Chapter 8 - Construction and Relating Solid Part Models in CAD/CAM Systems

Abstract

Part modeling is the historical area of computer-aided design (CAD), drafting, and manufacturing. Five different aspects integrate part modeling in a comprehensive product-modeling environment: (1) associative modeling of engineering objects, (2) concurrent modeling in group work of engineers, (3) integration of wireframe, surface, and solid modeling, (4) modeling part variants and families, starting from the same geometry, and (5) inclusion of knowledge in part models. Modeling tools in part-modeling systems are included for the creation, integration, design analysis, model analysis, shape-related modification, positional modification, application-sequence modification (reordering), removal, and suppression of form features. Form features are created as solids by a task-based choice of volume modification, surface integration, and conditioning model construction operations as available in the modeling system. Hybrid modelers apply shape modification such as primary and volume combinations as an auxiliary means of part construction. Besides the integration of separately created surface, a surface can be constructed as a boundary of a solid by using one of the surface-creation rules and as a swept and lofted volume feature. Half of the symmetrical parts can be constructed and then mirrored using a selected flat surface sometimes called a “mirror.” The resultant half is associative with the original mirrored half. Any modification of the original half results in the same modification on the mirrored half. Inertia and mass properties, such as the absolute and relative inertial axis and center of gravity, are calculated using geometry and density information. These calculations are based on the closed volume of a solid. Estimation of the cost for a part can be involved in part modeling by defining appropriate formulas and relating them with features.