Material perspective in ultra-precision machining

Abstract

In material removal processes at ultra-precision scale, the undeformed chip thickness, UCT (a) can be in the order of a few microns or less and can even approach the nanoscale. At this range, the accuracy targets for today's ultra-precision machining (UPM) process cannot be achieved by simply downscaling the conventional machining processes. There are limitations of bringing down the machining process from macro to micro to nano-level due to the differences in material characteristics. Additionally, special attention is required to material microstructure for tool-workpiece interaction, which occurs entirely within a single grain or a few grains of the workpiece. Therefore, material related issues are gaining more importance during micro/nano-scale machining. Moreover, the cutting mechanics of micro/nano-scale machining differs from that of conventional machining due to the consideration of cutting tool (edge radius, nose radius) in UPM. The mechanism shifts from concentrated shearing to an ‘extrusion-like’ phenomena due to the ‘cutting edge radius effect’ when the UCT (a) falls below the size of cutting edge radius, CER (r). In order to investigate the cutting tool edge radius effect, the governing process parameter is identified as relative tool sharpness (RTS, a/r) which is quantified as the ratio of UCT(a) to CER (r). This has led to explore the effect of material microstructures on the transition of micro-to-nano scale cutting mechanism in UPM. In addition, size effect in diamond turning is explored by considering the relative scale between the CER and anisotropic migration of material microstructure along the nose of the tool.