Current literature reports tool probe profiles with features such as flats or flute, induce a greater stirring action and generate more heat than featureless tool profiles. This is due to the increased contact area. For the SSFSW process, this was necessary as the probe needed to generate all the heat required to plasticise the material and create the metallurgical bond. A tapered tool with flats was selected as the preferred tool profile. This was chosen as a tool with flats could operate at higher process forces than tools with flutes due to their greater cross sectional area. Various sized tool probes were designed with dimensions as shown in Table 4. This was done to get an idea of the forces exerted on the probe and head unit during the process when welding at different weld depths by starting with the small probe and progressing to the bigger probes. All the probes had similar features as shown in Figure: 3-17. For example each had; a 4˚ taper angle, neutral thread of 1mm pitch, three equally spaced flats. The tools were fastened to the draw bar via thread. Tools 1 and 2 were made from H13 W302 tool steel hardened to 52HRc. The literature showed that this was the general tool material used for tools used for the frictionstirwelding of plate thinner than 16mm. Tools 3 and 4 were made from MP 159, a Ni-Co alloy and were age hardened at 700˚C for 4 hours to improve the UTS. This Ni-Co alloy is the general tool material currently used for the FSW of plate thicker than 16mm.
Although the process has reached a stage of technical maturity for the “light alloys”, its application to metals such as steel, nickel and titanium has been slower to develop due to the severe loads and temperatures the tool experiences during the welding process , . Tool design and the development of advanced materials for FSW of steel has therefore become a significant area of research in recent years, focusing specifically on improving tool lifespan . This is the key to the future economic viability of the process. Perrett et al.  investigated frictionstirwelding of industrial steels using two different tool materials; polycrystalline boron nitride (pcBN) and a W-Re/pcBN composite. In both cases, welds in excess of 40m were completed without tool probe failure or any signs of weld defects. In addition to this Sorensen  studied the wear and fracture sensitivity of three grades of pcBN tools and obtained a tool life of approximately 60m when welding structural steel.
of the tool. Despite the high strength and thermal proper- ties, the PCBN tool has low fracture toughness and is also susceptible to wear problems, especially during the plunge period of the weld due to the higher temperature generated which can cause a softening of the binder . The plunge period is also associated with a high plunge force which can encourage BN particles to detach from the tool and stick into the workpiece. The development in metal-com- posite material has encouraged manufacturers such as MegaStir to produce new grades of PCBN tools with a longer service life. This development was a step forward in order to commercialize the FSW of high melting alloys. For example, a FSW tool made from Q70 (70%PCBN, 30%WRe) has a higher toughness compared to the previous one which included an AlN binder . The melting point of a Q70 tool PCBN material was determined to exceed 3000 C, and the microstructure and tool image are shown in Fig. 1a and b, respectively . The Q70 tool has been used extensively by TWI to join many steel grades including 316L stainless steel, 304 stainless steel, and DH36 and EH46 steel grades which are under considera- tion in this work. PCBN-WRe Q70 tool as shown in Fig. 1b consists of a shoulder and probe surrounded by a collar of a Ni–Cr alloy which works as an insulator for the tool from the environment, so the heat generated during the FSW is almost distributed between the PCBN tool and the
The rotating tool in FSW is responsible for heat generation and material deformation during the welding process and has two main features; the shoulder and the pin. The last two decades have seen significant advances in both tool material and tool design, allowing a wide range of materials to be welded (such as soft aluminium or magnesium alloys or hard carbon or stainless steels) with a range of thicknesses and desired weld quality in terms of a low number of defects and distortion. During the welding process, the tool is subjected to a range of loading conditions as a result of its contact with the hot, highly plasticised material being welded. Through determining the rates and magnitude of tool wear, the development of tool geometry can be modelled, and thus the effect of tool wear on weld quality can be determined, which has been seen to be a particular issue when welding hard alloy workpieces [6, 7]. The workpiece material and process parameters, such as tool rotational speed and tilt angle, weld traverse speed and plunge force, are the main factors which affect tool life
Although the process has reached a stage of technical maturity for the “light alloys”, its application to metals such as stee l, nickel and titanium has been slower to develop due to the severe loads and temperatures the tool experiences during the welding process , . Tool design and the development of advanced materials for FSW of steel has therefore become a significant area of research in recent years, focusing specifically on improving tool lifespan . This is the key to the future economic viability of the process. Perrett et al.  investigated frictionstirwelding of industrial steels using two different tool materials; polycrystalline boron nitride (pcBN) and a W-Re/pcBN composite. In both cases, welds in excess of 40m were completed without tool probe failure or any signs of weld defects. In addition to this Sorensen  studied the wear and fracture sensitivity of three grades of pcBN tools and obtained a tool life of approximately 60m when welding structural steel.
The frictionstirwelding process has been investigated further in more recent studies [16- 19]. In Zhang et al  the FE method based on nonlinear continuum mechanics was used to find strain distributions which correlated well with the microstructure zones in the weld. It was also found that there was a quasi-linear relation between the change of axial load on the shoulder and the plastic strain. In Buffa et al  the FE method was used to investigate FSW in aluminium. Specifically the welding of sheets of various thicknesses and tools setups were investigated. In Hwang et al  various experimental techniques were used to investigate the FSW process. Thermocouples were used to determine temperature histories at various locations on the workpiece, hardness tests were carried out on base metal and heat affected zones and tensile tests were carried out to determine tensile strength. Blignault et al  described the design, development and calibration of a rotating transducer which allows measurement of FSW process responses such as forces, energy and temperature.
Workpiece geometry can also be a challenge especially in material with high thickness, Seaman and Thompson  investigated challenges in FSW of thick steel and found that the possibility of defects formation in the welded joints increases with increasing workpiece thickness due to the increase in thermal diffusion distance. As the time to dif- fuse heat by the tool into the depth of workpiece is insuf- ficient to create a uniform distribution of temperature throughout the thickness of the weld, isotherms will develop inside the FSW region. In this case, the top of the workpiece around the toolshoulder is expected to experi- ence better stirring conditions than the bottom of the weld; thus, the possibility of defects formation such as worm- holes will increase. The authors attributed defects to a lack of forging forces or the heat imbalance. Defects such as lack-of-fill were also found in the thick steel joints when the tool rotational speed and axial force increased, causing a loss in material support behind the tool. Reducing heat input by increasing weld heat extraction or by increasing the shoulder radius has been suggested in order to constrain the stirred material.
HRS-FSW has been demonstrated to have the potential to create strong metallurgical joints with lower process forces than typically observed in FSW. The fixed shouldertool has been shown to have an observable impact on the microstructure and resulting micro hardness. It was also shown that the tendency to create weld porosity and wormholes can be largely suppressed. The quenching effect of the fixed shoulder could also be enhanced by the addition of cooling lines tool to maintain a large temperature differential. Since it is well known that 2024 and 7075 alloys are very quench-rate sensitive, with higher strengths for higher quench rates, this innovation may provide a new way to enhance the mechanical properties of frictionstir welds in 2XXX and 7XXX alloys. It is anticipated that this tooldevelopment could appreciably improve the fatigue life of the as-welded material, since the stress concentrations of the weld track can be eliminated by the use of a fixed shoulder.
The inﬂuence of nonlinear frictionstirwelding (FSW) tool control on joint properties was investigated. Although FSW is widely applied to linear joints, it is impossible for ﬁve-axis FSW machines to maintain all FSW parameters in optimum conditions during nonlinear welding. Nonlinear FSW joints should be produced according to an order of priority for FSW parameters. Tensile test results of butt joints with rectangular change in the welding direction on the plate plane (L-shape butt joints) change with various welding parameters. Results show that a turn to the retreating side is encouraged when the welding direction changes. The method of zero inclination tool angles is eﬀective for nonlinear and plane welding. [doi:10.2320/matertrans.L-MRA2008807]
compared to weld, where the tool rotates perpendicular to the workpiece, when placed at an angle facing the direction gave high strength joint. As discussed when tool tilted at an angle of more than 1° void formation is observed and this condition is for a plate not more than 4mm thickness. The tool tilt angle is based on the thickness of plates to be used. It is observed that in some cases of FSW steel weld TMAZ zone is not seen and in other cases HAZ and TMAZ zones are clearly distinct. TMAZ zone is influenced by both mechanical and thermal cycles, while HAZ zone is influenced by only thermal cycles. Peak temperatures can be seen only in the HAZ zone, due to this hardness in the region will be more. Differentiating TMAZ zone from HAZ zone is most preferably difficult and hence in most of the weld, the region is differentiated as two zones in HAZ viz. HAZ zone 1 and HAZ zone 2. Fatigue life and fracture toughness of FSW steel weld is not explained and studied till yet. When compared to aluminum and its alloys, the characterization study on FSW steels are very less. Only based on the tensile strength and impact toughness, the quality of FSW steel welds are evaluated. Hence more characterization study is needed for deeper knowledge of FSW welds. Corrosion in steel and iron is a natural phenomenon, which occurs at a faster rate than any other metal. Hence alloying element is added, to improve corrosion resistance. Study of corrosive nature in the weld region of FSW of steel is not carried out in any of the previous studies. Further tool wear is an important criterion to be considered before planning for FSW of steel. One practical remedy for controlling the tool wear is preheating the tool and work piece and the other is as said before that selecting a suitable alloying element. Corrosion and tool wear is not only the properties for study, there is lots of characterization study that is need for FSW of steels to undergo and understand.
I declare that this thesis entitled “Mechanical Properties of Aluminium Alloy 1100 Series Thick and Thin Materials Welded Using Bobbin FrictionStirWelding” is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidate of any other degree.
FSW is a solid state process that enables long length welding without melting the base material and provides important metallurgical advantages compared to fusion welding. The stirring and forcing also results in a fine grain structure in the weld, resulting in a weld joint of good quality. In order to improve weld quality and minimize weld defects, it is important to study the relationship between frictionstirwelding parameters, heat generation and material flow during the welding process. This chapter lists a broad review of literature related to FSW of aluminium alloys. Review monitoring techniques such as FSW process parameters, heat generation, tool design, acoustic emission, electric motor currents and soft computing methods. 2
A commercially available Aluminium alloy 6061-T6 having 100 mm in length, 75 mm in width and 1 mm in thickness was used. All the plates were machined to dimensions mentioned above with square grooved as shown in the Fig. 3. The square grooves were cut by a wire cut machine to get a minimum gap between grooves. The FSW tool used is shown in the Fig. 4. The operating parameters for the FSW are given in the Table3. The tool was arranged to rotate in the clock wise direction and the work piece was moved in the opposite direction which is called as the advancing side. Only transverse specimen was produced and to be tested on the tensile test. The test specimens were machined from the central part of the joint according to ASTM E8M-01  subsize standard for sheet type material (gauge length 25 mm, width 6 mm, and overall length 100 mm). All samples were produced with minimal defects and conformed to specified dimensions with a tolerance of 0.1mm. The specimens were tested at room temperature using 10 KN Servopulser Series Servo- hydraulic testing machines with front-opening hydraulic grips. Table 4 shows the dimensions of the test specimen as per ASTM .
Since the tool plays a primordial role in this technique, a number of modifications to obtain appropriate FSW tool solutions for welding polymers were required. Given that polymers behave differently than metallic materials during FSW, new tool developments are needed to minimize the defects in order to achieve sound welds. In FSW, pin and shoulder geometry of the tool profoundly affect the weld quality. Considering the importance of tool geometry, wide research on tool design has also been performed. Different types of tool Geometry are shown in the fig. below
Numerous different fusion and solid-state welding processes are able to weld Cu and Cu alloys. Common fusion processes such as oxy-fuel welding, resistance welding and arc welding processes are typically chosen to weld Cu and its alloys, while diffusion welding, frictionwelding, explosion welding and roll welding are common solid-state welding techniques used for the same task. In welding of Cu, its high thermal conductivity is a major factor affecting the weldability of the material. The thermal conductivities for the various alloys differ. Pure and nearly-pure Cu such as Oxygen-free Cu (C10200) and electrolytic tough pitch Cu (C11000) have a thermal conductivity of 391 W/m ∙ K while heavily alloyed Cu such as Cu nickel (C71500) and nickel silver (C75200) have thermal conductivities as low as 29 W/m ∙ K. Other Cu alloys have thermal conductivities somewhere in between. When arc welding Cu with high thermal conductivities it is important to adjust the welding parameters so that it maximizes the heat input of the process into the joint. Some volatile, toxic alloying chemicals are often existent in Cu and Cu alloys. This generally results in much more release of toxic fumes than when welding ferrous metals so that it requires a more effective ventilation system to protect the welding operator than normally. This is generally avoided in solid-state welding processes that operate under the fusion temperature of the material. Solid-state techniques are also much more suitable for welding dissimilar materials. Al-Cu joints are made by techniques such as diffusion welding, frictionwelding, cold welding, ultrasonic welding and recently FSW .
Frictionstirwelding (FSW) is primarily used for aluminium also used for copper in certain industrial application. In the present study FSW of 5mm pure copper plates is done on vertical machining center with cylindrical H13 material tool. Surface temperatures are measured using pyrometer. Temperature graphs are plotted. The welded Joint at 950 RPM tool rotational speed and at 7mm/min tool traverse speed found satisfactory in visual inspection.
Abstract— In the proposed work, two different aluminium alloys such as Al 6061 and Al 6063 of same family was selected to study the mechanical properties of the joint prepared by FrictionStirWelding. The experiments were conducted by changing the spindle speed in three different levels by maintaining the other parameters unvarying. Welded workpieces were tested for its tensile strength and micro structure in order to understand the behavior of the welding process. The results revealed that the tensile strength is increased initially when the spindle speed increases and decreased beyond the certain level. Microstructural analysis showed that, in stir zone grain refinement was happened due to which mechanical properties were improved.
pieces. Then these plates are made burr free by filing so that when two plates are kept in fixture simultaneously for frictionwelding, then there should not be any gap present between two pieces in order to make better samples for frictionwelding. In this work the tool rotation speed kept constant at 3080 rpm, transverse speed was 30mm/min. and tool tilt angle was taken 2 0 .Tool tilt angle given to provide required pressure in the welding.
ABSTRACT: Frictionstirwelding (FSW) is a relatively new solid-state joining process. It is an emerging solid state joining process in which the material that is being welded does not melt and recast .This joining technique is energy efficient, environment friendly, and versatile. The principal advantages are low distortion, absence of melt related defects and high joint strength. In FSW parameters play an important role like tool design and material, tool rotational speed, welding speed and axial force. This paper focuses on process parameters that are required for producing effective frictionstirwelding joints by using two types of tool pin profile for the welding of Aluminum alloy 6061-T6 and to find out the best tool pin profile.
Although FSW is now widely used for the welding of aluminum and other soft alloys, premature tool failure limits its application to hard alloys such as steels and titanium alloys. The tool pin experiences severe stresses at high temperatures due to both the bending moment and torsion. It is shown that the optimum tool pin geometry can be determined from its load bearing capacity for a given set of welding variables, tool and work-piece materials. The traverse force and torque during FSW were computed using a 3D heat transfer and viscoplastic material flow model, considering the temperature and strain rate-dependent flow stress of the work-piece material . These computed values were used to determine the maximum shear stress experienced by the tool pin due to the bending moment and torsion for various welding variables and tool pin dimensions. The proposed methodology was used to explain the failure and deformation of the tool pin in independent experiments for the welding of both L80 steel and AA7075 alloy. The results demonstrated that the short tool life in a typical FSW of steels is contributed to by low values for safety factors in an environment of high temperature and severe stress. An experimental study of tool life in the FSW of titanium alloys sheets provided useful insights . Numerical simulation provided important information for the fixture design and analysis of experimental results. Tungsten and Rhenium alloy W25Re tools were found to be the most reliable among those considered. Scutelnicu et al.’s paper  addressed a comparative study on FSW and Tungsten Inert Gas (TIG) assisted FSW of copper. The base materials were preheated by an additional heat source and some remarkable advantages were obtained. These included as: faster and better plasticization of the base material, reduced FSW tool wear and clamping forces, faster welding speed and improved joint quality. The aim of the investigation was to develop two FE models, simulating the welding of copper by FSW and TIG-assisted FSW procedures. These are useful in predicting the temperature distribution, the peak temperature of the process and temperature changes in the cross section of the welded joints.