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MENG 351, Lecture 3 Dr. Hesham Hegazi
Geometric Modelingin
Computer Aided Design (CAD)
MENG 351, Lecture 3 Dr. Hesham Hegazi
Geometric Modeling
• Definition: Geometric modeling is the technique we use to describe the shape of an object.
MENG 351, Lecture 3 Dr. Hesham Hegazi
CAD Computer- Aided Drafting and Design
• 2D - Two Dimensional• 3D - Three Dimensional
– Wire Frame Models– Surface Models– Solid Models– Parametric Models
MENG 351, Lecture 3 Dr. Hesham Hegazi
3-D Wire Frame Modeling• Disadvantages:
– Not able to fully define real objects
(No volume and mass)– Displays only edges of
a model
MENG 351, Lecture 3 Dr. Hesham Hegazi
Surface Modeling• Surface models
provide a more complete description of the object, but is still not as good as the solid model.
MENG 351, Lecture 3 Dr. Hesham Hegazi
Surface Modeling
MENG 351, Lecture 3 Dr. Hesham Hegazi
Solid ModelingSolid
B-Rep CSG
Boundary Representation:•Extrusion•Revolving•Sweeping•Blending of 2-D profiles
Constructive Solid Geometry:•Construction of solid by combining primitives using Boolean operators of union, intersection, and difference•Uses solid primitives (cylinder, cone, etc.) as building blocks
MENG 351, Lecture 3 Dr. Hesham Hegazi
Solid Modeling
MENG 351, Lecture 3 Dr. Hesham Hegazi
Solid Modeling
MENG 351, Lecture 3 Dr. Hesham Hegazi
Parametric Modeling
Parametric Modeling
Constraint-Based ModelingDimension-Driven Modeling
Uses parameters to specify dimensions of entities
Uses geometric constraints such as parallelism, concentricity, etc.
MENG 351, Lecture 3 Dr. Hesham Hegazi
Design
Design
Personal Expression(Artisitic)
Product/ProcessDevelopment(Technical)
Aesthetic(Industrial Design)
Functional(Engineering Design)
Engineering Design Cycle
Product Process
MENG 351, Lecture 3 Dr. Hesham Hegazi
Basic Geometric Entities
• Point (X,Y,Z)• Line (X,Y,Z) Start (X,Y,Z) End• Circle (X,Y,Z) Center & Diameter• Arc (X,Y,Z) Center , Radius, Start & End
Angle or Point
MENG 351, Lecture 3 Dr. Hesham Hegazi
More advanced Approaches• Feature-based modeling
– Uses features such as holes, ribs, pockets, slots– More advanced than CSG
• Assembly modeling– Modeling of assembled parts– Utilizes much of the same technology as solid
modeling• Product modeling
– Includes not only the geometry of an object, but also any information that is needed to design, develop, and produce the product. (e.g. stress-analysis)
MENG 351, Lecture 3 Dr. Hesham Hegazi
Basic CAD Functions
• Viewing Commands (zoom, pan, etc..)• File commands (new, open, save, etc..)• Drawing Commands (line, circle,
rectangle, arc, spline, 3D shapes, etc..)• Modifying Commands (Trim, erase,
extend, copy, move, Extending, etc..)
MENG 351, Lecture 3 Dr. Hesham Hegazi
Neutral File Formats
• DWG – AutoCAD Drawing file• DXF - Drawing Exchange Format• IGES - Initial Graphics Exchange
Specification• CADL- CADKEY Advanced Design
Language• STL - Sterolithography.
MENG 351, Lecture 3 Dr. Hesham Hegazi
Future Directions of 3-D Modeling
• Geometric modeling will be “supplanted by product modeling which not only includes the geometry of the object, but any information or data that is needed to design, develop, produce and support the product through its entire life cycle.”
MENG 351, Lecture 3 Dr. Hesham Hegazi
Commercial CAD Software
• Pro Engineer (http://www.ptc.com/)• Unigraphics (http://www.ugsolutions.com/)• Autocad (http://www.autodesk.com/)• CADKEY (http://www.cadkey.com/)• Microstation• CATIA
(http://www-.ibm.com/solutions/engineering/eshome.nsf/public/catmain)
• VisualCADD (http://www.imsisoft.com/products/visualcadd/index.cfm)• TurboCAD (http://www.turbocad.com/)• SolidWorks (http://w ww.solidworks.com/)