A constraint-based tolerance analysis in a multi-operation single setup and multi-operation multi-setup part–fixture assembly

Abstract

This paper presents a constraint-based approach to tolerance analysis in a multi-operation single setup and multi-operation multi-setup part–fixture assembly. First, several error sources are identified, modeled individually, and combined into a single accumulated error model that contribute to the final accumulated tolerances. This is used to determine the position and orientation of a machined feature. Second, the accumulated errors are expressed a function of the deviation parameters of the small displacement torsor (SDT). Third, a relationship is established between the tolerance requirements and the SDT parameters using a constraint-based mapping. The constraints capture the essential property of the part accuracy requirements and serve as boundaries for the machined feature. The method has the following advantages: (a) it establishes a direct link between error sources and part accuracy requirements, (b) it provides a direct way of evaluating the effect of each error source as well as their combined effect on part accuracy, and (c) it serves as a feedback system with the capability of providing advanced knowledge of the various physical behaviors of the part-to-fixture elements. Two simple examples are used to illustrate the approach.