Micromechanical machining uses physical cutting tools in high precision machines to fabricate parts with micrometers features and sub-micrometer tolerances. An advantage of this process is the ability to use any machinable material, quick process planning and material removal, and three-dimensional geometry only limited by the machine and tools used. Disadvantages are that forces are placed on micro cutting tools causing deflection and possible breaking. Deflection reduces process precision and tool breakage results in repeated set up, slower production, and poorer tolerances. Nevertheless, these processes have created many diverse prototypes ranging from biomedical to space applications.
Micromechanical machiningMicromechanical machining generally consists of micromilling, microdrilling, and diamond micromachining. Diamond machining uses relatively large tools with very sharp cutting edges. The cutting edge radius of a new diamond tool is typically on the order of 100 nm. The overall size of the diamond used for a tool provides good stiffness and little if any deflection under the action of cutting forces. Diamond has an extremely high elastic modulus of 1000 GPa and a cleavage strength of 4 GPa making it a stiff and strong tool material. A disadvantage of the very sharp cutting edge is that high heat flux passes through the edge because of heat generation during cutting. This is especially true when a high surface speed is used along with a small tool feed to obtain very smooth surfaces. When cutting metals, a significant portion of the heat is carried away with the chip or into the work piece.When machining plastics though, nearly all the heat is transferred through the diamond cutting edge resulting in more rapid wear of the edge. The high heat flux will cause the diamond to revert to graphite under extreme conditions. This effect is so severe that machining plastic will wear a diamond tool approximately three-times faster than when machining oxygen-free high conductivity copper. Additionally, metals that readily absorb carbon, such as ferrous alloys, will quickly wear a diamond tool under normal cutting conditions due to diffusion of the diamond into the work piece.In contrast to diamond tools, metal micromilling tools have a much duller cutting edge with a radius of a few micrometers. The radius of the cutting edge is much larger than the thickness of the material layer removed. The process appears to be that of machining with a very dull cutting edge resulting in high forces. Because the tool is structurally weak a typical axial depth-of-cut is only a few micrometers to help reduce forces. The radial depth of cut is normally less than one micrometer, and often on the order of tens of nanometers, due to the high rotational speed and slow feed rate of the tool. This places the cutting forces at the end of the cantilevered tool causing high stress and deflection. As the axial depth of cut into the material is reduced, or as the feed per revolution of the tool is decreased, the cutting forces greatly increase ...
