Theoretical Study of Factors Affecting the Effective Rake Angle of AFM Tips for Nanomachining Applications

Abstract

The effect of the tip bluntness of AFM probes on their effective rake angle during AFM-based nanoscale machining is analyzed. It is known that the rake angle of a cutting tool impacts the outcomes of machining processes, such as the cutting forces, the produced surface roughness, and the residual stress. While the edge radius of cutting tools may be approximated as infinitely sharp in conventional macroscale machining, this is not the case when conducting nanoscale machining operations with an AFM probe. In particular, the undeformed chip thickness may be of the same order of magnitude to that of the tip radius. This apparent bluntness of AFM probes directly affects the effective rake angle during such nanoscale machining operations. Hence, an accurate tip bluntness description should be considered. In addition, the influence of the penetration depth of the tip into the processed material and the effect of the tilt of probes, when mounted on AFM instruments, should also be studied. Here, the shape of an AFM probe tip was approximated by a power law function. As expected, it was found that the shallower the penetration for a certain tip shape, the more negative the rake angle is. Also, blunter tips result in more negative rake angles for the same depth. Regarding the impact of the tilt angle, it was found that the tilted orientation provided less-negative angles for all tip bluntness and depth values when the workpiece velocity is oriented in a direction parallel to the long axis of the AFM probe cantilever and pointing away from it. Also, for a given depth, tip bluntness, and thus wear, affects the rake angle of tilted tips more than vertical ones. Thus, these factors should be considered by practitioners during the implementation AFM-based nanomachining.