Tool Risk Setting in Statistical Tolerancing and its Management in Verification, in Order to Optimize Customer's and Supplier's Risks

The statistical tolerancing aims to enlarge tolerances while limiting the customer risk. The rules are largely shared when the factors vary according to a normal law. But a lot of manufacturing processes cannot deliver a mean exactly centered or stable, and some are multi-generator. This paper will clarify the different options of calculation; define what is “tool risk” and how to set it. In the second part we will define the criteria of verification according to the hypothesis and the settings made during design, and the way to detect appearance of a tool risk and fix it. In appropriate contexts, this coupling tolerancing-verification allows high benefit by enlarging tolerances while mastering the risks, that is the target of statistical tolerancing.