Tolerance analysis

The tolerance analysis is a method for describing and analyzing the effects of manufacturing errors in multistage manufacturing processes. The results of a tolerance analysis is a mathematical model that describes the relationship between the process capabilities of individual production steps and the resulting process capability for superior product features.

Each production process has a finite production accuracy. Therefore Every component has small deviations from its ideal geometry. If components are processed with geometric variations in a multistage manufacturing process further, then add the geometric errors of the individual parts. If components are, for example, joined in an assembly process, transfer the geometric errors of the items on the assembly. The geometric quality of the final product is determined by the quality of the parts.

The geometries of the individual parts and the parameters of the manufacturing processes must be tolerated so that the overall quality of customer claims in terms of function and appearance met. The tolerance analysis is used to forecast the achievable manufacturing quality based on the tolerances of the individual parts and processes. The operative connection between the relevant post and providers to be examined technical parameter is also referred to as a tolerance chain. If it is geometric variables, it is called according to DIN 7186 also of individual dimensions and closing moderation. The tolerance chain describes the relationship between the individual measurements and the respective closing dimension.

Arithmetic tolerance calculation

The classical arithmetic tolerance calculation is based on the approach of complete interchangeability. It ensures compliance with the required tolerance for the investigation feature for any combination of components. From this procedure leads to very small tolerances for the geometry elements of the items and the parameters of the manufacturing process. These small tolerances can be met only through the use of complex manufacturing process. Because of the associated high production costs, this type of tolerance calculation for especially mission-critical or safety related features is employed.

Statistical tolerancing

The exact expression of a finished workpiece can not be predicted. The behavior of a large amount of manufactured components, however, can statistically describe. The statistical tolerancing provides a forecast of the distribution of a characteristic examination based on the statistical distributions of the elements of the tolerance chain. By considering the distribution of the elements of the tolerance chain statistical tolerancing from the reality is better than the arithmetic tolerancing.

From the forecast of production quality by the tolerance analysis, the need of process and design optimization measures are derived. The optimization process is supported by the mathematical model of the tolerance chain, as it quantifies the effects of individual tolerances on the test feature. According to the Pareto principle, the optimization process should focus on the main Contributor, that is, the individual tolerances that have a strong effect on the expression of the trait investigation.

• Engineering Design
• Metrology
• Six Sigma