are performed in order to predict the feasibility of the process, the final shape of the welded blank, and the distribution of the main process variables, i.e. temperature, strain and strain rate. It is found that a quite large range of different thicknesses can be successfully friction stir welded with good nugget integrity. [Copyright &y& Elsevier]
- Published
- 2008
- Full Text
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12. Improving friction stir welding of blanks of different thicknesses
- Author
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Fratini, L., Buffa, G., and Shivpuri, R.
- Subjects
- *
WELDING , *THICKNESS measurement , *ALUMINUM alloys , *TENSILE architecture - Abstract
Abstract: Friction stir welding (FSW) appears to be a promising process even in the welding of blanks of different thicknesses. Actually, such particular tailor welded blanks (TWBs) are usually characterized by a reduction in ductility due to the utilized fusion welding process. In this paper the authors, starting from a preliminary feasibility study, investigate the possibility to improve the mechanical performances of friction stir welded blanks of aluminum alloy with different thicknesses. Both experiments and a FE analyses are developed for a few case studies with different thickness ratios between the blanks. The numerical investigations are performed with the aim to highlight the material temperature distribution during the process in order to determine process conditions for which an almost symmetric thermal flow is obtained in the two blanks of the joint. In this way, a few simple process design rules are derived and verified through experiments. In particular a thickness ratio up to 2 was considered and a joint resistance of about the 80% of the parent material ultimate tensile strength was observed. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
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13. On microstructural phenomena occurring in friction stir welding of aluminium alloys
- Author
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Barcellona, A., Buffa, G., Fratini, L., and Palmeri, D.
- Subjects
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ALUMINUM alloys , *WELDING , *FRICTION , *SOLDER & soldering - Abstract
Abstract: The results of experimental activity on friction stir welding (FSW) of aluminum alloys are reported. Butt joints of two different materials, namely AA2024-T4 and AA7075-T6, were investigated from a metallurgical point of view. Grain dimensions and insoluble particle densities were investigated both in the parent materials and in the joints. Furthermore, the effect of post-welding heat treatments on the joint strength was studied. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
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14. Friction Stir Welding of Tailored Blanks: Investigation on Process Feasibility.
- Author
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Buffa, G., Fratini, L., Hua, J., and Shivpuri, R.
- Subjects
WELDING ,MANUFACTURING processes ,RESIDUAL stresses ,DEFORMATIONS (Mechanics) ,METALS - Abstract
Abstract: Tailor welded blanks (TWBs) are conventionally produced by laser or traditional welding processes. In either case, the joints are created by solid-liquid-solid phase transformations that result in undesirable microstructures and tensile residual stresses detrimental to joint performance. This study investigates feasibility of an alternate joining process, friction stir welding (FSW). The joining of AA7075-T6 blanks of different thickness is investigated through FE analyses and controlled experiments. It is found that for a successful joint, the welding parameters have to be carefully designed so that the resulting metal flow and the temperature history during FSW are consistent for the two thicknesses. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
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15. A continuum based fem model for friction stir welding—model development
- Author
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Buffa, G., Hua, J., Shivpuri, R., and Fratini, L.
- Subjects
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WELDING , *IRONWORK , *SEALING (Technology) , *MANUFACTURING processes , *METALWORK - Abstract
Abstract: Although friction stir welding (FSW) has been successfully used to join materials that are difficult-to-weld or unweldeable by fusion welding methods, it is still in its early development stage and, therefore, a scientific knowledge based predictive model is of significant help for thorough understanding of FSW process. In this paper, a continuum based FEM model for friction stir welding process is proposed, that is 3D Lagrangian implicit, coupled, rigid-viscoplastic. This model is calibrated by comparing with experimental results of force and temperature distribution, then is used to investigate the distribution of temperature and strain in heat affect zone and the weld nugget. The model correctly predicts the non-symmetric nature of FSW process, and the relationships between the tool forces and the variation in the process parameters. It is found that the effective strain distribution is non-symmetric about the weld line while the temperature profile is almost symmetric in the weld zone. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
16. Design of the friction stir welding tool using the continuum based FEM model
- Author
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Buffa, G., Hua, J., Shivpuri, R., and Fratini, L.
- Subjects
- *
WELDING , *SEALING (Technology) , *ALUMINUM alloys , *MICROMECHANICS , *COMPOSITE materials - Abstract
Abstract: In friction stir welding (FSW), the welding tool geometry plays a fundamental role in obtaining desirable microstructures in the weld and the heat-affected zones, and consequently improving strength and fatigue resistance of the joint. In this paper, a FSW process with varying pin geometries (cylindrical and conical) and advancing speeds is numerically modeled, and a thermo-mechanically coupled, rigid-viscoplastic, fully 3D FEM analysis able to predict the process variables as well as the material flow pattern and the grain size in the welded joints is performed. The obtained results allow finding optimal tool geometry and advancing speed for improving nugget integrity of aluminum alloys. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
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17. Continuous dynamic recrystallization phenomena modelling in friction stir welding of aluminium alloys: a neural-network-based approach.
- Author
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Fratini, L. and Buffa, G.
- Subjects
ARTIFICIAL neural networks ,ARTIFICIAL intelligence ,RECRYSTALLIZATION (Metallurgy) ,MODELING (Sculpture) ,WELDING ,FINITE element method - Abstract
The current paper focuses on the continuous dynamic recrystallization phenomena (CDRX) occurring in friction stir welding processes of AA6082 T6 aluminium alloys. In particular, in order to predict the average grain size, a properly trained neural network is linked to the finite element method (FEM) model of the process. The utilized net, which takes as inputs the local values of strain, strain rate, and temperature, was trained starting from experimental data and numerical results. The obtained results show the capability of the artificial intelligence (AI) technique in conjunction with the FE tool to predict the final microstructure in the joint section. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
18. AA6082-T6 Friction Stir Welded Joints Fatigue Resistance: Influence of Process Parameters.
- Author
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Cirello, A, Buffa, G, Fratini, L, and Pasta, S
- Subjects
ALUMINUM alloys ,JOINTS (Engineering) ,METALLIC composites ,WELDING ,BLACKSMITHING ,SOLDER & soldering ,MANUFACTURING processes - Abstract
In the paper the results of a wide range of experiments on friction stir welding (FSW) of aluminium alloys are reported. In particular, the AA6082-T6 butt joints fatigue resistance was investigated by varying the most relevant process parameters. In addition, a revolutionary pitch was utilized in order to investigate the effects of the tool rotating speed and the tool feed rate. Observations of the fracture insurgence were developed for different levels of applied load. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
19. Local Mechanical and Morphological Characterization of Friction Stir-Welded Butt Joints.
- Author
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Barletta, M, Buffa, G, Casamichele, L, and Fratini, L
- Subjects
JOINTS (Engineering) ,MECHANICAL efficiency ,WELDING ,FRICTION ,BEARINGS (Machinery) ,BLACKSMITHING ,METALWORK ,MANUFACTURING processes - Abstract
In this paper the results of an experimental investigation into the local mechanical and morphological characterization of AA6082-T6 friction stir-welded (FSW) butt joints are illustrated. The softening effects of the welding process are highlighted through the use of micro-indentation tests on the top surface of the specimens. The effect of post-welding heat treatments was investigated, also. [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
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20. Surface and mechanical characterization of stationary shoulder friction stir welded lap joints: experimental and numerical approach
- Author
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Filomena Impero, Livan Fratini, Attilio Masnata, Antonino Squillace, Fabio Scherillo, Gianluca Buffa, Buffa, G., Fratini, L., Impero, F., Masnata, A., Scherillo, F., Squillace, A., Buffa G., Fratini L., Impero F., Masnata A., Scherillo F., and Squillace A.
- Subjects
0209 industrial biotechnology ,FEM ,Materials science ,Stationary Shoulder ,Friction Stir Welding ,02 engineering and technology ,Welding ,Surface finish ,Strain rate ,Microstructure ,Indentation hardness ,law.invention ,Friction Stir Welding, Stationary Shoulder, FEM, Roughness, Microstructure ,020303 mechanical engineering & transports ,020901 industrial engineering & automation ,Lap joint ,0203 mechanical engineering ,law ,Friction stir welding ,General Materials Science ,Composite material ,Roughne ,Joint (geology) ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione - Abstract
Friction Stir Welding (FSW) is one of the most used solid-state welding processes in the aeronautical, aerospace, ground transportation and naval fields. Stationary Shoulder Friction Stir Welding (SSFSW) is a recently introduced variant of the process allowing lower heat input into the joints, with beneficial effects in terms of joint mechanical properties, microstructure and top surface finish. In the paper, lap joints produced by SSFSW and made out of AA6082-T6 aluminum alloy sheets have been analyzed with the aim to investigate the effect of the stationary shoulder on the lap joints surface, metallurgical, and mechanical properties. The lap joints produced by SSFSW have been compared to the ones produced by “conventional” FSW in order to highlight the differences between the two processes. The top surface of the joints obtained with the two processes has been quantitatively evaluated. Finally, a dedicated numerical model has been utilized to highlight the causes of the observed differences through the distributions of the main field variables, namely temperature, strain and strain rate. It was found that SSFSW results in narrower weld nugget and smaller areas involved by micro hardness reduction caused by smaller peak temperature and high temperature zone. Additionally, better surface quality was found for the joint welded by SSFSW with lower heights and flash, allowing to avoid subsequent finishing operations needed for most industrial applications.
- Published
- 2020
21. Dissimilar Al/steel Friction stir welding lap joints for automotive applications
- Author
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Gianluca Buffa, P. Russo Spena, Livan Fratini, Davide Campanella, Campanella, D, Russo Spena, P, Buffa, G, Fratini, L., Campanella, D., Spena, P., and Buffa, G.
- Subjects
Materials science ,Filler metal ,Metallurgy ,Welding ,Electric resistance welding ,law.invention ,Flash welding ,Explosion welding ,Physics and Astronomy (all) ,law ,Friction stir welding ,Friction stir welding, low carbon steel, AA6016 aluminum alloy, joint quality ,Cold welding ,Friction welding ,Composite material - Abstract
A widespread usage of aluminum alloys for the fabrication of car-body parts is conditional on the employment of appropriate welding methods, especially if dissimilar welding must be performed with automotive steel grades. Dissimilar welding of aluminum alloys and steel grades poses some issues concerning the formation of brittle intermetallic compounds, difference in physical and chemical properties of the parent metals, and poor wetting behavior of aluminum. Friction stir welding is considered to be a reasonable solution to obtain sound aluminum/steel joints. A study on the join quality of dissimilar lap joints of steel and aluminum alloy sheets after friction stir welding is proposed here. A low carbon steel is joined with AA6016 aluminum alloy to study preliminarily the feasibility to assembly car-body parts. The joints, welded with tool rotation and feed rate varying in a wide range, have been studied from a visual examination and microstructural point of view. Optical microscopy has been used to characterize the microstructure of the examined sheets in as-received and welded conditions. Micro-hardness measurements have been carried out to quantitatively analyze the local hardness of the welded joints. Set welding process parameters are identified to assemble without the presence of macroscopic defects the examined steel and aluminum welded parts.
- Published
- 2015
22. Application of linear friction welding for joining ultrafine grained aluminium
- Author
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Marta Orłowska, Gianluca Buffa, Davide Campanella, Livan Fratini, Łukasz Morawiński, Lech Olejnik, Małgorzata Lewandowska, Orlowska M., Olejnik L., Campanella D., Buffa G., Morawinski, Fratini L., and Lewandowska M.
- Subjects
0209 industrial biotechnology ,Materials science ,Strategy and Management ,Metallurgy ,Superplasticity ,02 engineering and technology ,Welding ,Management Science and Operations Research ,021001 nanoscience & nanotechnology ,Industrial and Manufacturing Engineering ,Grain size ,law.invention ,Grain growth ,Fusion welding ,020901 industrial engineering & automation ,Severe plastic deformation ,law ,Ultimate tensile strength ,Aluminium ,Friction welding ,Ultrafine grained microstructure ,Deformation (engineering) ,0210 nano-technology ,Linear friction welding ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione - Abstract
Ultrafine grained (UFG) materials are of great potential in industry due to their enhanced mechanical strength and other promising features, such as ability to superplastic deformation or excellent corrosion resistance. Nevertheless, one of the main limitations lies in their low thermal stability, which leads to excessive grain growth at elevated temperature. It influences mainly further processes performed at high temperature, such as joining. It causes detrimental problems during conventional fusion welding, as significant grain growth is observed and therefore the advantages as a result of small average grain size disappear. Therefore, the idea of applying solid state joining process seems to be suitable for UFG materials. Among the group of solid state welding processes there are methods based on friction. One of these methods, which is suitable for samples in the form of rectangular bars, is linear friction welding (LFW). Present study is the first comprehensive work describing the results of UFG aluminium welded using LFW method with additional emphasis put on a position of shear planes of welded samples. The results have shown, that UFG regime has not been preserved in a weld zone. Welding of UFG sample with an average grain size of 1 μm resulted in a grain growth in weld zone to 1.6−2 μm. Chosen parameters allowed to weld samples only locally, nevertheless, results from tensile tests performed on mini samples showed a great potential of the LFW method for joining UFG samples. The tensile strength of welds was in the range of 83–90 % of initial material.
- Published
- 2020
23. Mechanical and metallurgical characterization of AA6082-T6 sheet-bulk joints produced through a linear friction welding based approach
- Author
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Dario Baffari, A. Barcellona, Livan Fratini, Davide Campanella, Gianluca Buffa, Buffa G., Baffari D., Barcellona A., Campanella D., and Fratini L.
- Subjects
0209 industrial biotechnology ,Aluminum alloy ,Materials science ,Oscillation ,Metallurgy ,Process (computing) ,02 engineering and technology ,Welding ,Microstructure ,Characterization (materials science) ,law.invention ,Material flow ,020303 mechanical engineering & transports ,020901 industrial engineering & automation ,0203 mechanical engineering ,law ,visual_art ,Sheet-bulk ,visual_art.visual_art_medium ,General Materials Science ,Friction welding ,Sheet metal ,Linear friction welding - Abstract
In the last decades, new flexible manufacturing processes have been developed to face the demands, by many industrial fields, for highly customized complex functional parts. The peculiar design of these components often overcomes conventional sheet metal and bulk metal forming processes capabilities. In order to face this issue, new hybrid techniques, capable of exploit key advantages of different processes, have to be developed. In this study, a method to obtain sheet-bulk joints, based on the Linear Friction Welding process, is proposed. The feasibility of the technique was investigated through an experimental campaign carried out with varying pressure and oscillation frequency using AA6082-T6 aluminum alloy. The main mechanical and metallurgical properties of the produced joints, including typical material flow defects, were highlighted. It was found that sound hybrid sheet-bulk joints can be produced by the proposed approach. Finally, it was highlighted how the height of the weld center zone plays a key role on the mechanical properties of the produced joints.
- Published
- 2020
24. A two steps Lagrangian–Eulerian numerical model for the simulation of explosive welding of three dissimilar materials joints
- Author
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Livan Fratini, Gianluca Buffa, Davide Campanella, Campanella D., Buffa G., and Fratini L.
- Subjects
Materials science ,Explosive material ,Computer simulation ,Detonation ,Mechanical engineering ,Welding ,Industrial and Manufacturing Engineering ,law.invention ,Eulerian analysis, Explosive welding, FEM model, Lagrangian analysis, Solid state welding ,Explosion welding ,Lap joint ,law ,Joint (geology) ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Lagrangian analysis - Abstract
Explosion welding (EXW) is a solid-state joining process used to produce lap joints out of metal plates of dissimilar materials. During the process, a controlled explosive detonation results in a pressure wave pushing one of the plates to be welded, called flyer, against the other with high velocity. The high pressure and temperature generated, because of the impact energy decaying into heat, create the conditions for solid bonding phenomenon to take place. Due to the complexity of experimental tests, numerical simulation is considered a fundamental design tool for the process. Different approaches are found in literature to simulate the process. In this paper, a dual step Lagrangian–Eulerian approach is proposed to evaluate the effect of different explosives on the final quality of the weld. The numerical model was developed using the commercial software ABAQUS. A three dissimilar materials joint is considered, made of two outer plates of AA5083 aluminum alloy and A516 steel, respectively, and an intermediate layer made of AA1050 aluminum alloy. The model was first validated by comparing the wavy profile of the intermediate layer after the weld, and then used to evaluate the effect of different explosive by analyzing the distribution of the main process parameters as well as the presence of voids.
- Published
- 2021
25. Effect of position and force tool control in friction stir welding of dissimilar aluminum-steel lap joints for automotive applications
- Author
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Davide Campanella, Attilio Masnata, Gianluca Buffa, Livan Fratini, M. Wasif Safeen, P. Russo Spena, Safeen M.W., Russo Spena P., Buffa G., Campanella D., Masnata A., and Fratini L.
- Subjects
0209 industrial biotechnology ,Materials science ,Polymers and Plastics ,Carbon steel ,Alloy ,Context (language use) ,02 engineering and technology ,Welding ,engineering.material ,Industrial and Manufacturing Engineering ,law.invention ,020901 industrial engineering & automation ,AA6016 aluminum alloy ,0203 mechanical engineering ,law ,Friction stir welding ,Composite material ,Joint (geology) ,Tensile testing ,Friction stir welding (FSW) ,Mechanical Engineering ,Dissimilar material ,Welding parameters ,Dissimilar materials ,DC05 low carbon steel ,020303 mechanical engineering & transports ,Lap joint ,Mechanics of Materials ,engineering - Abstract
Widespread use of aluminum alloys for the fabrication of car body parts is conditional to the use of appropriate welding methods, especially if dissimilar welding must be performed with automotive steel grades. Friction stir welding (FSW) is considered to be a reasonable solution to obtain sound aluminum-steel joints. In this context, this work studies the effects of tool position and force control in dissimilar friction stir welding of AA6061 aluminum alloy on DC05 low carbon steel in lap joint configuration, also assessing proper welding parameter settings. Naked eye and scanning electron microscopy (SEM) have been used to detect macroscopic and microscopic defects in joints, as well as to determine the type of intermixture between aluminum and steel. The joint strength of sound joints has been assessed by shear tension test. Results point out that tool force control allows for obtaining joints with better quality and strength in a wider range of process parameters. A process window has been determined for tool force conditions to have joints with adequate strength for automotive purposes.
- Published
- 2020
26. Enhancement of mechanical properties of FSWed AA7075 lap joints through in-situ fabrication of MMC
- Author
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Davide Campanella, Gianluca Buffa, Livan Fratini, Buffa, G., Campanella, D., and Fratini, L.
- Subjects
0209 industrial biotechnology ,Friction stir processing ,Materials science ,Strategy and Management ,Friction Stir Welding ,Lap joint ,02 engineering and technology ,Welding ,Management Science and Operations Research ,Indentation hardness ,Industrial and Manufacturing Engineering ,AA7075 ,law.invention ,020901 industrial engineering & automation ,law ,Friction stir welding ,Composite material ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Groove (music) ,Metallurgy ,021001 nanoscience & nanotechnology ,Grain size ,Strategy and Management1409 Tourism, Leisure and Hospitality Management ,Shear (sheet metal) ,Metal Matrix Composite ,0210 nano-technology - Abstract
Friction Stir Processing (FSP) has been demonstrated feasible to create local Metal Matrix Composites (MMCs) in light alloys matrix. In this research, local MMCs were produced contextually to the weld using Friction Stir Welding (FSW). SiC particles were added to AA7075 lap joints by creating a proper groove on the top surface of the bottom sheet. Different welds were produced with increasing number of tool passes. The effect of the multiple passes was investigated through shear tests, macro and micro observations, average grain size and microhardness measurements. The welded joints were compared to a reference weld produced with no reinforcements. It was found that poor mixing between matrix and reinforcement phase is obtained with one tool pass. On the contrary, proper mixing is obtained with three tool passes, resulting in an increase in the maximum load in shear tests of 50% with respect to the reference conditions.
- Published
- 2017
27. Strategies for numerical simulation of linear friction welding of metals: a review
- Author
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Gianluca Buffa, Livan Fratini, Buffa, G., and Fratini, L.
- Subjects
010302 applied physics ,FEM ,Work (thermodynamics) ,Materials science ,Computer simulation ,Numerical analysi ,Mechanical Engineering ,Mechanical engineering ,02 engineering and technology ,Welding ,021001 nanoscience & nanotechnology ,01 natural sciences ,Industrial and Manufacturing Engineering ,Finite element method ,Material flow ,law.invention ,Reciprocating motion ,law ,Residual stress ,0103 physical sciences ,Friction welding ,0210 nano-technology ,Linear friction welding - Abstract
Linear friction welding (LFW) is a solid-state joining process used to weld non-axisymmetric components. Material joining is obtained through the reciprocating motion of two specimens undergoing an axial force. During this process, the heat source is determined by the frictional work transformed into heat. This results in a local softening of the material and plays a key role in the onset of the bonding conditions. In this paper, a critical analysis of the different approaches used to simulate the LFW processes is provided. The focus of the paper is the comparison of different modeling strategies and the most relevant outputs available, i.e. temperature, strain and stress distribution, material flow, axial shortening and residual stress. Major issues arising due to the complexity of the process are discussed, highlighting strengths and weaknesses of each approach.
- Published
- 2017
28. Linear friction welding of dissimilar AA6082 and AA2011 aluminum alloys: microstructural characterization and design guidelines
- Author
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Gianluca Buffa, Livan Fratini, Marco Cammalleri, Davide Campanella, Umberto La Commare, Buffa, G., Cammalleri, M., Campanella, D., Fratini, L., and La Commare, U.
- Subjects
0209 industrial biotechnology ,Materials science ,Oscillation ,Metallurgy ,chemistry.chemical_element ,02 engineering and technology ,Welding ,021001 nanoscience & nanotechnology ,Microstructure ,Grain size ,Characterization (materials science) ,law.invention ,020901 industrial engineering & automation ,chemistry ,Aluminium ,law ,General Materials Science ,Friction welding ,Composite material ,0210 nano-technology ,Linear Friction Welding, Dissimilar welds, Aluminum alloys, Grain size ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Joint (geology) - Abstract
This paper presents the results of an experimental and numerical campaign on Linear Friction Welding of dissimilar AA2011-T8 and AA6082-T6 aluminum alloys. Experimental tests were carried out with constant oscillation amplitude and process time. Varying oscillation frequency, interface pressure, specimen geometry and mutual position were used. Grain size measurements, HV tests and EDX analysis were considered to characterize the microstructure of the joints as a function of the input process parameters. A thermal numerical model was utilized to predict the temperature profiles in the joints during the process. The obtained results allowed the identification of four weld categories: sound joints, “bonding limit” condition and two different unwelded joints. The investigation of the causes of the different joint behavior permitted to obtain a few design guidelines on the LFW of dissimilar alloys with different geometry.
- Published
- 2015
29. In-process control strategies for friction stir welding of AZ31 sheets with non-uniform thickness
- Author
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Michela Simoncini, Umberto La Commare, Gianluca Buffa, Livan Fratini, Archimede Forcellese, Davide Campanella, Buffa, G., Campanella, D., Forcellese, A., Fratini, L., la Commare, U., and Simoncini, M.
- Subjects
0209 industrial biotechnology ,Materials science ,Friction stir welding ,02 engineering and technology ,Welding ,Rotation ,Industrial and Manufacturing Engineering ,law.invention ,020901 industrial engineering & automation ,law ,Tailor welded blank ,Composite material ,Magnesium alloy ,Joint (geology) ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Mechanical Engineering ,Metallurgy ,Rotational speed ,Computer Science Applications1707 Computer Vision and Pattern Recognition ,021001 nanoscience & nanotechnology ,Microstructure ,Grain size ,Computer Science Applications ,Control and Systems Engineering ,0210 nano-technology ,Software - Abstract
Two different in-process control strategies were developed and compared with the aim to produce AZ31 magnesium alloy joints by friction stir welding on sheet blanks with a non-uniform thickness. To this purpose, sheets with dip or hump zones were welded by either changing the rotational speed or the tool plunging in order to keep constant the value of the vertical force occurring during the welding stage of the process. The influence of the main process parameters on the tool force, the micro- and macromechanical properties, and the joints microstructures in the dip and hump zones were analyzed. The results showed that using the rotational speed change-based approach, the hump zones are subjected to increased heat input with consequent increase of the heat-affected zone extension and average grain size (up to 11 μm). On the contrary, using the tool plunge change-based approach, the weld seam thickness in the dip zones is reduced, resulting in a decreased joint strength, with respect to tool rotation approach, equal to about 18%.
- Published
- 2018
30. Experimental and Numerical Analysis of Microstructure Evolution during Linear Friction Welding of Ti6Al4V
- Author
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Livan Fratini, Gianluca Buffa, Sergio Esposito, Antonello Astarita, Marco Cammalleri, Davide Campanella, Antonino Squillace, Antonino Ducato, Buffa, G., Campanella, D., Cammalleri, M., Ducato, A., Astarita, A., Squillace, A., Esposito, S., Fratini, L., Buffa, Gianluca, Campanella, Davide, Cammalleri, Marco, Ducato, Antonino, Astarita, Antonello, Squillace, Antonino, Esposito, Sergio, and Fratini, Livan
- Subjects
FEM ,Materials science ,Metallurgy ,Titanium alloy ,Welding ,Strain rate ,Phase transformation ,Microstructure ,Indentation hardness ,Industrial and Manufacturing Engineering ,law.invention ,LFW ,Reciprocating motion ,Artificial Intelligence ,law ,Martensite ,Ti-6Al-4V ,Friction welding - Abstract
Linear Friction Welding (LFW) is a solid state welding process used to joint bulk components. In the paper, an experimental and numerical study on LFW of Ti6Al4V titanium alloy is presented. A laboratory designed LFW machine has been used to weld the specimens with different contact pressure and oscillation frequency. The joint microstructure has been experimentally observed with SEM and EDS. A dedicated numerical model, able to predict temperature, strain and strain rate distribution as well as the phase volume fraction evolution, has been utilized to predict the final microstructure in the welded parts. It was found that complete transformation of the alpha phase into beta phase occurs during the process. After cool down, martensitic structure is obtained at the core of the weld due to high temperatures reached during the process and high cooling rates occurring at the end of the reciprocating motion. Microhardness measurements confirmed increased hardness in the Weld Zone with respect to the parent material
- Published
- 2015
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31. Comparison between FSW and bonded lap joints - A preliminary investigation
- Author
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Davide Campanella, Livan Fratini, Chiara Mandolfino, Carla Gambaro, Gianluca Buffa, Enrico Lertora, Lertora, E., Campanella, D., Mandolfino, C., Gambaro, C., Fratini, L., and Buffa, G.
- Subjects
FSW tool ,Materials science ,Adhesive bonding ,Aluminium alloy ,FSW ,Epoxy ,Welding ,FSW, Aluminium alloy, FSW tool ,law.invention ,Fusion welding ,Physics and Astronomy (all) ,Lap joint ,law ,visual_art ,visual_art.visual_art_medium ,Friction stir welding ,Composite material ,Joint (geology) ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione - Abstract
Difficult to weld aluminium alloys can be effectively joined by different alternative processes. Friction Stir Welding (FSW), among the solid-state processes and adhesive bonding represent two very attractive techniques. They allow the production of highly resistant joints avoiding the formation of the typical fusion weld defects. The aim of this work is to identify, analyse and compare the mechanical properties of AA6016 aluminium alloy joints made out of 1 mm thick sheets. FSW lap joints were and epoxy bonded joints were produced. Using the FSW results as benchmark, the overlap required in the bonded joint was identified to ensure the same static strength. Once the geometric configurations of the joints are known, the static and dynamic resistance of welds and bonding have been compared.
- Published
- 2017
32. In-process tool rotational speed variation with constant heat input in friction stir welding of AZ31 sheets with variable thickness
- Author
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Gianluca Buffa, Michela Simoncini, Archimede Forcellese, Davide Campanella, Livan Fratini, Buffa, G., Campanella, D., Forcellese, A., Fratini, L., and Simoncini, M.
- Subjects
Work (thermodynamics) ,Materials science ,Metallurgy ,Rotational speed ,Welding ,Microstructure ,law.invention ,Physics and Astronomy ,law ,Friction stir welding ,Composite material ,Magnesium alloy ,Constant (mathematics) ,Joint (geology) ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione - Abstract
In the present work, friction stir welding experiments on AZ31 magnesium alloy sheets, characterized by a variable thickness along the welding line, were carried out. The approach adapted during welding consisted in maintaining constant the heat input to the joint. To this purpose, the rotational speed of the pin tool was increased with decreasing thickness and decreased with increasing thickness in order to obtain the same temperatures during welding. The amount by which the rotational speed was changed as a function of the sheet thickness was defined on the basis of the results given by FEM simulations of the FSW process. Finally, the effect of the in-process variation of the tool rotational speed on the mechanical and microstructural properties of FSWed joints was analysed by comparing both the nominal stress vs. nominal strain curves and microstructure of FSWed joints obtained in different process conditions. It was observed that FSW performed by keeping constant the heat input to the joint leads to almost coincident results both in terms of the curve shape, ultimate tensile strength and ultimate elongation values, and microstructure.
- Published
- 2017
33. Analytical bonding criteria for joint integrity prediction in friction stir welding of aluminum alloys
- Author
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Gianluca Buffa, Sergio Pellegrino, Livan Fratini, Buffa, G., Pellegrino, S., and Fratini, L.
- Subjects
business.product_category ,Materials science ,Metallurgy ,Metals and Alloys ,Process (computing) ,Mechanical engineering ,Welding ,Industrial and Manufacturing Engineering ,Finite element method ,Computer Science Applications ,law.invention ,law ,Modeling and Simulation ,Ceramics and Composites ,Range (statistics) ,Die (manufacturing) ,Friction stir welding ,Extrusion ,business ,Joint (geology) ,Friction stir welding Aluminum alloys FEM Bonding criterion - Abstract
In this study, two bonding criteria, previously used for porthole die extrusion, are applied to FSW starting from the local value of the main field variables calculated through a specifically developed 3D numerical model of the process. Their applicability and effectiveness have been assessed through an experimental and numerical campaign carried out with the main process parameters varying in a wide range. The pressure–time–flow criterion was demonstrated to be better suited for FSW processes when large welding speed is used.
- Published
- 2014
34. Using a neural network for qualitative and quantitative predictions of weld integrity in solid bonding dominated processes
- Author
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Livan Fratini, Gianluca Buffa, Giuseppe Patrinostro, Buffa, G, Patrinostro, G, and Fratini, L
- Subjects
business.product_category ,Materials science ,Artificial neural network ,Mechanical Engineering ,Metallurgy ,Friction Stir Welding ,Process (computing) ,Mechanical engineering ,Welding ,Strain rate ,Neural network ,Aluminum alloys ,Computer Science Applications ,law.invention ,Roll bonding ,law ,Modeling and Simulation ,Die (manufacturing) ,Friction stir welding ,General Materials Science ,Extrusion ,Bonding criterion ,business ,Civil and Structural Engineering - Abstract
Solid-state bonding occurs in several manufacturing processes, as Friction Stir Welding, Porthole Die Extrusion and Roll Bonding. Proper conditions of pressure, temperature, strain and strain rate are needed in order to get effective bonding in the final component. In the paper, a neural network is set up, trained and used to predict the bonding occurrence starting from the results of specific numerical models developed for each process. The Plata-Piwnik criterion was used in order to define a quantitative parameter taking into account the effectiveness of the bonding. Excellent predictive capability of the network is obtained for each process.
- Published
- 2014
35. Micro and macro mechanical characterization of friction stir welded Ti–6Al–4V lap joints through experiments and numerical simulation
- Author
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Livan Fratini, Gianluca Buffa, Marion Merklein, Matthias Schneider, Buffa, G., Fratini, L., Schneider, M., and Merklein, M.
- Subjects
FEM ,Materials science ,Friction stir welding ,Lap joints ,Metallurgy ,Metals and Alloys ,Titanium alloy ,Welding ,Microstructure ,Indentation hardness ,Industrial and Manufacturing Engineering ,Grain size ,Computer Science Applications ,law.invention ,Lap joint ,law ,Modeling and Simulation ,Ceramics and Composites ,Composite material ,Joint (geology) - Abstract
Lap joints of Ti–6Al–4V were produced and the effect of the main process parameters was studied through macro and micro investigations highlighting mechanical resistance, microhardness profiles, grain size and phase distributions. A dedicated numerical model was used to link the input process parameters to temperature and strain distributions and to the final microstructure in the welded joint. It is found that the strain produced in the stir zone by proper combination of process parameters plays a fundamental role in the final microstructure and mechanical properties of the joints.
- Published
- 2013
36. Mechanical and microstructural characterization of friction stir welded skin and stringer joints
- Author
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Livan Fratini, Gianluca Buffa, Paola Leo, Emanuela Cerri, Leo, P., Cerri, E., Fratini, L., Buffa, G., Leo, Paola, E., Cerri, G., Buffa, and L., Fratini
- Subjects
Materials science ,Mechanical Engineering ,Metallurgy ,Welding ,Microstructure ,Indentation hardness ,Industrial and Manufacturing Engineering ,Grain size ,Friction stir welding, skin–stringer, grain dimension, microstructure, 2024-T4, 7075-T6 ,law.invention ,Lap joint ,law ,Friction stir welding ,Grain boundary ,Composite material ,Joint (geology) - Abstract
A microstructural and mechanical investigation on lap joints welded by friction stir welding and made out of a 7075-T6 stringer and a 2024-T4 skin is presented. In particular, the metallurgical and mechanical properties of joints have been studied at different tool feed rates (V = 35, 50, 100 mm/min) and constant rotation speed (R = 500 r/min). Temperature distributions have been monitored during the process. It is found that in the welded area, the recrystallized zone (nugget) has an average grain size of about 3 µm and exhibits coarsened MgZn2 particles on grain boundaries. The maximum values of microhardness in the welded skin increase with the process temperature, while they just slightly vary with process temperature in the stringer. From the mechanical point of view, the joint welded at R = 500 r/min and V = 50 mm/min exhibits both the highest strength and average microhardness value in the welded area.
- Published
- 2013
37. FEM based prediction of phase transformations during Friction Stir Welding of Ti6Al4V titanium alloy
- Author
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Gianluca Buffa, Antonino Ducato, Livan Fratini, Buffa, G., Ducato, A., and Fratini, L.
- Subjects
Plastic welding ,Materials science ,Mechanical Engineering ,Metallurgy ,Titanium alloy ,Welding ,Condensed Matter Physics ,Electric resistance welding ,law.invention ,Fusion welding ,FrictionStirWelding Titanium alloys FEM model Phase transformation ,Mechanics of Materials ,law ,Friction stir welding ,General Materials Science ,Friction welding ,Embrittlement - Abstract
Friction Stir Welding (FSW) is a solid state welding process patented in 1991 by TWI; initially adopted to weld aluminum alloys, it is now being successfully used also for high resistant materials. Welding of titanium alloys by traditional fusion welding techniques presents several difficulties due to high material reactivity with oxygen, hydrogen, and nitrogen with consequent embrittlement of the joint. In this way FSW represents a cost effective and high quality solution. The final mechanical properties of the joints are strictly connected to the microstructural evolutions, in terms of phase change, occurring during the process. In the paper a 3D FEM model of the FSW welding process, based on a thermo-mechanical fully coupled analysis, is presented. The model, tuned both for the thermo-mechanical analysis and the phase transformation through experimental data, is able to predict the phase volume fraction in the typical zones of the joints at the varying of the main process parameters. The obtained results permit to assess that the tuned FEM model of the FSW process can be utilized as an effective design tool.
- Published
- 2013
38. On tool stirring action in friction stir welding of work hardenable aluminium alloys
- Author
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Livan Fratini, Davide Campanella, Gianluca Buffa, Buffa, G, Campanella, D, and Fratini, L
- Subjects
Work (thermodynamics) ,Materials science ,Metallurgy ,chemistry.chemical_element ,Welding ,Condensed Matter Physics ,Finite element method ,law.invention ,Transverse plane ,chemistry ,Aluminium ,law ,Butt joint ,Friction stir welding ,FSW, Mechanical properties, FEM ,General Materials Science ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Joint (geology) - Abstract
In the paper solid state bonding conditions obtained in friction stir welding (FSW) of AA5754-H111 butt joints are analysed, considering the so called zigzag line in the transverse section of the joints. A wide experimental campaign was carried out varying both tool advancing speed and tool rotational one. The effects of the process on the mechanical properties of the joint were highlighted and micro- and macro-observations were used in order to explain the reasons of the enhanced mechanical properties found for the welded material. Numerical results derived from a FEM model previously developed by the authors were utilised to point out the different mechanical and metallurgical behavior of the obtained joints.
- Published
- 2013
39. Weld quality prediction in linear friction welding of AA6082-T6 through an integrated numerical tool
- Author
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Davide Campanella, Livan Fratini, Gianluca Buffa, Sergio Pellegrino, Buffa, G., Campanella, D., Pellegrino, S., and Fratini, L.
- Subjects
0209 industrial biotechnology ,Engineering ,Aluminum alloy ,Field (physics) ,Interface (computing) ,Neural Network ,02 engineering and technology ,Welding ,Industrial and Manufacturing Engineering ,law.invention ,020901 industrial engineering & automation ,Quality (physics) ,law ,Friction welding ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,FEM ,Artificial neural network ,business.industry ,Oscillation ,Metals and Alloys ,Structural engineering ,021001 nanoscience & nanotechnology ,Finite element method ,Computer Science Applications ,Modeling and Simulation ,Ceramics and Composites ,Linear Friction Welding ,0210 nano-technology ,business - Abstract
A numerical and an experimental campaign were carried out with varying oscillation frequency and interface pressure. The local values of the main field variables at the contact interface between the specimens were predicted by a Lagrangian, implicit, thermo-mechanical FEM model and used as input of a dedicated Neural Network (NN). The NN, integrated in the FEM environment, was designed in order to calculate both a Boolean output, indicating the occurrence of welding, and a continuous output, indicating the quality of the obtained solid state weld. The analysis of the obtained results allowed three different levels of bonding quality, i.e., no weld, sound weld and excess of heat, to be correctly identified and predicted.
- Published
- 2016
40. Effect of the mutual position between weld seam and reinforcement on the residual stress distribution in Friction Stir Welding of AA6082 skin and stringer structures
- Author
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Giuseppe Vincenzo Marannano, Livan Fratini, Gianluca Buffa, Antonino Pasta, Buffa, G., Fratini, L., Marannano, G., and Pasta, A.
- Subjects
0209 industrial biotechnology ,Engineering ,Friction Stir Welding ,Residual stre ,02 engineering and technology ,Welding ,Rotation ,law.invention ,Weld seam ,020901 industrial engineering & automation ,0203 mechanical engineering ,Stringer ,law ,Residual stress ,Skin and stringer ,Friction stir welding ,Reinforcement ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Civil and Structural Engineering ,Cut compliance ,business.industry ,Mechanical Engineering ,Structural engineering ,Building and Construction ,020303 mechanical engineering & transports ,visual_art ,visual_art.visual_art_medium ,Sheet metal ,business ,FE analysi - Abstract
In the paper, a numerical and experimental study was carried out to highlight the effect of the distance d between the weld seam and the reinforcement on the residual stress distribution in Friction Stir Welded AA6082-T6 structures. An L-shaped profile was welded to a sheet metal with varying tool rotation and distance d from the weld seam. The Cut Compliance method was used to determine the resulting longitudinal residual stress. A dedicated FE model for FSW was set up, validated and utilized to predict the longitudinal residual stress in the assembled part. The analysis allowed the identification of a few design guidelines in order to reduce the detrimental effects of the residual stresses.
- Published
- 2016
41. Dissimilar titanium/aluminum friction stir welding lap joints by experiments and numerical simulation
- Author
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Gianluca Buffa, M. De Lisi, Livan Fratini, E. Sciortino, Buffa, G., De Lisi, M., Sciortino, E., and Fratini, L.
- Subjects
0209 industrial biotechnology ,Materials science ,Polymers and Plastics ,AA2024 ,Lap joint ,02 engineering and technology ,Welding ,Rotation ,Industrial and Manufacturing Engineering ,law.invention ,020901 industrial engineering & automation ,law ,Shear strength ,Friction stir welding ,Mechanics of Material ,Composite material ,Joint (geology) ,Finite element method (FEM) ,Polymers and Plastic ,Friction stir welding (FSW) ,Mechanical Engineering ,Ti6Al4V ,Titanium alloy ,021001 nanoscience & nanotechnology ,Material flow ,Mechanics of Materials ,0210 nano-technology - Abstract
Dissimilar lap joints were produced by friction stir welding (FSW) out of Ti6Al4V titanium alloy and AA2024 aluminum alloy sheets. The joints, welded with varying tool rotation and feed rate, were studied by analyzing the maximum shear strength, Vickers microhardness and optical observations. A dedicated numerical model, able to take into account the presence of the two different alloys, was used to highlight the effects of the process parameters on temperature distribution, strain distribution, and material flow. The combined analysis of experimental measurements and numerical predictions allowed explaining the effects of tool rotation and feed rate on the material flow. It was found that tool rotation had a larger impact on the joint effectiveness with respect to feed rate. A competition between material mixing and heat input occurs with increasing tool rotation, resulting in higher joint strength when lower values of tool rotation are used.
- Published
- 2016
42. In-process tool force and rotation variation to control sheet thickness change in friction stir welding of magnesium alloys
- Author
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Gianluca Buffa, Michela Simoncini, Livan Fratini, Archimede Forcellese, Buffa, G., Fratini, L., Simoncini, M., and Forcellese, A.
- Subjects
Physics and Astronomy (all) ,Materials science ,law ,Metallurgy ,Ultimate tensile strength ,Formability ,Friction stir welding ,Rotational speed ,Welding ,Friction welding ,Magnesium alloy ,Electric resistance welding ,law.invention - Abstract
Two different in-process control strategies, developed in order to produce sound joints in AZ31 magnesium alloy by Friction Stir Welding on sheet blanks with a non-uniform thickness, are presented and compared. To this purpose, sheets with dip or hump were machined and welded by either changing the rotational speed or the tool plunging in order to keep constant the vertical force occurring during welding. The mechanical strength of the joints was measured in the zones where the sheets before welding were characterised by different thicknesses. The sheets welded by the two different strategies are characterized by very similar ultimate tensile strength values. Finally, the results showed that the two approaches permit to successfully weld sheets with non-uniform thickness with a reduced loss in the mechanical strength.
- Published
- 2016
43. Joining Ti6Al4V and AISI 304 through friction stir welding of lap joints: experimental and numerical analysis
- Author
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Gianluca Buffa and Buffa, G.
- Subjects
Materials science ,Friction stir welding ,Lap joint ,02 engineering and technology ,Welding ,01 natural sciences ,law.invention ,Stainless steel ,law ,0103 physical sciences ,General Materials Science ,Friction welding ,Composite material ,Joint (geology) ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,010302 applied physics ,FEM ,Titanium alloy ,021001 nanoscience & nanotechnology ,Finite element method ,Material flow ,Materials Science (all) ,0210 nano-technology - Abstract
The results of an experimental and numerical analysis on Friction Stir Welding of dissimilar lap joints made out of AISI304 and Ti-6Al-4 V thin sheets are presented. The mixed joints, welded with varying process parameters, have been characterized from a mechanical and metallurgical point of view. A numerical model able to take into account the behaviour of the two different materials has been used. The numerical results have been utilized to explain the joint properties and the occurring material flow. The effect of the heat input, tilt angle and sheets mutual position has been investigated. It is found that both hooking defects and tunnels may occur with incorrect choice of process parameters. Good nugget integrity is obtained when the titanium sheet is used as upper sheet and high heat input is conferred to the joint. Finally, welding speed influences the nugget morphology as low values contribute to minimize the formation of the hooking defect.
- Published
- 2016
44. Investigations on the linear friction welding process through numerical simulations and experiments
- Author
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Dario La Spisa, Livan Fratini, Davide Campanella, Gianluca Buffa, Fratini, L., Buffa, G., Campanella, D., and La Spisa, D.
- Subjects
Work (thermodynamics) ,Materials science ,Process (computing) ,Mechanical engineering ,Welding ,Fixture ,Welding, Friction, Solid state bonding, Finite element method (FEM) ,law.invention ,Process conditions ,law ,Friction welding ,Axial force ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Softening - Abstract
Linear Friction Welding (LFW) is a solid-state joining process applied to non-axisymmetric components. LFW involves joining of materials through the relative motion of two components undergoing an axial force. In such process the heat source is given by the frictional forces work decaying into heat determining a local softening of the material and eventually bonding conditions. In the paper the authors present a designed and assembled laboratory fixture for LFW operations and the results of an experimental and numerical campaign aimed to weld steel parts. The dedicated fixture permitted to highlight the effect of the most important process parameters. Process conditions allowing effective bonding conditions were highlighted and local conditions of pressure and temperature determining effective bonding of the specimens were determined.
- Published
- 2012
45. Improved FE model for simulation of friction stir welding of different materials
- Author
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L. Lo Monaco, Gianluca Buffa, Livan Fratini, Buffa, G., Fratini, L., and Lo Monaco, L.
- Subjects
Materials science ,Mechanical engineering ,Welding ,Condensed Matter Physics ,Friction stir welding, T joints, Different materials, FEM ,Finite element method ,Material flow ,law.invention ,Stringer ,Residual stress ,law ,Friction stir welding ,General Materials Science ,Composite material ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Failure mode and effects analysis ,Joint (geology) - Abstract
One of the most relevant aspects of friction stir welding is the possibility to weld different materials. In the present paper, the authors present an improved continuum finite element model for the simulation of friction stir welding processes aimed to obtain T joints, made of a stringer in AA7175-T73511 and of a skin in AA2024-T4. The model, taking into account the thermomechanical behaviours of the two different materials, is utilised to study the occurring material flow and residual stress state. Numerical results are compared with experimental observations: the model is able to predict the material flow, obtaining important information on the joint failure mode.
- Published
- 2010
46. A new fixture for FSW processes of titanium alloys
- Author
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Gianluca Buffa, Fabrizio Micari, V. F. Ruisi, Livan Fratini, Fratini, L., Micari, F., Buffa, G., and Ruisi, V.F.
- Subjects
Materials science ,business.industry ,Welding, aluminium alloys, FSW, FEM ,Mechanical Engineering ,Metallurgy ,Solid-state ,chemistry.chemical_element ,Titanium alloy ,Welding ,Fixture ,Industrial and Manufacturing Engineering ,law.invention ,chemistry ,law ,Aerospace ,business ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Titanium - Abstract
FSW of titanium alloys is nowadays one of the most challenging welding operations, even with a solid state process, due to the thermo-mechanical and thermo-chemical characteristics of such materials. Due to the relevant application of titanium alloys in the aeronautic and aerospace industries, in the recent years few attempts were carried out to develop FSW processes aimed to maximize the mechanical performances of the welded parts. In the paper a new fixture is presented allowing obtaining effective FSW joints of titanium blanks, which were investigated through mechanical and metallurgical tests highlighting the peculiarities of FSW of titanium alloys.
- Published
- 2010
47. Towards Tool Path Numerical Simulation in Modified Friction Stir Spot Welding Processes
- Author
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Gianluca Buffa, Livan Fratini, Buffa, G, and Fratini, L
- Subjects
FSSW, FEM ,Engineering ,Computer simulation ,business.industry ,Metallurgy ,General Engineering ,Mechanical engineering ,Recrystallization (metallurgy) ,Welding ,Strain rate ,law.invention ,Robot welding ,law ,Friction stir welding ,Friction welding ,business ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Spot welding - Abstract
Spot welding can be considered a very common joining technique in automotive and transportation industries as it permits to obtain effective lap-joints with short process times and what is more it is easily developed through robots and automated systems. Recently the Friction Stir Spot Welding (FSSW) process has been proposed as a natural evolution of the already known Friction Stir Welding (FSW) process, allowing to obtain sound spot joints that do not suffer from the insurgence of typical welding defects due to the fusion of the base material. In the paper, a modified Friction Stir Spot Welding (FSSW) process, with a spiral circular movement given to the tool after the sinking stage, is proposed. A continuum based numerical model for Friction Stir Spot Welding process is developed, that is 2D Lagrangian implicit, coupled, rigid-viscoplastic. This model is used to investigate the distribution of the main field variables, namely temperature, strain and strain rate, as well as the Zener-Hollomon parameter which, in turn, strongly affects the Continuous Dynamic Recrystallization (CDRX) process that takes place in the weld nugget. Numerical and experimental results are presented showing the effects of the process parameters on the joint performances and the mechanical effectiveness of the modified process.
- Published
- 2009
48. Friction stir welding of lap joints: Influence of process parameters on the metallurgical and mechanical properties
- Author
-
A. Prisco, Gianluca Buffa, Livan Fratini, G. Campanile, Buffa, G, Campanile, G, Fratini, L, and Prisco, A
- Subjects
Materials science ,FSW, FEM, Lap-joint ,Mechanical Engineering ,Alloy ,Metallurgy ,Rotational speed ,Welding ,engineering.material ,Condensed Matter Physics ,law.invention ,Lap joint ,Mechanics of Materials ,law ,engineering ,Friction stir welding ,General Materials Science ,Direct shear test ,Ductility ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Joint (geology) - Abstract
Aluminum alloys are widely used in the aircraft industries even if such materials present lower ductility with respect to steels, anisotropy phenomena and, more important, they are often “difficult” to be welded or even “non-weldable”. In the last years the friction stir welding process (FSW) was proposed and applied in order to get good mechanical and technological performances of the joints. In this paper, an experimental and numerical investigation on the lap joining of AA2198-T4 aluminum alloy blanks by FSW is presented. In particular the joints strength and metallurgical properties are investigated by varying the joint configuration and the tool geometry and rotational speed. It is found that the use of cylindrical–conical pin tools and the correct choice of the relative sheet positioning increase the welded nugget extension and integrity improving the mechanical performances of the obtained joints.
- Published
- 2009
49. Friction stir welding of tailored joints for industrial applications
- Author
-
V. F. Ruisi, Gianluca Buffa, Livan Fratini, Buffa, G, Fratini, L, and Ruisi, VF
- Subjects
Engineering ,business.industry ,Metallurgy ,Mechanical engineering ,Welding ,Fixture ,Electric resistance welding ,Forging ,Clamping ,law.invention ,Robot welding ,FSW, Tailored blanks ,law ,Friction stir welding ,General Materials Science ,Friction welding ,business ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione - Abstract
Friction stir welding (FSW) is an energy efficient and environmentally "friendly" (no fumes, noise, or sparks) welding process, during which the workpieces are welded together in a solid-state joining process at a temperature below the melting point of the workpiece material under a combination of extruding and forging. Since its invention in 1991 by TWI, such process has been reaching a continuously increasing popularity among aerospace, automotive and shipbuilding industries due its capability to weld unweldable or difficult-to-weld light alloys in different joint morphologies. In this paper a wide experimental campaign is carried out in order to obtain T and lap joints characterized by dimensions of industrial interest from two sheets, the stringer and the skin, of different materials. In particular a peculiar clamping fixture has been designed in order to assure a perfect contact between the stringer and the skin and to develop the “transparency” welding; a proper welding tool has been utilized allowing to obtain at the same time a sound joint and the designed final component fillet radii. Finally T-pull tests together with macro and micro observations have been developed at the varying of the main process parameters.
- Published
- 2009
50. On the influence of tool path in friction stir spot welding of aluminum alloys
- Author
-
Gianluca Buffa, Livan Fratini, Mario Piacentini, FRATINI, L, BUFFA, G, and PIACENTINI, M
- Subjects
Materials science ,Metallurgy ,Metals and Alloys ,Process (computing) ,Mechanical engineering ,chemistry.chemical_element ,Welding ,Microstructure ,Industrial and Manufacturing Engineering ,Computer Science Applications ,law.invention ,Tool path ,Spot ,chemistry ,law ,Aluminium ,Modeling and Simulation ,Ultimate tensile strength ,Ceramics and Composites ,Settore ING-IND/16 - Tecnologie E Sistemi Di Lavorazione ,Joint (geology) ,Spot welding - Abstract
Friction stir spot welding (FSSW) has been proposed as an effective technology to spot weld the so-called “difficult to be welded” metal alloys. In the paper, a variation of the FSSW process has been considered. A tool path is given after the sinking phase nearby the initial penetration site; in this way a larger welding spot is obtained and more material is involved in the bonding process. The process mechanics of such modified FSSW process is highlighted and the joint strength undergoing tensile tests is considered at the varying both of the assigned tool path and of a few process parameters. Macro- and micro-analyses are made in order to analyze the local material microstructure evolution. It is found that improved performances, with respect to the “traditional” FSSW process, are obtained for all the considered case studies.
- Published
- 2008
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