Modeling Of Friction Stir Welding Process Research Articles

Probing finite element modelling of defects in friction stir welding by tailoring mass scaling factor

Friction stir welding (FSW), a solid-state welding process primarily used to join the low melting point materials, often encounters surface and subsurface defects. Modelling surface texture and internal volumetric defects in the FSW process using any numerical method is computationally expensive. The analysis of thermo-mechanical behavior of the FSW process using coupled Eulerian-Lagrangian (CEL) method is sensitive to mass scaling factor (MSF). Tailoring this factor for a computationally efficient model is a promising approach to predict defect in FSW process. The influence of MSF on the computational framework of the CEL finite element method (FEM) in the context of defect formation for two different types of materials (difference in densities) is addressed in the present work. The progress of different energies associated with the CEL approach is indicative of the solution availability by the application of MSF. The variation of these energies is significantly high in FSW process when encountering a defect and dictates the optimum conditions of MSF. An optimum range of MSF is deliberated on account of an efficiently model of FSW process. The simulated surface and subsurface defects, and the discrete temperature data are compared with experimental observation. The maximum difference between the predicted and experimentally measured tunnel defect is ∼ 0.75 mm, whereas the predicted temperature is within 5% of experimental result. It establishes the reliability of the developed numerical model and directs to trigger the model parameters for minimizing the computational time by tailoring the MSF. The optimum range of MSF between 106 and 107 strikes a balance between the result accuracy and computational feasibility for welding of AZ31B. Here, the distribution of strain and strain rate is representative of predicting the defect formation, such as, void, no material zone, crack, surface texture etc. The strain rate is almost double on the retreating side (RS) compared to advancing side (AS) due to the presence of the tunnel defect on AS.

Numerical simulation of friction stir welding of pure copper plates

Friction Stir Welding (FSW) is a joining process which is performed at low temperatures, lower than the melting temperature of the base material, thus it is considered a solid state welding process. This feature makes it suitable for copper welding, material whose thermal diffusivity is higher than that of most steel alloys. Large heat losses identified at copper welding by fusion welding processes are thus reduced using FSW process. Because of the shown efficiency and the innovative character of this process, many actions have been initiated in order to optimize it. The aim of this paper is to develop a three-dimensional coupled thermo-mechanical finite element (FE) model of FSW process for pure copper plates using the Coupled Eulerian-Lagrangian (CEL) formulation given in the FE code ABAQUS V6.13. The CEL formulation is one of the few formulations that are capable of handling with such large deformations. The developed numerical model was validated by comparing its results related to the temperatures calculated in the process time with those measured in performed experiments using the same process parameters. This model was capable of simulating the FSW of copper plates and of anticipating the temperature distribution and burrs formation in the weld bead.

Computational analysis of the intermetallic formation during the dissimilar metal aluminum-to-steel friction stir welding process

The extent of inter-material mixing and the formation of intermetallic compounds play a critical role in the structural integrity and mechanical properties of the joints in the case of dissimilar metal friction stir welding. In general, there is a critical volume fraction of the intermetallic compounds in the mix zone of the friction stir welding-joint at which the mechanical properties of the joint are maximized. That is, insufficient inter-material mixing and the accompanying sub-critical volume fraction of the intermetallic compounds results in insufficient inter-material bonding and inferior joint strength. Conversely, super-critical volume fraction of the intermetallic compounds typically gives rise to the joint embrittlement. To address the problem of the effect of the friction stir welding process parameters on the extent of intermetallic compound formation, a multi-physics computational framework has been developed and applied to the case of dissimilar metal friction stir welding involving commercially pure (CP) aluminum and AISI 1005 low-carbon steel. The multi-physics framework comprises the following main modules: (a) finite-element-based friction stir welding-process modeling; (b) quantum-mechanics, atomistic and CALPHAD-type continuum material thermodynamics analyses of the intermetallic compound-nucleation process; (c) a continuum-type analysis of multi-component diffusion-controlled growth of the intermetallic compounds; and (d) Kolmogorov–Johnson–Mehl–Avrami type analysis of the evolution of the intermetallic compound volume fraction within the friction stir welding joint as a function of the friction stir welding process parameters. The results obtained revealed that: (i) the extent and the spatial distribution of the intermetallic compounds is a sensitive function of the friction stir welding-process parameters; and (ii) among the six potential Al-Fe intermetallic compounds, FeAl and Fe3Al are associated with the largest volume fractions and, hence, play a key role in both attaining the required joint strength and in the potential loss of the joint fracture toughness.

A fast and accurate two-stage strategy to evaluate the effect of the pin tool profile on metal flow, torque and forces in friction stir welding

Pin geometry is a fundamental consideration in friction stir welding (FSW). It influences the thermal behaviour, material flow and forces during the weld and reflects on the joint quality.This work studies four pin tools with circular, triflute, trivex, and triangular profiles adopting a validated model of FSW process developed by the authors. The effect of the rotating tool geometry on the flow behaviour and process outcomes is analysed. Additionally, longitudinal and transversal forces and torque are numerically calculated and compared for the different pin shapes. The study is carried out for slip and stick limiting friction cases between pin and workpiece.The main novelties of the paper are a “speed-up” two-stage simulation methodology and a piecewise linear version of the constitutive model, both of them conceived for the use in real case industrial applications, where the achievement of accuracy with affordable simulation times is of importance.The Norton-Hoff constitutive model is adopted to characterize the material behaviour during the weld. The piecewise linear version of the model developed by the authors greatly facilitates the convergence of the numerical solution ensuring both computational efficiency and accuracy. A two-stage computational procedure is applied. In the first stage, a forced transient is carried out; in the second one, the magnitudes of interest are computed.The study shows that the proposed modelling approach can be used to predict and interpret the FSW behaviour for a specific pin geometry. Moreover, the reduction of the simulation time using the two-stage strategy can be up to 90%, compared to a standard single stage strategy.

Heat Generation Performance of a Homemade Friction Stir Welding Tool

Friction Stir Welding (FSW) is getting its popularity because it is considered as an environmentally friendly manufacturing. Homemade FSW tool to be attached to a conventional milling machine was designed and fabricated. Experimental investigation of FSW process of the Aluminum alloy work piece to observe its heat generation was performed. Since heat generation is the main objective in a FSW process, the importance of identification of heat generation performance in a welded specimen is paramount. Heat generation of a welded specimen during FSW was measured using infra red thermal camera. The limitation of the measurement is it only captured the heat generation at surrounding area and surface of the welded specimen. Therefore, the heat generation inside contact area could not be identified. To overcome this problem, a finite-element model of the FSW process was developed. A model consists of a solid model of half the welded specimen since the symmetrical behavior of the geometry and boundary condition was assumed. Heat transfer analysis of a solid body model of a work piece was computed. It was observed that FSW parameters which involved dominantly in the heat generation were spindle speed, feeding rate and normal force. The heat generation model of FSW process was validated with the one from the experimental investigation. Good agreement between the numerical and the experimental investigation result has been made.

Numerical Simulation of Temperature Distribution and Material Flow During Friction Stir Welding of Dissimilar Aluminum Alloys

Joining dissimilar materials is required in many engineering applications and conventional fusion welding of dissimilar materials often results in defective welds. Friction Stir Welding (FSW) has paved way for joining dissimilar alloys and defect-free joints have been obtained for a number of dissimilar material combinations. Numerical modelling of FSW process can provide reasonable insight into the physics of the process and will aid in minimising the number of experimental trials. In this paper, Computational Fluid Dynamics (CFD) based numerical model is developed to predict the temperature distribution and material flow during FSW of dissimilar aluminum alloys AA2024 and AA7075. Volume of fluid approach is used and the FSW process is modelled as a steady-state visco-plastic laminar flow past a rotating cylindrical tool. Results indicate that peak temperature in the welded plates increases with the increase of Tool Rotation Speed (TRS) and Shoulder Diameter (SD), whereas the peak temperature decreases with increase in Welding Speed (WS). Increasing TRS and SD increases material flow, while increasing WS decreases material flow in the stir zone.

Thermo-Mechanical Modelling of Friction Stir Welding Process

Friction stir welding (FSW) is a solid-state welding process where no gross melting of the material being welded takes place. Numerical modelling of the FSW process can provide realistic prediction of the thermo-mechanical behaviour of the process. Latest literature relating to finite element analysis (FEA) of thermo-mechanical behaviour of FSW process is reviewed in this paper. The recent development in thermo-mechanical modelling of FSW process is described with particular reference to two major factors that influence the performance of FSW joints: material flow and temperature distribution. The main thermo-mechanical modelling used in FSW process are discussed and illustrated with brief case studies from the literature.

Numerical modeling of friction stir welding process: a literature review

This survey presents a literature review on friction stir welding (FSW) modeling with a special focus on the heat generation due to the contact conditions between the FSW tool and the workpiece. The physical process is described and the main process parameters that are relevant to its modeling are highlighted. The contact conditions (sliding/sticking) are presented as well as an analytical model that allows estimating the associated heat generation. The modeling of the FSW process requires the knowledge of the heat loss mechanisms, which are discussed mainly considering the more commonly adopted formulations. Different approaches that have been used to investigate the material flow are presented and their advantages/drawbacks are discussed. A reliable FSW process modeling depends on the fine tuning of some process and material parameters. Usually, these parameters are achieved with base on experimental data. The numerical modeling of the FSW process can help to achieve such parameters with less effort and with economic advantages.

Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic Impact Loading Conditions

A critical assessment is carried out of the microstructural changes in respect of the associated reductions in material mechanical properties and of the attendant ballistic-impact failure mechanisms in prototypical friction stir welding (FSW) joints found in armor structures made of high-performance aluminum alloys (including solution-strengthened and age-hardenable aluminum alloy grades). It is argued that due to the large width of FSW joints found in thick aluminum-armor weldments, the overall ballistic performance of the armor is controlled by the ballistic limits of its weld zones (e.g., heat-affected zone, the thermomechanically affected zone, the nugget, etc.). Thus, in order to assess the overall ballistic survivability of an armor weldment, one must predict/identify welding-induced changes in the material microstructure and properties, and the operative failure mechanisms in different regions of the weld. Toward this end, a procedure is proposed in the present study which combines the results of the FSW process modeling, basic physical-metallurgy principles concerning microstructure/property relations, and the fracture mechanics concepts related to the key blast/ballistic-impact failure modes. The utility of this procedure is demonstrated using the case of a solid-solution strengthened and cold-worked aluminum alloy armor FSW-weld test structure.

Modeling of Friction Stir Welding of AL7075 Using Neural Networks

Friction stir welding (FSW) is a solid state welding process, which is used for the welding of aluminum alloys. It is important to note that the mechanical properties of the FSW process depends on various process parameters, such as spindle speed, feed rate and shoulder depth. Two different tool materials, such as High speed steel (HSS) and H13 are considered for the welding of Al 7075. The present paper deals with the modeling of FSW process using neural networks. A three layered feed forward neural network (NN) has been used to model the FSW of aluminum alloys. It is important to note that the connection weights and bias values of the NN are optimized with the help of a binary coded genetic algorithm (GA). The training of the NN with the help of GA is a time consuming process. Hence, offline training has been provided to optimize the connection weights and bias values of the neural network. Once, the training is over, the GA trained neural network will be used for online prediction of the mechanical properties of FSW process at different operating conditions.

Numerical and Experimental Investigations on the Loads Carried by the Tool During Friction Stir Welding

A computational fluid dynamics (CFD) model is presented for simulating the material flow and heat transfer in the friction stir welding (FSW) of 6061-T6 aluminum alloy (AA6061). The goal is to utilize the 3-D, numerical model to analyze the viscous and inertia loads applied to the FSW tool by varying the welding parameters. To extend the FSW process modeling, in this study, the temperature-dependant material properties as well as the stick/slip condition are considered where the material at the proximity of the FSW tool slips on the lower pressure regions. A right-handed one-way thread on a tilted FSW tool pin with a smooth, concaved shoulder is, additionally, considered to increase the accuracy of the numerical model. In addition, the viscous and frictional heating are assumed as the only sources of heat input. In the course of model verification, good agreements are found between the numerical results and the experimental investigations.