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3.2.6 NIST Ceramic Machining Consortium
Lisa M. Gill
James J. Filliben Statistical Engineering Division, ITL
Said Jahanmir
Lewis Ives Ceramics Division, MSEL In July of 1992, a research program on ceramic machining was initiated by the Materials Science and Engineering Laboratory prompted by the results of a comprehensive survey of U.S. industry which confirmed that the primary impediment to the widespread use of advanced ceramics is the high cost of machining. To assure that industry needs were properly addressed and to take advantage of expertise existing at other research institutions, NIST established a consortium with members from industry, academia, and government. Currently, their are 23 active members. The mission of the program is to assist U.S. industry in the development of precision machining for the manufacturing of cost-effective advanced ceramic products. A primary goal of the consortium is to collect and analyze data on the effect of grinding parameters on ceramic properties/performance. Of particular interest is how the strength and surface integrity vary with the grinding parameters, and the determination of grinding conditions that result in high material-removal rates without significantly decreasing the strength of the ceramic. An experiment involving eight different commercial and industrial grinding facilities was designed to evaluate the influence of grinding conditions on the flexure strength of three ceramic materials: sintered reaction bonded silicon nitride (SRBSN), reaction bonded silicon nitride (RBSN) and sintered silicon nitride (SSN). Given the overall goals of the experiment and the constraints due to time, money and the available material, a full factorial in four primary factors partially confounded incomplete block design was constructed and implemented. The grinding parameters varied were table speed, down feed, grit size and the direction of grinding with respect to the tensile direction of the four-point bend flexure specimens used in the study. A relatively high removal rate grind regime was investigated.
The results showed that, even under the most aggressive grinding conditions, no significant
change in flexure strength was measured when grinding was parallel (longitudinal direction)
to the tensile direction. All conditions resulted in a decrease in flexure strength when
grinding was perpendicular (transverse direction) to the tensile direction. In addition, in the
transverse direction, there was a significant effect due to wheel grit size and an interaction
between table speed and down feed (for SRBSN). The other two materials had similar
conclusions.
Figure 16: Bihistogram of Longitudinal Grinding Direction versus Transverse Grinding Direction for SRBSN, RBSN, SSN (top to bottom). The shift in the histogram represents the effect direction has on the strength of the ceramic. The effect is evident in all three materials and in the same direction; that is, transverse grinding resulted a lower flexure strength.
Date created: 7/20/2001 |