Automatic Tolerance Specifications: Challenges and Solutions

In CAD/CAM integration, computer-assisted tolerancing is a critical challenge, in which tiny changes can affect both design and production requirements. The approaches of specifying tolerances on mechanical products has progressively evolved over the last decades. In conventional design practice, dimensional tolerance was applied where; permissible variation limits were simply assigned to dimensions regarded as sufficient for form and function. This is no longer sufficient, now that the advent of geometric dimensioning and tolerancing (GD&T) has brought to light the idea that part characteristics need to be controlled in many different ways (size, shape, orientation, location, profile, runout). The difficulty associated with this complexity has prompted the development of software tools for the design of geometric tolerances. This document reviews the approaches currently used for the determination of geometric and dimensional tolerances and the need to develop computer-aided support tools. In the description of tolerance specification representation models, particular attention is paid to the structural models. The main inputs in each approach is discussed, with a focus on the difference between the different process treatments of these inputs, which allows to final sets of tolerancing cases. The main approaches proposed in this paper are described and compared.