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3.2.7 NIST Ceramic Machining Consortium

Lisa M.  Gill

James J.  Filliben

Raghu Kacker

Statistical Engineering Division, CAML

Said Jahanmir

Lewis Ives

Ceramics Division, MATLS

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. In order to be competitive, both nationally and internationally, advanced machining operations of ceramics needed to be better understood and more efficiently carried out. The program was lead by and continues under the direction of Said Jahanmir of the Ceramics Division. 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. The goal is to develop measurement methods, produce and collect data, and produce reference materials and databases to assess the influence of machining properties and performance on advanced ceramics. 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. The role of the consortium members is vital to the success of the program; they participate in the research projects by providing materials, testing, technical advice, and other in-kind contributions. Currently, the 21 members actively involved are:

Ceradyne Inc. General Electric Co. Tech. Assessment & Transfer
Cercom, Inc. General Motors Corp. Torrington Co.
Cincinnati Milacron, Inc. Georgia Inst. of Tech. Univ. of Delaware
Corning Inc. Kansas State Univ. Univ. of Maryland
Dow Chemical Co. Landis/Western Atlas Corp. Univ. of Massachusetts
Eaton Corp. Lehigh Univ. Univ. of Rochester
Ford Motor Co. Stevens Institute of Tech. West Advanced Ceramics, Inc.
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. These data and other evaluated data gathered from the literature and consortium members are being assembled in a computerized database. This Ceramic Machinability Database will provide access to data for different types of ceramics and will help users, such as manufacturing engineers, tooling managers, and machinists, develop machining plans for the cost-effective production of ceramic parts. One project in the program evaluates the feasibility of several non-destructive methods (such as ultrasonics and thermal wave measurement methods) to detect and characterize the machining damage in ceramics. In addition, the generation of reliable surfaces is an important issue; hence, another project seeks to determine the effects of grinding conditions in the "ductile regime" grinding process to establish the role of microstructure and grinding parameters in obtaining damage-free surfaces and the fundamental mechanisms involved in the material-removal process during grinding of silicon nitrides. The purpose is to determine the influence of grinding parameters, such as down feed, wheel grit size, and table speed, on machinability and ceramic strength, and to determine optimal settings. Further, an exploration of the relationship between ceramic microstructure and ceramic properties (e.g., grain size, distribution of second phases, hardness, and fracture toughness) is underway. The Statistical Engineering Division has played a critical role from the beginning. In particular, for the silicon nitride project, it was recognized that the conclusions regarding important grinding parameters may potentially be contaminated by other factors such as laboratory, batch, etc. This large-scale multi-laboratory experiment thus required a careful experiment design to assure the validity of the conclusions. Early on in this multi-year project, SED members Raghu Kacker and Lisa Gill provided the expertise in constructing an experiment design with enough scope that project goals were efficiently and unambiguously achieved. More recently, after the experimental data was collected, SED members Lisa Gill and James Filliben provided the data analysis expertise in ascertaining important grinding factors, uncovering significant non-grinding factors, identifying interactions, and establishing optimal settings. At each of the semi-annual meetings, Lisa Gill provided to consortium members well-received detailed presentations of such conclusions along with the supporting data analysis methodology (a few representative analysis graphics from the talks are provided below). A jointly co-authored paper entitled "Effects of Grinding on Strength of Sintered Reaction Bonded Silicon Nitride" will be presented at the Second International Conference on Machining of Advanced Materials (September 30, 1996, Eurograss Aachen, Germany).


Figure 19: Probability Plot Correlation Coefficient Plot (SRBSN, Longitudinal, Batch 1): The character of the plot is the lab identification number. The 3-Parameter Weibull is the best distribution overall, but the 2-Parameter Weibull and Normal distributions still do a reasonable job representing the distribution of the data. The Lognormal distribution does not do so well.

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Date created: 7/20/2001
Last updated: 7/20/2001
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