1 Copyright © #### by ASME “DRAFT” Proceedings of Insert Conference Abbreviation: IMECE2004 2004 ASME International Mechanical Engineering Congress November 13-19, 2004, Anaheim, California, Anaheim Hilton IMECE2004-59061 GEOMETRIC DIMENSION AND TOLERANCE MODELLING AND VALIDATION SYSTEM BASED ON OBJECT ORIENTED PARADIGM FOR 3D SOLID MODEL Monir M. Koura Professor, Design and Production Engineering Department, Ain Shams Univ., Egypt Ibrahiem M. Elewa Professor, Production Engineering and Mech. Design Dept., Mansoura Univ., Egypt Rajit Gadh Professor, Mech. and Aerospace Engg. Dept., UCLA, Los Angles, CA, USA Shiv Prabhu Research Engineer, Mech. and Aerospace Engg. Dept., UCLA, Los Angles, CA, USA Khaled. A. Mohamed Lecture, Engineering Science Dept., Suez Canal University, Egypt ABSTRACT This paper introduces an approach for modeling and representation of geometric tolerances on any 3D solid model using Objected Oriented Programming (OOP) paradigm. The modeling scheme is supported by a comprehensive validation engine, which certifies the tolerance type against the 3D geometry context both syntactically and semantically. The major objective of this work is to develop a methodology for interfacing tolerance modeling with boundary representation (B-Rep) based 3D solid model geometry. We will demonstrate that OOP paradigm is very efficient and flexible for tolerance model representation, which is required within the interactive design process. Five categories of tolerance classes have been developed for form, location, position, runout and profile, which extend a general tolerance class through inheritance. An instance of the general tolerance class will be initialized when picking a feature or a group of features to tolerance, depending upon feature(s’) characteristics and attributes. To apply a tolerance object the system obtains the 3D geometric data from the solid model using the feature extraction paradigm. When the required tolerance type is selected for modeling, an instance from the specified tolerance type class will be initialized through inheritance from the general feature tolerance class and gathers the necessary information / tolerance data. An intelligent validation engine supports the modeler is introduced. The engine validates any selected tolerancing activity in two stages. Firstly it ensures that the selected feature or group of features is suitable for the selected tolerance type. Secondly it ensures that the data specified does not lead to over/under-dimensioning. The paper also discusses a prototype system implemented to test the modeler and the validation engine. The results have been very encouraging while testing the system on a number of engineering models. KEYWORDS Geometric Tolerance, Dimensioning and Tolerancing, Solid Model, Feature Extraction and Recognition, Object Oriented Programming. 1 Introduction Today, solid modelling systems are widely used for various kinds of applications in mechanical engineering. Geometric models created by solid modelling systems include most of the relevant information and data about the part shape [1]. This capability allows solid-modelling systems to provide the geometric and to some extent process data necessary for carrying out design and manufacturing activities such as finite- element analysis, mass property calculation, static and dynamic interference checking, and NC-code generation and verification [2, 3]. However, they do not represent tolerances (geometric tolerances are assumed) in a form suitable for automation of many design and manufacturing activities, such as manufacturing, assembly planning, inspection and tolerance analysis. Geometric tolerances state the maximum allowable variation of a form or its position from the perfect geometry as implied in the drawing [1]. The concepts of geometric dimensioning and tolerancing (GD & T) permit a clear definition and expression of dynamic functional relationships of geometric elements, which may vary from one production part to the next [8 Thesis]. There are both ISO and ANSI standards for geometric tolerances [4, 5, 6]. The standards are based on design practices, and are more suitable for human use and