Tolerance Allocations on Products: A Life Cycle Engineering Perspective

Abstract

Since manufacturing cannot (part after part) produce components that exactly achieve every stated nominal value – tolerances must be assigned to the nominal values. Many tolerance allocation methods have been developed, and practitioners consider these along with different stages of the product life cycle when determining tolerances. For example, product designers usually allocate tolerances according to the functionality of the products. On the other hand, process planners often do not consider the use stage, and instead consider process costs, precision, and accuracy, and how one process may impact another process. Thus, an “optimal” tolerance that considers only one stage of a product’s life cycle is generally not optimal when other stages are considered. In principle, product life cycle management (PLM) and computer-aided engineering (CAE) software tools should be able to determine optimal tolerances. An investigation of engineering research and available PLM/CAE software tools, with respect to tolerance allocation, is reported. Emphasis is placed on a systematic analysis of the ability to perform tolerance allocation from a life cycle engineering (LCE) perspective. Problems caused by tolerance allocation methods that focus only on certain life cycle stages are analyzed, such as over-design, mistaken scrapping of satisfactory products, and poorly performing products. Based on the gaps between manufacturers’ needs and available methods, some future research directions are suggested.