Tolerance and Stack Analysis Manual and Advance approach

In the last few years, CAT industry has known a significant improvement and over the same period a number of CAT systems have been emerged. Each system is used for a special task in a specific stage of design process.

In this section, the main CAT systems used in the current tolerancing practices are analyzed. The information is obtained from CAT software vendors and some works related to this subject. However, there are many existing CAT systems developed in the research area, Anselmetti et al. [A1, A2] has developed QUICK GPS (Geometric Product Specification), this CAT system generates automatically part tolerance specifications which is based on junction analysis between parts within the designer methodology.

In the same time, designers used empirical approach based on their experience to define tolerancing values. But, the introduction of CAT systems has changed the rules. It has offered to designers a scientific approach based on modeling and analyzing. Currently, CAT systems are designed to carry out two main tasks: tolerancing analysis and tolerancing synthesis.

For tolerancing analysis aspect, they are based on standard arithmetic models (Worst case) or statistical models (Root Sum Square), and advanced simulation algorithm as Monte Carlo. The Monte Carlo simulation performs assembly tolerancing analysis using a random number generator which selects values for each manufactured variable, based on the type of statistical distribution assigned by the designer. The final result will more realistic than standard tolerancing analysis method. For tolerancing synthesis aspect, several CAT systems propose the possibility to identify main contributors, and therefore, the most influence link of a tolerancing chain. This functionality is very important for designers to optimize tolerancing values in order to reduce manufacturing costs.