(Session 4A)Effects of Liquid Cooling of the Tool During Friction Stir Welding of AA 6061-T6

摘要

In researching liquid cooling of the tool for FSW of AA 6061-T6, it was discovered that, when using liquid cooling of tooling, it was necessary to reduce to spindle speed 41% below experimentally validated parameters for uncooled tools. Additionally, it was discovered that a liquid cooled tool resulted in a 9% increase in spindle torque, 9% increase in spindle power, a 33% increase in forge force, and an increase in the size of the material plastically deformed by the tool. Furthermore, the absence of liquid cooling of the tool at the reduced spindle speed produced unconsolidated welds.Further investigation showed that these results are consistent with FSW models developed by Nunes and Schmidt et al. Calculated results from the analytical model developed by Schmidt et al. show that increased flow stress is required to achieve higher spindle power values seen in welds run with liquid cooled tools. The lower calculated temperature of the material surrounding the liquid cooled tool is responsible for the increase in flow stress. Consequently,(and consistent with Nunes' model) the forge force increases, which, in turn, increases the prevalence of stick, demonstrated by the increase in torque. The increased prevalence of stick results in a larger volume of material being plastically deformed by the tool, which results in more deformation heating in the material surrounding the tool. Increased deformation heating explains why the spindle speed must be reduced when liquid cooling of tool is implemented.