Simulation and Experimental Investigation of Scallop Removal Using Friction Stir Processing and Complex Toolpath

Machining of complex geometries is conventionally accomplished through the use of a ball-end mill and a helical toolpath which follows along the contours of the geometry at incremental depths. While effective for the majority of geometries, this method produces scallops which result from the ball-end mill radius and the step size of the toolpath. The size of these scallops, which degrades the surface finish, can be minimized by utilizing a relatively small step size. However, this results in increased machining time. A novel method of scallop removal is simulated and experimentally tested herein on 6061-T6511 aluminum. This method applies a friction stir processing effect to the workpiece by rotating a ball-end mill tool in reverse over the surface of the material subsequent to ball-end mill cutting passes. Additionally, the path constructed for scallop removal was a self-intersecting epicycloid which plastically deforms the scallops in order to reduce the surface roughness and impart favorable compressive surface stress. In this study, the surface variability produced from this process is reported for several different tool paths, determined experimentally and through simulation. Future studies will investigate the microstructural effects of this process, as well as the resulting microhardness and residual stress profile.