FrictionStirWelding (FSW) is a solid state welding process that uses a third body (tool) to join two faces of the work pieces. Heat is generated between the tool and work piece material due to friction of the tool shoulder with the work piece surface. This leads to rise in temperature which makes the material soft near the FSW tool. Then, both the work piece materials mechanically intermix at the place of the joint to produce the welding. FSW has been successfully used to join similar as well as dissimilar materials. It has also been effectively used to join materials that are difficult-to-weld materials by conventional fusion welding methods. Fusion welding when used to join dissimilar metals leads to defects like lack of fusion, distortion, crack formation, incomplete penetration and undercut. FSW, being solid state welding process, can successfully eliminate most of the defects which occur due to melting of material during welding. Some of the important parameters in FSW are tool rotation speed, transverse speed, tool pin dimension, tool tilt angle, offset of the tool from weld line and tool pin profile. From literature survey it was observed that these parameters affect the quality of weld. So, the influence of the parameters is needed to be established on the weld quality. In this context, the present work highlights the significance and effect of tool rotation speed, welding speed, tool pin profile and offset of the tool on weld quality. Different destructive and non-destructive tests have been carried out on the weld to get insight into the weld and its properties. Frictionstir spot welding (FSSW) is a type of FSW, which is used to create a spot weld. The effect of tool rotation speed, dwell time and tool pin dimension has been investigated on spot welding of different materials. Three types of welding have been done in FSSW: similar metals, dissimilar metals and metal-polymer. Face centred central composite design of response surface methodology has been implemented to design the experimental layout for different experiments. Tensile strength test, bending strength test, visual inspection, radiography test and Vickers hardness test are the major tests that have been implemented on the weld to analyse the weld quality. Analysis of variance has been used to analyse the data, find the significant and non-significant parameters and estimate their effect.
The joining of dissimilar AA2024 and AA6061 aluminium plates of 5mm thickness was carried out by frictionstirwelding (FSW) technique. Optimum process parameters were obtained for joints using statistical approach. Five different tool designs have been employed to analyse the influence of rotation speed and traverse speed over the microstructural and tensile properties. In FSW technique, the process of welding of the base material, well below it’s melting temperature, has opened up new trends in producing efficient dissimilar joints. Effect of welding speed on microstructures, hardness distribution and tensile properties of the welded joints were investigated. By varying the process parameters, defect free and high efficiency welded joints were produced. The ratio between tool shoulder diameter and pin diameter is the most dominant factor. From microstructural analysis it is evident that the material placed on the advancing side dominates the nugget region. The hardness in the HAZ of 6061 was found to be minimum, where the welded joints failed during the tensile studies.
The welding tool is the key part of the FrictionStirWelding (FSW) process. It is well known from literature that the shoulder of the tool is the main source of heat generation. It confines the material expulsion and moves the material at the contact interface. The pin is the secondary heat source and its main function is to stir and mix the material from both sides of the joining line. The geometry of both the shoulder and pin has a significant influence on the weld formation, weld quality, and weld mechanical properties and so on. Extensive studies on the effect of tools were carried out by experiments [1-9]. Hattingh, et.al  systematically examined and reported influences of tool geometry factors on weld tensile strength. Six geometric factors were studied: number of flutes, flute angle, flute depth, pin taper angle, pin diameter and thread pitch. The data indicated that the most successful tool designs were likely to incorporate three tapered flutes, a pin diameter taper and have a thread form with a pitch of around 10% of the pin diameter and perhaps 15% of the plate thickness.
The losses in the process of FrictionStirWelding resulting from the effects of microstructure are represented in the difference between the power input and the value of the generated heat which is profitable in the welding process. Friction between the workpiece and the tool is one of the main sources of heat generation in the frictionstirwelding process. From an analytical point of view, the total heat generation Qtotal that is basically resulting by friction can be distinguished in the generated heat amount under the tool shoulder Q1 and the generated heat amount around the tool pin Q2 in addition to the generated heat amount under the tool pin Q3.  It is worth mentioning here that the tool shoulder plays a major role in generation of heat when dealing with low thickness workpieces while in the case of high thickness workpieces the tool probe shows more activities. Besides, the pressure under the shoulder is boosted either by value of the applied force or the shoulder form which both affect the heat generation. Localised plastic deformation is the other main source to heat generation, which occurs in the tool faying layers of workpiece. Energy of deformation is divided into two parts; the first is stored in the material microstructure, and however, the other is transformed to heat. In spite of that, there are no experimental measurements for these two parts, but according to the numerical modeling, the values of the acquired heat from this plastic deformation fluctuate from 2% to 20%.
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.
Since FSW is performed on steels an important factor to be considered is corrosion properties. If the weld shows homogeneous electrochemical potential then there is possibility of minimal corrosion, without considering environmental reactions. When salt spray test is conducted on HSLA steel no significant weight loss or tendency to pit is seen [79,102]. Studies research in this relevant field is very limited and should take this property as serious and solutions should be found out. This is because the chemical composition of the weld region is identical to that of the plates. Tool wear in FSW of steels occurs because of high temperature evolved during welding and when tool is plunged into the work plate. When tool is plunged initially into the workpiece, friction occurs between the tool and workpiece [93, 94]. Possibility of removal of tool material at the shoulder edge and deformation tool at high temperature can change the dimension. Tools can be replaced after 1.5-2m after weld . When quenched and tempered C-Mn steel was welded using PCBN tool, very little wear was observed 6m of weld . If the hardness of the tool is high then the nature of brittleness definitely will be higher, so tempered steels with good ductility gives the tool life longer . Tool wear can be controlled by selecting proper tool for welding and most preferably using alloy elements which can withstand high temperature. Dimension and structure of Tool design is also an important factor, which favors tool wear. Even a good tool design with proper process parameter [100,104] can contribute in reducing the tool wear. Preheating the tool and workpiece will improve the weld quality and tool wear will be minimal. Further more research is needed to concentrate in this area, because the cost of tool is also a constraint for performing welding. If the life of tool is limited and needs often replacement, then cost of welding seems to hurdle.
The heat inputs, temperatures, material flow distributions and the resulting local and overall tensile properties were compared for FSW in similar and dissimilar combinations of 2017-T6 and 6005A-T6 aluminium alloys . Predictions of a 3D FE model of the tensile test transverse to the weldline were assessed towards local deformation fields measured by digital image correlation. Deformation systematically localises on the weakest HAZ, which is on the 6005A side in joints with 2017-T6. The use of FSW on plastics has had very limited success due to their thermal and viscoelastic properties. Viblade is a new variant of FSW for plastics; this welding process heats the workpiece material by a blade and a shoulder which vibrate in a linear reciprocating motion parallel to the joint line. Design of Experiments (DoE) was used to investigate the influence of the process parameters and blade geometry on the width of HAZ and on the mechanical resistance of the joint . Furthermore, a 2D FE thermal analysis was developed to analyze the thermal phenomena involved in the process. A new nonlinear time reversal technique was presented for the detection and localization of a scattered zone (damage) in a multi-material medium . In particular, numerical findings on FSWed aluminum plate-like structure were reported. Damage was introduced in the HAZ and modeled using a multi-scale material constitutive model (Preisach-Mayergoyz space). Studies were conducted for two different transducer configurations. Particular attention was devoted to find the optimum time-reversed window to be re-emitted in the structures. The methodology was compared with traditional time-reversal acoustics (TRA), showing significant improvements.
Visual inspection of the specimens revealed various defects such as tunnel and voids in the weld as shown in Figure 2. The type and size of these defects can be attributed to the lack of penetration resulted from insufficient material flow un- der and around the pin. This is mainly due to the low-or excess heat input which, in turn, did not permit the tool to fill the zone behind the pin. This can be concluded considering that most of the observed defects were located at the welding line and/or shifted to the AS in agreement with prior studies  . However, the slipping of metal on the pin is considered another incentive for defects to form at the advancing zone as observed by Leitão et al. .
technique; two types of defects have been detected including weld root defect at the weld joint bottom and kissing bond defect at the AS of the weld. The first macrocrack (weld root defect) which starts from plate back and reach 2 mm length into the SZ as shown in Fig. 6a can be attributed to the lack in material flow as a result of high traverse speed. This type of defect coincides with previous study by Stevenson et al.  which specified as weld root defects resulted from the lack in plunge depth of the FSW tool. The insufficient heat input accompanied by the lack in material flow may be caused in a stagnant zone formation as proved by modeling studies . The material in this region will be vulnerable to crack formation under the normal plunge force, so any uneven surface or sharp edge will act as a stress concentration point as labeled in Fig. 6a. The second crack on the AS of W 2D at the weld root as
Thermal and mechanical models developed in the  are used as base models for carrying out parametricstudies. The very first step is to identify important independent input factors & response variables. Response variables selected are: (a) Maximum temperature T, (b) residual stress R. Input variables affecting T are: (a) Heat input H, (b) welding speed (S) and variables affecting are: H, S and clamping location (C). Identification of the range and the specific levels at which selected factors have to be varied. Table I lists the process parameters, their range and selected levels used in this study for maximum temperature T and residual stress R.
Frictionstirwelding (FSW) is a solid state joining method in which the base metals do not melt. Its advantages compared to conventional welding methods include producing welds with higher integrity, minimum induced distortion and low residual stress. FSW is used largely for aluminium alloys, but recent developments have focused on higher temperature parent mate- rials such as steel. Modelling of frictionstirwelding, particularly for high-temperature alloys, is a challenge due to the cost and complexity of the analysis. It is a process that includes material flow, phase change, sticking/slipping and complex heat exchange between the tool and workpiece. A review of numerical analysis of FSW is available in  He et al. Many studies have been carried out on FSW modelling of aluminium alloys; however, FSW modelling of steel is still limited. Nandan et al.  used a 3- D numerical analysis to simulate heat transfer and material flow of mild steel during FSW. In their work, the viscosity was calcu- lated from previous extrusion work where the range in which steel can experience flow was rated from 0.1 to 9.9 MPa.s. Heat was mainly generated from viscose dissipation and frictional sliding in the contact region between the tool and the workpiece and was controlled by a spatial sticking-sliding parameter based on the tool radius. There has also been extensive work done on modelling of DH36 mild steel carried by Toumpis et al. . In their model, the viscoplastic thermo-mechanical behaviour was characterised experimentally by a hot compression test. They established a 3D thermo-fluid model to simulate the material flow, strain-rate and temperature distribution. Micallef et al.  carried out work on CFD modelling and calculating the heat flux of FSW DH36 6-mm plates by assuming full sticking conditions * M. Al-moussawi
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.
A constantly rotated non-consumable cylindrical-shouldered tool with a profiled probe is transversely fed at a constant rate into a butt joint between two clamped pieces of butted material. The probe is slightly shorter than the weld depth required, with the tool shoulder riding atop the work surface. Frictional heat is generated between the wear- resistant welding components and the work pieces. This heat, along with that generated by the mechanical mixing process and the adiabatic heat within the material, cause the stirred materials to soften without melting. As the pin is moved forward, a special profile on its leading face forces plasticised material to the rear where clamping force assists in a forged consolidation of the weld. This process of the tool traversing along the weld line in a plasticised tubular shaft of metal results in severe solid state deformation involving dynamic re-crystallization of the base material.
In 1991 the welding institute of UK innovates a new weld process which is named as Frictionstirwelding (FSW) by its name itself, it signifies that process can be accomplished by the heating generation between the tool and the Workpiece due to friction and plastic deformation of workpiece take place.  Later with the progressive develop the field of material technology and computation plentiful research has been done via experimentally and computationally. Rodes et al 1997 7075 Al plate has been successfully joined by frictionstir techniques. Unlike fusion welding, this is a solid-state process with no evidence of melting. The weld is characterized by a recrystallized nugget having a 2-4 pm grain size.
Frictionstirwelding (FSW)is a solid-state process that utilizes localized heat generated between a non-consumable rotating tool and the work piece to create a joint. Seminal investigations have established the feasibility of FSW copper over a range of parameters. In this method, the plates-to-be-welded clamped together rigidly in butt or overlapcondition and a stirring tool with a suitable geometry movesalong them, while the pieces-to-be-joined are moved over eachother in conventional frictionwelding method. The stirring tool Fig.1 rotating at a high rate is plunged into the clamped plates causing friction. The heat caused by the friction between the tool shoulder and the work piece results in an intense local heating that does not melt the plates to be joined, but plasticizes the material around the tool.The shoulder of the tool also prevents the plasticized material from being expelled from the weld. The friction at the pin surface provides additional frictional heat to the work pieces to a lesser extent.
FSW of steel is expected to deliver substantial commercial and technical benefits to the marine manufacturing sector such as reduced pre-weld preparation and re-work, manpower savings, scope for redesign of assembly lines, and low distortion, high quality welds of excellent fatigue properties. In one example from FSW of aluminium, Norwegian shipyard Fjellstrand reported that “using prefabricated FSW panels has enabled a 40% increase in production capacity and turn-over at the yard”. Issues associated with setup, fixture and tooling costs along with reduced health and safety, training, consumable and material usage costs compared to conventional fusion welding techniques should also influence the introduction of this innovative welding process in industry if it can be transferred into welding steel. There are a number of currently identified obstacles, deeper scientific understanding of the process on steel, engagement with the shipbuilding industry, use of fillet welds, different thicknesses and joint design, which will be required to overcome before full acceptance of the process is achieved.
Abstract-FrictionstirWelding is the type of welding used as a solid state joining process for materials that is different alloys of aluminum, magnesium etc. and also for hard materials like steels because it avoids the common problems obtained in conventional welding processes. The fact that joining of alloys could be usually faced problems in many sectors that includes automotive, aerospace, ship building industries, electronics etc. where fusion welding is not possible due to large difference in physical and chemical properties of the components to be joined. Difficulties in conventional welding processes is porosity formation, solidification cracking, and chemical reaction may arise during welding of dissimilar materials although sound welds may be obtained in some limited cases with special attentions to the joint design and preparation, process parameters and filler metals.
Figure 8 shows a motif of the optical images of the cross-section of a FSW AA5052- AA6061 R1400F080 specimen. The diﬀerent regions of the dissimilar frictionstir weld are marked in the ﬁgure. It can be noticed that the interface between AA5052 and AA6061, which initially was linear prior to welding, now has a non- linear, wavy, and distorted appearance. The interface appears to be serrated throughout the thickness of the weld. This interface can be considered to be an imperfection and was termed as “joint- line remnant”. Several researchers have studied the formation of complex intercala- tion structures consisting of swirl-like features and intermingled dissimilar lamellae during the intermixing occurring in FSW of dissimilar materials.
8. Woo, W., Chooa, H., Donald, B., Feng, Z. and Liawa, P. K., (2006), “Angular distortion and through-thickness residual stress distribution in the Friction-stir processed 6061-T6 aluminum alloy”, Materials Science and Engineering Journal Vol. 437, No. 1, pp. 64–69.
Siddiquee et al.  performed frictionstirwelding on austenitic stainless steel plates on an indigenously retrofitted vertical milling machine. AISI-304 equivalent grade stainless steel was welded by FSW using tungsten carbide tools with tapered cylindrical (conical) pin. The results of ANOVA showed the order of importance in which the parameters have affected the UTS in terms of percent contributions i.e. welding speed with (56.83% contribution), shoulder diameter (27.44% contribution) and tool rpm(15.73% contribution). Ramachandran et al.  studied the effect of tool axis offset from the joint interface and geometry of the FSW tool pin on the mechanical and metallographic characteristics of dissimilar FSW welded aluminium alloy and HSLA steel were. The constant FSW parameters used were; tool rotational speed of 500rpm, welding speed of 45 mm/min, and axial load of 7 kN and tool tilt angle of 1.50 o . The effect of tool axis offset was investigated by continuously changing the tool axis offset by keeping the tool traverse direction at an angle to the joint interface. FSW tool having TC pin with 100 o taper angle has produced the best joint at a tool axis offset of 2 mm towards the Al alloy.