Papers by Keyword: Friction Stir Welding (FSW)

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Authors: A. Alimoradi, M. Loh-Mousavi, R. Salekrostam
Abstract: The Friction Stir Welding (FSW), a relatively new welding process, was developed in 1991 at the Welding Institute near Cambridge, England. There are two tool speeds to be considered in friction-stir welding; how fast the tool rotates and how quickly it traverses the interface. These two parameters have considerable importance and must be chosen with care to ensure a successful and efficient welding cycle. The relationship between the welding speeds and the heat input during welding is complex. In this paper the friction stir welding (FSW) process of stainless steel alloys has been modeled using a three dimensional finite element method. A coupled thermal viscoplastic model was used for the simulation. Tool speeds and temperature distribution are coupled and solved together using this method. The relationship between the welding speeds and the heat input during welding is obtained by numerical analysis, and the stress contour occurred by temperature field and tool force is surveyed. In addition, the effects of FSW process conditions on heating mainly near the tool pin are investigated in this paper.
Authors: Barnik Saha Roy, Subhash Chandra Saha, John Deb Barma
Abstract: A 3D thermal pseudo mechanical model formulated in an Eulerian frame considering a quassisteady approach to Friction Stir welding modeling of AA6061 Aluminium alloy is proposed and implemented using nonlinear finite element code in Comsol Multiphysics v 4.1. The effect of different operating parameters on the temperature distribution was analyzed. The material flow is found to be enhanced with the increase in traverse speed and angular velocity of the pin with a pronounced swirl on the advancing side. The distribution of equivalent plastic strain and dynamic viscosity was found to correlate with the distribution of the microstructure zones in the weld.
Authors: Sabrina Gastebois, Lionel Fourment
Abstract: The numerical simulation of Friction Stir Welding (FSW) is carried out using an Arbitrary Lagrangian or Eulerian (ALE) formulation. Its computational cost is reduced by appealing to the parallel version recently developed within the Forge software. The accuracy of the numerical model is increased by enhancing the state variables remapping algorithm and by introducing a better suited time integration scheme based on the cylindrical coordinates. The pin and shoulder threads are modelled in order to account for this crucial phenomenon on material heating. The developed model provides quite satisfactory temperature fields for the FSW of a butt joint of 6061 aluminium, as compared to experimental results. It allows simulating welding defects such as tunnels holes or flashes. The study then focuses on numerical simulations and experimental measurements of a lap joint of a 7175 aluminium sheet on a 2024 aluminium sheet for an aeronautical application.
Authors: Zheng Hua Guo, Gang Yao Zhao, Li Ming Ke, Li Xing, Shun Feng Zhu
Abstract: Friction stir welding(FSW), a new solid-state joining process, is wildly used in the fields of aviation, aerospace and other high technology industries for many advantages over traditional fusion welding. Computer modeling is an important tool for the prediction and optimization of the FSW process. According to the characteristics of FSW of 7075 aluminum alloy plate, a 3D coupled thermo-mechanical FE model of this process was built under the ABAQUS/explicit environment based on the solution of several key techniques, such as heat boundary condition treating, material properties definition, ALE adaptive meshing technology, etc., and validated experimentally. Then, simulation and analysis of the complex plastic deformation behavior of the process were carried out. The results show that in the stable stage of the welding, the zone of equivalent plastic deformation decreases from the top surface of weld to the bottom surface; the plastic deformation of metal ahead of the welding tool is larger than that behind the welding tool; moreover the zone of equivalent plastic deformation is concentrated behind the tool.
Authors: Hasan I. Dawood, Kahtan S. Mohammed, Mumtaz Y. Rajab, Nurafifah R. Ismail
Abstract: In this study, two sets of pure aluminum strips 3 mm in thickness were friction stir welding (FSW) together in a regular Butt joint pattern. Two rotational speeds of 1750 RPM and 2720 RPM were utilized to perform the welding process. The transverse speed and the axial load were kept constant at 45 mm/min and 6.5 kN respectively. As a welding tool, cylindrical shoulder and pin geometry was selected. For comparison purposes other similar strip pair sets were butt welded using the conventional metal inert gas arc welding technique (MIGAW). The welding quality, power input, microstructure, macrostructure and the mechanical properties of the weld joints yielded from these two welding techniques were examined. The types of the fumes and the amount of the released gases during these two welding processes were measured and compared. The results proved that the solid state friction stir welding is clean, cost effective and environment friendly process as opposed to the conventional metal inert gas arc welding.
Authors: Roberto G. Citarella, Pierpaolo Carlone, Marcello Lepore, Gaetano S. Palazzo
Abstract: Medium to high strength aluminum alloys, such as 2xxx, 6xxx, and 7xxx series, are actually considered of great interest in the transport industries. For aeronautical applications, the precipitation hardenable AA2024 (Al-Cu) alloy is gaining considerable attention, in particular for the realization of nose barrier beam or fuselage panels. In this context, remarkable research effort is currently focused on the application of the Friction Stir Welding (FSW) process, as a suitable alternative to fusion welding processes. The interest in aeronautical application of FSW process is also justified by the reduction of production costs and weight and by the increase of strength and damage tolerance with respect to riveted lap joints. The implementation of the technique in safety-critical components, however, requires a deeper understanding of static strength as well as of fatigue behavior of FSWed assemblies. In this sense some experimental results have already been presented in the inherent literature, relatively, for instance, to AA6082-T6 and AA6061-T6, AA6063-T6, AA2024-T351, AA2024-T8 alloys processed by FSW. Despite the unavoidable relevance of experimental testing, a numerical approach able to predict the mechanical behavior of FSWed assemblies is very desirable, in order to achieve time and cost compression and to implement computational optimization procedures. This paper deals with a numerical investigation on the influence of FSW process parameters, namely the rotating speed and the welding speed, on fatigue crack growth in AA2024-T3 butt joints. The computational approach is based on a combined Finite Element Method (FEM) and Dual Boundary Element Method (DBEM) procedure, in order to take advantage of the main capabilities of the two methods. In particular, linear elastic FE simulations have been performed to evaluate the process induced residual stresses, by means of a recently developed technique named contour method. The computed residual stress field has then been superimposed to the stress field produced by an applied fatigue traction load in a Dual Boundary Element Method (DBEM) environment, where the simulation of a crack, initiated and propagating along the previously mentioned cutting line, can be performed in an automatic way. A two-parameters crack growth law is used for the crack propagation rate assessment. The DBEM code BEASY and the FEM code ANSYS have been sequentially coupled in the aforementioned numerical approach by using a BEASY interface module and in house developed routines. Computational results have been compared with experimental data, showing a satisfactory agreement. The influence of process parameters on the residual stresses distribution has also been highlighted.
Authors: Jia Liang Zhang, Bei Zhi Li, Xin Chao Zhang, Qing Xia Wang
Abstract: Friction stir welding processes involve many variables. Engineers and operators often find it difficult to effectively design or control it. The objective of this work is to develop a friction stir welding platform of thin plates to improve welding quality and to increase production efficiency. The study is conducted by using finite element modeling and temperature field analysis technology to obtain optimization parameters, and using virtual instrument, multi-sensor data fusion to monitor the force of the stirring spindle. Experiment results show that the developed platform can reach the requirements of processing quality and is cost-effective.
Authors: Bahman Meyghani, Mokhtar Awang, Sattar Emamian
Abstract: High rotational motion from the welding tool generates a significant amount of the heat during friction stir welding (FSW). Basically, during FSW the heat is mostly coming from the frictional force between the tool shoulder and the plates. Therefore, a precise calculation of the friction coefficient can increase the accuracy of the finite element analysis (FEA) of the process. However, researchers have applied constant values, and that causes a gap between the reality and the simulated model especially after the welding plunging step. In this study, a mathematical formulation is proposed in order to calculate the temperature dependent values of the friction coefficient and also to explore the influence of the temperature in the friction coefficient. To solve the governing equations of the process, the MATLAB® software is used. The results indicate that, from 25°C to the AA 6061-T6 melting point (580°C), the values of the friction coefficient fall steadily in a range of 0.207089 to 0.000582. Furthermore, the material shear stress and the material yield stress decrease consistently as the temperature rises. Consequently, the influence of the temperature in the contact input parameters and the material properties are discussed in detail and a good correlation with the published results is achieved.
Authors: Gianluca Buffa, Livan Fratini, Fabrizio Micari
Abstract: Friction Stir Welding (FSW) is an energy efficient and environmentally "friendly" welding process. The parts 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. This technology has been successfully used to join materials that are difficult-to-weld or ‘unweldable’ by fusion welding methods. In the paper a neural network was set up and trained in order to predict the final grain size in the transverse section of a FSW butt joint of aluminum alloys. What is more, due to the relationship between the extension of the “material zones” and the joint resistance, the AI tool was able to furnish indications for the design of the welding process. Experimental tests and subsequent microstructure observations were developed in order to verify the numerical predictions.
Authors: Pierpaolo Carlone, Gaetano S. Palazzo
Abstract: In recent years, remarkable interest has been focused on the Friction Stir Welding (FSW) process, by academic as well as industrial research groups. Conceptually, the FSW process is quite simple: a non-consumable rotating tool is plunged between the adjoining edges of the parts to be welded and moved along the desired weld line. Frictional and viscous heat generation increases the work piece temperature, softening the processing material and forcing it to flow around the pin. Although FSW has been effectively applied in welding of several materials, such as copper, steel, magnesium, and titanium, considerable attention is still focused on aluminum welding, in particular for transport applications. Recent literature clearly evidenced microstructural variations in the stir zone, imputable to continuous dynamic recrystallization phenomena, leading to the formation of a finer equiaxed grains. Moreover, depending on the specific alloy, thermal cycles can induce coarsening or dissolution of precipitates in the thermo-mechanically affected zone (TMAZ) and in the heat affected zone (HAZ). The influence of the aforementioned microstructural aspects on mechanical properties and formability of FSWed assemblies is also well recognized. The aim of this paper is to numerically and experimentally investigate the influence of process parameters, namely rotating speed and welding speed, on microstructural aspects in AA2024-T3 friction stir butt welds. A three-dimensional Computational Fluid Dynamic (CFD) model has been implemented to simulate the process. A viscoplastic material model, based on Wright and Sheppard modification of the constitutive model initially proposed by Sellars and Tegart has been implemented in the commercial package ANSYS CFX, considering an Eulerian framework. Tool-workpiece interaction has been modeled assuming partial sticking/sliding condition, and incorporating both frictional and viscous contributions to the heat generation. Microstructural aspects have been numerically predicted using the Zenner-Holloman parameter and experimentally measured by means of conventional metallographic techniques. Satisfactory agreement has been found between simulated and experimental results. The influence of process parameters on mechanical properties has also been highlighted.
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