SiC Ceramics - Achieving High Performance and Minimum Damage

41, S. Malkin, J. E. Ritter, "Grinding Mechanisms and Strength Degradation for Ceramics," Journal of Engineering for Industry, pp. 167-174. (May 1989). This paper presents a critical review and evaluation of knowledge of the grinding mechanisms for ceramic materials and their influence on the finished surface and mechanical properties. Two main research approaches are identified: a machining approach and an indentation fracture mechanics approach. The machining approach has typically involved measurement of the grinding forces and specific energy coupled with microscopic observations of the surface morphology and grinding detritus. Any proposed mechanisms of abrasive-workpiece interaction must be consistent with the magnitude of the specific energy and its dependence on the grinding conditions. The indentation fracture mechanics approach assumes that the damage produced by grinding can be modeled by the idealized flow system produced by a sharp indenter. Indentation of a ceramic body is considered to involve elastic/plastic deformation with two principal crack systems propagating from the indentation site; lateral cracks which lead to material removal and radial/median cracks which cause strength degradation. Each of these approaches provides insight into grinding behavior and strength degradation, but each has its shortcomings. 42, W, Konig, J. Wemhoner, V. J, Tennery, " G r i n d i n g of Si/SiC Ceramics - Achieving High Performance and Minimum Damage," Third International Symposium on Ceramic Materials, Las Vegas, NV (USA), 27-30 Nov 1988, pp. 12251235. American Ceramic Society Inc., Columbus, OH (USA), Si/SiC components almost invariably have to be finished by grinding. This entails problems both of reduced component strength (due to surface damage) and of the low material removal rate which can be achieved. The paper presents methods for a Si/SiC-adapted surface grinding strategy based on an analysis of process kinematics and a study of the basic mechanisms of material removal. Such methods ultimately lead to a considerable increase in both material removal rate and component strength. 43, W. Konig, C. Schmitz-Justen, N. Koch, "Grinding Optical Glasses with Fine Diamond," Industrial Diamond Review, 50(536), pp. 20-25. (Jan 1990). This paper describes that the properties of the glass material have an important effect on the attainable surface quality in sphere grinding. In addition to the glass's mechanical and thermal properties, the different chip sizes produced during grinding are responsible. Fine grain wheels should be used for the production of high quality surfaces. They can reduce the chip thickness and thus also the surface roughness. The material has a significant effect on wear, particularly with fine grain diamond wheels. The reasons are the dimensions of the chips, which are transported from the grinding zone and therefore cause difficulties with increasing size, in addition to mechanical and thermal parameters. As anticipated, higher wheel wear rates and workpiece surfaces of higher quality are more likely to be achieved with softer bonds than with hard bonds. Competition in the optical industry, particularly with certain Far-Eastern countries, necessitates the attainment of identical or better qualities in a shorter production time by diamond wheel and method optimization. For example, double layer diamond wheels and extremely fine grain diamond cup wheels sometimes permit omission of the finish grinding production stage. Surface roughness and subsurface damage zones can be reduced by the use of such wheels and adapted process control. Subsequent machining operations (e.g. finish grinding) can sometimes be eliminated. With a higher workpiece quality, the total machining time for a lens can sometimes clearly be reduced. 44, S. Chandrasekar, T. N. Farris, B. Bhushan, "Grinding Temperatures for Magnetic Ceramics and Steel," ASME/STLE Joint Tribology Conference, Fort Lauderdale, FL, USA, 1989. 7 pages. American Soc of Mechanical Engineers (ASME), New York, NY, USA. Grinding temperatures are measured using an infrared sensor in ferrite and steel. For reference purposes, temperatures are also measured in a reduced model for grinding which consists of a single diamond grain sliding across the workpiece surface at high speed. The results include temperature as a function of sliding velocity, rate of temperature decay as the grain moves away from contact, and histograms of the frequency that grains on the grinding wheel attain a given temperature. It is found that temperature measurements can be used to detect out-of-roundness in the wheel. (Edited author abstract) 32 Refs. 45, H. Schulz, H. Damariturk, "High Cutting Speeds Bring About Changes in the Cutting Process," Werkstatt und Betrieb, 123(5), pp. 373-377. (May 1990). Increased cutting speeds do not only permit reduced machining times and thus improved productivity, but also result in better surface quality and higher dimensional accuracy. This is contrasted with increased tool wear and higher tool costs. Current updating regarding different cost factors is therefore essential for optimum production. A point of special interest in this connection is to monitor the temperature during metal removal. A special measuring system located at the tool tip has been developed for direct measurement of this factor. (Author abstract) 14 Refs. (In German).

Precision Machining of Advanced Ceramics," 3rd International Symposium on Ceramic Materials and Components for Engines, Las Vegas, NV (USA), 27-30 Nov 1988. pp. 1159-1169. American 46, W. Konig, M. Popp, V. J. Tennery, "High

Ceramic Society Inc., Columbus, OH (USA). Potential reduction of friction and wear through the use of advanced ceramic materials for engine components such as seals, bearings and valve adjusting plates is of great interest, Since there is no running-in effect with ceramic materials, however, an extremely high precision finishing process is required for such components. The complicated machining characteristics of ceramics pose additional problems. The present paper discusses problems related to precision machining of advance ceramics. A number of solutions with considerable potential in terms of reliable quality and efficiency are presented. 47, M. Chang, "High

Precision Non-contact Three-dimensional Surface Topography Measurement for Finemachined Surfaces," Journal of the Chinese Society of Mechanical Engineers, 10(4), pp. 295-302. (Aug 1989). An automated three-dimensional surface topography measuring instrument using heterodyne technique for obtaining surface characteristics of finemachined surfaces is presented. The measurement algorithm and the related systematic error sources are described. Height variations of 1 nm can be resolved, while the theoretical resolution is below 1 ~. Scan length has no theoretical limitations, which depends on the surface roughness region of the test sample and the number of the pixels of the CCD sensor. With the noncontact method of measuring surface characteristics, it is possible to develop an on-line or in-process measurement device. (Author abstract) 9 Refs. 48, I. E. Minis, E. B. Magrab, 1. O. Pandelidis, "Improved Methods for the Prediction of Chatter in Turning, Part 1. Determination of Structural Response Parameters," Journal of Engineering for Industry, Transactions ASME, 112(1),

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