Thermo-mechanical modelling of the Friction Stir Spot Welding process: Effect of the friction models on the heat generation mechanisms

Friction Stir Spot Welding involves complex physical phenomena, which are very difficult to probe experimentally. In this regard, the numerical simulation may play a key role to gain insight into this complex thermo-mechanical process. It is often used to mimic specific experimental conditions to forecast outputs that may be substantial to analyse and elucidate the mechanisms behind the Friction Stir Spot Welding process. This welding technique uses frictional heat generated by a rotating tool to join materials. The heat generation mechanisms are governed by a combination of sliding and sticking contact conditions. In the numerical simulation, these contact conditions are thoroughly dependent on the used friction model. Hence, a successful prediction of the process relies on the appropriate selection of the contact model and parameters. This work aims to identify the pros and cons of different friction models in modelling combined sliding-sticking conditions. A three-dimensional coupled thermo-mechanical FE model, based on a Coupled Eulerian-Lagrangian formulation, was developed. Different friction models are adopted to simulate the Friction Stir Spot Welding of the AA6082-T6 aluminium alloy. For these friction models, the temperature evolution, the heat generation, and the plastic deformation were analysed and compared with experimental results. It was realized that numerical analysis of Friction Stir Spot Welding can be effective and reliable as long as the interfacial friction characteristics are properly modelled. This approach may be used to guide the contact modelling strategy for the simulation of the Friction Stir Spot Welding process and its derivatives.

Numerical Simulation of Friction Stir Spot Welding of Aluminium-6061 and Magnesium AZ-31B

Friction stir spot welding process is a solid state joining process which has attracted great attention due to its ability to join low melting point light weight alloys such as aluminium and magnesium with high efficiency. In order to understand the complex thermo-mechanical joining process involved with friction stir spot welding, a numerical simulation study was done using ABAQUS finite element software. The simulation primarily aims to interpret the effect of a set of process parameters and tool geometry on the workpiece plates. Johnson-Cook damage criteria model was used to obtain the stress and strain distribution on the workpiece consisting of aluminium 6061 and magnesium AZ-31B placed in a lap configuration. Temperature distribution of the workpiece was obtained by simulating a penalty based frictional contact between the tool and the plate. The thermal results showed that the maximum temperatures attained were significantly lower than the melting points of the base materials indicating that the material mixing and joining occurred as a result of superplastic deformation process instead of melting. Change in material flow behaviour was also observed by the model as pin and shoulder geometries changed.

Fundamental Aspects, Mechanical Behaviour and Mathematical Understanding of Friction Spot Stir Welds: A Review

The energy-saving and environmental conservation are increasingly important issues in manufacturing and service industries worldwide that have received considerable attention in recent years. Most importantly, this process eliminates the grain solidification errors generated by the standard fusion process. Thus, in this papers types and methods of stir welding will be explained and discussed accordingly . Friction stir spot welding is a tunable method as it allows an effective control and amendment of processing parameters using refill and powder-assisted schemes that can solve the problem of the keyhole and mechanical weaknesses in the joining of light metals processed by conventional Friction stir spot welding. This comprehensive review mainly focuses on the fundamental aspects of Friction stir spot welding processes and their impacts on the microstructural features and mechanical performance and mathematical understanding of various similar and dissimilar systems. To conclude, the challenges in further modification of Friction stir spot welding and future outlooks in different engineering applications are presented.

Experimental and Numerical Analysis of Refill Friction Stir Spot Welding of Thin AA7075-T6 Sheets

The refill friction stir spot welding (refill FSSW) process is a solid-state joining process to produce welds without a keyhole in spot joint configuration. This study presents a thermo-mechanical model of refill FSSW, validated on experimental thermal cycles for thin aluminium sheets of AA7075-T6. The temperatures in the weld centre and outside the welding zone at selected points were recorded using K-type thermocouples for more accurate validation of the thermo-mechanical model. A thermo-mechanical three-dimensional refill FSSW model was built using DEFORM-3D. The temperature results from the refill FSSW numerical model are in good agreement with the experimental results. Three-dimensional material flow during plunging and refilling stages is analysed in detail and compared to experimental microstructure and hardness results. The simulation results obtained from the refill FSSW model correspond well with the experimental results. The developed 3D numerical model is able to predict the thermal cycles, material flow, strain, and strain rates which are key factors for the identification and characterization of zones as well for determining joint quality.

Simulation of Friction Stir Spot Welding of Copper and Aluminium During Plunging Phase

Simulation is limited and remains briefly addressed in the literature of friction stir spot welding (FSSW) process in joining dissimilar copper and aluminium. Thus, this study simulated the FSSW process of copper and aluminium to investigate the peak temperature during the plunging phase produced by all possible combinations of levels for tool rotational speed, plunge rate, and plunge depth according to the full factorial design. The modeling was established by Coupled Eulerian-Lagrangian (CEL) model and ‘dynamic, temperature-displacement, explicit’ analysis. The highest peak temperature of 994.4 oC was produced by 2400 rpm rotational speed, 100 mm/min plunge rate, and 1.6 mm plunge depth. The combination was suggested to be the optimum welding parameters in joining copper to aluminium as sufficient heat input was essential to soften the area around the welding tool and adequately plasticize the material. Three sets of confirmation tests presented consistent responses with a mean peak temperature of 994.4 °C, which validated that the response produced by the suggested optimum welding parameters was reliable. The statistical result reported that the variability in the factors could explain 84.12% of the variability in the response. However, only the rotational speed and plunge depth were statistically significant. The residual plots showed that the regression line model was valid.

Pengaruh Interlayer Elektroplating Zinc pada Kekuatan Mekanik Friction Stir Spot Welding Aa1100-Ss400

Sambungan FSSW dengan material yang berbeda banyak digunakan pada kendaraan. Namun, masalah muncul ketika material tersebut tidak tersambung dengan sempurna. Penggunaan interlayer Zn mampu meningkatkan kemampuan sambungan. Variasi penggunaan dwell time dan diameter shoulder digunakan untuk memperjelas peranan interlayer electroplating Zn. Pengujian tarik geser yang telah dilakukan membuktikan bahwa penggunaan interlayer electroplating Zn memiliki kemampuan sambungan yang lebih baik. Nilai maksimal pengujian tarik geser sebesar 3.8 kN. Nilai maksimal sambungan tanpa interlayer elektroplating Zn 2.5 kN. Pengujian kekerasan menunjukkan nilai yang lebih besar 63 HV dari pada sambungan tanpa menggunakan interlayer elektroplating Zn.