Development of a heat source model for friction stir welding tools considering probe geometry and tool/workpiece interface conditions

Over the past 25 years, friction stir welding (FSW) tools have evolved from simple cylindrical geometries to complex conical profiles which incorporate flutes, threads, and multiple facets. Due to the limits of physical testing, finite element (FE) modeling is widely used to analyze FSW tool behavior. However, simulation accuracy is dependent on the tool/work interface conditions and the heat source model that is used. While a uniform probe/workpiece interface conditions are typically assumed in most heat source models, recent work indicates that slip rates on curved (lobe) and flat (facet) surfaces differ considerably. In the present work, a quick stop device was used to observe the steady-state interface conditions for a hexagonal (three lobes and three facets) probe and a generalized heat source model is proposed for asymmetric tools having an arbitrary number of surfaces. A 3D finite element model based on FLUENT was also developed and used to simulate three different probe configurations. A comparison of simulated and experimental temperature profiles showed good agreement and confirmed that heat generation increases with the number of probe facets but approaches a limit as lobes begin to approximate facet surfaces at small edge lengths. Analysis of FSW welds showed that increasing the number of facets promotes lateral flow and results in a wider plasticized zone. It is expected that the study findings will be useful in improving the accuracy of heat source models and understanding how probe geometry affects welding behavior.