Development and Standardization of Quality-oriented Statistical Tolerancing in China

The development of the quality-oriented statistical tolerancing (ST) technique and its standardization in China are briefly introduced in this paper. Based on the new development in the academic area of geometrical product specifications (GPS) and statistical process control (SPC), it is out that the ST technique must be innovated and improved to face the challenges of the modern manufacturing environment. The principle of quality-oriented ST and the mathematical models are given. A set of standardized process quality indices (PQIs) for evaluating the nonconforming of process, process centring and quality loss has been presented. This evaluation system based on PQIs and the standardized two-dimensional interface relative to the process mean and the standard deviation of process has relatively strong compatibility and adaptability with the process capability analysis and SPC that are widely applied in the modern manufacturing environment. The standardized PQIs may also be used as a part of population specifications. The serial ST standards published by the standardization committee of China and their main applications with a case study are introduced, and are expected to play important roles for assuring the designated dimensional specifications and population specifications with preset confidence interval.