Machinery's Handbook, 31st Edition
MICROFABRICATION PROCESSES AND PARAMETERS 1191 Table 11. Pecking Cycle, Drill Dia. D = 0.005 inch
Pecking cycle #
Hole depth (inch)
Pecking depth, P (inch)
Aspect ratio
P / D 1.83 1.53 1.27 1.06 0.88 0.74 0.61 0.51 0.43
1 2 3 4 5 6 7 8
0.0100 0.0192 0.0268 0.0332 0.0385 0.0429 0.0466 0.0497
2.00 3.83 5.36 6.63 7.70 8.58 9.32 9.93
0.0092 0.0076 0.0064 0.0053 0.0044 0.0037 0.0031 0.0026
9 0.0021 Microturning.— Product miniaturization and the demand for ultraprecision products drives the rapid development of micro/nano turning. This technology produces polished and high quality spherical and aspherical parts from metals, ceramics, semiconductors, and polymers that cannot be economically produced by traditional grinding, lapping, or polishing processes. Micro/nano turning also produces intricate shapes with low or no subsurface damage because it operates in the ductile-regime mode (see Ductile Regime Micromachining on page 1172). 0.0522 10.44 Diamonds are commonly used for micro/nano turning. Polycrystalline diamond (PCD) tools are sintered from microsize diamond grains. PCD tools are less expensive but with limited capability due to large edge radius (few hundred nanometers) and lower edge strength due to attrition wear. Single crystalline diamond (SCD) tools are best for micro/nano turning because they: • Have single crystalline structure that allows a sharp cutting edge as small as 10 nm • Have the highest thermal conductivity among all engineering materials • Retain high strength and hardness at high temperature • Have high elastic and shear moduli to resist plastic deformation, and • Have a low coefficient of friction A diamond tool, however, is costly and brittle. A tool with zero or negative rake angle (i) improves its edge strength, and (ii) forms a hydrostatic compressive stress field in the material just in front of and below the tool, and therefore, minimizes crack initiation. Sin gle crystal diamond typically have the (110) crystal plane as the rake face and are brazed onto a steel shanks of different shapes and sizes. Not all materials can be successfully micro/nano turned with a diamond tool. Ferrous alloys and silicon carbide (SiC) are not suitable for diamond turning because of diffusion from the highly concentrated carbon in the diamond tool to a lower concentration zone of carbon in the workpiece materials. Other materials, although machinable with diamond, should be homogeneous and contain few if no impurities. Any hard inclusions might either damage a sharp diamond edge or be sheared off and smear against the machined surface. Fig. 36a shows hard beryllides in beryllium copper CA173 that plow and smear a mirror finish surface ( Fig. 36b). Table 12. Examples of Diamond Machinable Materials Semiconductor Metal Ceramic Plastics
Cadmium telluride Gallium arsenide Germanium Lithium niobate Silicon Silicon nitride Zinc selenide Zinc sulphide
Aluminum alloys Copper alloys Electroless nickel Gold Magnesium Silver Zinc
Aluminum oxide Zirconium oxide Optical glasses Quartz
Acrylic Fluoroplastics Nylon Polycarbonate Polymethylmethacrylate Propylene Styrene
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