Prediction of Surface Profile in Friction Stir Welding Using Coupled Eulerian and Lagrangian Method

Friction stir welding (FSW) is widely accepted by industry because of multiple advantages such as low-temperature process, green technology, and capable of producing good quality weld joints. Extensive research has been conducted to understand the physical process and material flow during FSW. The published works mainly discussed the effects of various process parameters on temperature distribution and microstructure formation. There are few works on the prediction of defect formation from a physics-based model. However, these models ignore chip formation or surface morphology and material loss during the FSW process. In the present work, a fully coupled 3D thermo-mechanical model is developed to predict the chip formation and surface morphology during welding. The effects of various process parameters on surface morphology are also studied using the current model. Coupled Eulerian-Lagrangian (CEL) technique is used to model the FSW process using a commercial software ABAQUS. The model is validated by comparing the results in published literature. The current model is capable of predicting the material flow out of the workpiece and thus enables the visualization of the chip formation. The developed model can extensively be used to predict the surface quality of the friction stir welded joints.

CEL is a combination of Eulerian and Lagrangian techniques. The workpiece is modeled as a Eulerian domain while the tool as a Lagrangian domain. The Eulerian domain is divided into two parts, the top part is a void domain, while the bottom part is the material domain. The top void domain enables the visualization of chip formation and the flow of chips. The tool is modeled as a solid, deformable-body. The material model is considered as visco-plastic behavior and is represented by a widely used Johnson-Cook (JC) model where the flow stresses characterize the constitutive laws as a function of strain, strain rate, and temperature. The mass scaling phenomena are utilized that artificial increase the mass of an element to enhance the value of the stable time increment during explicit analysis for speeding up the actual simulation time for the CEL approach. The well-established heat conduction equation is used for the estimation of the temperature field both in the workpiece and the tool. All the surfaces have restricted movement so that the material cannot flow out of the workpiece domain. The bottom surface of the workpiece is constrained in the z-direction. Rotation and translations velocity is applied to the workpiece. The general contact for the CEL analysis enables the interactions between Lagrangian and Eulerian material parts. In the contact surfaces, Coulomb’s friction model is used, and the coefficient of friction is considered as temperature-dependent values. Both the sliding and sticking friction conditions are implemented in the present analysis.

The temperature distribution with respect to the weld centerline at different points is obtained for the validation of the developed model. The chip formation is numerically predicted for welding taking place at 1200 rpm, 280 mm/min, and 0.2 mm plunge depth. The analysis of the temperature field and strain rate field during deformation are also performed. The temperature distribution and chip formation in FSW process are presented in the paper. The simulation of the surface morphology is observed.