Solid State Joining Process Research Articles

An Inverse Approach Towards Determination of Friction in Friction Stir Spot Welding

Friction stir spot welding (FSSW) is a solid-state joining process in which a rotating tool is pressed against two materials to be joined for creating a spot weld. The rotating tool comprises a pin with a shoulder. The pin gets inserted inside the material, whereas the shoulder rubs on the surfaces of the two materials. The process encounters friction at the pin-workpiece and shoulder-workpiece interfaces. In order to carry out a realistic simulation of the process, the knowledge of friction is a must. In most of the published work, scant attention has been devoted to the quantitative determination of friction force. This article proposes an inverse approach to the determination of friction force in FSSW. It is assumed that the frictional behaviour at the pin-workpieces interface is sticking in nature and at times, there is a possibility that frictional shear stress is more than the shear strength of the materials due to welding of asperities. This aspect is analysed by carrying out a number of finite element simulations using DEFORM-3D on a shoulder-less pin and validating it through in-house experiments. Later on, a hybrid friction model (combination of Coulomb’s and constant shear models) is used on the shoulder-workpieces interface. The friction parameters are adjusted through an optimization approach by minimizing the error between experiments and simulation. In a typical case, the friction factor (m) on the pin-workpiece interface was found to be 1.05. Friction at the shoulder-work interface was best represented by a hybrid model, with m = 0.77 for the high-pressure region and µ = 0.29 for the low-pressure region, where µ is the Coulomb’s coefficient of friction. Computations with estimated friction predicted temperatures with a reasonable accuracy. It also predicted fairly accurate torque for a tool of different size.

LINEAR FRICTION WELDING – PROCESS DEVELOPMENT AND APPLICATIONS IN AEROSPACE INDUSTRY

Linear Friction Welding (LFW) is a solid-state joining process very well adapted to titanium alloys, producing high integrity joints with fine grain, hot-forged microstructure and narrow heat affected zone. The first industrial application of this process was found in aircraft engines, for the manufacturing of “blisks” (“bladed disks”): linear friction welding the blades onto a disk provides economic savings and reduces the manufacturing time, compared to machining the whole blisk from solid. While the diffusion of LFW process in the blisk manufacturing market is still at the early stages and have promising growth potential, the process is now being developed for aircraft structures such as clips, brackets, hinges, fittings, and larger parts like seat rails, wing ribs, lintels and fuselage frames. The LFW process allows not only to manufacture a given part at a lower cost, it also open new part design possibilities, that were not available with traditional manufacturing processes. The manufacturing process of Ti-6Al-4V structural and engine parts by LFW is explained, highlighting advantages, limitations and part design best practices. Several LFW candidate parts are introduced and evaluated through feasibility, mass savings, post weld operations and overall cost savings.

Review on modelling of friction stir welding using finite element approach and significance of formulations in simulation

Friction stir welding (FSW) is a solid-state joining process, which is gaining significance in many joining applications, by overcoming the limitations of other fusion welding processes. For successful incorporation of its potential during industrial applications, mechanism of joining needs to be properly comprehended. The solution lies in developing effective and reliable finite element (FE) model of the FSW process, which would help in getting an insight of the process phenomena (like material flow, heat generation, etc.) during the process. The overall result could be used to observe the effect of process parameters on weld quality. Several attempts have been made to develop an FE model for FSW using different techniques. However, building an efficient model that emulates reality is still to be realised. Here, a review is made to know the current state of various FE modelling techniques and identifying better techniques for simulating FSW and its variants. This review also highlights shortcomings (for ex: mesh distortion, simulation time, the capability of defect prediction) of previous models and discusses on grey areas which are still to be addressed in the broader perspective of FSW and its allied processes using FE approach. [Submitted 06 July 2017; Accepted 29 September 2018]

Friction Stir Welding of Dissimilar AA6061-T6 to AZ31B-H24 Alloys

Abstract: Friction Stir Welding (FSW) is a solid-state joining process that uses a non-consumable tool to join two facing workpieces without melting the workpiece material. FSW is predominantly used for welding lightweight materials such as aluminum and magnesium alloys. In the present investigation, AA6061-T6 and AZ31B-H24 alloys were joined by FSW using the following parameters: rotational speed of 400, 800, 1200 and 1600 rpm, welding speed of 30 and 60 mm/min and tilt angle of 1° and 3°. In some cases, a tool offset of 1 mm was used into the Mg-based alloy. Microstructural characteristics of the weld joints were analyzed by optical microscopy and scanning electron microscopy. The experimental results show that dissimilar welds can be obtained by placing the AA6061-T6 alloy on the advancing side under two processing conditions: i) without a tool offset using a welding speed of 30 mm/min, a rotational speed of 400 rpm and a tilt angle of 1° (M7) and ii) with a tool offset and a welding speed of 30 mm/min, using a rotational speed of 1200 rpm and a tilt angle of 3° (M3). Al3Mg2 and Al12Mg17 intermetallic compounds were observed in the stir zone. Hardness and tensile strength of joints M7 varied from 76 to 129 HV, and 88.2 MPa respectively, and these properties varied from 95 to 153 HV, and 18.95 MPa in joints M3.

Review on Modeling of Friction Stir Welding Using Finite Element Approach and Significance of Formulations in Simulation

Friction stir welding (FSW) is a solid-state joining process, which is gaining significance in many joining applications, by overcoming the limitations of other fusion welding processes. For successful incorporation of its potential during industrial applications, mechanism of joining needs to be properly comprehended. The solution lies in developing effective and reliable finite element (FE) model of the FSW process, which would help in getting an insight of the process phenomena (like material flow, heat generation, etc.) during the process. The overall result could be used to observe the effect of process parameters on weld quality. Several attempts have been made to develop an FE model for FSW using different techniques. However, building an efficient model that emulates reality is still to be realised. Here, a review is made to know the current state of various FE modelling techniques and identifying better techniques for simulating FSW and its variants. This review also highlights shortcomings (for ex: mesh distortion, simulation time, the capability of defect prediction) of previous models and discusses on grey areas which are still to be addressed in the broader perspective of FSW and its allied processes using FE approach. [Submitted 06 July 2017; Accepted 29 September 2018]

Temperature distribution and residual stress in Friction Stir Welding process

Friction Stir Welding is an advanced solid state joining process invented as an alternative to join materials which are unfavourable to join using fusion welding technique. In Friction Stir Welding, the non-consumable tool is rotated and is slowly dived into the centreline and simultaneously progressed along that line. The heat generation in the process is a combined effect of frictional heating and heat because of the plasticization of the material. In this paper, the Finite Element package COMSOL Multiphysics 5.2a is used to develop a three dimensional numerical model to generate thermal profiles during welding, which is validated through experimentation. Due to the differential heating and cooling and the plasticization of the material, residual stresses develop in the material. The nature of the residual stresses significantly affects the quality of the joints. To analyse the residual stresses developed, three different approaches; namely experimental, analytical and numerical methods are used. Experimentally, residual stress is obtained by X-Ray Diffraction technique, Masubuchi and Martin’s longitudinal stress equation is used for analytical measurements and also residual stress is obtained numerically. The three approaches used for measurement of residual stresses are in well agreement with each other.

Mechanical Performance Prediction for Friction Riveting Joints of Dissimilar Materials via Machine Learning

Solid-state joining techniques have become increasingly attractive for joining similar and dissimilar materials because it enables further optimization of lightweight components. In contrast to fusion-based joining processes, solid-state joining prevents the occurrence of typical defects such as pores or hot cracking. Machine learning algorithms are powerful tools to identify and quantify relationships between essential features along the process-property chain. In particular, different supervised machine learning algorithms can be used to perform regression analyses and establish correlations between process parameters as well as resulting properties. This can help to circumvent the demand for conducting a vast number of additional experiments to determine optimized process parameters for desired material properties. Additionally, this knowledge can be utilized to obtain a deeper understanding of the underlying mechanisms. In this study, a number of regression algorithms, such as support vector machines, decision trees, random forest and 2nd-order polynomial regression have been applied to correlate process parameters and materials properties for the solid-state joining process of force-controlled friction riveting. Experimental data generated via a central-composite Design of Experiments, serves as source of two separate data sets: one for training and one for testing the machine learning algorithms. The performances of the different algorithms are evaluated based on the determination coefficient R2 and the standard deviation of the predictions on the test data set. The trained algorithms with the best performance measures can be used as predictive models to forecast specific influences of process parameters on mechanical properties. Through the application of these models, optimized process parameters can be determined that lead to desired properties.

Local Binary Pattern for the Evaluation of Surface Quality of Dissimilar Friction Stir Welded Ultrafine Grained 1050 and 6061-T6 Aluminium Alloys

Friction Stir Welding process is an advanced solid-state joining process which finds application in various industries like automobiles, manufacturing, aerospace and railway firms. Input parameters like tool rotational speed, welding speed, axial force and tilt angle govern the quality of Friction Stir Welded joint. Improper selection of these parameters further leads to fabrication of the joint of bad quality resulting groove edges, flash formation and various other surface defects. In the present work, a texture based analytic machine learning algorithm known as Local Binary Pattern (LBP) is used for the extraction of texture features of the Friction Stir Welded joints which are welded at a different rotational speed. It was observed that LBP algorithm can accurately detect any irregularities present on the surface of Friction Stir Welded joint.

Examination of Mechanical Property for Friction Stir Welding Joint of Al6061 and Al5083

Friction Stir Welding is a solid-state joining process of similar or dissimilar materials. The dissimilar joining of aluminum alloy Al6061 and Al5083 with the plates of 6 mm thickness was carried out by friction stir welding. The objective of present research is to enhance the mechanical properties by changing the advancing side of material during welding and optimizing the various process parameters such as tool rotation speed and traverse feed for higher weld strength. The influence of welding process parameters on strength of weld joint has been evaluated by tensile test. The tool rotational speeds were taken between 500 to 1000 rpm and tool traverse speeds were taken between 40 to 125 mm/min. The maximum tensile strength yielded 98.90 MPa when the Al6061 keep in an advancing side and 32 MPa when Al5083 keep in advancing side during weld joint at 1000 rpm and 50 mm/min. It was observed that the advancing sides of materials also play a key role for joint strength while keeping remaining process parameters constant during welding.

Surface Quality Analysis of Friction Stir Welded Joints by Using Fourier Transformation and Local Binary Patterns Algorithms

Abstract: Friction Stir Welding process is an advanced solid-state joining process which finds application in various industries like automobiles, manufacturing, aerospace and railway firms. Input parameters like tool rotational speed, welding speed, axial force and tilt angle govern the quality of Friction Stir Welded joint. Improper selection of these parameters further leads to fabrication of the joint of bad quality resulting groove edges, flash formation and various other surface defects. In the present work, a texture based analytic machine learning algorithm known as Local Binary Pattern (LBP) and Fourier transformation algorithm are used for the extraction of texture features of the Friction Stir Welded joints which are welded at a different rotational speed. It was observed that LBP algorithm can accurately detect any irregularities present on the surface of Friction Stir Welded joint and Fourier transformation method can detect the groovy edges present on the Friction Stir Welded joint. In the case study, an image based defect recognition system by using Fourier transformation method is constructed. Five types of filters i.e. Ideal Filter, Butterworth Filter, Low pass Filter, Gaussian Filter and High Pass Filter were used. The results showed that the high pass filter has more capability to detect the edges in comparison to other four filters. It was also observed that Ideal filter has a lot of distortions when compared to the Gaussian Filter and Butterworth Filter.

Studies on the effect of welding parameters for friction stir welded AA6082 reinforced with Aluminium Oxide

Abstract Friction Stir Welding (FSW) is a relatively new process which has proved to be a much more viable joining process for all Aluminium Alloys than earlier techniques, such as Metal Inert Gas, Tungsten Inert Gas, Laser Welding and Resistance Welding. Friction Stir Welding is the fastest evolving joining technology and the principal prospective technique for implementing integral fuselage structure in aircraft manufacturing. Friction Stir Welding is a solid-state joining process that uses a non-consumable tool to join two facing work pieces without melting the work piece material. The main objective of the work is to study the effect of mechanical properties like Hardness, Tensile strength along with Microstructure by varying the tool rotational speed of 500 rpm, 710 rpm, 1000 rpm and 1400 rpm during the Friction Stir Welding of Aluminium Alloy 6082 with different reinforcement percentages of 5%, 10% and 15% of Aluminium Oxide (Al2O3). FSW process parameters were optimized using the ANOVA method and Response Surface Methodology to determine the optimum values of Tensile strength of the joints.

Experimental investigation on ultrasonic spot welding of aluminum-cupronickel sheets under different parametric conditions

ABSTRACTUltrasonic spot welding (USW) is a solid-state joining process which is preferably adopted in the joining of lithium-ion battery tabs for hybrid electric vehicles. It has several benefits over traditional fusion welding techniques like shorter weld time, no formation of the heat-affected zone (HAZ), less energy consumption and lower operating cost. The present research work explores the effect of various welding factors like weld time, weld pressure and vibration amplitude on the tensile shear strength for joining aluminum (AA1060) with cupronickel (UNS C71500) sheets. The results indicated that tensile shear load raised with grow in weld time and achieved the peak value of 809 N. The various types of weld qualities were also identified such as ‘under weld’, ‘good weld’ and ‘over weld’ based upon the nature of bond formation at several weld parametric conditions. The detailed microstructural investigation on the welding region revealed the bonding mechanism with the mechanical interlocking feature and the correlation between the weld strength and the bond density was also established.

Characterisation of Friction Stir Weld Discontinuities by Non-destructive Evaluation

Friction stir weld (FSW) is an advanced metal joining process recently practised in aerospace industries with application spanning across other engineering fields as well. Friction stir welding being solid-state joining process, the weld is characterised by superior weld properties with proper parameter setting. The morphology of FSWs varies from other welds due to the plastic state formation of the material as against the liquid state of fusion encountered in conventional welding process. The nature of the discontinuities in these joints is significantly different. The presence of discontinuities in the welds due to its unique weld formation process has made the failure pattern in these products also unique. Hence, a comprehensive non-destructive evaluation (NDE) assessment of FSWs is attempted with different techniques and their detecting capability has been discussed. Conventional NDE methods, namely radiography, ultrasonics and eddy current techniques used in FSW discontinuity detection are discussed and compared for each type of discontinuity.

Effect of the Field Shaper Geometries in Electromagnetic Crimping of Tubes on Rods

Abstract Electromagnetic crimping is a solid state, high-speed, and high strain-rate joining process. Finite element analysis, as well as experimental study, was carried out on three types of field shapers, namely, tapered, taper-stepped, and stepped. In all three field shapers, the effective length, outer diameter, inner diameter, total length, and materials properties were constant. These field shapers were kept inside the same multi-turn solenoid coil for all the experiments. It was found that the taper-stepped field shaper results better regarding impact velocity, Lorentz force, temperature generation, less heating, and uniformity in crimping among the three types of field shapers.

A Study on Influence of Underwater Friction Stir Welding on Microstructural, Mechanical Properties and Formability in 5052-O Aluminium Alloys

Friction stir welding (FSW), a solid-state joining process is extensively using in the welding of aluminum alloy sheets. In order to save energy and reduce emission, lightweight materials like aluminum alloys were introduced into steel car body, which requires the development of effective joining processes. In the present study, welding was carried out in two different conditions, in the air (CFSW) and underwater (UWFSW) at various welding speeds to weld 5052-O aluminum alloy sheets. The effect of UWFSW on microstructural developments, mechanical properties, and formability was evaluated and compared. Grain refinement is an important opportunity to improve the mechanical properties of FS welds. Considerable grain refinement was obtained in UWFSW joints, which is smaller than that in the CFSW joints. The results indicated an increase in tensile strength, hardness, the percentage of elongation, and formability of UWFSW weld sheets. The results of the tensile test, hardness test, microstructure and fractography as in good correlation with improved properties.

Optimization of Process Parameters for Friction Stir Welding of Dissimilar Aluminium Alloy AA6061 to AA5183 using TOPSIS Technique

Friction stir welding has proven to be the most promising solid state joining process. It can be used to get high weldability in joining of high strength aerospace aluminium alloys and other metallic alloys which used to be low with traditional fusion welding process. This paper emphasises on finding the optimum process parameter for friction stir welding of dissimilar aluminium alloy AA6061 to AA5183 using multi criteria decision making method (MCDM). Friction stir welding was done at different tool rotational speed and transverse velocity and mechanical properties such as tensile strength, percentage elongation and hardness were studied for each weld specimen. Finally optimization was done using TOPSIS (Techniqueof Ordered Preference by Similarity to Ideal Solution). The result revealed that the tool rotational speed of 1200 rpm and welding speed of 80mm/min are the optimum welding parameters.

Optimization of Process Parameters for Friction Stir Welding of Dissimilar Aluminium Alloy AA6061 to AA5183 using TOPSIS Technique

Friction stir welding has proven to be the most promising solid state joining process. It can be used to get high weldability in joining of high strength aerospace aluminium alloys and other metallic alloys which used to be low with traditional fusion welding process. This paper emphasises on finding the optimum process parameter for friction stir welding of dissimilar aluminium alloy AA6061 to AA5183 using multi criteria decision making method (MCDM). Friction stir welding was done at different tool rotational speed and transverse velocity and mechanical properties such as tensile strength, percentage elongation and hardness were studied for each weld specimen. Finally optimization was done using TOPSIS (Techniqueof Ordered Preference by Similarity to Ideal Solution). The result revealed that the tool rotational speed of 1200 rpm and welding speed of 80mm/min are the optimum welding parameters

Design and Development of Manufacturing Facilities for Friction Stir Welding Process using Conventional Milling Machine

Friction stir welding (FSW) is a solid-state joining process that has many advantages including the ability to join high strength alloy as well as dissimilar metals which are hard to be joined by conventional fusion techniques. This welding process involves the penetration of rotating tool which consist of shoulder and prolonged by a pin into a metal plate. The process is followed by advancing speed to weld the metal plate. However, it requires a specialized machine to perform the joining process. A new FSW system including its tools may be costly and thus becomes the main barrier to the development of this FSW process in industry. One of the possible solutions is by adapting the current conventional milling machine with additional rotating and feeding principles to suit the FSW process requirement. In this work, suitable tools, jigs and fixtures for FSW process using conventional milling machine were designed. The design of the tool, jigs and fixtures were fabricated and tested by joining two similar plates of A6061 aluminium alloys. The investigation shows promising results with defect-free welds, good strength and smooth surface finish without gap creation between the welded plates.

Friction Stir Welding of Aerospace Alloys

Friction Stir Welding (FSW) is a solid state joining process which possesses a great potential to revolutionise the aerospace industries. Distinctive materials are selected as aerospace alloys to withstand higher temperature and loads. Sometimes these alloys are difficult to join by a conventional welding process but they are easily welded by FSW process. The FSW process in aerospace applications can be used for: aviation for fuel tanks, repair of faulty welds, cryogenic fuel tanks for space vehicles. Eclipse Aviation, for example, has reported dramatic production cost reductions with FSW when compared to other joining technologies. This paper will discuss about the mechanical and microstructure properties of various aerospace alloys which are joined by FSW process.

Friction Stir Welding for Marine Applications: Mechanical Behaviour and Microstructural Characteristics of Al-Mg-Si-Cu Plates

Friction stir welding is a multipurpose solid-state joining process mainly used for aluminium and steel plates and frames. Friction stir welded non-ferrous metallic alloys, similar or dissimilar, in particular aluminium alloys, provide opportunities for the improvement and developement of new product designs. This paper investigates the correlation between the mechanical behaviour and morphological structures of friction stir welded Al-Mg-Si(Cu) alloy plates in two temper conditions. Micro Vickers hardness and tensile tests were carried out. Additionally, morphology was investigated using optical microscopy and scanning electron microscopy. Samples subjected to the post weld heat treatment were shown to have the best properties owing to the formation of a significant number of hardening particles which, added to the nugget grain refinement, resulted in the increase of the material strength.