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TWI has been using a new, more accurate approach to modelling friction stir welding (FSW) which has the potential to reduce reliance on experimental trials and cut the cost of FSW process adoption.
Friction stir welding is a joining technology with a proven track record in producing high-strength, low-distortion joints with excellent fatigue and corrosion properties across a wide range of applications from aerospace components to consumer goods.
One of the key challenges with FSW of high-temperature materials is the inability of the tool material to withstand the heat and forces generated during the process without losing strength or suffering excessive wear. Existing modelling techniques struggle to simulate this, and to accurately predict the influence of tool geometry on the integrity of the weld.
To address these challenges, TWI has been exploring the use of a new modelling approach: the Coupled Eulerian-Lagrangian (CEL) method.
CEL Modelling offers benefits over conventional computational fluid dynamics or traditional “Lagrangian” finite element methods due to its ability to accurately capture the high-temperature, high-deformation physics of the FSW process that take place between the workpiece and tool. In conventional Lagrangian modelling, material occupies finite elements and under an applied force, the element deforms. In CEL, the material flows through a fixed mesh. This allows for the high strains experienced under FSW processing (often exceeding 100%) to be accurately simulated. Moreover, the method is capable of incorporating the exact tool geometry from a CAD file and modelling the thermo-mechanical coupling between the tool and workpiece (including heat transfer between the two and heat loss to the environment).
To validate this new modelling approach, TWI generated models of previous experimental weld trials where temperatures, tool forces and tool torques were measured. The entire joining process including the plunge, dwell, linear traverse, and tool retraction was simulated. Specifically, the modelling work focussed on the joining of two aluminium alloy 6082-T6 plates. TWI then performed a directly coupled thermo-mechanical analysis with Abaqus, comparing the results of the simulation to the experimental measurements.
The results indicate strong agreement between the experiments and simulations. With this newly validated modelling approach, CEL simulations of the FSW joining process can be used to better understand distortion and residual stresses that may arise during FSW processing. These more accurate simulations can help reduce the number of experimental trials, providing a more cost-effective solution to exploring FSW applications such as the joining of dissimilar materials.
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