Abstract
This paper summarizes the results of exploratory studies of the statistics of actual values (minimal enclosing zones) of essentially two-dimensional geometric position, circularity. and runout tolerances. Data for the studies were collected via CMM measurements of IOO-sample lots of commercial washers and automotive valve seats. Phenomenological models were devised to predict the measured statistics, and agree reasonably well with the experimental data.
The metric used to assess the effects of non-normality is failure rate, i.e. the probability that a part selected randomly from a population will fail to meet a fixed tolerance specificat ion. Significant differences are noted in the failure rate estimated for features exhibiting the modeled, non-normal statistics versus those having normal statistics. The paper shows that blind use of techniques that rely on normal statistics, such as those based on the Cp, Cpk process control indices, can be dangerous when the actual statistics are not normal.
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© 1998 Springer Science+Business Media Dordrecht
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Braun, P.R., Morse, E.P., Voelcker, H.B. (1998). Research In Statistical Tolerancing: Examples of Intrinsic Non-normalities, and their effects. In: ElMaraghy, H.A. (eds) Geometric Design Tolerancing: Theories, Standards and Applications. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-5797-5_3
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DOI: https://doi.org/10.1007/978-1-4615-5797-5_3
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