Research On Thermo-mechanical Process Simulation And Life Prediction Of Tool Pin In Friction Stir Welding

In friction stir welding(FSW)process,the tool pin is the weakest component of the tool,and the deformation or breakage is an important factor affecting its life.While,few literatures have implemented to research the tool pin life.Therefore,in this paper,a Fluent thermal-fluid-solid coupling model is developed to compute the temperature and pressure fields of the tool,and then the results are imported into ANSYS software for steady-state thermal analysis,static structural analysis,modal analysis,stress analysis and fatigue analysis to study the thermo-mechanical process,the tool structural dynamics and the tool pin life in friction stir welding.Thus,a numerical methodology for the thermo-mechanical-life analysis of friction stir welding is established.Fluent thermal-fluid-solid coupling is utilized to simulate the thermo-mechanical process of friction stir welding.The resulted thermal cycle of workpiece,tool transversal force and tool torque are consistent well with the experimental values.Then,the temperature and pressure fields of the tool are transferred to ANSYS software for steady-state thermal analysis and static structural analysis to compute the temperature and stress distributions of the tool respectively.The results show that the tool is most likely to break at the advancing side near the root toward front side of the tool pin.Based on modal analysis,the effects of the welding stress and the tool protruding length on the tool modal frequency are studied.It is found that the welding stress can lead to a reduction of about 12% of the tool modal frequency.With the increase of the tool protruding length,the tool modal frequency rapidly decreases at first and then slowly decreases.Stress analysis and fatigue analysis are applied to compute the load bearing capacity and fatigue life of the tool pin respectively,then the effect of welding parameter on tool pin life is studied.The results show that the tool pin life increases with the increase of the rotational speed and decreases with the increase of the welding speed.At the rotational speed of 355 rpm,when the welding speed is 5 mm/s,the tool pin life is 6490 m;when the welding speed increases to 10.7 mm/s,the tool pin will undergo yield deformation,and the tool pin life is 0.The effects of the diameter and taper angle of the tool pin on its life are investigated.It is found that with the increase of tool pin diameter,the tool pin transversal force changes little,while the tool pin torque increases obviously,resulting in that the tool pin life cannot be significantly increased at a lower speed ratio.With the increase of the tool pin taper angle,the tool pin transversal force is basically unchanged,and the tool pin torque increases slightly,thus the tool pin life will greatly increase.