Micro and Nanomachining Technology-Size, Model and Complex Mechanism

This chapter focused on the emerging global trend toward the miniaturization of manufacturing processes, equipment and systems for micro and nanoscale components and products, i.e., small equipment for small parts. The present need for smallness of parts stems mainly from two requirements: greater compactness in the utilization of space and portability. The mechanical and electrical devices that make up these items need to be produced in ever-decreasing sizes, with tightly specified dimensions and accuracies. Although these miniature devices may be machined by various techniques, their shaping through material removal constitutes a major means of production. Innovations in the area of micro and nanofabrication have created opportunity to manufacture structures at the nanometer and millimeter scales. These ultraprecision machining processes include STM based nanofabrication and abrasive machining (including lapping, polishing and honing) which can be characterized by either two body or three body abrasive interactions. There are various ways to classify precision material removal processes. We have presented one above, based on the “uncut chip thickness”. Combinations of these techniques and established methods of manufacturing that produce hybrid manufacturing processes will create the short term "stepping stones" required to meet the demand generated to economically manufacture microscale products. In this chapter, some dominant micro and nanomachining techniques that are currently used to fabricate structures in the nanometer scale up to the millimeter scale are introduced.

The machining allowance and chip thickness can be reduced to less than approximately 1 μm in ultraprecision manufacturing such as single point diamond turning (SPDT). Metal surfaces can be finished under precisely controlled machine and environmental conditions. Accuracies of, respectively, 10 and 1 nm have been attained in practice and under experimental conditions (aided by advanced control techniques). Under the highly precise motion of such a machine tool, the primary factor affecting machining accuracy is the controllability or repeatability of the thickness of cut, that is, the undeformed chip thickness effectively removed at the cutting edge. Experiments with a specially prepared fine diamond cutting tool used on such a machine tool have confirmed that very fine chips, of undeformed thickness as small as 1 nm, can be removed in the turning of some highly machineable work materials. However, the accuracy attainable, and mechanisms such as chip formation and surface generation in microcutting are still not well understood, owing to the limitations in availability of experimental and measurement techniques, and in analytic methods for studying such machining conditions. Micro & nanocutting that occurs in a small region which contains only a few layers of molecules can consequently be atomistic, or discrete in nature, rather than continuous, as is assumed in conventional continuum mechanics. In studies of such atomistic processes, which are difficult to investigate experimentally, computer simulation by molecular techniques is useful. Further advancements in the machining technology can be aided through a theoretical understanding of micro & nanomachining. Molecular dynamics (MD) simulation, like other simulation techniques can play a significant role in addressing a number of machining problems at the atomic scale. It may be noted that atomic simulations are providing new data and exciting insights into various phenomenon in micro & nanomanufacturing processes that cannot be obtained readily by any other theory or experiment. The diversity of these processes renders difficult of using a generalized theoretical analysis of micro & nanomachining, however, the methods of molecular dynamics are becoming increasingly attractive for studies of micromachining, especially as the technology advances toward the shaping of parts in the nanometric range. The foundations of molecular dynamics that are needed for theoretical treatments of micromachining therefore form the basis of MNT. Several such analyzing of micro & nanomachining have been developed. In this chapter, the principle of molecular dynamics (MD) simulation on micro & nanomachining and the procedures used to determine the accuracies attainable are described. As noted above, the case of diamond machining and chemical mechanical polishing are used to illustrate the technique, although molecular dynamics is now being increasingly used in studies of many other methods of micro & nanomachining.

The dimensional tolerance achieved by precision machining technology is on the order of 1 nm and the surface roughness is on the order of 0.1 nm. The dimensions of the parts or elements of the parts produced may be as small as 1 μm, and the resolution and the repeatability of the machine used must be of the order of 1 nm (10 nm). Unlike conventional machining processes, precision machining processes are not based on the removing the metal in the form of chips using a wedge shaped tool. When metal is removed by machining there is substantial increasing in the specific energy required with decrease in chip size. Since the shear stress and strain in metal cutting is unusually high, discontinuous microcracks usually form on the metal-cutting shear plane. Owing to the complexity of elasticplastic deformation at nanometer scale, the worldwide convinced precision materials removal theory is not built up until now. As the complexity associate with the precision machining process involve high strains, strain rates, size effects and temperature, various simplifications and idealizations are necessary and therefore important machining features such as the strain hardening, strain rate sensitivity, temperature dependence, chip formation and the chip-tool interface behaviors are not fully accounted for by the analytical methods. Experimental studies on precision machining are expensive and time consuming. Moreover, their results are valid only for the experimental conditions used and depend greatly on the accuracy of calibration of the experimental equipment and apparatus used. Advanced numerical techniques such as Finite Element Method (FEM) is a potential alternative for solving precision machining problems. Characterizing the surface, subsurface, and edge condition of machined features at the precision scale in the FEM analysis are of increasing importance for understanding, and controlling the manufacturing process.

MNT is a technology that accurately produces geometrically dimensional shapes in the micro & nanometer scale. An emphasis on micro & nanoscale entities will make our manufacturing technologies and infrastructure more sustainable in terms of reduced energy usage and environmental pollution. The minimizing of the workpiece and the small depth of cut makes the materials removal or deformation in the MNT different from the traditional machining technique. Materials properties follow from their atomic and microscopic structures and exhibit different properties at different scales. Bulk materials of micro & nanometer scale are relatively large and may be expected to behave as “macroscopic” object in some respects. At the same time they are small enough to permit the long-time simulations necessary for investigation of microscopic properties such as self-structural organization processes. It is difficult to deeply investigate materials deformation or failure mechanism using single macroscopic or phenomenological scale method. Multiscale method can study material behavior at different length scale and temporal scale simultaneously which can uncover important properties and materials response in MNT from atomic to microscopic to mesoscopic to macroscopic scales. Multiscale method offer the best hope for bridging the traditional gap that exists between experimental approach, the theoretical approach and computational modeling for studying and understanding the deformation and removal mechanism of materials in MNT. Multiscale method conform to the basic natural philosophy ideas, namely, every things should evolve from quantitative change to qualitative change. Owing to the central role that multiple scale methodology appears poised to play in the computational mechanics and materials science in the foreseeable future, this chapter introduces multiscale method and some recent applications.

The physical process involved in the MNT is unique which makes it a special area of machining science. The reason for this is that the minimizing of the workpiece or machining precision level is greatly improved in the MNT comparing with the traditional machining technique. Mechanical properties of materials are scale dependent based on the strain gradient plasticity and the effect of dislocation-assisted sliding. When material is removed by machining, there is a substantial increase in the specific energy required with decrease in chip size. It is generally believed that this is because all metals contain defects (grain boundaries, missing and impure atoms, etc.), and, when the size of the material removed decreases, the probability of encountering a stressreducing defect decreases. Furthermore, the dominate role of the volume force in the larger scale is replaced by the surface force such as adhesive force at this micro & nanolength scale. The generation and dissipation of heat and the materials plastic deformation also involved different control mechanism from the macroscopic scale. Traditional metal cutting principle cannot give a reasonable explanation about phenomenon in the MNT. MNT is a novel challenge that should be studied in depth using ideas of modern physics that deals with the problems of complexity. This chapter devoted to the introduction of studying MNT using complexity theory (selforganization, nonequilibrium thermodynamics, fractal theory etc.) and some new corresponding developments.