In the process of friction stir welding(FSW),the friction behavior at the tool-workpiece interface directly affects heat input and material flow.Therefore,accurate estimation of the friction coefficient at the interface is important for modeling of the FSW process.In this paper,a new approach to calculate the temperature dependent friction coefficient is proposed for modeling the bobbin-tool friction stir welding(BT-FSW)process.At the same time,the coupled Eulerian-Lagrangian(CEL)method is used to model the BT-FSW process of an aluminum alloy,and the friction heat,plastic deformation heat and material flow are considered.The interface temperature data obtained from the experiments are matched with the interface temperature data calculated by the model.The inverse algorithm is designed to calculate the temperature dependent friction coefficient.With the increase of welding temperature,the friction coefficient first slowly decreases,then rapidly increases,and then rapidly decreases,and finally slowly decreases to close to zero.The calculated friction coefficient is compared with the calculated results of previous literatures,and the differences and similarities of the friction coefficients with temperature are analyzed based on the modified adhesive friction theory.The results show that the model established using the temperature dependent friction coefficient can accurately reproduce the BT-FSW process.
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