Composing Distribution Function Zones for Statistical Tolerance Analysis

More and more often in industry practical exigencies force the designer to
specify part tolerances statistically. Since most products are assemblies of
parts, in order to assess the part-level designs he must consider their
assembly-level implications. In particular, he must be able to combine
specified part-level variabilities to obtain an assembly-level variability.
In the simplest situation it is assumed that the populations of parts are
statistically independent and that the relevant part-level values combine
linearly to produce a linear gap function. Even this simplest case has wide
applicability. In ISO two approaches for statistically specifying mechanical
parts are being discussed. One of these defines acceptability of a population
of parts by requiring that the distribution function of the relevant values
of the parts be bounded by a pair of specified distribution functions. For
this approach to be useful, then, a method to compose part-level specifications
to yield assembly-level description is required. This paper supplies such a
method for the case of statistically independent populations of parts and
linear gap functions.

By: M. A. O'Connor and V. Srinivasan

Published in: RC20723 in 1997


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