Understanding the surface generation mechanism during micro-scratching of Ti-6Al-4V

A lot of grinding research in the past has been emulated using single grit scratching. This limits studying surface generation mechanism due to overlapping scratches inherent to the grinding process. It not only affects the surface generation mechanism, but also limits studying elastic recovery which has a significant effect on the final form and topography including the roughness generated after grinding. Taking Ti-6Al-4V as a testbed, this investigation was directed on comparing single scratches with adjacent scratches, which are often referred to as double scratches in literature. During the experiments, the effect of scratch speed and the scratch separation distance on the cutting forces, material pile-up area ratio (PA), groove depth, material removal area (MRA), and sub-surface deformation were investigated. It was found that the scratch speed significantly affects the pile-up and groove depth because of phenomena like stress build-up and elastic recovery. A complementary analytical model of ploughing and shearing forces developed here led to the observation that the minimum chip thickness can only be around 0.1 to 0.2 times the radius of the indenter. Elastic recovery was found to be larger at the middle of the scratch, which was confirmed by the stress-strain relations derived from the FEM simulations. It was also observed that the spacing between two subsequent scratches can significantly affect the scratched surface quality. These experiments show that the severe ploughing and mid-region ridge features can be avoided by having the scratch pitch to be at least one third of the grit tip radius.