Force In Friction Stir Welding Research Articles

An approach for predicting the tool forces in friction stir welding of AA6061-T6 aluminium alloy

An approach for predicting the tool forces in friction stir welding of AA6061-T6 aluminium alloy

Force data-driven machine learning for defects in friction stir welding

This study proposes a strategy for developing force-data-driven machine learning models to precisely predict defects and their types in friction stir welding (FSW). The characteristics of the three component forces in FSW, including traverse force (Fx), lateral force (Fy), and plunge force (FZ) are studied. The change in the force wave corresponded well with the variation in the defect. Fyavg had the best correlation with the characteristics of tunnel defects, whereas some other time-frequency features had negligible effects on the defect variation. The machine learning models built with the input of 15 force features could detect defects with an accuracy of 95.8% and classify them into tunnels and porosities with an accuracy of 98.0%. The abnormal increase in Fyavg, caused by the buildup of redundant material transported to the retreating side, was the main characteristic of force change when a defect was formed.

Investigation on Effect of Strain Rate and Heat Generation on Traverse Force in FSW of Dissimilar Aerospace Grade Aluminium Alloys.

The emergence of the aerospace sector requires efficient joining of aerospace grade aluminium alloys. For large-scale industrial practices, achievement of optimum friction stir welding (FSW) parameters is chiefly aimed at obtaining maximum strain rate in deforming material with least application of traverse force on the tool pin. Exact computation of strain rate is not possible due to complex and unexposed material flow kinematics. Estimation using micro-structural evolution serves as one of the very few methods applicable to analyze the yet unmapped interdependence of strain rate and traverse force. Therefore, the present work assessed strain rate in the stir zone using Zener Holloman parameter. The maximum and minimum strain rates of 6.95 and 0.31 s−1 were obtained for highest and least traverse force, respectively.

Determination of the traverse force in friction stir welding with different tool pin profiles

ABSTRACTA methodology is developed for the estimation of the traverse force in friction stir welding (FSW) for various pin profiles by combining the results of numerical modelling and experimental monitoring. The effect of pin profiles on the traverse force is evaluated by introducing a modified ratio of the plastic deformation zone, which is obtained by numerical modelling. The formula is validated with the experimental data in the literature and indicates that the traverse force decreases exponentially with increasing ratio of the plastic deformation zone. The proposed methodology provides a concise approach for the estimation of the traverse force for various pin profiles in FSW and can be adopted for the design and assessment of the FSW tool.

Analysis for the forces in FSW for aluminum alloy considering tool geometry and process velocities

In the friction stir welding (FSW) technique, the friction stir tool is submitted to a system of forces that influences the main phenomena of the process. However, experimental studies for all the forces in FSW have received little attention. For a better process understanding, an analysis of the individual contribution of each part of the tool on the forces is required. In this paper, the influence of the pin and shoulder on the axial force is separately considered as a function of the rotational, plunging and welding speeds. Three experimental designs were carried out for the tool pin, the tool shoulder and the complete tool. Additionally, the welding and transverse forces are measured during FSW experiments for different combinations of the main process parameters. The results showed an important contribution of the pin to avoid excessive loads during the plunging phase and an interaction between the effects of the tool geometry, and rotational and plunging speeds factors on the maximum axial force.

Mechanistic models for the forces in FSW of aluminum alloy 5052-H34

Friction stir welding (FSW) technique produces welded joints with better quality than most widely used welding methods. The absence of material melting and the small energy requirement are the main features of this process. Friction stir welding forces influence the process and its main phenomena. However, models and experimental studies for the forces involved in FSW have received little attention. In this paper, the influence of the pin and shoulder on the axial force is separately considered and three models are developed to describe the axial force as a function of the tool geometry and the rotational, plunging, and welding speeds. The axial force is individually modeled for the plunging and welding phases. Additionally, a model is developed to describe the welding force as a function of rotational and welding speeds for the complete tool. The axial, welding, and transverse forces are measured during FSW experiments for different combinations of the main process parameters, and the results are used as input data for the estimation of the model parameters via inverse problem. The results showed a good agreement between the experimental data and the models.

Finite element simulation of pin shape influence on material flow, forces in friction stir welding

Selection of tool geometry is an important aspect for an efficient friction stir welding (FSW), as it influences material flow, forces, and other output responses. In the present paper, a three-dimensional coupled thermo-mechanical model is proposed based on Lagrangian method to evaluate the performance of two different pin shapes, i.e., smooth conical and threaded conical. Experimentally obtained axial force and spindle torque are used to validate the model. Particle tracking method is used to visualize the material flow on advancing side, retreating side, and centerline of the weld. Results reveal that material flow is non-symmetric and unstirred region is lower for the threaded pin as compared to the smooth. Higher slip rate is predicted for threaded pin as compared to the smooth pin. Vertical flow is observed for the threaded pin and is almost negligible for smooth pin.

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.

Prediction of fatigue life of welding tool in friction stir welding of AA6061-T6

Computational fluid dynamics model is proposed for the calculation of tool forces in friction stir welding of AA6061-T6. Then, a finite element model is established to calculate the fatigue stress of the welding tool. Damage accumulation method and KBM multiaxial fatigue formulation are used to predict the fatigue life of the welding tool. Results indicate that the fatigue stresses on the tool pin are in tension at the front side and in compression at the rear side. Fatigue life of the welding tool can be increased with the increase of the rotation speed and can be decreased with the increase of the transverse speed. Both the increase of the shoulder diameter and the pin diameter can lead to the increase of the fatigue life of the welding tool.

Using a novel fixture to study of temperature and applied forces during friction stir welding

This paper aims to study the effect of rotation and travel speeds on important parameters such as temperature, and transient and stable axial and longitudinal forces in friction stir welding (FSW) of aluminum AA7075-T6 to find appropriate welding parameters. For simultaneous measurement of axial force, longitudinal force and temperature, a novel fixture is designed and manufactured, which allows force measurement in the friction stir welding (FSW) process without the need to employ expensive equipment. The results show that increasing the travel speed increases both the stable axial and longitudinal forces, whereas increasing the rotation speed decreases both of them. However, the temperature trend upon increment of translation and rotation speeds is contrary to the trend for the axial and longitudinal forces. Furthermore, transient applied forces during the dwell phase are found to be highly fluctuating and much greater compared to the stable forces. Thus, transient forces may be considered as the determining factors for choosing welding.

Numerical and experimental study on influence of tool plunging force and shoulder size on thermal history of friction stir welding

Friction stir welding (FSW) process is a solid stated joining process. Important process parameters include the tool rpm, travel speed, tool dimensions and the downward force on the tool. Heating is caused by rubbing of the tool faces against the workpiece and by visco–plastic dissipation of mechanical energy. There is a unique combination of shear and normal forces in FSW. In this present study gaps of FSW were determined and two very much important process parameters effect on FSW (i.e., tool plunging force and shoulder size) was presented. This study investigates the effect of tool plunging force and tool shoulder size on heat generation of FSW by using 3–D finite element (FE) transient thermal analysis. It was noticed that both plunging force and shoulder diameter have considerable effect on FSW process. Suitable correlations have been made between shoulder diameter vs. peak temperature and tool plunging force vs. peak temperature. Also generalised optimum parameters were established by considering the above said parameters. The present developed FE model results were well matched with experimental results. [Received 29 September 2013; Revised 31 July 2014; Accepted 3 October 2014]

Simultaneous measurement of tool torque, traverse force and axial force in friction stir welding

Simultaneous measurement of the tool torque, traverse force and axial force during friction stir welding process is of great significance to the understanding of the underlying process mechanism and the optimizing of the process parameters. Different from the traditional measurement methods using load cell or rotating component dynamometer, an indirect but economical methodology is used in this study for the simultaneous measurement of the traverse force, axial force and tool torque by monitoring the output torques of the servo motors and main spindle three-phase AC induction motor inside the FSW machine. The values of the traverse force, axial force and tool torque are determined under different welding conditions, and the influencing factors are examined. The measured results in friction stir welding of AA2024-T4 aluminum alloys at different combinations of tool rotation speed and welding speed lay foundation for process optimization.

Monitoring torque and traverse force in friction stir welding from input electrical signatures of driving motors

Experimental measurements of torque, traverse force and thermal cycles in friction stir welding (FSW) are challenging due to the simultaneous rotational and linear motions of the tool and the deformation of workpiece material around the tool pin. We propose here a methodology to measure the torque and the traverse force by monitoring the current and power transients of the electrical motors that drive the rotational and linear motions of the FSW tool respectively. The measured values of torque and traverse force in FSW of AA 7075-T6 and AA 2524-T351 at different combinations of tool rotational speed and tool shoulder diameter are validated with the corresponding computed results from a well tested numerical model. The proposed method alleviates the need to use expensive torque and force dynamometers, and provides an economical and robust route for indirect measurement of real time torque and traverse force in FSW.

Experimental Investigations on Characteristics and Welding Forces in Friction Stir Welding of AA 6061-T6 Aluminum Alloy

Friction stir welding (FSW) technology requires a meticulous understanding of the process and consequent mechanical properties of the welds in order to be used in the production of high performance components. This paper deals with an experimental campaign aimed at the evaluation of the mechanical properties of AA6061-T6 friction stir welded joints. The joints are obtained by varying the welding parameters, namely, tool rotating speed and feed rate. The non-threaded tool is made of hot work die steel H13. The quality of the joints is evaluated in terms of both hardness and tensile strength. Moreover, for going a step further to study and control welding heat input in FSW process, a piezoelectric load cell is installed between the fixture table and the machine tool workbench in order to measure the welding forces in different directions.

Predictions of tool forces in friction stir welding of AZ91 magnesium alloy

Adaptive remeshing technique based finite element model of friction stir welding was used for the investigation of tool forces in the welding processes. Results indicate that the maximum tool forces occur at the initial time in the translational stage. In the tool forces in the three directions, the axial force is the maximum. The tool force in the direction perpendicular to the welding line is the minimum. The tool forces in the three directions are all increased with the increase in transverse speed and decreased with the increase in angular velocity.

Influence of the FSW clamping force on the final distortion and residual stress field

Abstract Friction stir welding (FSW) is a solid state process, leading to joints with good mechanical performance. Low residual stresses and distortions are generally mentioned as further advantages, leading to the current high interest of the aeronautical industry in this process. In order to achieve these beneficial properties, the welding process requires clamping of the parts to be welded. To the authors knowledge clamping forces in FSW have not been studied in detail yet, neither their influence on residual stress and distortion. In the present work the clamping forces, both initially applied and their evolution during the welding process, were studied. Furthermore the influence of different clamping forces on the distortion and residual stress of the welded plates was analysed. The joints were subjected to mechanical testing and microstructural analysis in order to guarantee defect free joints in all cases and in order to be able to detect influences of the clamping process on joint performance. It was found that higher clamping forces lead to lower distortion and a more uniform residual stress distribution through the thickness. Higher clamping forces also lead to a lower defect probability through the creation of gaps between the plate halves.

Effect of Material and Pin Surface on Vertical Force in Friction Stir Welding

The information about the effect of material and pin surface on the vertical force in friction stir welding was collected and analyzed. The results shown that the vertical force experienced a steady process when tool was moving steadily in the workpiece; The vertical force in steady state was impacted by material, because the thermal and mechanical properties of different material were not same. The vertical force was the greatest when welding TC4 (about 8.40 KN), and the vertical force was greater when welding T2 (about 7.35 KN) than welding LY12 (about 3.10 KN). Pin surface also affected the vertical force; because threads generated forces when tool rotating in the workpiece. The vertical force was greater by using column pin with left thread (about 3.48 KN) than by using column pin with right thread (about 3.09 KN), and the vertical force was median (about 2.60 KN) by using column pin without thread.

Dynamic measuring and analysis on radial resistant force in friction stir welding

Radial resistant force against the moving tool was measured dynamically and influences of some factors on the force were analyzed.It shows that the force rises up sharply at the beginning of friction stir welding As soon as reaching the top it decreases down rapidly,and then goes to a value at which the welding procedure is steady.If increasing the rotation speed of tool,but keeping all other parameters and factors fLxed,the top force and the steady force are both decreased,and the times taken for reaching the top force and steady force are shortened. If increasing welding speed only,the top force goes up greatly, and the steady force increases or decreases in a rather small range,and the time taken for the top force changes a little,but the time for the steady force is prolonged;The influences of the diameter of pin on the force are complex,because the change of the diameter of pin leads to the variation of frictional heating power and the cooling power simultaneously.