Numerical modeling of friction stir welding process: a literature review
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paper_title: Recent Advances in Friction Stir Welding – Process, Weldment Structure and Properties

paper_content:

Friction-stir welding is a refreshing approach to the joining of metals. Although originally intended for aluminium alloys, the reach of FSW has now extended to a variety of materials including steels and polymers. This review deals with the fundamental understanding of the process and its metallurgical consequences. The focus is on heat generation, heat transfer and plastic flow during welding, elements of tool design, understanding defect formation and the structure and properties of the welded materials.
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paper_title: A thermal model of friction stir welding in aluminum alloys

paper_content:

A thermal model of friction stir welding was developed that utilizes a new slip factor based on the energy per unit length of weld. The slip factor is derived from an empirical, linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature and the welding energy. The thermal model successfully predicts the maximum welding temperature over a wide range of energy levels but under predicts the temperature for low energy levels for which heat from plastic deformation dominates. The thermal model supports the hypothesis that the relationship between the temperature ratio and energy level is characteristic of aluminum alloys that share similar thermal diffusivities. The thermal model can be used to generate characteristic temperature curves from which the maximum welding temperature in an alloy may be estimated if the thermal diffusivity, welding parameters and tool geometry are known.
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paper_title: An analytical model for the heat generation in friction stir welding

paper_content:

The objective of this work is to establish an analytical model for heat generation by friction stir welding (FSW), based on different assumptions of the contact condition between the rotating tool surface and the weld piece. The material flow and heat generation are characterized by the contact conditions at the interface, and are described as sliding, sticking or partial sliding/sticking. Different mechanisms of heat generation are behind each contact condition, making this study important for further understanding of the real FSW process. The analytical expression for the heat generation is a modification of previous analytical models known from the literature and accounts for both conical surfaces and different contact conditions. Experimental results on plunge force and torque are used to determine the contact condition. The sliding condition yields a proportional relationship between the plunge force and heat generation. This is not demonstrated in the experiment, which suggests that the sticking contact condition is present at the tool/matrix interface.
---
paper_title: Recent Advances in Friction Stir Welding – Process, Weldment Structure and Properties

paper_content:

Friction-stir welding is a refreshing approach to the joining of metals. Although originally intended for aluminium alloys, the reach of FSW has now extended to a variety of materials including steels and polymers. This review deals with the fundamental understanding of the process and its metallurgical consequences. The focus is on heat generation, heat transfer and plastic flow during welding, elements of tool design, understanding defect formation and the structure and properties of the welded materials.
---
paper_title: An analytical model for the heat generation in friction stir welding

paper_content:

The objective of this work is to establish an analytical model for heat generation by friction stir welding (FSW), based on different assumptions of the contact condition between the rotating tool surface and the weld piece. The material flow and heat generation are characterized by the contact conditions at the interface, and are described as sliding, sticking or partial sliding/sticking. Different mechanisms of heat generation are behind each contact condition, making this study important for further understanding of the real FSW process. The analytical expression for the heat generation is a modification of previous analytical models known from the literature and accounts for both conical surfaces and different contact conditions. Experimental results on plunge force and torque are used to determine the contact condition. The sliding condition yields a proportional relationship between the plunge force and heat generation. This is not demonstrated in the experiment, which suggests that the sticking contact condition is present at the tool/matrix interface.
---
paper_title: Recent Advances in Friction Stir Welding – Process, Weldment Structure and Properties

paper_content:

Friction-stir welding is a refreshing approach to the joining of metals. Although originally intended for aluminium alloys, the reach of FSW has now extended to a variety of materials including steels and polymers. This review deals with the fundamental understanding of the process and its metallurgical consequences. The focus is on heat generation, heat transfer and plastic flow during welding, elements of tool design, understanding defect formation and the structure and properties of the welded materials.
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paper_title: Finite element modeling of friction stir welding—thermal and thermomechanical analysis

paper_content:

Friction stir welding (FSW) is a relatively new welding process that may have significant advantages compared to the fusion processes as follow: joining of conventionally non-fusion weldable alloys, reduced distortion and improved mechanical properties of weldable alloys joints due to the pure solid-state joining of metals. In this paper, a three-dimensional model based on finite element analysis is used to study the thermal history and thermomechanical process in the butt-welding of aluminum alloy 6061-T6. The model incorporates the mechanical reaction of the tool and thermomechanical process of the welded material. The heat source incorporated in the model involves the friction between the material and the probe and the shoulder. In order to provide a quantitative framework for understanding the dynamics of the FSW thermomechanical process, the thermal history and the evolution of longitudinal, lateral, and through-thickness stress in the friction stirred weld are simulated numerically. The X-ray diffraction (XRD) technique is used to measure the residual stress of the welded plate, and the measured results are used to validate the efficiency of the proposed model. The relationship between the calculated residual stresses of the weld and the process parameters such as tool traverse speed is presented. It is anticipated that the model can be extended to optimize the FSW process in order to minimize the residual stress of the weld.
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paper_title: Improving Computational Performance through HPC Techniques: case study using DD3IMP in‐house code

paper_content:

The computational efficiency of the FEA is strongly dependent on the algorithmic and numerical efficiency of the FE solver. This is particularly important in case of implicit FE codes, such as DD3IMP, the in‐house static implicit FE solver under analysis in this work. This study describes the procedure adopted to identify the main computational bottlenecks of the FE solver in order to introduce the OpenMP directives and, consequently, to achieve a major speedup of the whole algorithm. The different parallelized branches of the code are tested using the well‐known square cup deep drawing example, considering different FE discretizations. The analysis of the preliminary results, concerning the CPU wall time, allows to demonstrate that the adoption of HPC techniques, such as the abovementioned OpenMP directives, enables to: (i) achieve a speedup factor close to the number of cores (in a single computer); (ii) solve a problem in a shorter time; (iii) solve a bigger problem in the same amount of time and, thus...
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paper_title: Numerical Simulation of the Friction Stir Welding Process Using both Lagrangian and Arbitrary Lagrangian Eulerian Formulations

paper_content:

The plunge and dwell phase of the friction stir welding (FSW) process is simulated using two different commercial finite element codes. FORGE3®, employing an updated Lagrangian approach with remeshing, is used to simulate the non‐steady state process of plunging the tool into the workpiece, while THERCAST® uses an Arbitrary Lagrangian Eulerian formulation to simulate the stationary dwell phase. Temperatures predicted by the model are compared to an experiment on AA 7075, with favorable results.
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paper_title: Experimental and numerical analysis of aluminium alloy 7075-T7351 friction stir welds

paper_content:

AbstractThis paper describes a systematic series of friction stir welding experiments using aluminium alloy 7075, designed to provide validation data for a numerical model of the process. The numerical model used the commercial computational field dynamics package, FLUENT, and the trials focussed on weld temperature and torque measurements. There were several significant findings that have both practical use and are pertinent to future modelling work. First, the temperature profiles and weld quality were affected by the type of tool material. Second, in thick section welds the material reached temperatures very near to the solidus. As a consequence this limited the heat generation, so the weld power was largely independent of the rotation speed. Third, several of the welds experienced the problem of surface scaling which was exacerbated by high rotation speeds and a high plunge depth. Finally, an empirical equation for predicting the weld power was derived from the experimental power input.
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paper_title: Comparison of ALE finite element method and adaptive smoothed finite element method for the numerical simulation of friction stir welding

paper_content:

In this paper, the material flow around the pin during friction stir welding (FSW) is simulated using a 2D plane strain model. A pin rotates without translation in a disc with elasto-viscoplastic material properties and the outer boundary of the disc is clamped. Two numerical methods are used to solve this problem and an analytical solution is derived. The analytical model is complementary to validate the two numerical methods, i.e. the arbitrary Lagrangian-Eulerian (ALE) method and the adaptive smoothed finite elements method (ASFEM).
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paper_title: Friction Stir Welding and Processing

paper_content:

Abstract Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.
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paper_title: Numerical simulation of transient temperature and residual stresses in friction stir welding of 304L stainless steel

paper_content:

Abstract Three-dimensional nonlinear thermal and thermo-mechanical numerical simulations are conducted for the friction stir welding (FSW) of 304L stainless steel. The finite element analysis code—WELDSIM, developed by the authors specifically for welding simulation, was used. Two welding cases with tool rotational speeds of 300 and 500 rpm are analyzed. The objective is to study the variation of transient temperature and residual stress in a friction stir welded plate of 304L stainless steel. Based on the experimental records of transient temperature at several specific locations during the friction stir welding process for the 304L stainless steel, an inverse analysis method for thermal numerical simulation is developed. After the transient temperature field is determined, the residual stresses in the welded plate are then calculated using a three-dimensional elastic–plastic thermo-mechanical simulation. The effect of fixture release after the welding on the residual stresses is also studied. Comparison with the residual stress fields measured by the neutron diffraction technique shows that the results from the present numerical simulation have good agreement with the test data.
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paper_title: A simple Eulerian thermomechanical modeling of friction stir welding

paper_content:

Abstract A simple three-dimensional thermomechanical model for friction stir welding (FSW) is presented. It is developed from the model proposed by Heurtier et al. (2006) based on a combination of fluid mechanics numerical and analytical velocity fields. Those velocity fields are introduced in a steady state thermal calculation to compute the temperature field during welding. They allow partial sliding between the shoulder and the workpiece, the amount of which is provided as an additional result of the model. The thermal calculation accounts for conduction and convection effects by means of the particular derivative. The complete thermomechanical history of the material during the process can then be accessed by temperature and strain rate contours. The numerical results are compared with a set of experimental test cases carried out on an instrumented laboratory device. The choices for modeling assumptions, especially tribological aspects, are discussed according to agreements or deviations observed between experimental and numerical results. The amount of sliding appears to be significantly influenced by the welding conditions (welding and tool rotational velocities), and physical interpretations are proposed for its evolution.
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paper_title: Analysis of transient temperature and residual thermal stresses in friction stir welding of aluminum alloy 6061-T6 via numerical simulation

paper_content:

Residual stress is lower in friction stir welding (FSW) compared with other melting weldment processes. This is due to being solid-state process in its nature. There are several advantages in utilizing stir welding process. Lower fluctuation and shrinkage in weldment metal-enhanced mechanical characteristics, less defects, and ability to weld certain metals otherwise impractical by other welding processes are to name just a few of these advantages. These have caused an ever increasing attention by the concerned to the process of FSW. In this investigation, three-dimensional numerical simulation of friction stir welding was concerned to study the impact of tool moving speed in relation with heat distribution as well as residual stress. Simulation was composed of two stages. Firstly, thermal behavior of the piece while undergoing the welding process was studied. Heat is generated due to the friction between tool and the piece being welded. In the second stage, attained thermal behavior of the piece from previous stage is considered as inlet heat of an elasto-plastic, thermo-mechanical model for the prediction of residual stress. Also, in the second stage, tool is eliminated and residual stress distribution is found after complete cooling of the piece and disassembly of the clamp. Material characteristic are introduced into the proposed model as temperature-dependent parameters. Obtained residual indicate that heat distribution along thickness varies and is asymmetrical enormously. Moreover, longitudinal residual stress in the weld which increases as speed of process and tool movement ascends. In the prediction of results of residual stress, only heat impact was studied. This was recognized as the main element causing minor difference in results obtained for simulation in comparison with that of actual experiment.
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paper_title: Thermal modelling of friction stir welding

paper_content:

The objective of the present work is to present the basic elements of the thermal modelling of friction stir welding as well as to clarify some of the uncertainties in the literature regarding the different contributions to the heat generation. Some results from a new thermal pseudomechanical model in which the temperature-dependent yield stress of the weld material controls the heat generation are also presented.
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paper_title: Effect of boundary conditions and heat source distribution on temperature distribution in friction stir welding

paper_content:

Welding experiments on Al-6005A have been carried out using a fully instrumented milling machine. The power input was calculated from the measured torque and forces. The thermal cycles were measured at various locations close to the weld centreline. A finite element pseudo-steady-state uncoupled thermal model was developed, taking into account the influence of the welding parameters on the power input. The distribution of the total power input between surface and volume heat sources was also studied. The measured and predicted thermal cycles are in good agreement when proper contact conditions between the workpiece and the backing plate are introduced.
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paper_title: A 3D numerical simulation of different phases of friction stir welding

paper_content:

An adaptive arbitrary Lagrangian–Eulerian formulation is developed to compute the material flow and the temperature evolution during the three phases of the friction stir welding (FSW) process. It follows a splitting approach: after the calculations of the velocity/pressure and temperature fields, the mesh velocity is derived from the domain boundary evolution and from an adaptive refinement criterion provided by error estimation, and finally state variables are remapped. In this way, the unilateral contact conditions between the plate and the tool are accurately taken into account, so allowing one to model various instabilities that may occur during the process, such as the role played by the plunge depth of the tool on the formations of flashes, the possible appearance of non-steady voids or tunnel holes and the influence of the threads on the material flow, the temperature field and the welding efforts. This formulation is implemented in the 3D Forge3 FE software with automatic remeshing. The non-steady phases of FSW can so be simulated, as well as the steady welding phase. The study of different process conditions shows that the main phenomena taking place during FSW can be simulated with the right sensitivities.
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paper_title: Accurate 3D friction stir welding simulation tool based on friction model calibration

paper_content:

Friction Stir Welding (FSW) is one of the most effective solid states joining process and has numerous potential applications in many industries. A FSW numerical tool, based on Forge® F.E software, has been developed. Its main features are an Arbitrary Lagrangian Eulerian (ALE) formulation and an adaptive remeshing procedure based on error estimation. A 3D FSW simulation based on friction models calibration has been presented using Eulerian and ALE formulation. Two friction models have been studied to model friction in the tool-plate interface in aluminium alloy 6061-T6: Norton’s and Coulomb’s. Comparisons with experimental results considering various travel speed has been performed.
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paper_title: An analytical model for the heat generation in friction stir welding

paper_content:

The objective of this work is to establish an analytical model for heat generation by friction stir welding (FSW), based on different assumptions of the contact condition between the rotating tool surface and the weld piece. The material flow and heat generation are characterized by the contact conditions at the interface, and are described as sliding, sticking or partial sliding/sticking. Different mechanisms of heat generation are behind each contact condition, making this study important for further understanding of the real FSW process. The analytical expression for the heat generation is a modification of previous analytical models known from the literature and accounts for both conical surfaces and different contact conditions. Experimental results on plunge force and torque are used to determine the contact condition. The sliding condition yields a proportional relationship between the plunge force and heat generation. This is not demonstrated in the experiment, which suggests that the sticking contact condition is present at the tool/matrix interface.
---
paper_title: Friction Stir Welding and Processing

paper_content:

Abstract Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.
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paper_title: Finite element simulation of material flow in friction stir welding

paper_content:

AbstractA brief summary of recent finite element simulation results for the friction stir welding process is presented. The focus of the present study is on the characterisation of material flow around the rotating tool pin. Material flow patterns predicted by finite element simulations are found to compare favourably with experimental observations. The simulation results also reveal that material particles tend to pass and move behind the rotating pin from the trailing side, rather than both sides, of the pin. Possible variations in the material flow pattern due to variations in process parameters are discussed.
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paper_title: An analytical model for the heat generation in friction stir welding

paper_content:

The objective of this work is to establish an analytical model for heat generation by friction stir welding (FSW), based on different assumptions of the contact condition between the rotating tool surface and the weld piece. The material flow and heat generation are characterized by the contact conditions at the interface, and are described as sliding, sticking or partial sliding/sticking. Different mechanisms of heat generation are behind each contact condition, making this study important for further understanding of the real FSW process. The analytical expression for the heat generation is a modification of previous analytical models known from the literature and accounts for both conical surfaces and different contact conditions. Experimental results on plunge force and torque are used to determine the contact condition. The sliding condition yields a proportional relationship between the plunge force and heat generation. This is not demonstrated in the experiment, which suggests that the sticking contact condition is present at the tool/matrix interface.
---
paper_title: An analytical model for the heat generation in friction stir welding

paper_content:

The objective of this work is to establish an analytical model for heat generation by friction stir welding (FSW), based on different assumptions of the contact condition between the rotating tool surface and the weld piece. The material flow and heat generation are characterized by the contact conditions at the interface, and are described as sliding, sticking or partial sliding/sticking. Different mechanisms of heat generation are behind each contact condition, making this study important for further understanding of the real FSW process. The analytical expression for the heat generation is a modification of previous analytical models known from the literature and accounts for both conical surfaces and different contact conditions. Experimental results on plunge force and torque are used to determine the contact condition. The sliding condition yields a proportional relationship between the plunge force and heat generation. This is not demonstrated in the experiment, which suggests that the sticking contact condition is present at the tool/matrix interface.
---
paper_title: Three-dimensional modeling of the friction stir-welding process

paper_content:

This paper presents an attempt to model the stir-welding process using three-dimensional visco-plastic modeling. The scope of the project is focused on butt joints for aluminum thick plates. Parametric studies have been conducted to determine the effect of tool speeds on plate temperatures and to validate the model predictions with available measurements. In addition, forces acting on the tool have been computed for various welding and rotational speeds. It is found that pin forces increase with increasing welding speeds, but the opposite effect is observed for increasing rotational speeds. Numerical models such as the one presented here will be useful in designing welding tools which will yield desired thermal gradients and avoid tool breakage.
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paper_title: Modelling heat flow around tool probe in friction stir welding

paper_content:

AbstractThe objective of the present paper is to investigate the effect of including the tool probe in the numerical modelling of three-dimensional heat flow in friction stir welding (FSW). The heat flow close to the probe/matrix interface is investigated. In the models presented, the heat is forced to flow around the 'probe hole'. In this manner, the material flow through the probe region, which often characterises other thermal models of FSW, is avoided. This necessitates controlling the convective heat flow by prescribing the velocity field in the narrow shear layer at the tool/matrix interface. As a consequence the sliding, sticking, or partial sliding/sticking condition can be modelled. Six cases are established, which are represented by three stages of refinement of the heat source model, combined with two different contact conditions, i.e. full sliding and full sticking.
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paper_title: Modelling heat flow around tool probe in friction stir welding

paper_content:

AbstractThe objective of the present paper is to investigate the effect of including the tool probe in the numerical modelling of three-dimensional heat flow in friction stir welding (FSW). The heat flow close to the probe/matrix interface is investigated. In the models presented, the heat is forced to flow around the 'probe hole'. In this manner, the material flow through the probe region, which often characterises other thermal models of FSW, is avoided. This necessitates controlling the convective heat flow by prescribing the velocity field in the narrow shear layer at the tool/matrix interface. As a consequence the sliding, sticking, or partial sliding/sticking condition can be modelled. Six cases are established, which are represented by three stages of refinement of the heat source model, combined with two different contact conditions, i.e. full sliding and full sticking.
---
paper_title: Friction Stir Welding and Processing

paper_content:

Abstract Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.
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paper_title: A process model for friction stir welding of age hardening aluminum alloys

paper_content:

In the present investigation, a numerical three-dimensional (3-D) heat flow model for friction stir welding (FSW) has been developed, based on the method of finite differences. The algorithm, which is implemented in MATLAB 5.2, is provided with a separate module for calculation of the microstructure evolution and the resulting hardness distribution. The process model is validated by comparison with in-situ thermocouple measurements and experimental hardness profiles measured at specific time intervals after welding to unravel the strength recovery during natural aging. Furthermore, the grain structure within the plastically deformed region of the as-welded materials has been characterized by means of the electron backscattered diffraction (EBSD) technique in the scanning electron microscope (SEM). Some practical applications of the process model are described toward the end of the article.
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paper_title: 3-dimensional CFD modelling of flow round a threaded friction stir welding tool profile

paper_content:

This paper describes the application of the computational fluid dynamics (CFD) code, FLUENT, to modelling the 3-dimensional metal flow in friction stir welding (FSW). A standard threaded tool profile is used for the analysis and features such as the tool rake angle, heat generation and heat flow are included. The primary goal is to gain a better understanding of the material flow around a complex FSW tool and to demonstrate the effect of the tool rake angle, and weld and rotation speed. The model captured many of the real process characteristics, but gave poor predictions of the welding forces. The model also generated an excessive amount of heat, which led to a large over-prediction in the weld temperature. These shortcomings can be overcome by using a viscosity relationship that includes material softening near the solidus or material slip at the tool interface.
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paper_title: Numerical simulation of three-dimensional heat transfer and plastic flow during friction stir welding

paper_content:

Three-dimensional visco-plastic flow of metals and the temperature fields in friction stir welding have been modeled based on the previous work on thermomechanical processing of metals. The equations of conservation of mass, momentum, and energy were solved in three dimensions using spatially variable thermophysical properties and non-Newtonian viscosity. The framework for the numerical solution of fluid flow and heat transfer was adapted from decades of previous work in fusion welding. Non-Newtonian viscosity for the metal flow was calculated considering strain rate, temperature, and temperature-dependent material properties. The computed profiles of strain rate and viscosity were examined in light of the existing literature on thermomechanical processing. The heat and mass flow during welding was found to be strongly three-dimensional. Significant asymmetry of heat and mass flow, which increased with welding speed and rotational speed, was observed. Convective transport of heat was an important mechanism of heat transfer near the tool surface. The numerically simulated temperature fields, cooling rates, and the geometry of the thermomechanically affected zone agreed well with independently determined experimental values.
---
paper_title: Friction Stir Welding and Processing

paper_content:

Abstract Friction stir welding (FSW) is a relatively new solid-state joining process. This joining technique is energy efficient, environment friendly, and versatile. In particular, it can be used to join high-strength aerospace aluminum alloys and other metallic alloys that are hard to weld by conventional fusion welding. FSW is considered to be the most significant development in metal joining in a decade. Recently, friction stir processing (FSP) was developed for microstructural modification of metallic materials. In this review article, the current state of understanding and development of the FSW and FSP are addressed. Particular emphasis has been given to: (a) mechanisms responsible for the formation of welds and microstructural refinement, and (b) effects of FSW/FSP parameters on resultant microstructure and final mechanical properties. While the bulk of the information is related to aluminum alloys, important results are now available for other metals and alloys. At this stage, the technology diffusion has significantly outpaced the fundamental understanding of microstructural evolution and microstructure–property relationships.
---
paper_title: 3-dimensional CFD modelling of flow round a threaded friction stir welding tool profile

paper_content:

This paper describes the application of the computational fluid dynamics (CFD) code, FLUENT, to modelling the 3-dimensional metal flow in friction stir welding (FSW). A standard threaded tool profile is used for the analysis and features such as the tool rake angle, heat generation and heat flow are included. The primary goal is to gain a better understanding of the material flow around a complex FSW tool and to demonstrate the effect of the tool rake angle, and weld and rotation speed. The model captured many of the real process characteristics, but gave poor predictions of the welding forces. The model also generated an excessive amount of heat, which led to a large over-prediction in the weld temperature. These shortcomings can be overcome by using a viscosity relationship that includes material softening near the solidus or material slip at the tool interface.
---
paper_title: Three-dimensional modeling of the friction stir-welding process

paper_content:

This paper presents an attempt to model the stir-welding process using three-dimensional visco-plastic modeling. The scope of the project is focused on butt joints for aluminum thick plates. Parametric studies have been conducted to determine the effect of tool speeds on plate temperatures and to validate the model predictions with available measurements. In addition, forces acting on the tool have been computed for various welding and rotational speeds. It is found that pin forces increase with increasing welding speeds, but the opposite effect is observed for increasing rotational speeds. Numerical models such as the one presented here will be useful in designing welding tools which will yield desired thermal gradients and avoid tool breakage.
---
paper_title: Numerical simulation of three-dimensional heat transfer and plastic flow during friction stir welding

paper_content:

Three-dimensional visco-plastic flow of metals and the temperature fields in friction stir welding have been modeled based on the previous work on thermomechanical processing of metals. The equations of conservation of mass, momentum, and energy were solved in three dimensions using spatially variable thermophysical properties and non-Newtonian viscosity. The framework for the numerical solution of fluid flow and heat transfer was adapted from decades of previous work in fusion welding. Non-Newtonian viscosity for the metal flow was calculated considering strain rate, temperature, and temperature-dependent material properties. The computed profiles of strain rate and viscosity were examined in light of the existing literature on thermomechanical processing. The heat and mass flow during welding was found to be strongly three-dimensional. Significant asymmetry of heat and mass flow, which increased with welding speed and rotational speed, was observed. Convective transport of heat was an important mechanism of heat transfer near the tool surface. The numerically simulated temperature fields, cooling rates, and the geometry of the thermomechanically affected zone agreed well with independently determined experimental values.
---
paper_title: Modelling heat flow around tool probe in friction stir welding

paper_content:

AbstractThe objective of the present paper is to investigate the effect of including the tool probe in the numerical modelling of three-dimensional heat flow in friction stir welding (FSW). The heat flow close to the probe/matrix interface is investigated. In the models presented, the heat is forced to flow around the 'probe hole'. In this manner, the material flow through the probe region, which often characterises other thermal models of FSW, is avoided. This necessitates controlling the convective heat flow by prescribing the velocity field in the narrow shear layer at the tool/matrix interface. As a consequence the sliding, sticking, or partial sliding/sticking condition can be modelled. Six cases are established, which are represented by three stages of refinement of the heat source model, combined with two different contact conditions, i.e. full sliding and full sticking.
---
paper_title: Modelling heat flow around tool probe in friction stir welding

paper_content:

AbstractThe objective of the present paper is to investigate the effect of including the tool probe in the numerical modelling of three-dimensional heat flow in friction stir welding (FSW). The heat flow close to the probe/matrix interface is investigated. In the models presented, the heat is forced to flow around the 'probe hole'. In this manner, the material flow through the probe region, which often characterises other thermal models of FSW, is avoided. This necessitates controlling the convective heat flow by prescribing the velocity field in the narrow shear layer at the tool/matrix interface. As a consequence the sliding, sticking, or partial sliding/sticking condition can be modelled. Six cases are established, which are represented by three stages of refinement of the heat source model, combined with two different contact conditions, i.e. full sliding and full sticking.
---
paper_title: Numerical simulation of three-dimensional heat transfer and plastic flow during friction stir welding

paper_content:

Three-dimensional visco-plastic flow of metals and the temperature fields in friction stir welding have been modeled based on the previous work on thermomechanical processing of metals. The equations of conservation of mass, momentum, and energy were solved in three dimensions using spatially variable thermophysical properties and non-Newtonian viscosity. The framework for the numerical solution of fluid flow and heat transfer was adapted from decades of previous work in fusion welding. Non-Newtonian viscosity for the metal flow was calculated considering strain rate, temperature, and temperature-dependent material properties. The computed profiles of strain rate and viscosity were examined in light of the existing literature on thermomechanical processing. The heat and mass flow during welding was found to be strongly three-dimensional. Significant asymmetry of heat and mass flow, which increased with welding speed and rotational speed, was observed. Convective transport of heat was an important mechanism of heat transfer near the tool surface. The numerically simulated temperature fields, cooling rates, and the geometry of the thermomechanically affected zone agreed well with independently determined experimental values.
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paper_title: A thermal model of friction stir welding in aluminum alloys

paper_content:

A thermal model of friction stir welding was developed that utilizes a new slip factor based on the energy per unit length of weld. The slip factor is derived from an empirical, linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature and the welding energy. The thermal model successfully predicts the maximum welding temperature over a wide range of energy levels but under predicts the temperature for low energy levels for which heat from plastic deformation dominates. The thermal model supports the hypothesis that the relationship between the temperature ratio and energy level is characteristic of aluminum alloys that share similar thermal diffusivities. The thermal model can be used to generate characteristic temperature curves from which the maximum welding temperature in an alloy may be estimated if the thermal diffusivity, welding parameters and tool geometry are known.
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paper_title: Development of Trivex friction stir welding tool Part 2 – three-dimensional flow modelling

paper_content:

This paper describes the application of the computational fluid dynamics (CFD) code, FLUENT, to modelling the metal flow in friction stir welding (FSW). Building on a two-dimensional model, and preliminary trials with a novel 'Trivex' tool design, discussed in the companion paper immediately before this one, a full three-dimensional model was developed. The model predicted the temperature, and the traversing and down forces, which were compared against experiments. The model incorporated a novel 'slip' boundary condition, based on that developed in two dimensions. A conventional 'Triflute' tool was modelled and compared with the new 'Trivex' tool design. The model correctly predicted that the Trivex tool had lower traversing and down forces than its Triflute counterpart. To assist understanding of the material flow, streamlines around each of the tools were plotted. Ultimately the technique could be used to size the pin features reducing the need for costly experiments.
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paper_title: Experimental and numerical analysis of aluminium alloy 7075-T7351 friction stir welds

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AbstractThis paper describes a systematic series of friction stir welding experiments using aluminium alloy 7075, designed to provide validation data for a numerical model of the process. The numerical model used the commercial computational field dynamics package, FLUENT, and the trials focussed on weld temperature and torque measurements. There were several significant findings that have both practical use and are pertinent to future modelling work. First, the temperature profiles and weld quality were affected by the type of tool material. Second, in thick section welds the material reached temperatures very near to the solidus. As a consequence this limited the heat generation, so the weld power was largely independent of the rotation speed. Third, several of the welds experienced the problem of surface scaling which was exacerbated by high rotation speeds and a high plunge depth. Finally, an empirical equation for predicting the weld power was derived from the experimental power input.
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paper_title: Effect of boundary conditions and heat source distribution on temperature distribution in friction stir welding

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Welding experiments on Al-6005A have been carried out using a fully instrumented milling machine. The power input was calculated from the measured torque and forces. The thermal cycles were measured at various locations close to the weld centreline. A finite element pseudo-steady-state uncoupled thermal model was developed, taking into account the influence of the welding parameters on the power input. The distribution of the total power input between surface and volume heat sources was also studied. The measured and predicted thermal cycles are in good agreement when proper contact conditions between the workpiece and the backing plate are introduced.
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paper_title: Three-dimensional modeling of the friction stir-welding process

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This paper presents an attempt to model the stir-welding process using three-dimensional visco-plastic modeling. The scope of the project is focused on butt joints for aluminum thick plates. Parametric studies have been conducted to determine the effect of tool speeds on plate temperatures and to validate the model predictions with available measurements. In addition, forces acting on the tool have been computed for various welding and rotational speeds. It is found that pin forces increase with increasing welding speeds, but the opposite effect is observed for increasing rotational speeds. Numerical models such as the one presented here will be useful in designing welding tools which will yield desired thermal gradients and avoid tool breakage.
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paper_title: 3-dimensional CFD modelling of flow round a threaded friction stir welding tool profile

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This paper describes the application of the computational fluid dynamics (CFD) code, FLUENT, to modelling the 3-dimensional metal flow in friction stir welding (FSW). A standard threaded tool profile is used for the analysis and features such as the tool rake angle, heat generation and heat flow are included. The primary goal is to gain a better understanding of the material flow around a complex FSW tool and to demonstrate the effect of the tool rake angle, and weld and rotation speed. The model captured many of the real process characteristics, but gave poor predictions of the welding forces. The model also generated an excessive amount of heat, which led to a large over-prediction in the weld temperature. These shortcomings can be overcome by using a viscosity relationship that includes material softening near the solidus or material slip at the tool interface.
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paper_title: Numerical Modeling of Friction Stir Welding: A Comparison of Alegra and Forge3

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NUMERICAL MODELING OF FRICTION STIR WELDING: A COMPARISON OF ALEGRA AND FORGE3 Alma H. Oliphant Department of Mechanical Engineering Master of Science The objective of this research was to evaluate the capabilities of ALEGRA, a Sandia National Labs hydrocode, and Forge3, a Transvalor S.A. product, to accurately model the Friction Stir Welding Process. ALEGRA and Forge3 are discussed in light of the inherent challenges of modeling Friction Stir Welding, and a rotational boundary condition is added to ALEGRA. Results are presented from Friction Stir Welding modeling outputs from both ALEGRA and Forge3. ALEGRA is shown to be incapable of modeling the Friction Stir Welding process, in large part due to its focus on shock propagation, which causes extremely small time steps. Forge3 is shown capable of modeling of the FSW plunge process in a transient manner, but overestimates the temperature profiles 90% to 100% in comparison to experimentally measured values. It appears that the adiabatic boundary condition is the source of much of the error. It is recommended that future work focus on improving estimates of the boundary conditions utilized in the Forge3 model.
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paper_title: A simple Eulerian thermomechanical modeling of friction stir welding

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Abstract A simple three-dimensional thermomechanical model for friction stir welding (FSW) is presented. It is developed from the model proposed by Heurtier et al. (2006) based on a combination of fluid mechanics numerical and analytical velocity fields. Those velocity fields are introduced in a steady state thermal calculation to compute the temperature field during welding. They allow partial sliding between the shoulder and the workpiece, the amount of which is provided as an additional result of the model. The thermal calculation accounts for conduction and convection effects by means of the particular derivative. The complete thermomechanical history of the material during the process can then be accessed by temperature and strain rate contours. The numerical results are compared with a set of experimental test cases carried out on an instrumented laboratory device. The choices for modeling assumptions, especially tribological aspects, are discussed according to agreements or deviations observed between experimental and numerical results. The amount of sliding appears to be significantly influenced by the welding conditions (welding and tool rotational velocities), and physical interpretations are proposed for its evolution.
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paper_title: Analysis of transient temperature and residual thermal stresses in friction stir welding of aluminum alloy 6061-T6 via numerical simulation

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Residual stress is lower in friction stir welding (FSW) compared with other melting weldment processes. This is due to being solid-state process in its nature. There are several advantages in utilizing stir welding process. Lower fluctuation and shrinkage in weldment metal-enhanced mechanical characteristics, less defects, and ability to weld certain metals otherwise impractical by other welding processes are to name just a few of these advantages. These have caused an ever increasing attention by the concerned to the process of FSW. In this investigation, three-dimensional numerical simulation of friction stir welding was concerned to study the impact of tool moving speed in relation with heat distribution as well as residual stress. Simulation was composed of two stages. Firstly, thermal behavior of the piece while undergoing the welding process was studied. Heat is generated due to the friction between tool and the piece being welded. In the second stage, attained thermal behavior of the piece from previous stage is considered as inlet heat of an elasto-plastic, thermo-mechanical model for the prediction of residual stress. Also, in the second stage, tool is eliminated and residual stress distribution is found after complete cooling of the piece and disassembly of the clamp. Material characteristic are introduced into the proposed model as temperature-dependent parameters. Obtained residual indicate that heat distribution along thickness varies and is asymmetrical enormously. Moreover, longitudinal residual stress in the weld which increases as speed of process and tool movement ascends. In the prediction of results of residual stress, only heat impact was studied. This was recognized as the main element causing minor difference in results obtained for simulation in comparison with that of actual experiment.
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Title: Numerical Modeling of Friction Stir Welding Process: A Literature Review

Section 1: Friction Stir Welding Process
Description 1: Describe the fundamental principles of friction stir welding (FSW), its phases, and the process mechanics.

Section 2: Process Parameters
Description 2: Discuss the main variables affecting the FSW process such as welding traverse speed, tool rotational speed, downward force, tilt angle, and tool design.

Section 3: Weld Microstructure
Description 3: Describe the thermomechanical interactions during FSW and the resulting microstructural regions like TMAZ and HAZ.

Section 4: Numerical Modeling
Description 4: Provide an overview of numerical modeling methods for FSW, including their benefits in visualizing and optimizing the process.

Section 5: Heat Generation
Description 5: Detail the heat generation mechanisms in FSW, including frictional heating and plastic deformation, and the influence of different contact conditions.

Section 6: Contact Condition
Description 6: Explain the critical role of contact conditions in numerical models, including Coulomb friction law and different states like sliding, sticking, and partial sliding/sticking.

Section 7: Heat Dissipation
Description 7: Discuss the various ways heat is dissipated during FSW, including through the tool, top surface, and bottom surface of the workpiece.

Section 8: Metal Flow
Description 8: Describe the material flow during FSW, its complexities, and the importance of understanding flow characteristics for optimal tool design.

Section 9: Numerical Flow Modeling
Description 9: Discuss methods and techniques for numerical modeling of metal flow in FSW, including both 2-D and 3-D analyses.

Section 10: Material Constitutive Behaviour for Flow Modeling
Description 10: Explain the material constitutive behavior required for accurate flow modeling in FSW, highlighting the dependency on temperature and strain rate.

Section 11: Numerical Simulation of FSW
Description 11: Provide examples of numerical simulations of the FSW process and their outcomes, such as the impact of tool movement speed on heat distribution and residual stress.

Section 12: Conclusions
Description 12: Summarize the importance of FSW modeling, the current challenges, and the potential future advancements that could make numerical simulation a viable optimization tool.