In a more sophisticated way, De Vuyst et al. ,  used the coupled thermo-mechanical FE code MORFEO to simulate the ‡ow around tools of simpli…ed geometry. The rotation and advancing speed of the tool were modeled using prescribed velocity …elds. An attempt to consider features associated to the geometrical details of the probe and shoulder, which had not been discretized in the FE model in order to avoid very large meshes, was taken into ac- count using additional velocity boundary conditions. In spite of that, the mesh used resulted to be large: a mesh of roughly 250,000 nodes and almost 1.5 million of linear tetrahedral elements was used. A Norton-Ho¤ rigid-visco-plastic constitutive equation was considered, with averaged values of the consistency and strain rate sensitivity constitutive parameters determined from hot torsion tests performed over a range of temperatures and strain rates. The computed streamlines were compared with the ‡ow visualization experimental results obtained using copper marker material sheets inserted transversally or longitudinally to the weld line. The simulation results correlated well when compared to markers inserted trans- versely to the welding direction. However, when compared to a marker inserted along the weld center line only qualitative match could be obtained. The correlation could have been improved by modeling the e¤ective weld thickness of the experiment, using a more realistic material model, for instance, by incorporating a yield stress or temperature dependent prop- erties, more exact prescription of the velocity boundary conditions or re…ning the mesh in speci…c zones, for instance, under the probe. The authors concluded that it was essential to take into account the e¤ects of the probe thread and shoulder thread in order to get realistic ‡ow …elds.
The analysis of the experimental welding of the forged panels of alloys AI 5083 and AI 7075 in the state of the maximum-hardness values showed that the elongation of the welded joint is bigger than that of the parent material, which can be explained with the formation of a structure with small grains in the mixed zone.A coupled thermo-mechanical model was developed to study the temperature fields and the plunge force of alloy AI 5083 under different rotating speeds: (300, 400 and 500) r/min during the FSW process of the plunge stage. The heat transfer through the bottom surface of the welding plate is controlled with the heat transfer coefficient of 1000 W/(m2 K). A constant friction coefficient of 0.3 is assumed between the tool and the welding plate and the penalty contact method is used to model the contact interaction between the two surfaces. The heat convection coefficients on the surface of the welding of 200 °C. the temperature fields in the transverse cross-section near the tool/matrix interface after 22.8 s, when the plunge speed is 12 mm/min and the rotation speed is 400 r/min. The temperature field is symmetric.
The material flow in the FSW of aluminum alloy T-joints was investigated by Fratini et al. . They varied the most relevant technological and geometrical parameters in both numerical simulations and experiments. Their research investigated the metal flow, a wide range of experimental tests and observations. They used a thin brass foil as marker, placed at the interface of the two blanks to be welded. Some relevant conclusions on the process mechanics and on the actual material flow determining the material bonding are outlined, permitting an insight into the FSW of T-joints. A 3D elastic-plastic and coupled thermo-mechanical FE model for FSW of 7075 aluminum alloy plate was developed based on the dynamic explicit code ABAQUS/explicit . The FSW process of 7075 aluminum alloy plate was simulated and the material flow behavior was analyzed. The results showed that in the horizontal direction of the plate, two patterns of material migration are produced: (1) the material rotates with the tool and finally deposits the tentative cavity behind the pin; (2) the material transfers in the mode of laminar flow. A coupled thermo-mechanical viscoplastic FE model based on the character of FSSW was presented by Gao et al. . The model was calibrated by comparing the temperature history obtained from the simulation with experimental data and subsequently used to investigate the effective strain distribution in the weld zone as well as the material flow and the shape of the stir zone. A coupled thermal/material flow model of the FSW process was developed and applied to the joining of Sc-modified aluminum alloy (7042-T6) extrusions . The model revealed that surface material is pulled from the retreating side into the weld zone where it is interleaved with in situ material. Due to frictional contact with the shoulder, the surface material is hotter than the in situ material, so that the final weld microstructure is composed of bands of material with different temperature histories. Based on the numerical simulation and on thermal analysis data from differential scanning calorimetry, a mechanism for the formation of onion rings within the weld zone was presented.
The forming behavior of tailor welded blanks (TWBs) has been widely studied since its develop- ment. In the numerical simulation studies, the TWBs are modeled as blanks composed of two different materials, and often, the presence of the weld bead is neglected in its FE discretization. The inﬂuence of the weld bead shape on the formability of FSW TWBs has been analyzed  . Several FE meshes were constructed in order to represent different weld bead geometries and numerical simulations of the cylindrical cup drawing were performed. Strong inﬂuence of the weld bead shape on the form- ability of the TWBs was observed when the weld was in overmatch relatively to the base material, and little inﬂuence when the weld was in under-match condition. An integrated model was utilized to pre- dict thermo-mechanical behavior during the FSW of an aluminum alloy  . A FE code, ABAQUS, was employed to solve the governing equations of heat conduction and plastic deformation, while a rigid- viscoplastic material behavior was utilized and the effects of different thermal and mechanical bound- ary conditions were considered in the simulation. A fully coupled thermo-mechanical 3D FE model was developed in ABAQUS/Explicit to analyze the primary conditions under which the cavity behind the tool was ﬁlled  . The model accounted for compressibility by including the elastic response of the aluminum matrix. The different thermo-mechanical states in the colder, stiffer far-ﬁeld matrix and the hotter, softer near-ﬁeld matrix resulted in contact at the tool/matrix interface, thus no void forma- tion was observed. Alfaro et al.’s paper  addressed the problem of numerically simulating the FSW process. Due to the special characteristics of the FSW (e.g. the high speed of the rotating pin, very large deformations, etc.), FE methods encounter several difﬁculties. Meshless methods somewhat alleviate these problems, allowing for an updated Lagrangian framework in the simulation. In particular, the accuracy will not be affected by mesh distortion. Some examples were shown on the performance of the Meshless methods.
The heat transfer process is one of the most important aspects in the FSW study. A good understanding of the heat transfer process in the work piece can be helpful in predicting the thermal cycles in the welding work piece, and the hardness in the weld zone, subsequently, can be helpful in evaluating the weld quality. In this process, the heat is originally derived from the friction between the welding tool (including the shoulder and the probe) and the welded material, which causes the welded material to soften at a temperature less than its melting point. The softened material underneath the shoulder is further subjected to extrusion by the tool rotational and transverse movements. It is expected that this process will inherently produce a weld with less residual stress and distortion as compared to the fusion welding methods, since no melting of the material occurs during the welding. Despite significant advances in the application of FSW as a relatively new welding technique for welding, the fundamental knowledge of thermal impact and thermomechanicalprocesses are still not completely understood. To study the variations of transient temperature and frictional heat developed in frictionstirwelding of 304L stainless steel plates, detailed three-dimensional nonlinear thermal and thermo-mechanical simulations are performed for the FSW process using Ansys
Riahi (2010) in this research residual stress is lower in frictionstirwelding (FSW) compared with other melting weldment processes. This is due to being solid-state process in its nature. There are several advantages in utilizing stirwelding process. Lower fluctuation and shrinkage in weldment metal enhanced mechanical characteristics, less defects, and ability to weld certain metals otherwise impractical by other weldingprocesses are to name just a few of these advantages. 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. Liu a (2013) In their research, the 4 mm thick 6061-T6 Aluminium alloy was self-reacting frictionstir welded at a constant tool rotation speed of 600 r/min. The specially designed self-reacting tool was characterized by the two different shoulder diameters. The results of transverse tensile test indicated that the elongation and tensile strength of joints increased with increasing welding speed. The defect-free joints were obtained at lower welding speeds and the tensile fracture was located at the heat affected zone adjacent to the thermal mechanically affected zone on the advancing side.
Theoretical and experimental evaluations of the residual stresses and thermal histories of dissimilar frictionstirwelding of Aluminium Alloys 5058 and 6061was researched (Jamshidi et al., 2012). A three-dimensional model was employed and ABAQUS software was used for FE analysis (Abbasi et al., 2015; Ikumapayi et al. 2015),  on AA6061-T6. The model results were compared with the experimental data and there was a reasonable agreement between the two which indicated that welding fixtures affect the tensile residual stresses significantly. In the same vein, (Raouache et al., 2016) presented the effect of the tool geometries on thermal analysis of the frictionstirwelding. In this presentation, COSMOL MULTIPHYSICS was used in the investigation and analysis of temperature distribution of workpiece and tool during FSW operation. 3-Dimensional FE was developed to study the thermal transient as also demonstrated(Oyinbo et al., 2015). It was also established that analyzed results were the same as the one found in the literature. It was also concluded that as the temperature increases, holding time and speed of rotation also increase. The effects of thermal boundary conditions of 6.35mm thick plates of AA7050-T7 was conducted during FSW conducted by (Upadhyay and Reynolds, 2010). Welding process was carried out at a sub-ambient temperature of – 25 0 C, this temperature measurement was made in the probe center and the least
Some studies are conducted earlier by researches to investigate the effect of residual stress on work- piece. Zhu and Chao (2004) developed a three-dimensional nonlinear thermal and thermo-mechanical simulations using finite element analysis code–WELDSIM on 304L stainless steel. They reported that the maximum temperature during the FSW is on the weld line and within the tool shoulder and the residual stress on the welds decreased significantly after fixture release as compared to those before fixture release. Chen and Kovacevic (2003) proposed a three-dimensional model based on finite element analysis to understand the thermo-mechanical process in the butt-welding of AA 6061-T6. They observed that the residual stress was greater in the longitudinal direction than that of the lateral. Dattoma et al. (2009) evaluated the residual stress fields in similar and dissimilar joints and they showed that in thicker joints very high longitudinal stresses were present and adequate shoulder geometries resulted in reduction of residual stress values. Staron et al. (2004) conducted experimental study on residual stress states in FSW joints and they are successful in reducing the tensile residual stress in the weld zone by induction of large compressive stresses through mechanical tensioning.
Latest generation of Al- Li alloys have considered as a futuristic materials for aerospace and spacecraft due to their inherent properties . However, the joining of these materials by conventional fusion welding is not recommended due to loss of alloying element as well as loss of joint strength. Frictionstirwelding (FSW) is an ideal joining process for Al-Li alloy. It is a widely growing joining process due to energy efficient, environment-friendly, economically effective and user-friendly operation. It was invented in 1991 by W. Thomas . In the early stage it was used only for the low melting point of materials but gradually it has applied almost all metals. Sound welding dependent on proper thermal management of FSW. It is controlled by selecting proper parameters. Many researchers have been working to enhance the mechanical properties by applying, hybrid processes and various backing plate with different thermal diffusivity and improved tool design.
For the assembled parts of workpiece and the hybrid PCBN tool, meshing was applied in a way that nodes between two diferent parts are connected. Multiple parts connections have been achieved in ANSYS Design Modeller by convert- ing diferent designed parts into one part using the function (Form new part). Patch conirming method has been used in order to control the growth and smoothness and to obtain an accurate surface meshing. Tetrahedrons assembly mesh- ing has been employed to cope with the complex connec- tion between the tool and workpiece. Minimum face sizing of 0.1 mm has been applied in the tool/workpiece contact region to obtain a very ine mesh and thus all the physical and non-linear properties can be captured. Coarser mesh (larger cell) has been represented elsewhere in the geometry where only the heat transfer occurs. To obtain a ine surface transition mesh on curved and normal angles, the advanced size function curvature has been employed with a growth rate of 1.1. The solution convergence and stability are highly dependent up on the mesh quality, unsuitable mesh can cause in an unexpected description for the model phys- ics outputs. For checking mesh quality, several metrics have been addressed before proceeding to model boundary condi- tions. The most important metric mesh in which any devia- tion from the standard can signiicantly afect the numerical analysis are: Aspect ratio, Skewness and Orthogonal quality.
process creates a characteristic asymmetry between the adjoining sides . FSW process demonstrated to very little distortions and the generated residual stresses are proved to be particularly low, compared to the traditional weldingprocesses [3–5]. The Frictionstir welded material produces three different areas: the weld nugget, the thermo- mechanically affected zone and the external heat affected zone. Thermo-mechanical plasticized zone is produced by friction between the tool shoulder and the top plate surface and by contact of the neighbouring material with the tool edges, inducing plastic deformation . Fig.1 shows the working principle of FSW . FSW joints usually consist of four different regions as shown in Fig.2. They are: (a) unaffected base metal (b) heat affected zone (HAZ) (c) thermo-mechanically affected zone (TMAZ) and (d) frictionstir processed (FSP) zone [8-9]. The formations of above regions are affected by the material flow behaviour under the action of a rotating non-consumable tool. However, the material flow behavior is predominantly influenced by the FSW tool profiles, FSW tool dimensions and FSW process parameters . The tool pin and shoulder are helpful for heat generation, and material by stirring producing the joint. In this process no melting occurs and the heat is generated internally by means of friction between the material-tool interface and the plastic deformation takes place without pre or post heating .
welding parameter change, the welding conditions get unsteady and the deviations of welding condition from proper values could occur. We should select the parameter with priority, because some parameters have greater inﬂu- ence on joint properties than other. The objective of this work is to clarify the inﬂuence of welding parameter change on joint properties. Nonlinear joints were made by keeping the selected parameter in permissible range. Tensile tests were carried out by specimens prepared from the joints. The eﬀects of un-selected parameter on the tensile properties were clariﬁed by the selection of the parameter with priority. These results will show the guidelines for high quality joints at nonlinear welding.
The force exerted by the tool between the intersections of weld plate should be considered during welding because when the axial force is high tool erosion and tool breakage might occur at extreme cases. By using dynamometer the force on tool can be calculated and this could be useful to predict the defect formation . When force is exerted by the tool, internal pressure is created at the bottom of tool shoulder. When the pressure gets higher the material is removed as flash and the joint area gets thinner, whereas when the pressure is low void occurs. At low traverse speed, weld is performed on a stainless plate and the peak temperature distribution on advancing side and retreating side were calculated. It is found that the peak temperature at the advancing side is more than the retreating side [46, 47]. However this result is similar to most of the alloys of aluminum [48-50]. At the edge of the tool shoulder the peak temperature will be high. Thermal cycles might affect the microstructure of welded materials. Sometimes it leads precipitation growth and dissolution of grain [51-54]. Cooling rates also affects the grain size particularly in age hardenable alloys. In high carbon steels the cooling rate influences the formation of martensite. When the traverse speed decreases, the cooling rate also decreases with the decrease in peak temperature. In order to avoid martensite formation low traverse speed with low rotational speed should be processed [55- 57].
FrictionStirWelding (FSW) is widely applied to aluminium alloy joints to find a wide range of industrial applications to produce lightweight parts in shipbuilding, aerospace, automotive and other manufacturing industries. Aluminium alloys welded with conventional processes are very susceptible to weld cracking, depending on the alloying element. Fusion welding of aluminium is generally assumed to be more difficult than welding steel due to oxide, reflectivity, low melting point alloying elements, and so on. Also, the high expansion coefficient is sensitive to the distortion, and the shrinkage of the aluminium alloy is an iron alloy. FSW can be used to combine all common aluminium alloys, including the 2xxx, 7xxx, and 8xxx series, which are typically challenging or impractical, using a common melting welding process. 1
Park Hwa Soon et al. studied frictionstirwelding of oxygen free copper and 60% Cu- 40% Zn copper alloy (60/40 Brass). They varied spindle rotational speed from 500 RPM to 2000 RPM and Tool traverse speed from 500mm/min to 2000mm/min. They obtained defect free joints over a wide range of welding conditions of tool rotational speed 1000 RPM to 2000 RPM and tool traverse speed from 500mm/min to 2000mm/min. They showed the hardness (Hv.) and tensile strength increases as tool traverse speed increases.
Traditionally, the FSW tool consists of a shoulder, which sits on the surfaces of the materials being welded, and a smaller pin, usually called probe, that almost fully penetrates the materials. While the tool rotates and travels along the joint surfaces, the shoulder keeps the softened materials down, preventing them from escaping. When the materials are softened, deformed and plasticized they generate the majority of the heat input of the process. The friction between the rotating shoulder and the welded material also provides additional heat input into the weld. Inside the materials, the probe breaks up the original surfaces of the joint and mixes them together. In order to achieve a fully penetrated joint the probe must penetrate to at least 0.5 mm from the bottom surface of the materials. The probe is commonly threaded in order to provide a downward push to the material, which thwarts pores and voids from forming . The design of the tool has been intensely researched and in some areas, conventional tools with flat shoulders and threaded pins have given way to other innovative shapes such as conical and scrolled shoulders and taper and plain probes .
Venkateswarlu et al.  carried out study on Aluminum alloy AA 2219 which is used for light weight structural applications. He investigated the influence of the base metal on characteristics of joints at different heat treated conditions of AA 2219 – T87 and AA 2219 – T62. He observed that for two different types heat treated condition joints, the elongation of the joint as well as the joints failure location characteristics varies. It was also observed that the joint efficiency of 2219 – T87 weld was higher than the 2219 – T86 welds. From Figure 4 and Figure 5, it is clearly seen that the tensile and yield strength of AA 2219 – T87 FrictionStir Welded joints are higher than the AA 2219 – T62 state of the welds. From Figure 6 and Figure 7 it is observed that the microstructural behaviour of both differently heat treated alloys, TMAZ and HAZ grain size of T87 welds are more elongated and coarser than the T62 welds.
Frictionstirwelding (FSW) is a solid-state joining process, invented at TWI Cambridge, involves joining or welding of 2 materials without using any filler material. This process has developed remarkably during the last 2 decades. FSW benefits over conventional welding techniques, along with growing industrial demands due to the absence of bulky filler material leading to lightweight designs. FSW found its way into becoming one of the fascinating engineering subjects of today. This method is used for welding similar and dissimilar materials together. Due to increase in polymeric material’s consumption in the industry, the possibility of increasing polymeric material welding received a considerable share of interest. There is very limited research done on po lymeric welding with FSW technique. This article reviews previous studies which were focused on welding parameters for different polymeric materials and are then analyzed. The main focus of this article is on welding polymers using FSW technique, welding strength, tool geometry and to observe and analyze the conditions under which optimum results of FSW process is obtained.
For the processes mentioned above, detailed attention is given at the quality of the joints. It should be noted that, both basic and complex configurations are being used for general assembly of the joining applications and also extrusions. The most basic joint design employed by researchers is the lap weld and partial penetration butt weld, which are both intrinsic for high volume production processes.
Scanning electron microscopy (SEM)-Energy Dispersive Spectroscopy (EDS) (model: JEOL JSM- 6048LV) has been used to identify the constituents of the material of work piece. Figure 1 shows the elements present in the work piece and their percentage. It is observed that 99.45 percent of the element is aluminium. The alloying elements found in the work piece are titanium, vanadium, chromium, manganese, iron, and zinc. During the FSW process, high stress is induced in the tool. The tool has been prepared with H-13 tool steel to get high strength and tool rigidity during welding. After the manufacturing of the tool, it was oil quenched to increase the hardness of the tool. For present work, three types of tools have been used for experimentation: threaded pin tool, straight pin tool and taper pin tool (Figure 2). The shoulder of each of the tool is 16 mm in diameter. The pin length is kept 5.7 mm for all the tools. 0.3 mm clearance is given to avoid any interference with the backing plate during welding. The straight pin tool is having the pin of diameter 6 mm throughout the length. The taper tool is made with the head of the pin as 5 mm and bottom as 10 mm. The threaded pin tool is made having 6 mm nominal diameter. Pin of each tool is given a slot on two sides to enhance the movement of the work piece material around tool pin.