Managing physical dependencies through location system design

Abstract

Many geometrical quality problems that arise during production and assembly can be traced back to the way parts are designed and located to each other; that is, how the interface geometry and locating schemes are designed and selected. Today, locating schemes are often generated after the geometry has been set, or as a consequence of the part geometries being designed. In many situations, locating schemes are not deliberately designed or defined at all. This often results in assembly and positioning situations that are not clearly defined, analysed or understood by the designer. Since the way parts are located to each other is critical for how geometrical variation will propagate and cause variation in critical product dimensions, more emphasis should be put on this activity in early design phases in order to avoid assembly and production problems later on. This work proposes a structured top-down procedure for selecting locating systems for parts and subassemblies, and presents design guidelines to assist assembly modelling. The procedure can be seen as a first step in robust design and tolerance analysis in the area of geometry design and assurance. The proposed procedure utilizes an assembly dependency matrix, a locating scheme library, a number of different part-sensitivity analyses and a set of design guidelines.