Systematic evaluation of constraint properties of datum flow chain

Abstract

Earlier, a concept of datum flow chain (DFC) was introduced which captures fundamental structure of an assembly. It documents strategy for constraining parts and locating them with respect to each other. It relates assembly level key characteristics, assembly sequences and choice of mating features to each other. This article presents a new method for evaluation of constraint properties of assemblies using DFC. This comprehensive method shall be able to evaluate certain types of DFC. It will find all under-constraints and over-constraints in the assembly. DFC is not limited only to constraint analysis. It can represent tolerance chains in the assembly under certain circumstances. However, sometimes assemblies may have multiple tolerance chains and stress-strain analysis may be required in order to do a meaningful tolerance analysis. Clearance on mating features may relieve the problems associated with multiple tolerance chains. However, it introduces uncertainty in the location of parts. DFC does not remain unique when the assembly has multiple tolerance chains. This article will present a classification of assemblies based on their constraint properties. This classification identifies when DFC becomes nonunique or when it can be used for tolerance analysis.