Automatic generation of min/max tolerance charts for tolerance analysis from CAD models

Abstract

The so-called min/max tolerance charts are popular for analysing tolerance accumulation in parts and assemblies, despite the fact that this method is limited to one-dimensional worst-case analysis. Since different chart construction rules apply to different tolerance classes, the user has to remember all the different rules to construct a valid tolerance chart. Constructing the charts manually, as is common practice in industry today, is time-consuming and error-prone. This paper presents procedures for automating tolerance charting. It requires a computer aided design (CAD) model with GD&T specifications as input. The automation is based on a data model called the constraint-feature-tolerance (CTF) graph and machine interpretable representation of charting rules specific to each tolerance class. This paper also presents procedures for automatically extracting dimension and tolerance stacks for any user defined analysis dimension, and automatic part arrangement in assemblies corresponding to worst case analyses. Important implementation issues are also discussed and several case studies are presented, the results of which have been verified by manual chart construction.