Virtual Part Arrangement in Assemblies for Automatic Tolerance Chart Based Stackup Analysis

Manual construction of design tolerance charts is a popular technique for analyzing tolerance accumulation in parts and assemblies, even though it is limited to one-dimensional worst-case analysis. Since charting rules are GD&T (geometric dimensioning & tolerancing) specification dependent, and the user has to remember all the different rules to construct a valid tolerance chart, manual charting technique is time-consuming and error-prone. The computer can be used for automated tolerance charting, which can relieve the user from the tedious and error-prone procedure while obtain the valid results faster. The automation of tolerance charting, based on the ASU GD&T mathematical model, involves (1) automation of stackup loop detection, (2) formulation of the charting rules for different geometric tolerances and determination of the closed form function for statistical analysis, (3) automatic part arrangement for an assembly level chart analysis, (4) development of the algorithms for chart analysis and automatic application of the charting rules. Since the authors’ previous DETC/CIE’03 paper already discussed tasks 1~2 and part of task 4, this paper will focus upon task 3, i.e. virtual part arrangement in assemblies for tolerance charts, and update the analysis algorithm (related to task 4). These two papers together will provide a complete coverage of automated tolerance charting technique popularly used in industry. The implementation will be briefly discussed as well, and case studies will be provided to demonstrate the approach to virtual part arrangement.