Tool Shoulder Diameter Research Articles

Influence of process parameters on mechanical and microstructural properties of friction stir welded AA5052

ABSTRACT The current research work explores the process parameters, namely, tool shoulder diameter, tool pin design, tool rotational as well as welding speed and its influence on mechanical and metallurgical qualities of aerospace grade 5052 aluminium alloy. The research observation shows the intermediate extent of process parameters indicates enhanced mechanical qualities compared to the lower and higher regimes. With considering different individual tools pin profiles, square pin (SQ) tool geometry yields the highest ultimate tensile strength in comparison with threaded cylindrical, tapered cylindrical, and straight cylindrical tool. A set of the best combination of process parameters with 24 mm shoulder diameter, SQ pin tool geometry at tool rotational speed of 1000 rev/min along with the welding speed of 40 mm/min, produced defect-free joint with excellent mechanical characteristics with an ultimate tensile strength of 92% compared to the base metal. Microstructural analysis of the best welded specimen (considering the above parameters) revealed 81% finer grain compared to base material that leads to enhanced mechanical attributes. Fractography detects ductile fracture of the welded specimen. The effect of individual process parameters on grain size, micro-hardness, flexural strength, bending angle and percentage of elongation of each sample are represented in this research article.

Friction Stir Welding of Aluminum 7075 Alloys

Abstract: Friction Stir Welding (FSW) is a solid-state welding method which was developed by The Welding Institute and patented in 1999. The process is solid state and relies on local forging of weld region to perform weld. New welding schedules are being continuously developed for materials that are traditionally difficult to join by fusion welding methods (e.g., TIG/MIG). These experiments are performed to find out the best possible parameters to smoothly weld the aluminium 7075 alloys. By using Taguchi robust design of experiment, we selected 3 parameters namely rotation speed and transverse speed and tool shoulder diameter against the optimization function of ultimate tensile strength. The tilt angle and the plunge depth are kept constant. The variation of tensile strength is mainly due to the change in tool shoulder diameter then with welding speed and then with rotation speed. The heat generated is modelled on ANSYS software by inserting the rotation speed, coefficient of friction , material properties , radius of pin etc. The model is validated by conducting the experiment through thermocouples. The model predicted a temperature of about 410 degrees Celsius and the experimental value is 380 degrees Celsius, showing that the welding temperature is about 80% of heat generation. The Taguchi experiment consist of 4 experiments with a range of rotation speeds of 900 and 1120 respectively and a welding speed of 64mm/min and 100 mm/min respectively. The tool shoulder diameter is kept 14mm and 17mm. the welds are cut in transverse direction in order to obtain the UTS test coupon. The best possible combination is found using Taguchi Analysis. This thesis is a collection of data and response variables that correctly informs at what conditions we should weld 7075 alloy. Appropriate SN ratio is calculated and high is the best is considered as our objective function is tensile strength. Some additional tests are also performed namely hardness and microstructure and heat generation in order to identify the behaviors of aluminium alloy. Hardness and heat generated are dependent on the tool shoulder diameter then on the welding speed. This conclusion is derived from Taguchi analysis. This study is useful for the selection of parameters for the further welding operations. However, a change in plunge depth can also be taken into consideration for future scope. As tunneling defect was observed in some runs thus plunge depth has to be varied. Also, the number of experiments can be increased in order to get more refined parameters. Also, the making of base material can also be taken into consideration because of the zinc precipitate distribution. Casted AA7075 has different properties, rolled AA 7075 can have different.

Numerical modelling of friction stir welding of pipes: Effect of tool shoulder on mechanical property and metallurgical characterization

One of the challenges during FSW of pipe is establishing sufficient contact between the tool shoulder and the pipes to be welded. With improper contact, the torque requirement increases, which thereby increases the power consumption. The present work focuses on the demonstration of a 3D thermo-mechanical model showing the influence of tool shoulder diameter on temperature rise, plastic strain development, spindle torque, material flow occurrence, and power consumption. The model showed a good correlation with experimentally observed temperature and maximum spindle torque for different rotational speeds. It was observed from the developed model that, an increase in the shoulder diameter increases the contact area and spread of maximum temperature resulting in a wider HAZ zone. Hence, optimization of the tool shoulder diameter was necessary, and it has been addressed considering its effect on contact area, heat generation, material flow, and spindle torque. The material flow behaviour has also been studied, and it was found that a larger shoulder diameter does not produce sufficient material stirring. The welded sample has been investigated by tensile strength and microstructure analysis. The optimum tool shoulder diameter of 16 mm resulted in joint strength efficiency of 90%.

Influence of Tool pin Profiles in Friction Stir Welding of Aluminum Alloy and Polycarbonate

In this study, the impact of tool pin profile on the dissimilar joining characteristics of aluminum alloy AA2017 and polycarbonate in friction stir welding (FSW) was examined. The tool pins made of SKD11 tool steel were used in the experiments of the FSW to join AA2017 and polycarbonate plates in a butt configuration at a tool rotation speed of 1320 and 1760 rpm and tool transverse speed of 60 mm/min. The tool shoulder diameter and tool pin height were set to 10 mm and 2 mm. The shapes of tool pin were cylindrical with and without groove, tapered cylindrical with and without groove, bobbin shaped with and without groove, square, triangular, pentagonal, hexagonal, oval, and ellipsoidal. The measurement of axial force was performed using a dynamometer. The changes in workpiece temperature at six locations during the process were measured using K-type thermocouples embedded in the plates. Microstructures of welded joints were examined by an optical microscope. Vickers Microhardness mapping was performed in and around the weld nugget zone, which is formed by the material flow between the two different base materials. From the result, the grooved tool pins generated less heat; while cylindrical, square, and oval type pins are also result in the superior properties of the welds during joining processes. Each tool pin had unique material flow behavior and weld formation, and the weld defects such as tunnel/voids occurred at the joint interface. The oval tool pin gives rise to the highest joint efficiency at a higher tool rotation speed, and the ellipsoidal tool pin generates the highest joint efficiency at a lower tool rotation speed was noticed.

A multi-objective optimization using response surface model coupled with particle swarm algorithm on FSW process parameters

In this study, multi-objective optimization of mechanical properties in friction-stir-welding of AH12 1050 aluminum alloy is performed using a combination of the response surface method and multi-objective particle swarm optimization algorithm. The process parameters are considered as tool pin diameter, shoulder diameter, rotational speed, feed speed, and tool tilt angle. The heat-affected zone’s yield strength, fracture strain, impact toughness, and hardness on the advancing and retreating sides are selected as the objective functions. Threaded and simple conical pins are utilized to evaluate the effect of the pin geometry on the specimen mechanical properties. Optimization model outputs are in agree with the obtained experimental results. The effects of process parameters on the mechanical properties of the friction-stir-welded sheets are studied. Results reveal that the lower rotational speed and higher feed speed improve the material strength and hardness. Moreover, the microstructural analysis demonstrates that the proposed methodology can achieve a fine-grained structure with the minimum defects. Improvement in the material flow is observed for the threaded cylindrical pin compared with the conical pin due to the geometric shape of the tool pin leading to more functional mechanical properties. It is found that the combination of the response surface methodology and the multi-objective particle swarm algorithm led to the modeling and optimization of the process with outstanding accuracy and low experimental cost.

Experimental investigation of friction stir spot welding of polymer-aluminum alloy weldments

The friction stir spot welding (FSSW) process is one of the main solid-state joining methods used widely for welding different materials and dissimilar metals. In this article, the welding of Polytetrafluoroethylene (PTFE) and aluminum alloy sheets by the FSSW process will be investigated experimentally. The joining of polymer (PTFE) and metal (AA1050 aluminum alloy) was done successfully. The effect of process parameters including tool rotational speed, penetration depth, initial holding time, dwell time, and tool shoulder diameter on the joint strength and elongation of the weldments will be studied using response surface methodology (RSM). The joint strength was increased by creating a threaded hole in the aluminum sheet. A mechanical lock was created between the softened PTFE and the edge of the threaded hole. The shear-tensile tests have been carried out for 32 designed experiments. The results show that the joint strength increased by increasing the initial holding time due to the better wettability of PTFE and aluminum sheet. The joint strength increased by increasing the tool rotational speed and tool diameter (better pouring of the hole and formation of the mechanical lock). Two different fracture modes have been observed in the samples: (1) fracture in the peripheral area of the joint (partial interfacial fracture mode) and (2) fracture in the mechanically locked area (pull-out mode with tearing).

Electrochemical behaviour of friction stir welded joints: Effect of tool shoulder diameter

In the present research work, the effect of shoulder diameter on the corrosion rate of stir zones (SZs) of dissimilar joints exposed to 3.5 M NaCl solution fabricated via friction stir welding (FSW) was studied in detail. In FSW, the tool shoulder diameter as one of the important process parameters significantly affects frictional heat input and material flow leading to the heterogeneous distribution of second phase particles (precipitates) that alters the electrochemical behaviour of FSWed joints. The influence of shoulder diameter on corrosion rate was analyzed via macro and microstructural characterization and open circuit potentiodynamic testing. The surface morphology and microstructural analysis of specimens reveal the occurrence of both pitting and intergranular corrosion (IGC) in base materials and SZs of welded specimens. Among the welded specimens, the SZ of weld I fabricated under shoulder size of 18 mm revealed the lower corrosion resistance. The potentiodynamic test revealed that weld I having very fine grains as compared to other joints exhibits the highest current density and corrosion rate.

Influence of shoulder diameter on interfacial microstructure and mechanical behavior in dieless friction stir riveting of CP-Copper to 321 stainless steel

This study investigated the influence of changes in the tool shoulder diameter on the microstructure, bonding, diffusion, and tensile-shear behaviors of the dieless friction stir rivetted CP-copper/Zn/AISI 321 stainless steel joints. The results reveal that the increase in the shoulder diameter increases the peak temperature, width of the brazed and stir zones, and the tensile-shear load (1944–2429 N) of the joints. The wider tool shoulder produced a good metallurgical/interfacial bonding at the stir zone and restrained upper sheet bulging (USB) effect at the brazed zone of the joint whereas USB-induced sheet separation and lateral unbonded path could not be prevented with the smaller tool shoulder diameter (12 mm). The change of the tool shoulder diameter changes the fracture behavior and the diffusion gradients of Cu from steep to gradual profile due to differences in the friction-induced heat input/temperature. A wider tool shoulder diameter is recommended for defect elimination and improved strength.

Study of optimum welding performance in friction stir welding of dissimilar Mg alloys using integrated RSM-TLBO algorithm

Lightweight with excellent strength of magnesium alloys has attracted its use in transportation industries but difficulty in fusion welding of magnesium alloys restricts its application. The present research investigates solid state friction stir welding of dissimilar AZ31-AZ91 magnesium alloys with aim to achieve optimum quality welds. Surface roughness, microstructure and mechanical properties of these joints have been investigated at different tool rotational speed, welding speed and tool shoulder diameter. Maximum joint strength obtained is 89.71% (as compare to AZ31) which is more than the previously reported joint strengths of dissimilar magnesium alloys. Further, mathematical relations for responses have been developed and utilised for multi-objective optimization using teaching-learning-based optimization algorithm. Eventually, teaching-learning-based optimization algorithm results suggest that the optimum value of surface roughness (3.3925 µm), grain size (12.6869 µm), tensile strength (237.9621 MPa), microhardness (69.3652 Hv) and flexural strength (333.2285 MPa) can be achieved at 921 rpm rotational speed, 30 mm/min welding speed and 15 mm shoulder diameter with overall improvement in multiple responses.

Experimental investigation and optimization of quality characteristics during friction stir welding of Al- and Zn-based magnesium alloy using artificial intelligence

Friction stir welding is successfully used to weld different wrought magnesium alloys. This work investigated the mechanical and microstructural behavior of the friction stir-welded AZ31B magnesium alloy. The experiments were conducted as per experimental runs designed by response surface methodology. An artificial neural network model was developed to produce a relationship between process variables (tool rotational speed, welding speed, and tool shoulder diameter) and characteristics of the friction stir-welded joints (tensile strength, percentage elongation, impact strength, microhardness, and grain size). The acceptable range of statistical parameters validated the adequacy of the model. The multi-objective optimization technique, genetic algorithm was used to obtain a set of Pareto optimal solutions. The best-compromised optimum solution for maximum tensile strength (164.2 MPa), percentage elongation (8%) impact strength (3.5 J), microhardness (85 Hv), and minimum grain size (13.1 μm) was validated by confirmation test with <3 percent absolute error percentage. The fractographical analysis has been performed and dimples and torn edges observed in fracture zones.

Evaluation of shear force and fractography of friction stir spot welded joints of AA 6082-T6 alloy

This experimental work investigates the tensile behavior of friction stir spot welded joints from 3 mm thick aluminum alloy AA6082-T6 sheets. Taguchi L9 Orthogonal array was used for process parameters - Tool rotational speed (TRS), Dwell time (DT) and Shoulder diameter (SD) with consideration of three levels. Friction Stir Spot Welding (FSSW) was performed on vertical milling machine. Tensile shear test was conducted on Universal testing machine (UTM) to find out the tensile shear failure load (TSFL). The optimal combinations of parameters were at tool rotational speed of 2,000 rpm, dwell time of 15 seconds and tool shoulder diameter of 16 mm. Tool rotational speed had a substantial effect on tensile shear strength of FSSW joint. Scanning Electron Microscopy (SEM) tests revealed that the changes in microstructure in different zones of FSSW joint were observed. Tensile shear specimen was analyzed using SEM to observe the behavior of fracture surfaces. Significant ductility in the fracture surface was an evident in the fractography. In this article, attention is focused on the influence of joining parameters on the mechanical behavior of the friction stir spot weld under the tensile shear load condition. Keywords: Fractography; friction stir spot welding (FSSW); heat affected zone (HAZ); scanning electron microscopy (SEM); thermo-mechanically affected zone (TMAZ).

Improvement in joint efficiency with high productivity and narrow weld formation in friction stir welding

High productivity, excellent joint strength and small weld bead make friction stir welding an emerging joining technique to join difficult to weld dissimilar aluminum alloys. Effect of rotational speed, traverse speed and shoulder diameter on the joint strength and elongation of the friction stir welded dissimilar aluminum alloys (AA7475-AA2219) is investigated. In addition, parameters are optimized to obtain joint with narrow weld bead and high joint efficiency using the entropy-weighted technique for order of preference by similarity to ideal solution method. Nine experiments are performed as per the L9 orthogonal array and mechanical properties of the welded joints are measured. Results of the study reveal that optimum values of ultimate tensile strength and percentage elongation are obtained at a rotational speed of 710 rev/min, welding speed of 250 mm/min and shoulder diameter of 10 mm resulting in good joint strength, high productivity and narrow weld bead. From the selected process parameter range, tool shoulder diameter is found to be the most significant parameter. The findings of the present study are discussed in light of the friction stir welding process mechanism, available literature, mechanical testing, microstructure and fractography.

Optimization of friction stir processing parameters for enhanced microhardness of AA5083/Al-Fe in-situ composites via Taguchi technique

Friction stir processing (FSP) is a novel technique to fabricate metal matrix composites (MMCs) and surface composites (SCs). In the present study, Taguchi’s technique is used for attaining the optimum value of microhardness for AA5083/Al-Fe in-situ surface composites (SCs) via FSP using 40 hours mechanical alloyed Fe-40wt% Al powder mixture. Three different process parameters i.e. tool shoulder diameter, tool rotational speed, and tool traverse speed each having three levels were selected for optimizing the microhardness of SCs. The experimental study was accomplished by employing Taguchi's L9 orthogonal array. The Microhardness of the fabricated composites was confirmed using Vickers tester after the single-pass FSP. The outcomes of the study were examined and studied using signal to noise (S/N) ratio. The analysis also confirms the results and displayed that the optimum value of microhardness of 123.3 Hv was obtained with the selected parameter of tool shoulder diameter of 21 mm, tool rotational speed of 900 rpm, and traverse speed of 63 mm/min.

Investigation of Shoulder diameter to Sheet Thickness (D/T) Ratio on Tensile Properties Friction Stir Welded AA2014-T6 Aluminum Alloy Joints

ABSTRACT 2xxx and 7xxx high strength alloy are well suited for components and structures that include a greater strength ratio and are typically used in the fabrication of fuselage, wing skins. AA2014 is hard to join using a fusion welding process because of its good thermal conductivity, oxidation behaviour and low fusion point, which can easily lead to burn through and porosity. To overcome the above difficulty, friction stir welding (FSW) is used. The formation of sound weld depends on process and tool parameters. The tool shoulder is the most predominant factor. About two-third of heat is generated at the interface of tool and sheet. Hence, in this investigation, the influence of the tool shoulder diameter (D) to sheet thickness (T) ratio on the tensile properties of FSW AA2014 joints was analysed. Five tools with varying D/T ratios (2.0, 2.5, 3.0, 3.5 and 4.0) were used. Microstructure and hardness measurement were performed to correlate strength properties of FSW joints. It is found that the joint welded with a D/T ratio of 3.0 disclosed superior joint tensile properties compared to other D/T ratios. It is mainly due to the development of fine-grained structure in stir zone of D/T 3.0 joints.

Investigation of Factors Affecting Friction Stir Welding of Polyethylene by ANOVA Analysis

The variables that are effective in joining high density polyethylene sheets by friction stir welding (FSW) have been investigated. In order to understand the effects of welding parameters, using Taguchi optimization, tool rotation speed, feed rate, shoulder diameter and pin diameter values were selected in a wide range. The results obtained with Taguchi optimization method were evaluated according to the highest / the best signal-noise ratio. Macro photographs taken cross-sectional view taken the weld seam, SEM images and hardness measurements were used to evaluate. As a result of the evaluation, the accuracy of the optimization was found to be approximately 96 %. As a result, feed rate and shoulder diameter were determined as the most effective parameter affecting the welding quality and welding performance. These two parameters (shoulder diameter and feed rate) have found to effect of approximately 65 % on tensile strength, weld quality and hardness. Finally, it has obtained that the most effective welding parameter was the shoulder diameter with 40.81 %.

Effect of tool diameter ratio on the microstructural characteristics of a solid-state processed aluminum based metal matrix composite

Abstract Stir cast aluminum based metal matrix composites (MMCs) with silicon carbide (SiC) reinforcement particles consist of cast product dendrites and large agglomerated reinforcements. The agglomeration of SiC particles creates a difference in properties in the composite system. Friction stir processing (FSP) is used to overcome the uneven distribution of SiC particles in the aluminum matrix. The friction stir processed (FSPed) microstructure is significantly influenced by the process parameters used for processing. In FSP, the effect of the tool diameter ratio (tool shoulder diameter to pin diameter) on material flow, material mixing, material consolidation is more predominant than other parameters. Hence, a perfect combination of shoulder diameter to pin diameter is required to produce sufficient material flow. In this investigation, the tool diameter ratio is varied from 2.0 to 4.0 for processing composite material and thus FSPed zones were subjected to micro structural characterization. It was concluded that a tool diameter ratio of 3.0 yielded a defect free stir zone with higher hardness compared to other ratios.

Enhancement of the Al/Mg Dissimilar Friction Stir Welding Joint Strength with the Assistance of Ultrasonic Vibration

The assistance of ultrasonic vibration during the friction stir welding (FSW) process has been verified as an effective approach for the improvement of joint strength. In the present study, experimentation on Al/Mg dissimilar alloys in butt joint configuration is implemented by employing FSW with and without the assistance of ultrasonic vibration. An optimized tool shoulder diameter of 12 mm is utilized, and the ultrasonic vibration is applied perpendicularly onto the tool along the welding direction, which is named UVaFSW. The results of joint appearance and macrostructure, characteristics of the intermetallic compounds (IMCs), as well as joint strength and fracture appearance are compared between Al/Mg FSW joints with and without ultrasonic vibration. It is demonstrated that the material intermixing between Al and Mg alloys is substantially strengthened in the UVaFSW joint compared with that in the FSW joint. Additionally, the ultrasonic vibration can be beneficial for the reduction of IMC thickness, as well as the formation of intermittently distributed IMC phases at the Al–Mg bonding interface. Consequently, the mechanical properties of Al/Mg FSW joints are significantly improved with the assistance of ultrasonic vibration. The maximum ultimate tensile strength is 206 MPa at tool rotation speed of 800 rpm and welding speed of 50 mm/min for the Al/Mg UVaFSW joint.

Investigation of exit-hole repairing on dissimilar aluminum-copper friction stir welded joints

Exit-holes in friction stir welded dissimilar aluminum-copper (Al–Cu) joints are repaired by using probeless tools, forcing the surrounding material to fill the exit-hole cavity. The repair by refilling the same base materials is performed in two steps using probeless tools of different diameters. In this study, two different conditions are investigated, keeping the processing parameters constant and varying the tool shoulder diameters. Namely, the repair is performed using a two steps sequence of probeless tools with shoulder diameters of: (1) 12 and 19 mm, and (2) 12 and 27 mm. The refill action is achieved using only the base materials. A comprehensive experimental campaign, including tensile tests, microhardness measurements, scanning electron microscopy and energy dispersive x-ray spectroscopy investigations, have been conducted to evaluate the effectiveness of the repairing. The results showed that the usage of probeless tool is an effective strategy to repair the exit-hole of dissimilar Al–Cu friction stir welds, with exclusive contribution from the same Al and Cu base materials in the cavity of the exit-hole. The original FSW joint with exit-hole, with a diameter of about 8 mm, repaired by shoulder diameters of 12 and 19 mm exhibited ultimate tensile strength about 13% higher than the values provided by the samples taken in the steady-state region of the weld bead The maximum and minimum hardness of the repairing zone made with shoulder diameters of 12 and 19 mm are 240 and 80 HV0.1, respectively, which are within the range of the friction stir welded regions indicated in previous studies.

Effect of tool material and process parameters on friction stir weld formation of maraging steel

ABSTRACT 18% Ni maraging steel is an ultra-high strength steel widely used in defence and aerospace applications. Fusion welding of maraging steel is encountered with a drop in properties due to the segregation of alloying element and hence, solid-state welding process such as friction stir welding (FSW) is a possible alternative. However, welding of high strength material using FSW is a challenge considering the tool material durability, tool material cost, and selection of tool geometry and process parameters. Therefore, the main focus of this paper is towards the selection of tool geometry, tool material, and process parameters that will result in least tool wear/failure in addition to obtaining defect-free welds of maraging steel using FSW. It was observed that polycrystalline cubic boron nitride (PCBN) and tungsten-molybdenum are durable tool material for welding maraging steel. It is recommended to use a minimum tool pin diameter (top 12 mm and bottom 8 mm) and shoulder diameter (20 mm) below which failure of pin and surface defects are encountered during FSW. It is also observed that there exists a narrow range of tool rotational speed (250–450 rpm) and tool travel speed (25 mm/min) at which defect-free maraging steel welds can be obtained.

Microstructure characterisation and mechanical behaviour of AA 6063 T-6 welded joint by friction stir welding

ABSTRACT Solid-state welding for low-melting point materials is suitable to produce defect-free weld joints. Therefore, in the present work AA 6063 alloy was welded using friction stir welding (FSW) to know the fracture strength of the welded joint along with the microstructural characterisation. The join was made using a tool of cylindrical shape having varied tool shoulder diameter. The qualities of weld joint are evaluated with the existence of weld defects and microstructure, whereas mechanical properties are obtained as tensile strength, bend test and micro-hardness. The hardness of welded samples at the nugget zone is more or less similar for all process parameters and tool shape. Whereas, the bending strength and tensile strength were found to be varied with rotational speed but decrease as a function of transverse speed. The fractured image revealed that the ductility is higher at the lower band angle. Microstructural examination revealed that the grain growth exhibited in the thermo-mechanical affected zone (TMAZ) and heat-affected zone (HAZ).