16.810 16.810 Engineering Design and Rapid Prototyping Engineering Design and Rapid PrototypingLecture 4 Computer Aided Design (CAD) Instructor(s) Prof. Olivier de Weck January 6, 2005Plan for Today  CAD Lecture (ca. 50 min)  CAD History, Background  Some theory of geometrical representation  SolidWorks Introduction (ca. 40 min)  Led by TA  Follow along step-by-step  Start creating your own CAD model of your part (ca. 30 min)  Work in teams of two  Use hand sketch as starting point 16.810 2Course Concept today 16.810 3Course Flow Diagram (2005) 16.810 CAD Introduction FEM/Solid Mechanics Design Optimization CAM Manufacturing Training Hand sketching CAD design Optimization Revise CAD design Assembly Parts Fabrication Problem statement Final Review Test Learning/Review Deliverables (A) Hand Sketch (B) Initial Airfoil (D) Final Design (E) Completed Wing (F) Test Data & (C) Initial Design Structural Tunnel Testing optional (G) CDR Package Xfoil Airfoil Analysis FEM/Xfoil analysis Assembly Cost Estimation Design Intro / Sketch & Wind 4What is CAD?  Computer Aided Design (CAD)  A set of methods and tools to assist productdesigners in  Creating a geometrical representation of the artifacts they are designing  Dimensioning, Tolerancing  Configuration Management (Changes)  Archiving  Exchanging part and assembly information between teams,organizations  Feeding subsequent design steps  Analysis (CAE)  Manufacturing (CAM)  …by means of a computer system. 16.810 5Ref: menzelus.comBasic Elements of a CAD System Input Devices Main System Output Devices Computer Keyboard Mouse CAD Software Database Hard Disk Network Printer CAD keyboard Plotter Templates Space Ball Human Designer 16.810 6Brief History of CAD  1957 PRONTO (Dr. Hanratty) – first commercial numerical- control programming system  1960 SKETCHPAD (MIT Lincoln Labs)  Early 1960’s industrial developments  General Motors – DAC (Design Automated by Computer)  McDonnell Douglas – CADD  Early technological developments  Vector-display technology  Light-pens for input  Patterns of lines rendering (first 2D only)  1967 Dr. Jason R Lemon founds SDRC in Cincinnati  1979 Boeing, General Electric and NIST develop IGES (Initial Graphic Exchange Standards), e.g. for transfer of NURBS curves  Since 1981: numerous commercial programs  Source: http://mbinfo.mbdesign.net/CAD-History.htm 16.810 7Major Benefits of CAD  Productivity (=Speed) Increase  Automation of repeated tasks  Doesn’t necessarily increase creativity!  Insert standard parts (e.g. fasteners) from database  Supports Changeability  Don’t have to redo entire drawing with each change  EO – “Engineering Orders”  Keep track of previous design iterations  Communication  With other teams/engineers, e.g. manufacturing, suppliers  With other applications (CAE/FEM, CAM)  Marketing, realistic product rendering  Accurate, high quality drawings  Caution: CAD Systems produce errors with hidden lines etc…  Some limited Analysis  Mass Properties (Mass, Inertia)  Collisions between parts, clearances 16.810 8Generic CAD Process StartEngineering Sketch Settings Units, Grid (snap), … 3D 2D dim -Construct Basic Create lines, radii, partSolids contours, chamfers = Boolean Operations extrude, rotate (add, subtract, …) Add cutouts & holes Annotations Dimensioning CAD file Verification Output Drawing (dxf)x.x IGES file 16.810 9Example CAD A/C Assembly  Boeing (sample) parts  A/C structural assembly  2 decks  3 frames  Keel  Loft included to show A/C  All Boeing parts in Catiafile format  Files imported into SolidWorks by format Loft FWD Decks Frames Kee l Nacelle interface/stayout zone to converting to IGES (Loft not shown) Aft Decks 16.810 10Vector versus Raster Graphics Raster Graphics .bmp -raw data format  Grid of pixels  No relationships between pixels  Resolution, e.g. 72 dpi (dots per inch)  Each pixel has color, e.g. 8-bit image has 256 colors 16.810 12Vector Graphics .emf format CAD Systems use vector graphics Most common interface file:  Object Oriented IGES  relationship between pixels captured  describes both (anchor/control) points and lines between them  Easier scaling & editing 16.810 13Major CAD Software Products  AutoCAD (Autodesk) Æ mainly for PC  Pro Engineer (PTC)  SolidWorks (Dassault Systems)  CATIA (IBM/Dassault Systems)  Unigraphics (UGS)  I-DEAS (SDRC) 16.810 14Some CAD-Theory Geometrical representation (1) Parametric Curve Equation vs. Nonparametric Curve Equation (2) Various curves (some mathematics !) -Hermite Curve -BezierCurve -B-Spline Curve - NURBS (Nonuniform Rational B-Spline) Curves Applications: CAD, FEM, Design Optimization 16.810 15Curve Equations Two types of equations for curve representation (1) Parametric equation x, y, z coordinates are related by a parametric variable (u or θ) (2) Nonparametric equation x, y, z coordinates are related by a function Example: Circle (2-D) Parametric equation xRcos θ, yR sin θ (0 ≤θ≤ 2π)= = Nonparametric equation 2 2+ 2 −x y R = 0 (Implicit nonparametric form) 2 (Explicit nonparametric form)y =± R x − 2 16.810 16Curve Equations Two types of curve equations xu y()](1) Parametric equation Point on 2-D curve: p= [() u Point on 3-D surface: p = [() uz()] xuy() u u : parametric variable and independent variable (2) Nonparametric equation yf() : 2-D , zf(x, y) : 3-D = x = Which is better for CAD/CAE? : Parametric equation θ∆ xRcos θ , yR sin θ (0 ≤θ≤ 2π ) It also is good for= = calculating the points at a certain interval along a curve2 2 2x yR +− = 0 2y=± Rx − 2 16.810 17Parametric Equations – Advantages over nonparametric forms 1. Parametric equations usually offer more degrees of freedom for controlling the shape of curves and surfaces than do nonparametric forms. e.g. Cubic curve= 3 + 2Parametric curve: xau bu cud + + = 3 + 2yeu fu gxh + + = 3 + 2Nonparametric curve: yax bx cxd + + 2. Parametric forms readily handle infinite slopes =dy dy / du ⇒ dx / du=0 indicates dy / dx =∞dx dx / du 3. Transformation can be performed directly on parametric equationse.g. Translation in x-dir. = 3 + 2Parametric curve: xau bu cudx 0+ + + = 3 + 2yeu fu gxh + + =− 0 − 02 −