Geometric Modeling Creating 3D solid geometry in a computer MAE 455 Computer Aided Design and Drafting Partial History of 1963 Geometric Modeling Wireframe Computer Graphics Invented Ivan Sutherland MIT MAE 455 Computer Aided Design and Drafting 2 Partial History DAC 1 General Motors early 1960 s MAE 455 Computer Aided Design and Drafting 3 Partial History of 1967 1973 Geometric Modeling Surface Modeling S A Coons Solid Modeling Constructive Solid Geometry Laning et al Draper Lab 1973 Solid Modeling Boundary Representation Ian Braid Cambridge U 1985 1990 Feature Modeling Pratt Wilson Parametric Modeling PTC MAE 455 Computer Aided Design and Drafting 4 Wireframe Modeling Stores positions of lines in 2D or 3D Helpful for drafting easy multiple views and easy editing Ambiguous surfaces limit the automation possibilities e g no volume calculation no NC tool path generation MAE 455 Computer Aided Design and Drafting 5 Surface Modeling Stores equations of surfaces Most 3D graphics libraries use surface modeling Good for visualizing complex surfaces and automated NC path generation of complex surfaces Material volume information is ambiguous or hard to determine therefore can t calculate volume From K Lee Principles of CAD CAM CAE Systems Addison Wesley MAE 455 Computer Aided Design and Drafting 6 Solid Modeling Various mathematical representations exist that each allow point set classification Is a given point inside or outside the solid region Solid models can be used for volume calculations Automatic FE mesh generation Collision determination in robotics or NC path generation MAE 455 Computer Aided Design and Drafting 7 Solid Modeling Functions Different ways that a user can create solid shapes Primitive creation Boolean operations Sweep operations Surface operations Engineering Feature Based modeling Parametric modeling MAE 455 Computer Aided Design and Drafting 8 Primitive Creation Primitives are simple solid shapes with simple mathematical surfaces Can be controlled by a small number of dimension and position parameters From K Lee Principles of CAD CAM CAE Systems Addison Wesley MAE 455 Computer Aided Design and Drafting 9 Boolean Operations Boolean operations are used to make more complicated shapes by combining simpler shapes 3 types of operations are possible union or join intersection difference or subtract Be careful From K Lee Principles of CAD CAM CAE Systems Addison Wesley MAE 455 Computer Aided Design and Drafting 10 Sweeping Operations Use 2D wireframe section s to generate a 3D solid This includes operations such as extrude revolve sweep loft From K Lee Principles of CAD CAM CAE Systems Addison Wesley MAE 455 Computer Aided Design and Drafting 11 Surface Operations These operate directly on the solid model faces edges and vertices to create a desired modification Examples chamfering rounding filleting drafting shelling From K Lee Principles of CAD CAM CAE Systems Addison Wesley MAE 455 Computer Aided Design and Drafting 12 Feature Based Modeling Features are shapes having engineering significance They usually are the geometric embodiment of machining operations or the function of a component Examples hole slot pocket boss Many systems provide for userdefined features Many people use the term Feature to refer to any kind of solid modeling operation From K Lee Principles of CAD CAM CAE Systems Addison Wesley MAE 455 Computer Aided Design and Drafting 13 Parametric Modeling Parameters are found in a CAD model as dimensions in 2D sketches dimensions on 3D geometry advanced systems only modeling operation parameters variables in user equations Entire part geometry can be controlled by a small number of key parameters MAE 455 Computer Aided Design and Drafting 14