A New Tolerance Analysis Method for Designers and Manufacturers

Abstract

Even when all manufactured parts for an assembly are produced within limits, these parts still may not assemble properly if the assembly tolerance analysis was inadequately performed. Naturally occurring shifts in a process can produce biased distributions which can result in increased assembly problems and a greater number of rejects than anticipated. The most common methods of analysis of assembly tolerance buildup are worst case and root sum squares. The limitations of each of these methods are discussed and a simple new method is proposed which accounts for expected bias. This new method includes both worst case and root sum squares as extreme cases.

A survey of research in the application of tolerance analysis to the design of mechanical assemblies

“…Mansoor [1963] proposed that the tolerance accumulation be represented as a WC sum plus a RSS sum. A similar model by , Greenwood and Chase [1987] and Chase and Greenwood [1988] introduced an estimated mean shift factor m i (a number between 0 and 1.0) which quantifies the expected mean shift as a fraction of the specified tolerances. Eq.…”

Simultaneous optimal selection of design and manufacturing tolerances with different stack-up conditions using genetic algorithms

“…Spotts (1978) proposed a method based on the average of the results obtained from the worst case and the RSS stack-up conditions (equation 5). Greenwood and Chase (1987) proposed a unified (also called estimated mean shift) method where the amount of mean shift could also be controlled (equation 6). This includes the worst case and RSS as extreme cases and can simulate anything in between.…”

Stacked tolerance analysis and allocation using assembly models

“…2. There is a variety of methodologies available in the literature to deal with the problem of analyzing tolerances assigned to the mating components of stacked assemblies Chase, 1987 andGreenwood, 1988). These are summarized below:…”