Crystal Orientation Dependence of Machining Damage, A Stress Model

17, S. M. Degtyarenko, "Contact Area Between the Component and the Intermittent Working Surface of the Grinding Wheel," Soviet Engineering Research, 9(11), pp. 54-59. (1989). An effective method for reducing the thermal stress loading in a grinding process is the use of intermittent grinding wheels (IW). The characteristics feature of such grinding wheels is variation of the contact area between the component and the cutting surface of the wheel in the grinding process. This paper is dedicated to development of numerical criteria for estimating the fluctuations in the contact area and for establishing requirements on the geometrical parameters of IW which combine the advantages of continuous and intermittent grinding wheels. 10 Refs. 18, G. M. Zhang, T. W. Hwang, G. Harhalakis, "Control of Surface Topographies Formed During Machining," Rensselaer',~ Second International Conference on Computer Integrated Manufacturing, Troy, NY, 21-23 May 1990. pp. 339-45. IEEE Comput. Soc. Press, Los Alamitos, CA. An approach is presented from a system engineering perspective to integrate tool-path control and surface topography generation for the quality control of machined surfaces. This approach is based on strategic links between variability of material properties, cutting mechanics in microscale, structural dynamics of machine tools, integration of toll vibratory and geometric motions, and surface topography generation. By combining experimental and analytical work. this research provides manufacturing industry with a computer-based method to control machined surface topographies. 19, Torrance A. A., "Correlation of Process Parameters in Grinding," Wear, 139(2), pp. 383-401. (Aug 1990). An energy method, which had previously been shown to represent well the cutting action of model abrasive grits, was combined with the usual relationships of grinding mechanics to obtain a mathematical model of grinding forces and surface roughness~ It was found that the model would predict accurately the experimental grinding charts of Peters, provided certain assumptions were made about the grit profiles. Good predictions were also obtained for the results of Lindsay, suggesting that it should be possible to develop the model further to account for all aspects of grinding. 31 Refs. 20, K. T. Wan, S. Lathabai, B. R. Lawn, "Crack Velocity Functions Thresholds in Brittle Solids - Final Report," .Int. ~d the European Ceramic Society 6, pp. 259-268. (1990). A unifying treatment of environment-sensitive crack velocity functions for intrinsically brittle solids is presented. The formalism is soundly based on the concept of thermal activation barriers, but is phenomenological in that it does not attempt to identify the explicit underlying physical and chemical processes responsible for these barriers. Equations prescribing the v-G (crack velocity versus mechanical energy release rate) characteristics at specified chemical concentrations (partial pressures) and temperatures are thereby presented. The equations incorporate the familiar three velocity regions into a composite function: region 1, chemically assisted fluctuations over stress-enhanced energy barriers: region 1II. similar but in the absence of environmental species: region 1I, a connecting flow-limited transport branch. Data for selected brittle solids, principally mica but also glass and sapphire, in moist environments are used to illustrate the formalism. 21, W. S. Blackley, R. O. Scattergood, "Crystal Orientation Dependence of Machining Damage. A Stress Model," Journal qf the American Ceramic Society, 73(10), pp. 3113-3115. (Oct 1990). The pitting damage occurring along preferred crystal orientations observed after single-point diamond turning of brittle materials dictates a limiting feed rate at which the material can be machined. Using elasticity theory, the orientation dependence of the pitting can be qualitatively explained. Calculations based on a line-force stress model predict the orientation dependence of the damage symmetry. The results are in good agreement with machining tests for a series of germanium single-crystal wafers. 7 Refs. 22, M. C. Gerchman, "Description of Off-axis Conic Surfaces for Non-axisymmetric Surface Generation," In-Process Optical Measurements and Industrial Methods, Vol 1266, Hague, Neth, 1990. pp. 262-267. Int Soc for Optical Engineering, Bellingham, WA. In this paper the equations that describe off-axis conic surfaces for a four axis approach to non-axisymmetric surface generation are derived. In addition, considerations that minimize the fourth axis range of motion are reviewed. An example, using a well known segmented astronomical mirror, is used to illustrate these considerations, 7 Refs. 23, A. Hamada, M. Kuroda, "Design and Evaluation of Molded Plastic Laser Scanning Optics Using a Concave F-theta Mirror," Optical Hard Copy and Printing Systems, Vol 1254, Santa Clara, CA, 1990. pp. 42-53. Int Soc for Optical Engineering, Bellingham, WA. A laser scanning optics module for use with a compact laser printer has been developed. This optics module features an f-theta concave mirror made from precision molded plastic rather than polished glass and which gives 300 dots per inch resolution. Compared with Minolta's previous compact laser printer, the size of the module has been reduced by forty percent and the production costs of the module have been halved. The reduction in size is achieved both by providing a fbrty percent wider scanning angle than that used previously and by using the concave f-theta mirror to reflect the scanning beam back in the direction from which it came. The production costs have been reduced by replacing the three glass lenses used in the previous module with two molded plastic elements of a single concave f-theta mirror and a single toroidal tens. It was calculated by using simulation software, and subsequently verified in practice, that even when submitted to a temperature increase of forty degrees centigrade flom the normal, the performance of this optics module is ensured. Because of the different rates of expansion between the module and the optical elements themselves as the temperature increases, plate springs are used to hold the elements in place, thus eliminating any strain on the optical surfaces. During the test, the spot diameters and the scanning line position of the optics were found to have the same degree of variation as the glass elements which had previously been used. 24, M. H. Krim, "Design of a Manufacturing Facility for 8 to 10-m Class Mirrors," Advanced Technology Optical 7Wescopes IV, Vol 1236 pt 2, Tucson, AZ, 1990. pp. 748-755. Int Soc for Optical Engineering, Bellingham, WA. There is considerable interest and excitement in the astronomical community about the near-term realization of 8 to 10 meter class telescopes. In this paper we describe the design of a polishing shop uniquely configured to accommodate these mirrors. Simply stated, these mirrors are very large, very heavy, and very flexible compared to existing telescope designs.

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JULY 1991 VOL 13 NO 3