Effect of Workpiece/Tool Heat Transfer and Friction Coefficients on Accuracy of Simulated Temperatures and Torques in a Friction Stir Welding Plunge

Abstract

Friction stir process models are typically validated by tuning heat transfer and friction coefficients until measured temperatures in either the tool or workpiece, but rarely in both, match simulated results. A three-dimensional finite element model for a tool plunge in an AA 6061-T6 is validated for temperature predictions in both the tool and workpiece using a friction coefficient that varies with time. Peak workpiece temperatures were within 1.5% of experimental temperatures and tool temperatures were off by 80 °C. The sensitivity of the predicted temperatures with respect to the workpiece/tool heat transfer coefficient was shown to be high for the tool and low for the workpiece, while the spindle torque was slightly underpredicted in the best case. These results show that workpiece/tool interface properties must be tuned by considering predictions on both sides of the heat generation interface in order to ensure a reliable process simulation.

Effect of Welding Parameters on Al/Mg Dissimilar Friction Stir Lap Welding with and without Ultrasonic Vibration

“…Welding load is the force that drives material deformation and flow during welding. Large welding loads will not only cause severe wear on the tool but will also lead to the breakage of the pin [24,25]. The larger traverse force is the main reason for this situation.…”

“…In the traveling stage, the force increases rapidly and then fluctuates periodically as a sine function. However, some scholars have pointed out that in Al/Mg FSLW, the liquid film generated by constitutional liquation during the welding process can change the friction state between the tool and the material, leading to fluctuations in welding load [7,25]. This sizeable periodic fluctuation could also be related to the screw transmission mechanism of the welding machine itself [24].…”

“…Generally speaking, the welding heat input is related to the welding parameters. Increasing the welding speed or decreasing the tool rotation speed can reduce the welding heat input [25][26][27]. Therefore, as the welding heat input decreases, the thermal softening degree of the material decreases, and the traverse force increases.…”

“…According to the results of EDS mapping (Figure 10e-h) and EDS point scanning (Point 3, Table 2), we can determine that this area shows IMCs, and the type is Al12Mg17. This large, non-layered structure of IMCs could be generated by constitutional liquation [25].…”

“…This indicates that applying UV is beneficial for improving the 2), we can determine that this area shows IMCs, and the type is Al 12 Mg 17 . This large, non-layered structure of IMCs could be generated by constitutional liquation [25].…”