Computer Aided Design (CAD)Plan for TodayWhat is CAD?Basic Elements of a CAD SystemBrief History of CADMajor Benefits of CADGeneric CAD ProcessVector versus Raster GraphicsVector GraphicsMajor CAD Software ProductsSolidWorks16.810 16.810 Engineering Design and Rapid PrototypingEngineering Design and Rapid PrototypingInstructor(s)Computer Aided Design (CAD)January 16, 2007Prof. Olivier de WeckLecture 3a16.8102Plan for Today CAD Lecture (ca. 50 min) CAD History, Background Some theory on geometrical representation FEM Lecture (ca. 50 min) Motivation for Structural Analysis FEM Background Break Start creating your own CAD models (ca. 2 hrs) Work in teams of two Follow “User Manual” step-by-step, sample part Then start on your own team projects Use hand sketch (deliverable B) as starting point16.8103Course Concepttodaylast time16.8104Course Flow Diagram (2007)CAD IntroductionFEM/Solid MechanicsAvionics PrototypingCAM ManufacturingHand sketchingInitial CAD designFEM analysisOptimizationRevise CAD designAssemblyParts FabricationProblem statementFinal ReviewTestLearning/Review Deliverables(A) Requirements and Interface Document(B) Hand Sketch(D) Manufacturing and Test Report with Cost Estimate(C) Solidworks CAD Model, Performance Analysis Design Intro / SketchFabrication, Assembly, Testing(E) CDR Package+ Guest Lectures16.8105What is CAD? Computer Aided Design (CAD) A set of methods and tools to assist product designers 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.16.8106Basic Elements of a CAD SystemInput DevicesHuman DesignerComputerCAD SoftwareDatabaseOutput DevicesHard DiskNetworkPrinterPlotterKeyboardMouseCAD keyboardTemplatesSpace BallRef: menzelus.comMain System16.8107Brief 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.htm16.8108Major 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, clearances16.8109Generic CAD ProcessStartSettingsUnits, Grid (snap), …Construct Basic SolidsBoolean Operations(add, subtract, …)AnnotationsDimensioningVerificationCreate lines, radii, partcontours, chamfersAdd cutouts & holesEngineering Sketchdim3D2Dextrude, rotateCAD fileDrawing (dxf)IGES fileOutput-=x.x16.81010 Boeing (sample) parts A/C structural assembly 2 decks 3 frames Keel Loft included to show interface/stayout zone to A/C All Boeing parts in Catiafile format Files imported into SolidWorks by converting to IGES formatLoftFWD DecksAft DecksFramesKeel(Loft not shown)Example CAD A/C AssemblyNacelle16.81011Vector versus Raster GraphicsRaster Graphics 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.bmp -raw data format16.81012Vector Graphics Object Oriented relationship between pixels captured describes both (anchor/control) points and lines between them Easier scaling & editing.emf formatCAD Systems usevector graphicsMost common interface file:IGES16.81013Major CAD Software Products AutoCAD (Autodesk) Æ mainly for PC Pro Engineer (PTC) SolidWorks (Dassault Systems) CATIA (IBM/Dassault Systems) Unigraphics (UGS) I-DEAS (SDRC)16.81014Some CAD-Theory(1) Parametric Curve Equation vs.Nonparametric Curve Equation(2) Various curves (some mathematics !)-HermiteCurve-Bezier Curve-B-Spline Curve- NURBS (Nonuniform Rational B-Spline) CurvesApplications: CAD, FEM, Design OptimizationGeometrical representation16.81015Curve EquationsTwo types of equations for curve representation(1) Parametric equationx, y, z coordinates are related by a parametric variable(2) Nonparametric equationx, y, z coordinates are related by a functionParametric equationcos , sin (0 2 )xR yRθθθπ==≤≤Example: Circle (2-D)Nonparametric equation2220xyR+− =22yRx=± −(Implicit nonparametric form)(Explicit nonparametric form)( or )uθ16.81016Curve EquationsTwo types of curve equations(1) Parametric equation():2-D, (,):3-Dyfx zfxy==(2) Nonparametric equationPoint on 2-D curve: [() ()]xuyu=pPoint on 3-D surface: [() () ()]xuyuzu=p: parametric variable and independent variableuWhich is better for CAD/CAE?: Parametric equationcos , sin (0 2 )xR yRθθθπ==≤≤2220xyR+−=22yRx=±−θΔIt also is good for calculating the points at a certain interval along a curve16.81017Parametric Equations –Advantages over nonparametric forms1. Parametric equations usually offer more degrees of freedom for controlling the shape of curves and surfaces than do nonparametric forms.e.g. Cubic curve32Nonparametric curve: yax bx cxd=+++3232Parametric curve: xau bu cu dyeu fu gxh=+++=+++3. Transformation can be performed directly on parametric equationse.g. Translation in x-dir.32000Nonparametric curve: ( ) ( ) ( )yaxx bxx cxx d=−+−+−+32032Parametric curve: xau bu cu d xyeu fu gxh=++++=+++//dy dy dudx dx du=⇒2. Parametric forms readily handle infinite slopes/ 0 indicates /dx du