(CAD) Computer Aided Design in Geometric · PDF fileMENG 351, Lecture 3 Dr. Hesham Hegazi...

MENG 351, Lecture 3 Dr. Hesham Hegazi

Geometric Modelingin

Computer Aided Design (CAD)


Geometric Modeling

• Definition: Geometric modeling is the technique we use to describe the shape of an object.


CAD Computer- Aided Drafting and Design

• 2D - Two Dimensional• 3D - Three Dimensional

– Wire Frame Models– Surface Models– Solid Models– Parametric Models


3-D Wire Frame Modeling• Disadvantages:

– Not able to fully define real objects

(No volume and mass)– Displays only edges of

a model


Surface Modeling• Surface models

provide a more complete description of the object, but is still not as good as the solid model.


Surface Modeling


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


Solid Modeling


Parametric Modeling

Parametric Modeling

Constraint-Based ModelingDimension-Driven Modeling

Uses parameters to specify dimensions of entities

Uses geometric constraints such as parallelism, concentricity, etc.


Design

Design

Personal Expression(Artisitic)

Product/ProcessDevelopment(Technical)

Aesthetic(Industrial Design)

Functional(Engineering Design)

Engineering Design Cycle

Product Process


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


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)


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..)


Neutral File Formats

• DWG – AutoCAD Drawing file• DXF - Drawing Exchange Format• IGES - Initial Graphics Exchange

Specification• CADL- CADKEY Advanced Design

Language• STL - Sterolithography.


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.”


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/)

(CAD) Computer Aided Design in Geometric · PDF fileMENG 351, Lecture 3 Dr. Hesham Hegazi...

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