Development of a high-speed high-precision micro-groove cutting process

摘要

A high-speed, high-precision chip formation-based micro-groove cutting process has been developed for cutting grooves in metals with nearly arbitrarily shaped cross-sections, which have widths and depths of a few hundred nanometers to a few microns, and lengths of tens of millimeters. A flexible tool, consisting of a single-point cutting geometry mounted on the end of a small cantilever, is moved along a workpiece surface while a constant cantilever deflection is maintained to apply a cutting load. Depth of cut for a given tool shape is determined by cutting load and workpiece material properties. A major advantage of the flexible tool concept is increased depth of cut precision. Furthermore, the use of a flexible tool enables the process to be robust against machine tool registration error, guide misalignment, and component inertial deflections. The process was implemented by fitting a 5-axis micro-scale machine tool with a specially constructed micro-groove cutting assembly.Early, experiments using diamond-coated AFM probes as tools demonstrated process viability up to cutting speeds of 25 mm/min and chip formation at the sub-micron scale. However, AFM probe geometries proved too fragile for this demanding application. High quality tools with improved cutting geometries were designed and fabricated via focused ion beam machining of single-crystal diamond tool blanks, and tool edge radii of 50 - 64 nm were achieved. The improved tools enabled well-formed rectangular grooves to be cut in aluminum at up to 400 mm/min with widths of 300 nm to 1.05 microns and depths up to 2 microns. Complex compound v-shaped grooves were also produced. Virtually no tool wear (less than 20 nm) was observed over a cutting distance of 122.4 mm. Small amounts of side burr formation occurred during steady-state cutting, and exit burr formation occurred when a tool exited from a workpiece. Parallel 1.05 micron wide grooves were controllably cut as close as 1.0 micron apart, and machining of intersecting grooves was successfully demonstrated. To better understand process mechanics including chip formation, side burr formation, and exit burr formation at the small size scale involved, a 3D finite element model of the process was developed. Validation with experimental results showed that on average the model predicted side burr height to within 2.8%, chip curl to within 4.1%, and chip thickness to within 25.4%. An important finding is that side burr formation is primarily caused ahead of a tool by expansion of material compressed after starting to flow around a tool rather than becoming part of a chip. Also, three exit burrs, two on the sides of a groove and one on the bottom of a groove, are formed when a thin membrane of material forms ahead of a tool and then ruptures as the tool exits a workpiece. Finally, conclusions about the process are drawn and recommendations for future work are presented.