The Functional Feature Model: Bridging the CAD/CAM Gap

Abstract

Abstract Commercial CAD systems were originally developed to support the generation of 2D engineering drawings, but evolved to support development of 3D product models. Conceptually, the product model replaces 2D engineering drawings as a means for communicating product information such as size, shape, features, datums, tolerances, and other engineering specifications. Because of their history, the software architecture and data models used by commercial CAD systems do not directly represent all the engineering product information contained in 2D engineering drawings. Computer Assisted Engineering (CAE) tools require engineering product specifications as input. When these tools are integrated directly with the CAD system, a database representation of the product model is required for their efficient operation. Without a direct link to the CAD system, information must be transferred using standard format files, or manually entered into the CAE application. To satisfy the requirements for direct integration of CAE applications with CAD systems, the Functional Feature Model (FFM) was developed. By definition, the Functional Feature Model (FFM) contains component geometry, feature definitions, datums, datum features, tolerances and other feature attributes accessed through a standard interface. The FFM was named to distinguish the functional features used by an engineer in the definition of part function, inspection, and assembly from the features employed by CAD systems in construction of geometry. Today, the FFM is used as the basis for CAE tools which perform analysis of product Geometric Dimensioning and Tolerancing (GD&T), 3D tolerance analysis of assemblies, and CMM programming. Any CAE application which requires the same or similar information as these applications can obtain its input from the FFM. The FFM is a mature, commercially proven prototype for a standard product model, containing the majority of engineering product information typically represented using 2D drawings annotated with Geometric Dimensional and Tolerancing (GD&T) symbols. The FFM can be used instead of 2D drawings to supply necessary product information to CAE applications. Using the FFM, there is no need to create the 2D engineering drawing, interpret the GD&T annotation, and enter the interpreted product information into the CAE application. It provides a standard interface (independent of CAD system) for commercial development of CAE applications, and is designed in a fashion which makes it appropriate for use as a basis for emerging product model standards. The FFM provides a prototype for related activities like the Standard for the Exchange of Product Model Data (STEP) initiative represented by the Product Data Exchange using STEP (PDES) organization in the USA. Corporate and government consortiums such as the Rapid Response Manufacturing (RRM) or Simulation Assessment Validation Environment (SAVE) initiatives could employ the FFM directly to support their objectives of developing the next generation design and simulation environment.