Alain Sergent

Manufacturing tolerance analysis based on the model of manufactured part and experimental data

Tolerance analysis has been the topic of many research publications in the recent past. It is a method to evaluate the quality of products in terms of functional tolerances. Most of the assessment procedures in process planning are based on trial-and-error runs, which are costly and time consuming. There is also a distinct lack of research focus in the area of process plan verification in which input variables are generated from experiments. This article first provides an overview of tolerance analysis. The limits of the previous studies are explored. A method to overcome problems in manufacturing tolerance analysis is then proposed. This method is based on the model of manufactured part and deviation domains to obtain mathematical formulations. These formulations are applied to manufacturing tolerance analyses in which experimental data are used as input variables. The results obtained are then used to verify process plans relative to functional tolerances or to identify achievable functional tolerances taking into account a given process plan and a given number of parts per million. A summary of the method used to obtain the experimental data is presented.

Weighted Inertial Tolerancing

The objective of tolerancing methods is to limit the variations of a characteristic while trying to minimize the cost of realization. Traditionally expressed in the form of an interval (min, max), it can also be expressed in a different form as in the case of inertial tolerancing. The principle of inertial tolerancing consists of tolerancing the mean square deviation in relationship to the target. This new tolerancing method has many properties that the property of additivity of the mean square deviation offers. However, when several characteristics are added to give a resulting characteristic, it leads to a significant tightening of the variations around the target in the case of a process with a small dispersion. Our proposal consists of defining a new alternative of inertial tolerancing: weighted inertial tolerancing. Its goal is to obtain the best possible compromise between statistical tolerancing and worst-case tolerancing method. One will be able to use it when it is not useful to guarantee an inertia on the resulting characteristic, but simply to limit the variations compared with the target.