INTRODUCTION TO COMPUTER AIDED DESIGN ANDpdf.ebook777.com/062/B0714Q4W36.pdf · computer aided...

COMPUTER AIDED DESIGN

AND

MANUFACTURING

INTRODUCTION

A Jomat Series Training Guide

Blake Coleman

TO

Jomat eri

esS

v

DEDICATION

To all lovers of contemporary engineering.

vi

TABLE OF CONTENT

DEDICATION v

TABLE OF CONTENT vi CHAPTER ONE 1

INTRODUCTION 1 GRAPHICS FUNDAMENTALS 5 GRAPHICAL REPRESENTATION 5 GRAPHICS TOOL BOX 6 GEOMETRIC ELEMENTS 7 GEOMETRICAL MANIPULATION 9

CHAPTER TWO 12

CONSTRUCTION OF SHAPES USING AXIS 12 CARTESIAN COORDINATE SYSTEM 12 GEOMETRIC MODELLING 13 METHODS FOR CONSTRUCTING SURFACES OR SOLIDS FROM OTHER GEOMETRY 19 A PARAMETRIC SOLID MODEL 21 CREATING SOPHISTICATED GEOMETRY 22 DEFINING DATUM POINTS 22 DEFINING DATUM AXES 23 DEFINING DATUM PLANES 24 STRATEGIES FOR MAKING A MODEL 26 GROUP TECHNOLOGY 30 PART FAMILIES 31 PARTS CLASSIFICATION AND CODING SYSTEMS 31 CODING STRUCTURES 33

CHAPTER THREE 34

DATA TRANSFER IN CAD 34 OVERVIEW OF AutoCAD 34 NUETRAL FILE FORMATS 34 INITIAL GRAPHICS EXCHANGE SPECIFICATION (IGES) 35 DATA EXCHANGE FORMAT (DXF) 36 GENERAL FILE STRUCTURE OF DXF 37

CHAPTER FOUR 40

CAM SYSTEM AND CONFIGURATION 40 CAM CLASSIFICATION 41 DEGREE OF FREEDOM IN CAM SYSTEMS 41 CAM WORKFLOW PROCESS 43 SELECTION OF MACHINE TOOL 43 SELECTION OF CUTTING TOOL 44 SELECTION OF TOOL PATH STRATEGY 45 SELECTION OF MACHINED GEOMETRY 45 SIMULATION 45 CREATE NC PROGRAM 46 DOCUMENTING 46 DATUM SETTING 47 SETTING THE WORK PIECE ORIGIN 47

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CHAPTER FIVE 49

CNC SYSTEM AND CONFIGURATION 49 NC MACHINE MOTIONS 50 MACHINE TYPES 50 PROGRAMMING SYSTEMS 52 NC PROGRAMMING FORMAT 56

CHAPTER SIX 63

CAD/CAM WORK STATION SETUP 63 DIMENSIONING GUIDELINES 63 MACHINE ZERO POINT 63 WORK SETTINGS AND OFFSETS 65 WORK COORDINATES 65 R PLANE OR GAGE HEIGHT 66 TOOL LENGTH OFFSET 66 CUTTER DIAMETER COMPENSATION 67 WORK HOLDING 68

CHAPTER SEVEN 70

CAM/CNC PROGRAMMING AND OPERATION 70 SAFETY FIRST 70 CUTTING TOOL FUNDAMENTALS 72 CANNNED CIRCLE 74 TYPES OF CANNED CYCLES 75 MULTITASKING MACHINES 79 CYLINDRICAL GRINDING 80 SPECIAL PURPOSE CNC MACHINES 81 MILLING AND DRILLING PROGRAMMING 82 FANUC COMPATIBLE PROGRAMMING 86

CHAPTER EIGHT 90

SIMULATION IN COMPUTER AIDED MANUFACTURING 90 TYPES OF SIMULATION 91 TECHNIQUES OF SIMULATION 91 SIMULATION PROCESS FOR MANUFACTURING SYSTEMS ANALYSIS 92 SIMULATION SOFTWARE PACKAGES 92 APPLICATION OF SIMULATION 93 SIMULATION IN AUTOMOTIVE INDUSTRY 93 PROCEDURE FOR SIMULATION USING SOFTWARE 95

REFERENCES 97

INDEX 99

CHAPTER ONE

INTRODUCTION The way things are done today evolved fromthe way thingswere done in thepast. You can understand the way engineering graphics is used today byexamininghowitwasusedinthepast.Graphicalcommunicationshassupportedengineeringthroughouthistory.Thenatureofengineeringgraphicshaschangedwiththedevelopmentofnewgraphicstoolsandtechniques. ANCIENT HISTORY Theearliestdocumentedformsofgraphicalcommunicationarecavepaintings.Theuseof toolsandotherfabricateditemsfor livingcomfortandconveniencewerealsocommunicated incavepaintings. However, thesepaintingstypicallydepicted a lifestyle, rather than any instructions for the fabrication of tools,products, or structures. How the items were made is still left to conjecture.The earliest large structures of significance were the Egyptian pyramids andNativeAmericanpyramids.

TheNativeAmericanpyramidswerebuiltforreligiousceremoniesorscientificuse,suchasobservatories.Makingtheselargestructures,withprecisioninthefittingoftheirpartsandwiththetoolsthatwereavailableatthetime,requiredmuch time, effort, and planning. Even with modern tools and constructiontechniques,thesestructureswouldbedifficulttore-createtoday.Themethodofconstruction for the pyramids is largely unknown-records of the constructionhave never been found-although there have been several theories over theyears. Two engineering construction methods helped the Roman Empireexpand to include much of the civilized European world. These methods wereusedtocreatetheRomanarchandtheRomanroad.The Roman arch, shown in Fig.1.1,was composed of stone thatwas precut toprescribed dimensions and assembled into an archway. The installation of thekeystoneatthetopofthearchtransferredtheweightofthearchandtheloaditcarriedintotheremainingstonesthatwerelockedtogetherwithfriction. Thisstructure took advantage of the compressive strength of stone, leading to thecreationoflargestructuresthatusedmuchlessmaterial.

Fig. 1.1 Pont-du-Gard Roman aqueduct (left) built in 19 BC

The Roman arch architecture was used to create many large buildings andbridges. Roman era aqueducts, which still exist today in Spain and other

CAD/CAM

countriesinEurope,areevidenceoftherobustnessofthisdesign.ThemethodusedtoconstructRomanroadspstone(insteadofasinglelayerofthenativeearth),formingpathswideenoughfor commercial and military use. In addition to the layered constructionmethods, theseroadswerealsocawaywater.Thisconstructionmethodincreasedtheprobabilitythattheroadswouldnotbecomeovergrownwithvegetationandwouldremainpassableeveninadverseweather.Asaresult,Romanarmieshadreliableoftheempire.

Todayfewengineeringprojectspeopleisresponsibleforallaspectsoftheprojectfrombeginningtoend.Manypeoplewithmanydifferenttinthedevelopmentandproductionphasesofaproject.Whetherthatpersonisthe engineer who conceives the overall idea or the fabricator who makes theindividualpiecesorthetechnicianwhoassembleoperate,theyallhavecommonquestions:■Whatisthispart,device,orstructuresupposedtodo?■Whatisitsupposedtolooklike?■Whataretheprecisegeometries■Whatisitmadeof?■Howisitmade?■Howdoesit�itintootherparts,devices,orstructures?■HowdoIknowifeverythingismadethewayitwassupposedtobemade?

Fig. 1.2 In conventional product design (above), phases of the development cycleoccur sequentially. Concurrent engineeringto accelerate the cycle.

countriesinEurope,areevidenceoftherobustnessofthisdesign.ThemethodusedtoconstructRomanroadsprescribedsuccessivelayersofsand,gravel,andstone(insteadofasinglelayerofthenativeearth),formingpathswideenoughfor commercial and military use. In addition to the layered constructionmethods, theseroadswerealsocrownedtoshedrainandhadgutterstocarry

Thisconstructionmethodincreasedtheprobabilitythattheroadswouldnotbecomeovergrownwithvegetationandwouldremainpassableeveninadverseweather.Asaresult,Romanarmieshadreliableaccesstoallcorners

Todayfewengineeringprojectsexistwhereasinglepersonorasmallgroupofpeopleisresponsibleforallaspectsoftheprojectfrombeginningtoend.Manypeoplewithmanydifferenttypesoftechnicalandnontechnicalskillsparticipateinthedevelopmentandproductionphasesofaproject.Whetherthatpersonisthe engineer who conceives the overall idea or the fabricator who makes theindividualpiecesorthetechnicianwhoassemblesthepartstomakethesystemoperate,theyallhavecommonquestions:

Whatisthispart,device,orstructuresupposedtodo?Whatisitsupposedtolooklike?Whataretheprecisegeometriesandsizesofitsfeatures?

Howdoesit�itintootherparts,devices,orstructures?HowdoIknowifeverythingismadethewayitwassupposedtobemade?

conventional product design (above), phases of the development cycleoccur sequentially. Concurrent engineering (below) combines two or more phases

2

countriesinEurope,areevidenceoftherobustnessofthisdesign.Themethodrescribedsuccessivelayersofsand,gravel,and

stone(insteadofasinglelayerofthenativeearth),formingpathswideenoughfor commercial and military use. In addition to the layered construction

rownedtoshedrainandhadgutterstocarryThisconstructionmethodincreasedtheprobabilitythattheroads

wouldnotbecomeovergrownwithvegetationandwouldremainpassableevenaccesstoallcorners

existwhereasinglepersonorasmallgroupofpeopleisresponsibleforallaspectsoftheprojectfrombeginningtoend.Many

ypesoftechnicalandnontechnicalskillsparticipateinthedevelopmentandproductionphasesofaproject.Whetherthatpersonisthe engineer who conceives the overall idea or the fabricator who makes the

sthepartstomakethesystem

HowdoIknowifeverythingismadethewayitwassupposedtobemade?

conventional product design (above), phases of the development cycle

(below) combines two or more phases

Introduction 3

Theobjectenvisionedbytheengineermustbethesameobjectproducedbythefabricator and the same object assembled into the working system by thetechnician. Graphical communication that follows universally acceptedstandardsforrepresentingshapesandsizesmakesthathappen.

Inordertoconstructanartifactweneedtodescribeittothepeoplewhohavethenecessaryskillsformaking it.Weneeda languagetodescribeour ideastoothers. Drawing is the universal language of engineers. For effectivecommunicationdrawingshavetofollowstandardconventionsandpractices.

The CAD is the abbreviation of Computer Aided Design, which means a wildrange of computer software tools, which support the design process. A CADsystem can be a simple 2D drawing system or a parametric associativehybridmodellingsystem.Theup-to-datemethodisthislastconcept,where:

theparametricmeansthedimensiondrivenmodelling, the associative means the live connection between the geometric

elements, thehybridmeanstheparallelandsynergicsurfaceandsolidmodelling.

Traditionally, engineering drawings are made by draftsmen on paper throughmanual drawing tools. With the advent of computers, these tasks areincreasingly being carried out on computers. Creating electronic drawingsenable easy modification and collaboration among geographically separatedparties. Most successful businesses invest substantially in research anddevelopmentinordertogaincompetitiveadvantage.Engineeringadvancesoffersales and marketing teams the ability to sell more products and gain a largermarketshare.Inordertofacilitatethis,engineersmustbeabletoquicklybringtheirdesignstomanufacturetoachievewhatisknownasspeedtomarket.Theuse of Computer-aided Design (CAD) has allowed engineers to communicatedesignsquickly.

TheCADsystemscanbeclassifiedbyseveralviewpoint. The first is the application field. The CAD systems are developed in every

industrial areas, so we can find systems in the field of mechanicalengineering,electricengineering,architecturaldesign,civilengineering,clothandshoedesign,medicalapplication.

Thetypeofthemodellingcanbe2D,whentherepresentationofthepart issimilar to the engineering drawing. The other method is the 3D modelling,whenthemodelofthepartisbuildinthevirtualspace.

The applied modelling method can be wireframe modelling, when only theedgesofthepartaredefined.IncaseofsurfacemodellingtheCADmodelishollow, only the boundary „skin” is defined. The solid modelling ensuresrealisticrepresentation,themodelconsistsofsimpleelementaryelements.

CAD/CAM 4

Incaseofparametricmodel,thesizeofthemodelisdrivenbythegeometricparameters.

Thesizeofanon-parametricmodel isdefinedbyuser’smodellingactivityandthedimensioningvalue isdrivenbythemodelledobject.Bymakinguseof thegeometryanddetailsfromCADmodels,machinescanbequicklyandaccuratelyprogrammedtoproducehighqualityparts.Thestepsoftheproductdevelopmentarethenextingeneralcase: Creation of product concept. The function, engineering, quality, market and

other requirements are collected in order to define the aim of thedevelopment.

Conceptional design. The possible solutions of each requirement aresummarized.

Synthesis.Unitetheseparatedelements. Design assessment. The result is investigated in order to check, than it is

suitablefortheinitialrequirements. Detail design.Thedetailsoftheproductaredesigned. Analysis of the design.Theproductdesigniscompleteforanalysisandevery

ofimportantpropertiescanbetested. Documenting. The result of the design process is the full design

documentation.

The product development and production process is supported by computersoftware.ThenameofthistechnologyisCAx–computeraidedsomething.Thesesoftware tools support the specific engineering activities. The help of thecomputer means different things. In case of manufacturing the CNC programsare generated by a CAM system, the CAE means the collection of everyengineering analysis and calculation. The task of the CAPP is to generate aprocess plan for manufacturing. The CAQA is the programming of coordinatemeasurementmachinesingeneral.

Themostoftenusedabbreviationsarethenext:•CAD–computeraideddesign•CAM–computeraidedmanufacturing•CAE–computeraidedengineering•CAPP–computeraidedprocessplanning•CAQA–computeraidedqualityassurance•CAPPS–computeraidedproductionplanningandscheduling•CAST–computeraidedstorageandtransport

These Computer Numerically Controlled (CNC) machines must receiveinformation in a format that takes account of how part geometry will beachieved by the machining method, for example turning, milling or drilling.Computer aided Manufacturing (CAM) software is available to accept CADinformation.Combinedwiththeknowledgeoftheengineerinordertosequence

Introduction

the tooling, this enables designs toshorttime.ThisunitwillenablelearnerstoproducecomponentdrawingsusingaCADsystemspecificallyfortransfertoaCAMsystem.TheywillalsodevelopanunderstandingofstructureddatawithinCAD/CAMsystemsandtheuseofdatatransfermethods.PracticalworkwillincludethesimulationofcutterpathsonaCAMsystemandtheproductionofacomponentfromatransferreddatafile. GRAPHICS FUNDAMENTALSDisplay devices Rasterdisplayconsistsofamatrixofpointscalledpixels.Animageismadeofanumberofpixels.(e.g.CRTdisplay)Vectordevicesdrawstraightlines.(plotters).

GRAPHICAL REPRESENTATIONThefollowinginformationneedtoberepresented.•General:coordinatesystem•Graphicsprimitives 2D Graphics: Thecoordinatesystem:2Ddrwaingusearighthandedcoordinatesystem.

2D Graphics: Units Engineers use lengthunits such asmeters or millimeters.Coordinates are realnumbers. But on a computer device such as a display screen, coordinates areintegers.Thefundamentalunitiunitsareconvertedintopixelsbythedraftingsoftware.Standardimageediting

the tooling, this enables designs to progress to manufacturingshorttime.Thisunitwillenablelearnerstoproducecomponentdrawingsusing

specificallyfortransfertoaCAMsystem.TheywillalsodevelopangofstructureddatawithinCAD/CAMsystemsandtheuseofdata

transfermethods.PracticalworkwillincludethesimulationofcutterpathsonaCAMsystemandtheproductionofacomponentfromatransferreddatafile.

GRAPHICS FUNDAMENTALS

consistsofamatrixofpointscalledpixels.AnimageismadeofaCRTdisplay)Vectordevicesdrawstraightlines.(

Fig.1.3

GRAPHICAL REPRESENTATION followinginformationneedtoberepresented.

coordinatesystem,units,colors

usearighthandedcoordinatesystem.

Fig.1.4

Engineers use lengthunits such asmeters or millimeters.Coordinates are realnumbers. But on a computer device such as a display screen, coordinates areintegers.Thefundamentalunitisapixel.Duringdisplay,highlevelengineeringunitsareconvertedintopixelsbythedraftingsoftware.Standardimageediting

5

progress to manufacturing in a relativelyshorttime.Thisunitwillenablelearnerstoproducecomponentdrawingsusing

specificallyfortransfertoaCAMsystem.TheywillalsodevelopangofstructureddatawithinCAD/CAMsystemsandtheuseofdata

transfermethods.PracticalworkwillincludethesimulationofcutterpathsonaCAMsystemandtheproductionofacomponentfromatransferreddatafile.

consistsofamatrixofpointscalledpixels.AnimageismadeofaCRTdisplay)Vectordevicesdrawstraightlines.(e.g.Pen

Engineers use lengthunits such asmeters or millimeters.Coordinates are realnumbers. But on a computer device such as a display screen, coordinates are

.Duringdisplay,highlevelengineeringunitsareconvertedintopixelsbythedraftingsoftware.Standardimageediting

CAD/CAM 6

software work with pixels and are not convenient for making engineeringdrawings.Colours In visible light, there is a continuous range of colours from violet to red. Allcolours are obtained by mixing three basic colours red, green and blue (RGB).Onewaytospecifyacolouristoindicatetheproportionofred,greenandblue.AnotherapproachistogiveanameorindextoeachpredefinedcombinationofRGB(indexedcolourrepresentation).Graphics primitives 2D drawings are made up of graphics primitives such as lines, curves, shapes,filled areas, markers and text. These are converted into pixels by graphicssoftware for producing graphics on output devices. Steps involved in thisconversionareknownasthegraphics pipeline. GRAPHICS TOOL BOX Primitives are usually arranged in the form of a toolbox in graphics software.Each primitive has an associated set of properties such as colour, style,thickness,font,etc.Weselecta“tool”fromthetoolbox,selectitspropertiesandinsertitintothedrawing.

Graphics primitives: Lines Alinesegmentisdeterminedby:Endpoints(x1,y1),(x2,y2)Apoint(x1,y1),lengthandaslope(degrees)Mathematicallyalineisrepresentedbytheequation y = m x + c Orinparametricformasx = tandy = m t + c Graphics primitives: Curves Acurveisrepresentedinparametricformas

x=f(t),y=g(t)Example:Parametricequationsforanellipsex=Acos(t),y=Bsin(t) Graphical input Weneedappropriateinputdevicesformakinggoodqualitydrawingsefficiently.Pointingdevicessuchasmouse,lightpensandtabletstyluscanbeusedtoinputcoordinates. Keyboard input is sometimes necessary to precisely inputcoordinate values. The graphical user interface should permit easily switchingbetween input devices. Features of a good graphical user interface for makingengineeringdrawingsareasfollows: Coordinates

Coordinateinformationshouldbeavailableatalltimes.Thecoordinateofanyobject should be available by moving a pointer device over it. It should be

Introduction 7

possibletochangeunitsandcoordinatesystemsduringthecourseofeditingadrawing.

Coordinate grid It is useful to display a grid consisting of coordinates at regular intervals.Irregularly spaced grids are also useful. The “snap” feature ensures that allobjectsarepositionedatexactpointsonthegrid.

Graphics primitives Arichsetofhigh-levelgraphicsprimitivesshouldbeavailable.Lines,circles,arcs,parabola,ellipses,splines,etc.areessential.Boxeswithsharpandroundedcornerssavemuchtime.

GEOMETRIC ELEMENTS InaCADsysteminthe3DvirtualspacethegeometricelementsarerepresentedinaDescartiancoordinatesystembyx,y,andzvalues.Thesimplestgeometricelementisthepoint,whichisusedasdatumelementsinaCADmodelling.Therepresentationofapointisdonebythe3coordinatevalue. Curves A curve is a continuous set of points. A curve can be defined by explicit orimplicit definition.The explicit formula is suitable for generating the points ofthe curve, and the implicit formula is suitable for investigating a location of apoint.

Fig.1.5

If the value of the formula is 0, the given point is the part of the curve.In the CAD practice the explicit definition is applied. The example shows thedefinitionofacircle.

CAD/CAM

Theradiiof thecircle isRandthecentrepoint isxdefinedbyexplicitformula.Theexampleshowsthedefinitionofaline,whichgothrough(x1,y1,z1)and(x2,y2

The classic curves, like line, circle, ellipse etc.) havegeneralcurvehasn’tgotadescription.Thesecurvescanbedefinedbypolynoms,which are adjusted by ai

continuously,whichisessentialformanyinvestigations

Complex curves

The set of factors are not so easy, therefore we use control points in the CADenvironmentinordertodefineacurvecurve goes through these points, orthese points. Both of these methods are used in theoretic mathematicdescriptionandinCADsystems.

Acomplexcurvecanbedefinedbymanypoints.Wecanusetwostrategy:•Useahighdegreepolynom,or•Multi-segmentlowdegreepolynoms.

Fig.1.6 Randthecentrepoint isxo,yo. The3Dcurvescanbe

definedbyexplicitformula.Theexampleshowsthedefinitionofaline,whichgo2,z2)points.

The classic curves, like line, circle, ellipse etc.) have explicit definition, but ahasn’tgotadescription.Thesecurvescanbedefinedbypolynoms,

i, bi, ci factors. The polynoms can be differentiatedcontinuously,whichisessentialformanyinvestigations.

Fig. 1.7

The set of factors are not so easy, therefore we use control points in the CADenvironmentinordertodefineacurve.Wecanspeakaboutinterpolation,ifthecurve goes through these points, or approximation, if the curve draws near tothese points. Both of these methods are used in theoretic mathematicdescriptionandinCADsystems.

canbedefinedbymanypoints.Wecanusetwostrategy:polynom,or

segmentlowdegreepolynoms.

8

. The3Dcurvescanbedefinedbyexplicitformula.Theexampleshowsthedefinitionofaline,whichgo

explicit definition, but ahasn’tgotadescription.Thesecurvescanbedefinedbypolynoms,

factors. The polynoms can be differentiated

The set of factors are not so easy, therefore we use control points in the CAD.Wecanspeakaboutinterpolation,ifthe

approximation, if the curve draws near tothese points. Both of these methods are used in theoretic mathematic

canbedefinedbymanypoints.Wecanusetwostrategy:

Introduction 9

The high degree polynoms sometimes become wave, therefore we prefer thesecond way of curve design. The connecting segments have to be continuous,andthecontinuityhasdifferentaspects. GEOMETRICAL MANIPULATION TransitionThe defined geometric elements should be modified or transformed in a CADsystem.Thistransformationisdonebypoint-by-point,sowehavetounderstandthe manipulation methods of a point. The simplest transformation is thetranslation, when the point, which is represented with r vector, is moved by tvector.

Fig. 1.8

Scaling In case of scaling, every coordinate values are multiple with a constant. Theseconstants can be same, this is the uniform scaling, or these factors can bedifferent. The scaling is calculated by matrix multiplication, where C is thescalingmatrix.

Fig. 1.9

CAD/CAM 10

Rotation about xi Therotationofanobjectmeanstherotationaroundaxicoordinateaxeswithaφi angle. If the rotation is performed around a general line, the coordinatesystem has to be transformed to the direction of the line. The rotation iscalculatedbymatrixmultiplication,whereFi istherotationmatrix.Theorderofthemultiplicationisimportantifmorerotationsareapplied.

Fig. 1.10

Mirror to plane Themirrorofanobjecthasdifferentways.Thefirstisthemirrortocoordinateplane. We use matrix multiplications, as previous. Si is the mirror matrix. Thematrix is very simple, depends on the actual plane, the sign of appropriatecoordinatevalueischanged.

Fig.1.11

Introduction 11

Mirror to xi axes

Thesecondwayisthemirrortoxiaxes.AstheSi,jmirrormatrixshows,thesignsofthevaluesofcoordinateaxisarechanged,expectthexi.

Fig. 1.12

Mirror to the origin Themirrortotheoriginisverysimple,everysignofthecoordinatevalueshavetobechanged.Thereforethemirrormatrixcontains-1inthemaindiagonal.

Fig. 1.13

CONSTRUCTION OF CARTESIAN COORDINATE SYSTEMAlmosteverythingthatcanbeproducedonaconventionalmachinetoolcanbeproduced on a computer numerical controladvantages. The machine tool movements used in producing a product are oftwobasic types:point-to-point (straight(contouringmovements).

The Cartesian, or rectangular, coordinate systemmathematicianandphilosopherRene’Descartes.Withthissystem,anyspecificpointcanbedescribedinmathematicaltermsfromanyotherpointalongthreeperpendicular axes. This concept fits machine tools perfectly since theirconstructionisgenerallybasedonthreeaxesofmotion(X,Y,Z)plusanaxisrotation. On a plain vertical millingmovement (right or left) of the table, the Y axis is the table cross movement(towardoraway fromthecolumn),andtheZaxis is theverticalmthekneeorthespindle.Previously,wehaveidentifiedapointinthexyan ordered pair that consists of two real numbers, an xcoordinate, which denote signed distances along the xrespectively, from the origincollectively referred to as the coordinate axes, divided the plane into fourquadrants.PLANES IN THREE-DIMENSIONAL SPACEUnlike two-dimensional spacethree-dimensional space contains infinitely many planes, just as twodimensional space consists of infinitely many lines. Three planes are ofparticular importance: the xyplane,whichcontainstheyandz-axes. Alternatively,thexy

CHAPTER TWO

CONSTRUCTION OF SHAPES USING AXIS

CARTESIAN COORDINATE SYSTEM Almosteverythingthatcanbeproducedonaconventionalmachinetoolcanbe

computer numerical control machine tool, with its manyadvantages. The machine tool movements used in producing a product are of

point (straight-linemovements)andcontinuouspath

Fig. 2.1

The Cartesian, or rectangular, coordinate system was devised by the FrenchmathematicianandphilosopherRene’Descartes.Withthissystem,anyspecific

bedescribedinmathematicaltermsfromanyotherpointalongthree. This concept fits machine tools perfectly since their

isgenerallybasedonthreeaxesofmotion(X,Y,Z)plusanaxis. On a plain vertical milling machine, the X axis is the horizontal

movement (right or left) of the table, the Y axis is the table cross movement(towardoraway fromthecolumn),andtheZaxis is theverticalm

Previously,wehaveidentifiedapointinthexyan ordered pair that consists of two real numbers, an x-coordinate and ycoordinate, which denote signed distances along the x-

the origin, which is the point (0; 0). These axes, which arecollectively referred to as the coordinate axes, divided the plane into four

DIMENSIONAL SPACE dimensional space, which consists of a single plane, the xy

dimensional space contains infinitely many planes, just as twodimensional space consists of infinitely many lines. Three planes are ofparticular importance: the xy-plane, which contains the x- and yplane,whichcontainsthey-andz-axes;andthexz-plane,whichcontainsthex

Alternatively,thexy-planecanbedescribedasthesetofallpoints

Almosteverythingthatcanbeproducedonaconventionalmachinetoolcanbemachine tool, with its many

advantages. The machine tool movements used in producing a product are oflinemovements)andcontinuouspath

was devised by the FrenchmathematicianandphilosopherRene’Descartes.Withthissystem,anyspecific

bedescribedinmathematicaltermsfromanyotherpointalongthree. This concept fits machine tools perfectly since their

isgenerallybasedonthreeaxesofmotion(X,Y,Z)plusanaxisofmachine, the X axis is the horizontal

movement (right or left) of the table, the Y axis is the table cross movement(towardoraway fromthecolumn),andtheZaxis is theverticalmovementof

Previously,wehaveidentifiedapointinthexy-planebycoordinate and y--axis and y-axis,

, which is the point (0; 0). These axes, which arecollectively referred to as the coordinate axes, divided the plane into four

, which consists of a single plane, the xy-plane,dimensional space contains infinitely many planes, just as two-

dimensional space consists of infinitely many lines. Three planes are ofand y-axes; the yz-

plane,whichcontainsthex-planecanbedescribedasthesetofallpoints

Construction of shapes using axis

(x;y;z)forwhichz=0.Similarly,theyz(0;y;z),whilethexz-planeisthesetofallpointsoftheform(x;0;z).

Thepoint(2;3;1)inxyz-space,denotedbytheletterP.TheorigintheletterO.TheprojectionsofPontodiamonds.Thedashed linesare linesegmentsplanesthatconnectPtoitsprojections.xy-plane into four quadrants,octants. Within each octant, all xcoordinates,andallz-coordinates.Inparticular,thefirstoctant istheoctant inwhichallthreecoordinatesarepositive.GEOMETRIC MODELLINGRequirementsofgeometricmodellingThefunctionsthatareexpectedofgeometricmodellingare:Design analysis: —Evaluationofareasandvolumes.—Evaluationofmassandinertiaproperties—Interferencecheckinginassemblies.—Analysisoftolerancebuild—Analysisofkinematics——Automaticmeshgenerationforfiniteelementanalysis.Drafting: —Automaticplanarcrosssectioning.—Automatichiddenlineandsurface—Automaticproductionofshadedimages.—Automaticdimensioning.


Similarly,theyz-planeisthesetofallpointsoftheformplaneisthesetofallpointsoftheform(x;0;z).

Fig. 2.2 space,denotedbytheletterP.Theorigin

theletterO.TheprojectionsofPontothecoordinateplanesareindicatedbythediamonds.Thedashed linesare linesegmentsperpendicular to thecoordinateplanesthatconnectPtoitsprojections.Justasthex-axisandy

plane into four quadrants, these three planes divide xyzoctants. Within each octant, all x-coordinates have the same sign, as do all y

coordinates.Inparticular,thefirstoctant istheoctant inwhichallthreecoordinatesarepositive.

GEOMETRIC MODELLING RequirementsofgeometricmodellingThefunctionsthatareexpectedofgeometricmodellingare:

Evaluationofareasandvolumes.Evaluationofmassandinertiaproperties.

checkinginassemblies.Analysisoftolerancebuild-upinassemblies.

—mechanics,robotics.Automaticmeshgenerationforfiniteelementanalysis.

Automaticplanarcrosssectioning.Automatichiddenlineandsurfaceremoval.Automaticproductionofshadedimages.Automaticdimensioning.

13

allpointsoftheformplaneisthesetofallpointsoftheform(x;0;z).

space,denotedbytheletterP.Theoriginisdenotedbythecoordinateplanesareindicatedbythe

perpendicular to thecoordinateaxisandy-axisdividethe

these three planes divide xyz-space into eighthave the same sign, as do all y-

coordinates.Inparticular,thefirstoctant istheoctant in

CAD/CAM

—Automaticcreationofexplodedviewsfortechnicalillustrations.Manufacturing: —Partsclassification.—Processplanning.—Numericalcontroldatagenerationandverification—Robotprogramgeneration.Production Engineering: —Billofmaterials.—Materialrequirement.—Manufacturingresourcerequirement.—Scheduling. Inspection and Quality Control:—Programgenerationforinspectionmachines.—ComparisonofproducedpRequichaandVoelker[1981]specifiedthefollowingpropertiestobedesiredofinanygeometricmodelling(solids)system. Theconfigurationofsolid(geometricmodel)muststayinvariantwithregard

toitslocationandorientation. Thesolidmusthaveaninteriorandmustnothaveisolatedparts. Thesolidmustbefiniteandoccupyonlyafiniteshape. Theapplicationofatransformationorotheroperationthataddsorremoves

partsmustproduceanothersolid. The model of the solid in E

points. However, it must have a finite number of surfaces, which can bedescribed.

The boundary of the solid must uniquely identify which part of the solid isexteriorandwhichisinterior.

GEOMETRIC MODELS Thegeometricmodelscanbebroadlycategorisedintotwotypes:1.Two-dimensional,and

Fig. 2.3 3D geometric representation techniques

Automaticcreationofexplodedviewsfortechnicalillustrations.

Numericalcontroldatagenerationandverification.Robotprogramgeneration.

Manufacturingresourcerequirement.

Inspection and Quality Control: Programgenerationforinspectionmachines.Comparisonofproducedpartwithdesign.

RequichaandVoelker[1981]specifiedthefollowingpropertiestobedesiredofinanygeometricmodelling(solids)system.

Theconfigurationofsolid(geometricmodel)muststayinvariantwithregardtoitslocationandorientation.

solidmusthaveaninteriorandmustnothaveisolatedparts.Thesolidmustbefiniteandoccupyonlyafiniteshape.Theapplicationofatransformationorotheroperationthataddsorremovespartsmustproduceanothersolid.The model of the solid in E3 (Euler space) may contain infinite number ofpoints. However, it must have a finite number of surfaces, which can be

The boundary of the solid must uniquely identify which part of the solid isexteriorandwhichisinterior.

canbebroadlycategorisedintotwotypes:dimensional,and2.Three-dimensional.

3D geometric representation techniques

14

Automaticcreationofexplodedviewsfortechnicalillustrations.

RequichaandVoelker[1981]specifiedthefollowingpropertiestobedesiredof

Theconfigurationofsolid(geometricmodel)muststayinvariantwithregard

solidmusthaveaninteriorandmustnothaveisolatedparts.

Theapplicationofatransformationorotheroperationthataddsorremoves

3 (Euler space) may contain infinite number ofpoints. However, it must have a finite number of surfaces, which can be

The boundary of the solid must uniquely identify which part of the solid is

canbebroadlycategorisedintotwotypes:

3D geometric representation techniques


Thethreeprincipalclassificationscanbe1.Thelinemodel,2.Thesurfacemodel,and3.Thesolidorvolumemodel

Fig. 2.4 A geometric model represented in wire

Fig. 2.5 Generation of 3D geometry using planar surfaces

GEOMETRIC CONSTRUCTION METHODSThethree-dimensionalgeometricconstruction2Dthatisnormallyusedare:•Linearextrusionortranslationalsweep•Rotationalsweep.

Fig. 2.6 Component model produced using translational (linear) sweep


Thethreeprincipalclassificationscanbe

3.Thesolidorvolumemodel

A geometric model represented in wire-frame model

Generation of 3D geometry using planar surfaces

GEOMETRIC CONSTRUCTION METHODS

dimensionalgeometricconstructionmethodswhichextendfromthe2Dthatisnormallyusedare:

ortranslationalsweep,and

Component model produced using translational (linear) sweep

15

frame model

Generation of 3D geometry using planar surfaces

methodswhichextendfromthe

Component model produced using translational (linear) sweep(extrusion)

CAD/CAM

Fig. 2.7 Component model produced using translational (linear) sweepwith taper in sweep direction

Fig. 2.8 Component model produced using translational (linear) sweepoverhanging edge

Fig. 2.9 Component produced by the rotational sweep



Component produced by the rotational sweep technique

16


Component model produced using translational (linear) sweep with an

technique


Fig. 2.10

Fig. 2.11 The Boolean operators and their effect on model construction

Fig. 2.12 The Boolean operators and their effect on model construction


10 Various solid modelling primitives

The Boolean operators and their effect on model construction


17



CAD/CAM

Fig. 2.13 Creating a solid with the 3D primitives in solid modellingthe model shown in the form of Constructive Solid Geometry (CSG)

Fig. 2.14 Example of filleting or blend method for model generation

Creating a solid with the 3D primitives in solid modellingthe model shown in the form of Constructive Solid Geometry (CSG)

Example of filleting or blend method for model generation

18

Creating a solid with the 3D primitives in solid modelling and

the model shown in the form of Constructive Solid Geometry (CSG)

Example of filleting or blend method for model generation


METHODS FOR CONSTRUCTING SURFACES OR SOLIDS FROM OTHER GEOMETRY When you extrude, sweepandsurfaces.

Opencurvesalwayscreatesurfaces,butclosedcurvescancreateeithersolidsorsurfacesdependingoncertainsettingssweep,loft,orrevolveanobject,youcreate:AsolidiftheModeoptionissettoSolid.AsurfaceiftheModeoptionissettoSurface.

About Solids Based on Other ObjectsYou can also create 3D solids from 2D geometry or other 3D objects. Forexample, a 3D solid can also be the result of extruding a 2D shape to follow aspecifiedpathin3Dspace.


METHODS FOR CONSTRUCTING SURFACES OR SOLIDS FROM OTHER

, sweep, loft, and revolve curves, you can create both solids

Fig. 2.15 Opencurvesalwayscreatesurfaces,butclosedcurvescancreateeithersolidsorsurfacesdependingoncertainsettings.Ifyouselectaclosedcurve

,loft,orrevolveanobject,youcreate:iftheModeoptionissettoSolid.

iftheModeoptionissettoSurface.

Fig. 2.16

Based on Other Objects

You can also create 3D solids from 2D geometry or other 3D objects. Forexample, a 3D solid can also be the result of extruding a 2D shape to follow a

Fig. 2.17

19

METHODS FOR CONSTRUCTING SURFACES OR SOLIDS FROM OTHER

, you can create both solids

Opencurvesalwayscreatesurfaces,butclosedcurvescancreateeithersolidsorcurveandextrude,

You can also create 3D solids from 2D geometry or other 3D objects. Forexample, a 3D solid can also be the result of extruding a 2D shape to follow a

CAD/CAM 20

Thefollowingmethodsareavailable: Sweep.Extendsa2Dobjectalongapath. Extrusion.Extendstheshapeofa2Dobjectinaperpendiculardirectioninto

3Dspace. Revolve.Sweepsa2Dobjectaroundanaxis. Loft.Extends the contours of a shape between one or more open or closed

objects. Slice.Dividesasolidobjectintotwoseparate3Dobjects. Sculpting Surfaces.Converts and trims a group of surfaces that enclose a

watertightareaintoasolid. Conversion.Converts mesh objects and planar objects with thickness into

solidsandsurfaces. Geometry that can be use as profiles and guide curves Thecurvesthatyouuseasprofileandguidecurveswhenyouextrude,sweep,loft,andrevolvecanbe: Openorclosed Planarornon-planar Solidandsurfaceedges Asingleobject(toextrudemultiplelines,convertthemtoasingleobjectwith

theJOINcommand) Asingleregion(toextrudemultipleregions,convertthemtoasingleobject

withtheREGIONcommand)

Splinesareoneofthemany2Dobjecttypesthatcanbelofted,extruded,swept,and revolved to create NURBS surfaces. Other 2D objects that can be usedincludelines,polylines,arcs,andcircles.Splines,however,aretheonly2Dobjectcustomized to create NURBS surfaces. Because they allow you to adjusttolerance, degree, and tangency, they are better suited than other types of 2Dprofiles(suchaslines,polylines,andcircles)forsurfacemodeling.

Fig. 2.18


A PARAMETRIC SOLID MODELThe tools that you need to create a parametricsoftware and a computer that is powerful enough to run the software. As youcreatethemodel,thesoftwarewilldisplayanimageoftheobjectwhichcanbeturned and viewed from any direction as if it actually existed in threedimensions.Usingthemousethroughagraphicaluser interface(GUIthe computer monitor). The GUI gives you access to various tools for creatingand editing your models. GUIs diffsoftware. However, most of the packages share some common approaches.Whencreatinganewmodel(i.e.,withnothingyetexisting),youwillprobablybepresentedwithadisplayof3three primary modeling planes, which are sometimes called theviewing planes or datum xz planes and are usually displayed from a viewing direction fromthreeplanescanbeseen,asshowninfig.2.19.

Nearlyallsolidmodelersuse2Sketchesaremadeononeoftheplanesofthemodelwitha2similartoadrawingeditorfoundonmost2begin a new model, you ofteplanes. When the sketching plane is chosen, some modelers will reorient theviewsoyouarelookingstraightatthe2sketching.


A PARAMETRIC SOLID MODEL The tools that you need to create a parametric model are solid modeling

software and a computer that is powerful enough to run the software. As youcreatethemodel,thesoftwarewilldisplayanimageoftheobjectwhichcanbeturned and viewed from any direction as if it actually existed in threedimensions.Usingthemouseandkeyboard,youwillinteractwiththesoftwarethroughagraphicaluser interface(GUI)onthecomputer’sdisplaydevice(i.e.,the computer monitor). The GUI gives you access to various tools for creatingand editing your models. GUIs differ slightly in different solidsoftware. However, most of the packages share some common approaches.Whencreatinganewmodel(i.e.,withnothingyetexisting),youwillprobablybepresentedwithadisplayof3-DCartesiancoordinatex-,y-,andzthree primary modeling planes, which are sometimes called the

planes.Theseplaneshelpyouvisualizethexy,yz,anxz planes and are usually displayed from a viewing direction fromthreeplanescanbeseen,asshowninfig.2.19.

Fig. 2.19

use2-Dsketchesasabasisforcreatingsolidfeatures.Sketchesaremadeononeoftheplanesofthemodelwitha2-Dsketchingeditorsimilartoadrawingeditorfoundonmost2-DCADdraftingsoftware.Whenyoubegin a new model, you often make a sketch on the one of the basic modelingplanes. When the sketching plane is chosen, some modelers will reorient theviewsoyouarelookingstraightatthe2-Dsketchingplane.Youcanthenbegin

21

model are solid modelingsoftware and a computer that is powerful enough to run the software. As youcreatethemodel,thesoftwarewilldisplayanimageoftheobjectwhichcanbeturned and viewed from any direction as if it actually existed in three

andkeyboard,youwillinteractwiththesoftware)onthecomputer’sdisplaydevice(i.e.,

the computer monitor). The GUI gives you access to various tools for creatinger slightly in different solid modelling

software. However, most of the packages share some common approaches.Whencreatinganewmodel(i.e.,withnothingyetexisting),youwillprobablybe

,andz-axesandthethree primary modeling planes, which are sometimes called the principal

.Theseplaneshelpyouvisualizethexy,yz,andxz planes and are usually displayed from a viewing direction from which all

Dsketchesasabasisforcreatingsolidfeatures.Dsketchingeditor

draftingsoftware.Whenyoun make a sketch on the one of the basic modeling

planes. When the sketching plane is chosen, some modelers will reorient theDsketchingplane.Youcanthenbegin

CAD/CAM

VALID PROFILES Beforeasolidfeaturecanbecreatedbyextrusionorrotationthe shape must be a closed loop. Extra line segmentssegments, or overlapping lines create problems because the software cannotdeterminetheboundariesofthesolidinthemodel.used to create a solid is called afrom the profile by a process known as extrusion. created from the profile by a process called revolution. To create a revolvedsolid,aprofilecurveisrotatedaboutanaxis.Theprocessissimilclay vase or bowl on a potter’s wheel. The profile of a revolved part is alsoplanar,andtheaxisofrevolutionliesintheprofileplane(sketchingplane).

Fig. 2.20 A solid created by extrusion of a 2

CREATING SOPHISTICATED GEOMETRYCreating protrusions and cuts by extending the sketch profiles madeoneitherthebasicmodelingplaneoroneoftheexistingsurfacesofthemodelresultsinawidevarietyofpossiblemodels.Evenmoresophisticatedmodelsbecreatedbyusingreferencegeometriescalledthemodel,displayed,andusedtocreatefeatures.Generally,solidmodelersofferat least three types of datumdatum points, datum axesactuallyexistontherealpart(i.e., theycannotbehelplocateanddefinefeature

DEFINING DATUM POINTSFollowing are some of the different ways a datumcreated.Thedefinitionsareshowngraphicallyin Atavertex Onaplanarsurfaceatspecifiedperpendiculardistancesfromtwo Attheintersectionofalineoranaxisandasurfacethatdoesnotcontainthe

line

nbecreatedbyextrusionorrotation,thefinalprofilethe shape must be a closed loop. Extra line segments, gaps between the linesegments, or overlapping lines create problems because the software cannotdeterminetheboundariesofthesolidinthemodel. Acompletedsketchthatisused to create a solid is called a profile. A simple solid model can be creat

y a process known as extrusion. A different model can beby a process called revolution. To create a revolved

isrotatedaboutanaxis.Theprocessissimilclay vase or bowl on a potter’s wheel. The profile of a revolved part is alsoplanar,andtheaxisofrevolutionliesintheprofileplane(sketchingplane).

Fig. 2.20 A solid created by extrusion of a 2-D profile

SOPHISTICATED GEOMETRY Creating protrusions and cuts by extending the sketch profiles madeoneitherthebasicmodelingplaneoroneoftheexistingsurfacesofthemodelresultsinawidevarietyofpossiblemodels.Evenmoresophisticatedmodelsbecreatedbyusingreferencegeometriescalleddatums,whichcanbeaddedtothemodel,displayed,andusedtocreatefeatures.Generally,solidmodelersoffer

datum geometries that can be placed into a model:, datum axes, and datum planes.Thesedatumgeometriesdonot

actuallyexistontherealpart(i.e., theycannotbeseenor felt)butareusedtohelplocateanddefinefeatures.

DEFINING DATUM POINTS Following are some of the different ways a datum point can be defined and

Thedefinitionsareshowngraphicallyinfig.2.21.

OnaplanarsurfaceatspecifiedperpendiculardistancesfromtwoAttheintersectionofalineoranaxisandasurfacethatdoesnotcontainthe

22

,thefinalprofileof, gaps between the line

segments, or overlapping lines create problems because the software cannotAcompletedsketchthatis

model can be createdA different model can be

by a process called revolution. To create a revolvedisrotatedaboutanaxis.Theprocessissimilartocreatinga

clay vase or bowl on a potter’s wheel. The profile of a revolved part is alsoplanar,andtheaxisofrevolutionliesintheprofileplane(sketchingplane).

D profile.

Creating protrusions and cuts by extending the sketch profiles madeoneitherthebasicmodelingplaneoroneoftheexistingsurfacesofthemodelresultsinawidevarietyofpossiblemodels.Evenmoresophisticatedmodels,however,can

,whichcanbeaddedtothemodel,displayed,andusedtocreatefeatures.Generally,solidmodelersoffer

that can be placed into a model:.Thesedatumgeometriesdonot

seenor felt)butareusedto

point can be defined and

OnaplanarsurfaceatspecifiedperpendiculardistancesfromtwoedgesAttheintersectionofalineoranaxisandasurfacethatdoesnotcontainthe


Fig. 2.21 Various ways to define a datum

DEFINING DATUM AXES Following are some of the different ways a datumcreated.Thedefinitionsareshowngraphicallyinfig.2.22.

Betweentwopoints(orvertices) Alongalinearedge Attheintersectionoftwoplanarsurfaces Attheintersectionofacylinderandaplanethroughitsaxis Alongthecenterlineofacylinderorcylindricalsurface

Fig. 2.22


Fig. 2.21 Various ways to define a datum point.

Following are some of the different ways a datum axis can be defined andcreated.Thedefinitionsareshowngraphicallyinfig.2.22.

Betweentwopoints(orvertices)

AttheintersectionoftwoplanarsurfacesAttheintersectionofacylinderandaplanethroughitsaxis

enterlineofacylinderorcylindricalsurface

Various ways to define a datum axis.

23

point.

axis can be defined and

Attheintersectionofacylinderandaplanethroughitsaxis

CAD/CAM

DEFINING DATUM PLANES Following are some of the different ways a datumcreated.Thedefinitionsareshowngraphicallyin■Throughthreenoncolinearpoints■Throughtwointersectinglines■Throughalineandanoncolinearpoint■Offsetfromanexisting�latsurfaceataspeci�ied■Throughanedgeoraxisona�latsurfaceatananglefromthatsurface■Tangenttoasurfaceatapointonthatsurface■Perpendiculartoa�latsurfaceandthroughalineparalleltothatsurface■Perpendiculartoa�latorcylindricalsurf■Tangenttoacylindricalsurfaceatalineonthatsurface

DEFINING DATUM PLANES Following are some of the different ways a datum plane can be defined andcreated.Thedefinitionsareshowngraphicallyinfig.2.23.

ThroughthreenoncolinearpointsThroughtwointersectinglinesThroughalineandanoncolinearpointOffsetfromanexisting�latsurfaceataspeci�ieddistanceThroughanedgeoraxisona�latsurfaceatananglefromthatsurfaceTangenttoasurfaceatapointonthatsurfacePerpendiculartoa�latsurfaceandthroughalineparalleltothatsurfacePerpendiculartoa�latorcylindricalsurfacethroughalineonthatsurfaceTangenttoacylindricalsurfaceatalineonthatsurface

24

plane can be defined and

Throughanedgeoraxisona�latsurfaceatananglefromthatsurface

Perpendiculartoa�latsurfaceandthroughalineparalleltothatsurfaceacethroughalineonthatsurface


Fig. 2.23 Various ways to

Calling out your datums in a drawing is one of the steps towards making surethatapartismanufacturedandinspectedinsuchawaythatitcanbereplacedwith another partmade fromthe same drawing and fit correctly. The datumstogether indicate how the part rests when it'sSurfacesaregenerallyeasierto inspectthanedgesbutyoucanextrapolatetheintersectionoftwosurfacesortheextensionofaconetoatheoreticalpointthatcanbeusedasareference.

Itdoesn'tmatterwhatyoucalthey appear in your feature control frames.little blocks of symbols and numbers that usually have "A|B|C" at the end.Reading the feature control frame from left to righprimarymountingfeature,themiddleisthesecondaryreferenceandthethirdisthetertiaryreference.Theordertellsyouhowtosetupyourpart inordertomachine or inspect it a specific feature.characteristicsofthefeatureareimportantandtheshapeofthetolerancezoneand the numbers tell you the size of the tolerance zoneANSIY14.5-2009-a standardcalledGD&TforGeometricDimensioningandTolerancing.

Fig. 2.24

A CAD application supports the annotations that are used in the standardtheunderlyingknowledgeofthestandardisn'tcoveredinthebookandrequires


Various ways to define a datum plane.

in a drawing is one of the steps towards making surethatapartismanufacturedandinspectedinsuchawaythatitcanbereplacedwith another partmade fromthe same drawing and fit correctly. The datumstogether indicate how the part rests when it's mounted on specific surfaces.Surfacesaregenerallyeasierto inspectthanedgesbutyoucanextrapolatetheintersectionoftwosurfacesortheextensionofaconetoatheoreticalpointthatcanbeusedasareference.

Itdoesn'tmatterwhatyoucallyourDatums.Whatmattersistheorderinwhichthey appear in your feature control frames. Feature control frames are thoselittle blocks of symbols and numbers that usually have "A|B|C" at the end.Reading the feature control frame from left to right, the first datumprimarymountingfeature,themiddleisthesecondaryreferenceandthethirdis

Theordertellsyouhowtosetupyourpart inordertomachine or inspect it a specific feature. The symbolcharacteristicsofthefeatureareimportantandtheshapeofthetolerancezoneand the numbers tell you the size of the tolerance zone All of this is part of

a standard for Dimensioning and tolerancing parts generallycalledGD&TforGeometricDimensioningandTolerancing.

4 feature control frame with its parts:

application supports the annotations that are used in the standardtheunderlyingknowledgeofthestandardisn'tcoveredinthebookandrequires

25

plane.

in a drawing is one of the steps towards making surethatapartismanufacturedandinspectedinsuchawaythatitcanbereplacedwith another partmade fromthe same drawing and fit correctly. The datums

mounted on specific surfaces.Surfacesaregenerallyeasierto inspectthanedgesbutyoucanextrapolatetheintersectionoftwosurfacesortheextensionofaconetoatheoreticalpointthat

WhatmattersistheorderinwhichFeature control frames are those

little blocks of symbols and numbers that usually have "A|B|C" at the end.t, the first datum is the

primarymountingfeature,themiddleisthesecondaryreferenceandthethirdisTheordertellsyouhowtosetupyourpart inorderto

The symbol tells you whatcharacteristicsofthefeatureareimportantandtheshapeofthetolerancezone

All of this is part ofng and tolerancing parts generally

application supports the annotations that are used in the standard, buttheunderlyingknowledgeofthestandardisn'tcoveredinthebookandrequires

CAD/CAM 26

agoodamountofstudyandtrainingtouseeffectively.UsuallythestartingpointforlearningGD&Tisatrainingclassofferedbyacompanycertifiedtoteachit.YoucanalsolearnaboutitfrombookspublishedbyASME(ASME.org)orotherpublishers like the IHS Drawing Requirements Manual. You can identify thedatumsonyourpartusingtheDatumFramecommand. Youcanrefertouptothree datums in a feature control frame. These represent the primary,secondary,andtertiarydatums.An engineering drawing datum point is a single reference point (usually acorner)thatallmeasurementsaregivenortakenfrom.Thismaintainsaccuracybyeliminatingpropagationofsmallerrors. Forexample,ifyouaretomeasurefroma corner to a hole, and then measure fromthat hole to another hole andfinally measure from there to another corner, you will invariably introduceseveralerrorswhichwouldpropagatethrougheverydimensionyouaddtothischain.Eachoneofthesemovesyoufurtherawayfromtheaccuracyyourtryingto achieve. By using the datum method, you will have taken all thesemeasurements from a single known point. In some complex geometries theremaybeseveraldatumpoints,buttheyareallusedtomaintainsimpleaudit-ableaccuracy.Datumpointscanbeusedin2Dor3Ddesigns.STRATEGIES FOR MAKING A MODEL You have a blank computer display in front of you, and your solid modelingsoftware is running. So where do you start? The first step in modeling a solidpartistodecomposeitintofeatures.Studythepartandtrytoidentifythebasefeature. Expanding on a previous statement, the base feature should besomething thatdescribes theoverallshapeof thepartorsomething thatgivesyou the greatest amount of functional detail that can be created with a singleextrusion, rotation, sweep, or blend. Next, break the rest of the part intosubsections that can be created using extruded, revolved, swept, or blendedshapes.Lookforstandardfeaturessuchasholesandslotsthataremanufacturedusing a particular process. Identify the edge features such as chamfers androunds. Once you have studied the part, you can create the model using thefollowingeight-stepprocedure:1. Createanydatumgeometriesorpathsrequiredtocreatethebasegeometry.2. Sketchandconstrainprofilesneededforthebase.3. Extrude,rotate,sweep,orblendtocreatethebase.4. Createanynecessarydatumgeometriesorpathstocreatethenextfeature.5. Forsketchedfeatures,sketchandconstrainorotherwisespecifythefeature

profiles;thenextrude,rotate,sweep,orblendtocreatethefeature.6. For standard features such as holes and edge features, specify the desired

parametersandplacementontheexistinggeometry.7. Arrayormirrorthefeatureifnecessarytocreateidenticalfeatures.8. Repeatsteps4–9untilthemodeliscomplete.


Once the model is complete, it canexample, additional associative constraintsdimensionalconstraintsordesigntablesmaybecreatedforfamiliesofparts.

ConsidertheguideblockinFigmodel for this part? What should be its base feature? What are its secondaryfeatures? One reasonable base feature would be an extrusion made with theprofileshowninFig.2.26.Thisextrusioninasingleoperationandisrepresentativeofthegeneralshapeofthepart.Thesketchismadeononeoftheconstrained.Notetheuseofhorizontalandverticalwould likely be applied automaticallyapproximatelyintheorientationsshown.Alsonotethatgrounded by constraining the vertex to be coincident with thecoordinatesystem;therefore,dimensionalconstraintslocatingtheprofileplanearenotneeded.Notetheuseofthecollinearconstrainthorizontal sketch segments, which eliminates the need to place separatedimensional constraints on the height of the segments. Once the profile iscomplete,itcanbeextrudedtothewidthofthepart,asshowninFigure

Fig.2.25. A solid model of this part is toperformed, and in what sequence should they be made?

a.


Once the model is complete, it can be modified to become more robust. Forexample, additional associative constraints may be added in place ofdimensionalconstraintsordesigntablesmaybecreatedforfamiliesofparts.

ConsidertheguideblockinFig.2.25asanexample.Howwouldyoubuildasolidmodel for this part? What should be its base feature? What are its secondary

One reasonable base feature would be an extrusion made with the.Thisextrusionwouldcapturemanydetailsofthepart

andisrepresentativeofthegeneralshapeofthepart.Thesketchismadeononeofthebasicplanesandisgeometricallyanddimensionallyconstrained.Notetheuseofhorizontalandverticalgeometryconstraints,whichwould likely be applied automatically if the segments were sketchedapproximatelyintheorientationsshown.Alsonotethatacorneroftheprofileisgrounded by constraining the vertex to be coincident with the

;therefore,dimensionalconstraintslocatingtheprofileplanearenotneeded.Notetheuseofthecollinearconstraint

segments, which eliminates the need to place separateconstraints on the height of the segments. Once the profile is

extrudedtothewidthofthepart,asshowninFigure

. A solid model of this part is to be created. What operations should be

performed, and in what sequence should they be made?

b.

27

be modified to become more robust. Formay be added in place of

dimensionalconstraintsordesigntablesmaybecreatedforfamiliesofparts.

asanexample.Howwouldyoubuildasolidmodel for this part? What should be its base feature? What are its secondary

One reasonable base feature would be an extrusion made with thewouldcapturemanydetailsofthepart

andisrepresentativeofthegeneralshapeofthepart.Thebasicplanesandisgeometricallyanddimensionally

geometryconstraints,whichif the segments were sketched

acorneroftheprofileisgrounded by constraining the vertex to be coincident with the origin of the

;therefore,dimensionalconstraintslocatingtheprofileontheplanearenotneeded.Notetheuseofthecollinearconstraintonthetwoshort

segments, which eliminates the need to place separateconstraints on the height of the segments. Once the profile is

extrudedtothewidthofthepart,asshowninFigure2.26(d).

be created. What operations should be

CAD/CAM

c. Fig2.26. The base feature is created by planes (a),constraining the sketch to create a profile(c) to the required depth to obtain the desiredThefirstfeaturetobeaddedistheslotacrosstheslotcanbemadeonthemodelbyanextrudedcutusingarectangularprofilethesketchingplaneshowninFigGeometricanddimensionalconstraintsaresketch is constrained to be colinear with the topguaranteeing that the slot always will be a slot (and not aheight of the part increases. An extruded cut is then made by ecompleted profile to the limit of the part or through the entire part. If thisextrudedcutwasmadetoaspecificlengthjustbeyondthelimitofthepart(e.g.,with a blind extrusion extending past the part), the resulting mappear identical to the desired model. However, blind extrusions like this areusually considered poorconstraintsofthepartareincreased,thethe part.Next, thehole is added.Simple throughholes can be created asa cutfeature by selecting the desired plane or face of the existing solid, sketching acircle,andextrudingacutornegativefeature.However,abetterwaytomakeaholeistousethestandardinthedatabase.

b. is created by sketching on one of the basic modeling

planes (a),constraining the sketch to create a profile (b), and extrudingdepth to obtain the desired result (d).

Thefirstfeaturetobeaddedistheslotacrosstheupperportionofthepart.TheslotcanbemadeonthemodelbyanextrudedcutusingarectangularprofilethesketchingplaneshowninFig.2.27.

Geometricanddimensionalconstraintsareaddedtothesketch.Oneedgeofthesketch is constrained to be colinear with the top edge of the base feature,guaranteeing that the slot always will be a slot (and not a square hole) if theheight of the part increases. An extruded cut is then made by e

to the limit of the part or through the entire part. If thisextrudedcutwasmadetoaspecificlengthjustbeyondthelimitofthepart(e.g.,

blind extrusion extending past the part), the resulting mthe desired model. However, blind extrusions like this are

usually considered poor modeling practice, because if selected lengthconstraintsofthepartareincreased,theslotnolongerextendsentirelythrough

t, thehole is added.Simple throughholes can be created asa cutselecting the desired plane or face of the existing solid, sketching a

acutornegativefeature.However,abetterwaytomakeadholefeature,whichwillidentifythefeatureasahole

28

of the basic modeling (b), and extruding the profile

upperportionofthepart.Theslotcanbemadeonthemodelbyanextrudedcutusingarectangularprofileon

addedtothesketch.Oneedgeoftheedge of the base feature,

square hole) if theheight of the part increases. An extruded cut is then made by extruding the

to the limit of the part or through the entire part. If thisextrudedcutwasmadetoaspecificlengthjustbeyondthelimitofthepart(e.g.,

blind extrusion extending past the part), the resulting model wouldthe desired model. However, blind extrusions like this are

modeling practice, because if selected lengthslotnolongerextendsentirelythrough

t, thehole is added.Simple throughholes can be created asa cutselecting the desired plane or face of the existing solid, sketching a

acutornegativefeature.However,abetterwaytomakeaholefeature,whichwillidentifythefeatureasahole


Fig 2.27. A slot is created by selecting a surface on the model to be the sketching plane in (a), on which a sketch is created and constrained in the magnified (b). The profile is extruded to the end of the part in (c), and the material is removed to create the result in (d).Therefore, if your part is to be manufactured by an automated productionsystem,theholescanberecognizedandathat the location dimensions of theimportant.Whydoesthismatter?Lookingathole should stay centered on the width of the part.width of the partchanges? Wouldn’t you want thehole tothewidth of the part? Using an associativeconstraint on the widththe hole, making it always equal to onedesignintentwillbemaintained.Nomatterwhousesyourmodelorchangesthedimensions, the intended symmetrywill remain embedded in the part. AddingtheholewithitsassociativeconstraintisshowninFigFinally, the round and filletRounds and fillets are associated with particular edges, so no sketching isinvolvedforthisstep.Simplypickthedesirededgeandapplytheroundorfilletfeature,specifyingthedesiredradius.Thein Fig. 2.29, and the fillet is shown in Figfeatures,sothemodelisnow

Fig. 2.28. The surface to which the hole is to be added is selected as the placementplane in (a). The location and diameter of the hole are specified in (b). An


. A slot is created by selecting a surface on the model to be the sketching in (a), on which a sketch is created and constrained in the magnified

extruded to the end of the part in (c), and the material is removed to create the result in (d).

part is to be manufactured by an automated productionsystem,theholescanberecognizedandautomaticallydrilledorbored.Thewaythat the location dimensions of the hole are included in the model is alsoimportant.Whydoesthismatter?Lookingatthepart,youmightassumethatthehole should stay centered on the width of the part. What willwidth of the partchanges? Wouldn’t you want thehole to remain centered onthewidth of the part? Using an associativeconstraint on the widththe hole, making it always equal to one-half the part’s width, ensures that

nintentwillbemaintained.Nomatterwhousesyourmodelorchangesthedimensions, the intended symmetrywill remain embedded in the part. Adding

withitsassociativeconstraintisshowninFig.2.28.

Finally, the round and fillet features need to be added to the model geometry.Rounds and fillets are associated with particular edges, so no sketching is

thisstep.Simplypickthedesirededgeandapplytheroundorfilletthedesiredradius.Theresultofaddingtheroundsisshown

, and the fillet is shown in Fig.2.30. There are no array or mirrorfeatures,sothemodelisnowcomplete.

The surface to which the hole is to be added is selected as the placementplane in (a). The location and diameter of the hole are specified in (b). An

29

. A slot is created by selecting a surface on the model to be the sketching

in (a), on which a sketch is created and constrained in the magnified view in extruded to the end of the part in (c), and the material is

part is to be manufactured by an automated productionutomaticallydrilledorbored.Theway

hole are included in the model is alsothepart,youmightassumethatthe

What will happen if theremain centered on

thewidth of the part? Using an associativeconstraint on the width locationofhalf the part’s width, ensures that the

nintentwillbemaintained.Nomatterwhousesyourmodelorchangesthedimensions, the intended symmetrywill remain embedded in the part. Adding

features need to be added to the model geometry.Rounds and fillets are associated with particular edges, so no sketching is

thisstep.Simplypickthedesirededgeandapplytheroundorfilletresultofaddingtheroundsisshown

. There are no array or mirror

The surface to which the hole is to be added is selected as the placement

plane in (a). The location and diameter of the hole are specified in (b). An

CAD/CAM

associative constraint is used on the variable names to ensure that it remains centered in (c), and the final result is shown in (d).

Fig. 2.29. The edges to be roundedin (b) as an associative constraint to ensure aof the rounding operation is

Fig. 2.30 The edge to be filleted isThe result of the fillet operation isDepending on the design intent, several different modeling strategies can beusedforthesamepart.Ifthedesignerwantstheentireparttobesymmetricalanother way to achieve the desired symmetry would be to create a twoextrusion of the base profiletwo-sided extrusion, no extra datumThen the slot is constrained to be symmetrical across the plane, and the holecenterisconstrainedtolieinthesymm

GROUP TECHNOLOGY Group technology is an operations management philosophy based on therecognition that similarities occur in the design and manufacture of discreteparts.Similarpartscanthenbearrangedintopartfamilies.Toimplementsuchasystem, some form of classification of partclassificationandcodingisconcernedwithidentifyingthesimilaritiesandusingthese similarities to evolve a classification code. Similarities are of two types:design attributes (such as geometric shaattributes (the sequence of processing steps required to make the part). Incompanieswhichemployseveraldesignengineersandmanufacturingadiverserange of products, such classificationsOneofthemajorbenefitsisavoidingtheduplicationofsimilarcomponents.Thiscan result in considerable savings in terms of design cost,processing cost andtoolingcost.Oneprimenecessity

constraint is used on the variable names to ensure that it remains final result is shown in (d).

edges to be rounded are selected in (a), and the radius is specified

constraint to ensure a full radius across therounding operation is shown in (c).

edge to be filleted is selected in (a), and the radius is specifiedoperation is shown in (c).

Depending on the design intent, several different modeling strategies can bet.Ifthedesignerwantstheentireparttobesymmetrical

another way to achieve the desired symmetry would be to create a twoextrusion of the base profile from the original sketching plane. By creating a

sided extrusion, no extra datum planes are needed to ensure symmetry.Then the slot is constrained to be symmetrical across the plane, and the holecenterisconstrainedtolieinthesymmetryplane.

is an operations management philosophy based on therecognition that similarities occur in the design and manufacture of discreteparts.Similarpartscanthenbearrangedintopartfamilies.Toimplementsuchasystem, some form of classification of parts and coding is required. Partclassificationandcodingisconcernedwithidentifyingthesimilaritiesandusingthese similarities to evolve a classification code. Similarities are of two types:

(such as geometric shape and size), and manufacturing(the sequence of processing steps required to make the part). In

companieswhichemployseveraldesignengineersandmanufacturingadiverserange of products, such classifications and coding has a number of other uses.Oneofthemajorbenefitsisavoidingtheduplicationofsimilarcomponents.Thiscan result in considerable savings in terms of design cost,processing cost and

.Oneprimenecessitytorealizethisistohaveagooddesignretrieval

30

constraint is used on the variable names to ensure that it remains

the radius is specified

full radius across the part. The result

radius is specified in (b).

Depending on the design intent, several different modeling strategies can bet.Ifthedesignerwantstheentireparttobesymmetrical,

another way to achieve the desired symmetry would be to create a two-sidedfrom the original sketching plane. By creating a

planes are needed to ensure symmetry.Then the slot is constrained to be symmetrical across the plane, and the hole

is an operations management philosophy based on therecognition that similarities occur in the design and manufacture of discreteparts.Similarpartscanthenbearrangedintopartfamilies.Toimplementsucha

s and coding is required. Partclassificationandcodingisconcernedwithidentifyingthesimilaritiesandusingthese similarities to evolve a classification code. Similarities are of two types:

pe and size), and manufacturing(the sequence of processing steps required to make the part). In

companieswhichemployseveraldesignengineersandmanufacturingadiverseand coding has a number of other uses.

Oneofthemajorbenefitsisavoidingtheduplicationofsimilarcomponents.Thiscan result in considerable savings in terms of design cost,processing cost and

torealizethisistohaveagooddesignretrieval

Construction of shapes using axis 31

system. The parts classification and coding is required in a design retrievalsystem, and in computer aided process planning the process routing isdeveloped by recognizing the specific attributes of the part and relating theseattributestothecorrespondingmanufacturingoperations. PART FAMILIES A part family is a collection of parts which are similar either because ofgeometry and size or because similar processing steps are required in theirmanufacture. The parts within a family are different, but their similarities areclose enough to merit their identification as members of the part family. Themajor obstacle in changing over to group technology from a traditionalproductionshopistheproblemofgroupingpartsintofamilies.Therearethreegeneralmethodsforsolvingthisproblem.i.Visualinspectionii.Productionflowanalysisiii.PartsclassificationandcodingsystemWhat is desirable in a computer integrated manufacturing environment is asoftwarewhichwillanalyzethegeometricmodelofthepartandcomeoutwithasetofalphabetic/numericcharacterswhichcanbroadlyembedsimilarities.

PARTS CLASSIFICATION AND CODING SYSTEMS Partsclassificationandcodingsystemscanbegroupedintothreegeneraltypes:i.Systemsbasedondesignattributesii.Systemsbasedonpartmanufacturingattributesiii.SystemsbasedonbothdesignandmanufacturingattributesSystems in the first category are useful for design retrieval and to promotedesignstandardization.Systemsinthesecondcategoryareusedforcomputer-aidedprocessplanning,tooldesign,andotherproductionrelatedfunctions.Thethirdcategoryrepresentsanattempttocombinethe functionsandadvantagesoftheothertwosystemsintoasingleclassificationscheme.Thetypesofdesignand manufacturing attributes typically included in classification schemes arelistedbelow: Part design attributes

Basic(External/Internal)shape Axisymmetric/Prismatic/sheetmetal Length/diameterratio Material Majordimensions Minordimensions Tolerances Surfacefinish

CAD/CAM

Part Manufacturing Attributes Majorprocessofmanufacture Surfacetreatments/coatings Machinetool/processingequipment Cuttingtools Operationsequence Productiontime Batchquantity Productionrate Fixturesneeded

Ifwe takea lookatamachinetoolmanufacturing industry, largepart familiescanbegroupedas:i.Heavyparts-beds,columnsetc.ii.Shafts,characterizedbylargeL/Dratiosiii.Spindles(longshafts,screwrodsincluded)iv.Non-rounds(smallprismaticparts)v.Gears,disctypeparts(whoseL/Dratiosaresmall)From the manufacturingconsiderable economy in tooling, set up time, part changeover times, machinespecifications etc. The classification of components in groups can lead toformation of cells where similar components are machined. Hconsiderationsareextraneoustotheprocessplanning EXAMPLEGiventhepartdesignofFig.2.19

The overall length/diameter ratio,L/D =1.6, so the first code = 1. The part issteppedonbothendswithascrewthreadononeend,sotheseconddigitcodewouldbe5thethirddigitcodeis1becauseofthethroughhole.Thefourthand

Part Manufacturing Attributes MajorprocessofmanufactureSurfacetreatments/coatingsMachinetool/processingequipment

Ifwe takea lookatamachinetoolmanufacturing industry, largepart families

beds,columnsetc.ii.Shafts,characterizedbylargeL/Dratiosiii.Spindles(longshafts,screwrodsincluded)

rounds(smallprismaticparts)v.Gears,disctypeparts(whoseL/Dratiosaresmall)

From the manufacturing point of view, group technology can bring inconsiderable economy in tooling, set up time, part changeover times, machinespecifications etc. The classification of components in groups can lead toformation of cells where similar components are machined. Hconsiderationsareextraneoustotheprocessplanningfunction.

GiventhepartdesignofFig.2.19,theformcodeforthispartisdiscussedbelow.

Fig. 2.19 Sample of a part length/diameter ratio,L/D =1.6, so the first code = 1. The part is

onbothendswithascrewthreadononeend,sotheseconddigitcodedigitcodeis1becauseofthethroughhole.Thefourthand

32

Ifwe takea lookatamachinetoolmanufacturing industry, largepart families

point of view, group technology can bring inconsiderable economy in tooling, set up time, part changeover times, machinespecifications etc. The classification of components in groups can lead toformation of cells where similar components are machined. However, these

function.

,theformcodeforthispartisdiscussedbelow.

length/diameter ratio,L/D =1.6, so the first code = 1. The part isonbothendswithascrewthreadononeend,sotheseconddigitcode

digitcodeis1becauseofthethroughhole.Thefourthand

Construction of shapes using axis 33

fifthdigitsareboth0,sincenosurfacemachiningisrequiredandtherearenoauxiliaryholes or gear teeth on the part. The complete form code in the Opitzsystemis“15100”.Toaddthesupplementarycode,wewouldhavetoproperlycode the sixth through ninth digitswith data ondimensions, material, startingworkpieceshape,andaccuracy

CODING STRUCTURES Apartcodingschemeconsistsofsymbolsthatidentifythepart’sdesignand/ormanufacturing attributes. The symbols in the code can be all numeric, allalphabetic,oracombinationofbothtypes.Therearethreebasiccodestructuresusedingrouptechnologyapplications:

i.Hierarchicalstructureii.Chaintypestructureiii.Hybridstructurewhichisacombinationoftheabovetwo

With the hierarchical structure, the interpretation of each succeeding symboldependsonthevalueoftheprecedingsymbols.Inthechaintypestructure,theinterpretationofeachsymbolinthesequence is fixedanddoesnotdependonthevalueofprecedingdigits.Mostofthecommercialpartscodingsystemsareusedinindustryareacombinationofthetwopurestructures.Whenselectingacodingsystemforacomponent’srepresentation,thereareseveralfactorstobeconsidered.Theyinclude:

i. Thegeometryofcomponents(i.e.,rotational,prismatic,deepdrawn,sheetmetaletc.)

ii. Thecodestructureiii. Thedigitalrepresentation(i.e.,binary,octal,hexadecimaletc.)iv. Materialofmanufacture-ferrous,nonferrous,plastics,compositesetc.

When using a code to represent an engineering design, it is important torepresentthebasicfeaturesofthedesign.Forprocessplanning,itisdesirabletohavecodesthatcandistinguishuniqueproductionfamilies.Someofthecodingsystemsthathavebeensuccessfullyimplementedinprocessplanningaregivenbelow:

i.OPITZsystemii.TheCODEsystemiii.TheKK-3systemiv.TheMICLASSsystemv.DCLASSsystemvi.COFORM(codingformachining)

When implementing a parts classification and coding system, most companiescan purchase a commercially available package or develop a system for theirownspecificuse.

CHAPTER THREE

DATA TRANSFER IN CAD

OneoftheearliestusesofCADwasisinthefieldofComputerAidedDesignandDrafting (CADD). This entails the use of CAD systemas an electronic form ofdrafting table, enhanced by the accuracy and computational power of thecomputer. The ability of the CAD system to generate the precise drawinggraphics,combinedwiththepowerofdigitalcomputingmadeitapowerfultoolforadesignerordraftsman.CADallowsausertocreatecomplexdrawingwithease, libraries of subassemblies and predrawn patterns are easily created andmaintained, dimensioning of engineering drawings can be automaticallyperformed and generation of excellent quality plots can be easily performed.Together, these functions constitute a powerful tool to enable designers toquickly and easily create accurate and complex designs both on paper and inelectronicformthatmaybeusedbyotherprocesses. OVERVIEW OF AutoCAD This is one of the most powerful and popular software packages that provideCADDcapabilitiesforMicrocomputers.IthasinitiallyaTwo-Dimensional(2-D)graphics package. The later versions have 3-D capabilities and several solidmodelling interfaces and programming capabilities. AutoCAD is menu drivenand is very much user friendly package. It can be used with minimum ofcomputer knowledge and is very much flexible. User can create his own pulldownmenus,Screenmenusforonescommonusage.Italsoprovidesscriptfilefacilitytoinputdrawingsdirectly. ItalsosupportsDrawingsInterchange(IGESandDXF)fileformats.AutoCADcanbeuseditselfasacomplexdrawingeditor. NUETRAL FILE FORMATS Paper blue prints are being replaced with computer databasesin defining product geometry and non geometry for all phases ofproduct design and manufacturing. Effective procedures for exchange of thesedatabases are to be developed. Fundamental incompatibilities among entityrepresentationgreatlycomplicateexchangingmodellingdataamongCAD/CAMsystems. The database exchange problem is complicated further by thecomplexity of CAD/CAM systems, the varying requirements of organizationsusingthem,therestrictionsonaccesstoproprietarydatabaseinformation,andtherapidpaceoftechnologicalchange.

TransferringdatabasebetweendissimilarCAD/CAMsystemsmustembracethecompleteproductdescriptionstoredinitsdatabase.Fourtypesofmodelingdatamakeupthisdescription.Theseareshape,nonshape,designandmanufacturingdata.Shapedataconsistsofbothgeometricalandtopologicalinformationaswell

Data transfer in CAD 35

aspartorformfeatures.Entityattributessuchasfont,color,andlayeraswellasannotationisconsideredpartoftheentitygeometricalinformation.Topologicalinformation applies only to products described via solid modelling. Featuresallow high-level concept communication about parts (hole, pocket etc.). Non-shapedataincludesgraphicsdatasuchasshadedimagesandmodelglobaldataas measuring units of the database and the resolution of storing the databasenumericalvalues.

Design data has to do with the information that designers generate fromgeometricmodelsforanalysispurposes.Manufacturingdataisthefourthtype.Itconsists of information as tooling, NC tool paths, tolerance, process planning,tool design and bill of materials. Data exchange formats like DXF and IGESfocused on CAD- to CAD exchange where primarily shape and non shape dataweretobetransferredfromonesystemtoanother. INITIAL GRAPHICS EXCHANGE SPECIFICATION (IGES) Initial Graphics Exchange Specificationwas the first specification forCAD dataexchangepublishedin1980asaNBS(NationalBureauofStandards)reportinUSA.IGESversion1.0wasacceptedandreleasedin1981asanANSIstandard.All major CAD vendors support IGES and it is currently by far the mostwidespreadstandardforCADdataexchange.IGESwasoriginallydevelopedfortheexchangeofdraftingdatalike2D/3Dwireframemodels,text,dimensioningdata, and a limited class of surfaces. Due to criticism and bad experience withthe data transfer using IGES, the standard has been gradually extended anddevelopedconcerningsupportedentities,syntax,clarity,andconsistency.Initial Graphics Exchange Specification is the standard exchange formatdeveloped to address the concept of communicating product data amongdissimilarCAD/CAMsystems.LikemostCAD/CAMsystems,anIGESmodelisbased on the concept of entities. The fundamental unit of information in themodel,andconsequentlyintheIGESfile,istheentity;allproductdefinitiondataare expressed as a list of predefined entities. Each entity defined by IGES isassigned a specific entity type number to refer to it in the IGES file. Entitynumbers 1 through 599 and 700 through 5000 are allocated for specificassignments.Entitytypenumbers600through699and10,000through99,999areforimplementor-definedentities.Entitiesarecategorizedasgeometricandnon-geometric.

Geometric entities represent the definition of the product shape andinclude curves and surfaces. Relations that may exist between variousentities are included as parameters. Non-geometric entities provideviews and drawings of the model to enrich its representation andinclude annotation and structure entities. Annotation entities includevarious types of dimensions (linear, angular, and ordinate), centrelines, notesgeneral labels, symbols and cross-hatching. Structure entities include views,

CAD/CAM

drawings,attributes(suchaslineandtextfonts,(e.g., mass properties),assemblies), symbols (e.g., mechanical and electrical symbols) and macros (todefineparametricparts).timearepracticalproblems.each entity has to have records in both the directory entry section andparameter data section with bipre-andpost-processorimplementations,suchtwhendealingwithDXFfiles.

DATA EXCHANGE FORMAT (DXF) It is necessary to export CAD data to other packages like analysis, CNCprogrammingorotherCADpackages.animation, it is entirely appropriate toexportthegeometrysothatitcanbeopenedinaexporting3DsolidmodelingCADfilesandimportingpackage,takeafewmomentsinyourCADsoftwareandtheirexportsettings.Afewofthepopularexportfiletypesusedforimportingmodelsintomajoranimationsoftwareinclude.3ds, .dxf, and .igs. By experimenting wiformats, you will quickly determine with which formats you make the fewesterrors.

Fig. 3.1 Drawing data exchange

This section describes the format of a DXF file in detail. ItinformationthatisneededtowriteprogramstoentityinformationobtainedbycertainisalsocalledasDrawing Interchange fileinto very large number of lines offeature extraction program, howeveridentify and extract the useful entity data.overall understanding of a dxf file structure, with morsection, which contains the geometric data of all the entities used for drawingthespecificprofileofthepart.

(suchaslineandtextfonts,colourslayersetc.),properties(e.g., mass properties), subfigures and external reference entities (forassemblies), symbols (e.g., mechanical and electrical symbols) and macros (to

ThesizeofIGESfilesandconsequentlytheprocessingpracticalproblems.IGESfilesarecomposedoffixedformatrecordsand

each entity has to have records in both the directory entry section andparameter data section with bi-directional pointers. This causes also

processorimplementations,suchtypeoferrorcouldrarelyoccurwhendealingwithDXFfiles.

DATA EXCHANGE FORMAT (DXF) It is necessary to export CAD data to other packages like analysis, CNCprogrammingorotherCADpackages.Inthecommercialpracticeofengineering

is entirely appropriate to model in a CAD environment and toexportthegeometrysothatitcanbeopenedina3Danimationpackage.Before

DsolidmodelingCADfilesandimportingthemintoyouranimationpackage,takeafewmomentstobecomefamiliarwiththeavailablefileformatsinyourCADsoftwareandtheirexportsettings.Afewofthepopularexportfiletypesusedforimportingmodelsintomajoranimationsoftwareinclude.3ds, .dxf, and .igs. By experimenting with the various export and import fileformats, you will quickly determine with which formats you make the fewest

Fig. 3.1 Drawing data exchange

This section describes the format of a DXF file in detail. It contains technicalneededtowriteprogramstoprocessDXFfilesorworkwith

entityinformationobtainedbycertainAutoLISPandADSfunctions.ADXFfile,Drawing Interchange file,hasasinglecolumnstructurerunning

into very large number of lines of data. All of this data is not required by thefeature extraction program, however the program has to read these lines toidentify and extract the useful entity data. This section aims at providing anoverall understanding of a dxf file structure, with more focus on the entitiessection, which contains the geometric data of all the entities used for drawing

ofthepart.

36

layersetc.),propertiessubfigures and external reference entities (for

assemblies), symbols (e.g., mechanical and electrical symbols) and macros (toThesizeofIGESfilesandconsequentlytheprocessing

IGESfilesarecomposedoffixedformatrecordsandeach entity has to have records in both the directory entry section and the

directional pointers. This causes also errors incouldrarelyoccur

It is necessary to export CAD data to other packages like analysis, CNCInthecommercialpracticeofengineering

environment and toionpackage.Before

themintoyouranimationavailablefileformats

inyourCADsoftwareandtheirexportsettings.Afewofthepopularexportfiletypesusedforimportingmodelsintomajoranimationsoftwareinclude.obj,.stl,

th the various export and import fileformats, you will quickly determine with which formats you make the fewest

contains technicalprocessDXFfilesorworkwith

AutoLISPandADSfunctions.ADXFfile,,hasasinglecolumnstructurerunning

data. All of this data is not required by thethe program has to read these lines to

This section aims at providing ane focus on the entities

section, which contains the geometric data of all the entities used for drawing

Data transfer in CAD

GENERAL FILE STRUCTURE OF DXF A Drawing Interchange File is simply an ASCII text file with afile type of .dxf and specially formatted text. The overall organizationofaDXFfileisasfollowing.1. HEADER Section: This section contains the general information about the

drawing.Eachparameterhasavariablenameandanassociatedvalue.2. TABLES Section:Thissectioncontainsdefinitionsofnameditems.

Linetype(LTYPE)tableLayertable(LAYER)Textstyletable(STYLE)Viewtable(VIEW)UserCoordinateSystem(UCS)tableViewportconfiguration(VPORT)tableDimensionStyletable(DIMSTYLE)ApplicationIdentificationtable(APPID)

3. BLOCKS section: This section contains Block definition entities describingtheentitiesthatmakeupeachBlockinthedrawing.

4. ENTITIES section: This section contains the drawingdetails,includinganyBlockreferences

5. END OF FILE. DXFfile(DrawingExchangeFilemanyCADsystemvendors.DXFformatiseasytointerpretthoughitisfile. The data pertaining to the drawing entities are included in the entitiessection.Fig.3.2showsaplatewithahole.ThecontentsoftheentitysectionoftheDXFfileofthiscomponentaregiveninTable

GENERAL FILE STRUCTURE OF DXF A Drawing Interchange File is simply an ASCII text file with a

type of .dxf and specially formatted text. The overall organizationofaDXFfileisasfollowing.

This section contains the general information about thedrawing.Eachparameterhasavariablenameandanassociatedvalue.

Thissectioncontainsdefinitionsofnameditems.Linetype(LTYPE)table

Textstyletable(STYLE)

System(UCS)tableViewportconfiguration(VPORT)tableDimensionStyletable(DIMSTYLE)ApplicationIdentificationtable(APPID)

This section contains Block definition entities describingtheentitiesthatmakeupeachBlockinthedrawing.

This section contains the drawing entities and theirdetails,includinganyBlockreferences

DXFfile(DrawingExchangeFile)isapopulardataexchangeformatadoptedbymanyCADsystemvendors.DXFformatiseasytointerpretthoughitisfile. The data pertaining to the drawing entities are included in the entities

showsaplatewithahole.ThecontentsoftheentitysectionoftheDXFfileofthiscomponentaregiveninTable3.1.

Fig.3.2platewithahole

37

A Drawing Interchange File is simply an ASCII text file with atype of .dxf and specially formatted text. The overall organization

This section contains the general information about thedrawing.Eachparameterhasavariablenameandanassociatedvalue.

Thissectioncontainsdefinitionsofnameditems.

This section contains Block definition entities describing

entities and their

)isapopulardataexchangeformatadoptedbymanyCADsystemvendors.DXFformatiseasytointerpretthoughitisalengthyfile. The data pertaining to the drawing entities are included in the entities

showsaplatewithahole.Thecontentsoftheentitysectionof

CAD/CAM

Table3.1PortionofDXFfileThereareseveralexistingalternativedataexchangeformats.TheseincludetheStandardProductDataExchangeFormat(SDF)ofVoughtCorporation(availablefor CADAM, CADDS-5, PATRAN, and PRIME etc.) Standard Interchang(SIF) of Intergraph Corporation (available for Applicon, Autotrol, and Calmaetc.), ICAM Product Data Definition Interface (PDDI), and VDA sculpturedsurface Interface (VDAFS), Electronic Design Interchange Format (EDIF),

Table3.1PortionofDXFfile

Thereareseveralexistingalternativedataexchangeformats.TheseincludetheStandardProductDataExchangeFormat(SDF)ofVoughtCorporation(available

5, PATRAN, and PRIME etc.) Standard Interchang(SIF) of Intergraph Corporation (available for Applicon, Autotrol, and Calmaetc.), ICAM Product Data Definition Interface (PDDI), and VDA sculpturedsurface Interface (VDAFS), Electronic Design Interchange Format (EDIF),

38

Thereareseveralexistingalternativedataexchangeformats.TheseincludetheStandardProductDataExchangeFormat(SDF)ofVoughtCorporation(available

5, PATRAN, and PRIME etc.) Standard Interchange Format(SIF) of Intergraph Corporation (available for Applicon, Autotrol, and Calmaetc.), ICAM Product Data Definition Interface (PDDI), and VDA sculpturedsurface Interface (VDAFS), Electronic Design Interchange Format (EDIF),

Data transfer in CAD 39

TransferandArchivingofProductDefinitionData(TAP)etc.Anotheralternativeto IGES is the neutral format outlined in ANSI Y14.26M standard. It must benotedherethatsomeofthefeaturesofmanyofthesealternativesaresuperiortothatofIGES.Seamless exchange of product data is critical to CAD/CAM/CAE systems. TheStandard for the Exchange of Product Data (STEP) is the enabler for suchseamless data exchange. It provides a worldwide standard for storing, sharingand exchanging product information among different CAD systems. AlthoughSTEP itself is the basis for Product Data Management System (PDM). It coversborder functionalities. It includes methods of representing all critical productspecifications such as shape information, materials, tolerances, finishes andproduct structure. Whereas the Initial Graphics Exchange Specification (IGES)standard has widespread use, it has its shortcomings. It does not convey theextensive product information needed in the design and manufacturing cycle.OftenIGEStranslatorsarerequiredtomovedesigndatafromoneCADsystemtoanother. STEP is often viewed as a replacement for IGES, though IGES is stillexpected to be in active use for some more time in the future. Although thecurrentfocusofSTEPisonmechanicalparts,STEPisadataexchangestandardthat would apply to a wide range of product areas, including electronics,architectural,engineeringandconstruction,apparelandshipbuilding.SubsequentreleasesofSTEPprovidedaddedfunctionalityintermsofthekindsof product supported and the extent of the product life cycle. While STEP isadvancing towards maturity, it had been investigated for the feasibility ofincorporation into framework system. Both STEP and Concurrent Engineeringsharethecommongoalofinfluencingtheproductcyclefromdesign,assembly,etc. to the disposal stages which have been realized in the CONSENS systemunderESPRITEP6896.Theobject-orienteddatabaseforCONSENShasaschemawith STEP definitions alongside company specific definitions. A module calledProduct Information Archive (PIA) provides functionality for STEPdata accessviaSDAI.Itisgenerictobeadoptedfordifferentdomains.Forexampleitisusedfor product information by the Aircraft Company, Deutshces Aerospace andelectronicsmanufacturingcompany,AEG.

CHAPTER FOUR

CAM SYSTEM AND CONFIGURATION The number of Computer-Aided Manufacturing (CAM) applications is growingrapidlyafterthedevelopmentofComputer-AidedDesign(CAD).CAMreliesonthe CAD data, such as graphics of the design, and so on. Therefore, therelationship between computer aided design and manufacturing processes isclosely tied. It is the relationship that provides the design of tooling, jigs, andfixtures and the generation of machine instructions for manufacturing andinspection. The range of CAM applications vary greatly from highly automatedtools which are predominantly graphics driven to pure language based toolswheremachinetoolprogrammersuse APT,andotherprogramming languagestocontrolthemachines.Inaddition,currenttechnologyprovidestheintegrationof both graphics and program languages in an application to maximize theproductivity.

The product development process is not finished by the CAD work, themodellingandthedrawing.TheCADmodelissuitableforotheractivities.Thischapterpresentssomeof them. The first is the3Dscanning,whenarealpartwillbeconvertedtotheCADmodelbydigitalization.Thereareseveralmethodswhich will presented in the beginning. This technology is suitable for digitalreproductionofapart. TherapidprototypingtechnologiesareabletocreatearealpartbasedontheCADmodel.Theapplicationofthemhasawildrangefromthevisualizationtothefunctionaltestorrealproduction.Onetypeofmachinepartscanbeproducedbycuttingtechnologies(turning,milling).InordertoproductivityandaccuracyCNCmachinetoolsareapplied,wherethemotionof thetoolsarecontrolledbytheCNCprograms.TheCAMsystemscanbegeneratedtheseprogramsbasedonCADmodelofthepart. TheaimoftheCAM systems is to connect the virtual CAD model and the real manufacturing.Thecomputeraidedmanufacturing(CAM)atfirstlookseemsaverycomplicatedandambitiousterm,butinrealitmeansonlythedesignofcuttingtoolpathandthegenerationofNCprogram.TheNCprogramisthealphanumericalcodeforcontroltheworkofCNCcontrolledautomaticmachinetools.Incaseofcomplexpartgeometrythedesignofcuttingtoolpath,whichwillgeneratethesurfaceofthe part, needs a lot of calculation, which takes lot of time. The CAM systemsperformthesecalculationsbasedonCADmodel.ThetypicalpartsofaCAMsystemarethenext:

Toolpathgeneration Editoftoolpath Optimizationoftoolpath Materialandtooldatabase

CAM system and configuration 41

Machiningtimecalculation NCpostprocessing

CAM CLASSIFICATION TheCAMsystemscanbeclassifiedbyseveralviewpoints.Thefirstisthetypeofthe machine tool or the applied cutting technology. So we can talk about CAMsystemsformilling,turning,cutting(laser,waterjet,oxyfuelcutting,plasmaarc,wire-edm)technologiesorcoordinatemeasuring.Theotherclassificationbasedon the degree of freedom. The degree of freedom is the one axis movingpossibility.Thedegreeoffreedomdependsthetechnologyandthedesignofthemachinetool.Letusseesomeexample.DEGREE OF FREEDOM IN CAM SYSTEMS •Numberofdirectionofmovingpossibilities•1D–movinginoneaxis –Drilling•2D–parallelmovingintwoaxis –Turning –Cutting(laser,plasma,water,wire-edm)•2.5D–machininginx-yplane+movingfordepth –Somemillingoperation:facemilling,roughing,z-levelmilling

In case of 1D the tool has only one moving direction, like drilling.Incaseof2Dthetoolcanmoveparallelintwodirection.Theturningandsomecutting technology is typically 2D manufacturing. The 2.5D means, that the 2Dparallelmovingpossibilitiesiscompletedbya3rdstepmotion,likesomemillingprocess.•3D–parallelmovinginthreeaxis –Finishingmillingoffreeformsurfaces –Coordinatemeasuringmachine•4D –Cuttingintwoparallelplane(eg.wireedm) –Twinspindlelathe•5D –5Dmilling:3linearaxis+2rotaryaxis•6D –Industrialrobots•xD –Multiaxismachinetools(e.g.Toolgrindingmachine)The 3D means simultaneous moving in 3 direction. The free form CNC millingand the coordinate measuring machine need this type of control.Thehigherdimensionsmeanscomplicatedmachinetools.The4Dcanbe2x2D,likeincaseofwireEDMoftwinspindlelate,or4simultaneousmoving,like3

CAD/CAM

linearand1rotational,orother.The5Distypicallymeans5D3linearmotioniscompletedby2rotational.Theindustrial6D control, like a humanoid robot, which has 6 rotary axesmachinetoolrequiredmoreaxes.Fig. 4.1 shows and summarized the typical workflow of a CAMThe order of the definition can be different in different CAM systems, but thedefinition of the listed data is required every case for appropriate work.Themostimportantapplicationhereafterwefocustothisapplication.

linearand1rotational,orother.The5Distypicallymeans5Detedby2rotational.Theindustrialrobotgenerallyhas

6D control, like a humanoid robot, which has 6 rotary axesmachinetoolrequiredmoreaxes.

shows and summarized the typical workflow of a CAMThe order of the definition can be different in different CAM systems, but thedefinition of the listed data is required every case for appropriate work.ThemostimportantapplicationoftheCAMsystemsisthemillinghereafterwefocustothisapplication.

Fig.4.1 CAM process

42

linearand1rotational,orother.The5Distypicallymeans5Dmilling,whentherobotgenerallyhasa

6D control, like a humanoid robot, which has 6 rotary axes. Some special

shows and summarized the typical workflow of a CAM system.The order of the definition can be different in different CAM systems, but thedefinition of the listed data is required every case for appropriate work.

oftheCAMsystemsisthemillingtechnology,so

CAM system and configuration

CAM WORKFLOW PROCESSTheCAMworkflowstartwiththemanufacturingplanthemanufacturingprocess,becauseduringtheCAMworkflowwetakeonlydefinition.The CAM system cannotcreate a process, cannot select tool, cannotdefinecuttingparameters.Theengineerwillis opened in the CAM system in native or neutral formats depends on CAMsystems and consider the advantagesand disadvantages. If needand possiblethe geometry is corrected of modified, and the blank materiadefined.SELECTION OF MACHINE TOOLThesecondstepisthemachinetoolselection.Herewehavetodefinesomebasicdata of the machine tool, like the size of the workplace, the limits of cuttingparameters. We have to select the type of CNCessential data for generate NC program. The next step is the definition thecoordinate system.The coordinate systemgives the null point of the program.InlotofCAMsystemwecandefine2planesoverthepart.Overthesafetyplanethe 3D rapid motion is enabled, under it, the tool can be move fast only inperpendiculartotheplane.Theretractplanedefinestheleveloftheconnectionmotions.Sometimesthesetwop

•Basicdata(workspace,limitsofcuttingparametersetc.)•TypeofCNCcontroller•Definecoordinatesystem•Definesafetyplanes

1–safetyplane,overthisplanethe3Drapidmotionenabled2–retractplane,planeofconnectionmotions


WORKFLOW PROCESS workflowstartwiththemanufacturingprocessplanning

planthemanufacturingprocess,becauseduringtheCAMworkflowwetakeonlydefinition.The CAM system cannotcreate a process, cannot select tool, cannotdefinecuttingparameters.Theengineerwilldefinethem.First,theCADis opened in the CAM system in native or neutral formats depends on CAMsystems and consider the advantagesand disadvantages. If needand possiblethe geometry is corrected of modified, and the blank materia

SELECTION OF MACHINE TOOL Thesecondstepisthemachinetoolselection.Herewehavetodefinesomebasicdata of the machine tool, like the size of the workplace, the limits of cuttingparameters. We have to select the type of CNC controller, because it is anessential data for generate NC program. The next step is the definition the

.The coordinate systemgives the null point of the program.systemwecandefine2planesoverthepart.Overthesafetyplane

the 3D rapid motion is enabled, under it, the tool can be move fast only inperpendiculartotheplane.Theretractplanedefinestheleveloftheconnectionmotions.Sometimesthesetwoplanesaresame.

•Basicdata(workspace,limitsofcuttingparametersetc.)

•Definecoordinatesystem

safetyplane,overthisplanethe3Drapidmotionenabled

plane,planeofconnectionmotionsFig. 4.2

43

processplanning.Wehavetoplanthemanufacturingprocess,becauseduringtheCAMworkflowwetakeonlydefinition.The CAM system cannotcreate a process, cannot select tool, cannot

definethem.First,theCADmodelis opened in the CAM system in native or neutral formats depends on CAMsystems and consider the advantagesand disadvantages. If needand possiblethe geometry is corrected of modified, and the blank material geometry is

Thesecondstepisthemachinetoolselection.Herewehavetodefinesomebasicdata of the machine tool, like the size of the workplace, the limits of cutting

controller, because it is anessential data for generate NC program. The next step is the definition the

.The coordinate systemgives the null point of the program.systemwecandefine2planesoverthepart.Overthesafetyplane

the 3D rapid motion is enabled, under it, the tool can be move fast only inperpendiculartotheplane.Theretractplanedefinestheleveloftheconnection

CAD/CAM

SELECTION OF CUTTING TOOLThe third step is the cutting tool selection or defines. Lot of CAMcontainsatooldatabase,whichcontainsgeometricdescriptionsofcuttingtools.This database contains the tools, which are exist in the machining workshop.TheCAMsystemneedonlythreegeometricparametersofcuttingtoolsincaseofmilling:diameter,lengthandcornerradius.Ingeneralthedatabasecontainstherecommendedcuttingdata.•Tooldatabase•Basicgeometricaldata –Diameter–D –Length-L –Cornerradius-R•Cuttingparameters: –Material –Roughing/Finishing –n(vc),vf

SELECTION OF CUTTING TOOL The third step is the cutting tool selection or defines. Lot of CAMcontainsatooldatabase,whichcontainsgeometricdescriptionsofcuttingtools.This database contains the tools, which are exist in the machining workshop.TheCAMsystemneedonlythreegeometricparametersofcuttingtoolsincase

:diameter,lengthandcornerradius.Ingeneralthedatabasecontainstherecommendedcuttingdata.

Finishing

Fig. 4.3

44

The third step is the cutting tool selection or defines. Lot of CAM systemscontainsatooldatabase,whichcontainsgeometricdescriptionsofcuttingtools.This database contains the tools, which are exist in the machining workshop.TheCAMsystemneedonlythreegeometricparametersofcuttingtoolsincase

:diameter,lengthandcornerradius.Ingeneralthedatabasecontains


SELECTION OF TOOL PATH STRATEGYThemostimportantpartofaCAMThetoolpathstrategydefinesthecharacterofthemachining.TheCAMengineerhastoselectthemostappropriatestrategy,considerthepartgeometryandthecutting tool. The CAM systems contain “standardoriented special strategies. One manufacturing task can be solved by severaldifferent ways; the CAM systems ensure lot of tools for successfulmanufacturing.

•Technologyorientedtoolpath•Standardstrategies+CAM•Onetask–morestrategies•Tool–Partgeometry

SELECTION OF MACHINED GEOMETRYInthenextstepwehavetoselectordefinedthegeometryrelatedtotheselectedstrategy.Wecanselectdifferenttype

•Axis–forholemaking,•Curve–engraving,slotmilling•Surface–surfacemilling,•Volume–roughmilling.

We can select the existing geometry elements of the CADdefine new elements. After the definition the CAMcalculations.Typicalittakeslessthe1minute. SIMULATION After the calculation we can control the result by simulations. The simplestsimulationisthesimpledisplayofthetoolwecanfollowthemachiningprocess,wecanseethegeneratedpartgeometry.Basically this simulation contains only the part and the tool geometry, but wecan complete the simulationtypeofthesimulationisthecollisioncheck,whenthecollisionbetweenthetooland the part, the tool and the fixture or machine tool, or the tool holder andother elements are detected.type of the simulation. Some CAM


SELECTION OF TOOL PATH STRATEGY ThemostimportantpartofaCAMsystemisthelistofmanufacturing

strategydefinesthecharacterofthemachining.TheCAMengineerhastoselectthemostappropriatestrategy,considerthepartgeometryandthecutting tool. The CAM systems contain “standard” strategies and CAM system

strategies. One manufacturing task can be solved by severaldifferent ways; the CAM systems ensure lot of tools for successful

•Technologyorientedtoolpathstrategies•Standardstrategies+CAMsystemorientedspecialstrategies

morestrategiesPartgeometry–Toolpathstrategy

Fig. 4.4

SELECTION OF MACHINED GEOMETRY Inthenextstepwehavetoselectordefinedthegeometryrelatedtotheselected

Wecanselectdifferenttypeofgeometricalelements:forholemaking,

engraving,slotmilling,surfacemilling,roughmilling.

We can select the existing geometry elements of the CAD model, or we canAfter the definition the CAM system performs the

calculations.Typicalittakeslessthe1minute.

After the calculation we can control the result by simulations. The simplestsimulationisthesimpledisplayofthetoolpath.Themanufacturingwecanfollowthemachiningprocess,wecanseethegeneratedpartgeometry.Basically this simulation contains only the part and the tool geometry, but wecan complete the simulation with the machine tool and the fixture. The othertypeofthesimulationisthecollisioncheck,whenthecollisionbetweenthetooland the part, the tool and the fixture or machine tool, or the tool holder andother elements are detected. The machining time calculation is an importanttype of the simulation. Some CAM systems are able to calculate more process

45

systemisthelistofmanufacturingstrategies.strategydefinesthecharacterofthemachining.TheCAMengineer

hastoselectthemostappropriatestrategy,considerthepartgeometryandthe” strategies and CAM system

strategies. One manufacturing task can be solved by severaldifferent ways; the CAM systems ensure lot of tools for successful

ecialstrategies

Inthenextstepwehavetoselectordefinedthegeometryrelatedtotheselected

model, or we cansystem performs the

After the calculation we can control the result by simulations. The simplest.Themanufacturingsimulation

wecanfollowthemachiningprocess,wecanseethegeneratedpartgeometry.Basically this simulation contains only the part and the tool geometry, but we

with the machine tool and the fixture. The othertypeofthesimulationisthecollisioncheck,whenthecollisionbetweenthetooland the part, the tool and the fixture or machine tool, or the tool holder and

ime calculation is an importantsystems are able to calculate more process

CAD/CAM 46

parameter, likemachiningpower.Thenextpicturesshowsomeexampleaboutsimulation.

Fig. 4.5

CREATE NC PROGRAM If the tool path is pass in the simulation, we can generate the NC code formachinetool.Thisprocessconsistsoftwostep.Firstwecreateanindependentgeneralcode,andduringthesecondstepthegeneralcodeistransformedtotheCNCcontrollerorientedformat.

Fig. 4.6

Howeverthe formatofNCcodeisstandard, thedifferentcontrollerusealittlebit different codes. This transformation is called postprocessing, and thesoftwarecomponentisthepostprocessor. DOCUMENTING Thelaststepisthedocumenting.TheCAMdocumentationcontainsallnecessarydataforproduction:•Locationofthecoordinatesystem•NameofNCprogram•Tooldata


•Cuttingparameters•Manufacturingtime

DATUM SETTING Beforepreparingaprogram,theoriginortheprogram(machining)originmustbedetermined.Thisdatumisthereferencepointforprogrammingandcutting.Theselectionofmachiningorigindependson:•Workpieceshape•Use/non-useoffixtures•Convenienceinprogramming•WorkpiecepreparationSomeexamplesoflocatingdatumonahorizontalmachiningcentreareshowninFig.4.7.

Fig. 4.7 (a) Locating Datum on a Horizontal Machining Centre

Fig. 4.7 (b) Locating Datum on a Horizontal Machining Centre

SETTING THE WORK PIECE ORIGINThe program coordinates are conveniently selected with reference to a workpiecedatumorworkpieceorigin.Theworkcoordinatesystemcanbeselectedtosuitthedatumusedfordimensioningtheworkpiece.InthepresentexamplethecentreofthetopsurfaceisasuitablepointtobeselectedasoriginandtheXandY-axesdirectionsareshowninFig.planviewandtheZ-axis isshownintheelevationinthefigure.TheZ


Beforepreparingaprogram,theoriginortheprogram(machining)originmustbedetermined.Thisdatumisthereferencepointforprogrammingandcutting.Theselectionofmachiningorigindependson:

ienceinprogramming

Someexamplesoflocatingdatumonahorizontalmachiningcentreareshownin

(a) Locating Datum on a Horizontal Machining Centre

(b) Locating Datum on a Horizontal Machining Centre

SETTING THE WORK PIECE ORIGIN The program coordinates are conveniently selected with reference to a workpiecedatumorworkpieceorigin.Theworkcoordinatesystemcanbeselectedtosuitthedatumusedfordimensioningtheworkpiece.Inthepresentexample

faceisasuitablepointtobeselectedasoriginandtheXaxesdirectionsareshowninFig.4.8.TheXandyaxesareshowninthe

axis isshownintheelevationinthefigure.TheZ

47

Beforepreparingaprogram,theoriginortheprogram(machining)originmustbedetermined.Thisdatumisthereferencepointforprogrammingandcutting.

Someexamplesoflocatingdatumonahorizontalmachiningcentreareshownin

(a) Locating Datum on a Horizontal Machining Centre

(b) Locating Datum on a Horizontal Machining Centre

The program coordinates are conveniently selected with reference to a workpiecedatumorworkpieceorigin.Theworkcoordinatesystemcanbeselectedtosuitthedatumusedfordimensioningtheworkpiece.Inthepresentexample

faceisasuitablepointtobeselectedasoriginandtheX-.TheXandyaxesareshowninthe

axis isshownintheelevationinthefigure.TheZ-axis is

CAD/CAM

normal totheworksurfaceandththetoolawayfromtheworksurface.

Fig. 4.8It may be noted that the axis directions indicated in Fig.movementsrelativetotheworkpiece.

normal totheworksurfaceandthepositivedirectionmeans themovementofthetoolawayfromtheworksurface.

4.8 Setting the Work Piece Datum

It may be noted that the axis directions indicated in Fig. 4.8movementsrelativetotheworkpiece.

48

epositivedirectionmeans themovementof

4.8 represent tool

CHAPTER FIVE

CNC SYSTEM AND CONFIGURATION

NumericalControl(NC)machiningreferstothemanufacturingtechniqueswithwhich machines, such as lathes and mills, are controlled by a series of codedinstructions, rather than by the manual control of an operator. This numericalcontrol system was first developed in the 1950s. In computer-aidedmanufacturing,operations are carriedout by Computerized Numerical Control(CNC)machines.TodaythetermsNCandCNCareusedinterchangeably.TheNCprograms may be manually written by a NC programmer, or may beautomaticallygeneratedbyusingthecapabilitiesofCAD/CAMsystem.NCprogramimplementsthecontrolalgorithmforpositioningthemotionaxes,providing the primary user-interface to the machine. After user-created NCprogramsaredevelopedintheCADsystem,theprogramsaredownloadedintothe control unit's memory by paper tape or floppy disk for execution inmanufacturingofparts.ModemCNCtechnologycannotonlycontrolasinglemachiningsequenceonaparticular work piece but also accomplish multimachining operations. Itachievesanautomatictoolchange,displaystheconditionofthecuttingtool,thetimeelapsed,andotherusefuldata.TheCNCtechnologyimproves:

Planning,flexibility,andscheduling; Setup,lead,andprocessingtime; Machineutilization; Toolingcost; Cuttingtoolstandardization; Accuracy,efficiency,andproductivity; Materialflowandworkpiecehandlingtime; Interchangeabilityofwork,tools,etc. Safety; Costestimating.

Obviously,computercontroltechnologyhaschangedmanufacturingtechnologymorethananyothersingledevelopment.

Earlymachinetoolsweredesignedsothattheoperatorwasstandinginfrontofthe machine while operating the controls. This design is no longer necessary,since in CNCthe operator no longercontrols the machine tool movements. Onconventional machine tools, only about 20 percent of the time was spentremoving material. With the addition of electronic controls, actual time spentremovingmetalhasincreasedto80percentandevenhigher.Ithasalsoreducedthe amount of time required to bring the cutting tool into each machiningposition.

CAD/CAM

Fig.

NC MACHINE MOTIONS ItisknownthattherearethreemajorNCmachinemotions.

1. Point-to-pointisthesimplesttypeofthemachinemotions.Itmovesatoolfromonespecifiedpositiontoanotherwhilesomeoperationsarecarriedout.Theactualpathbe considered. For instance, during the drillingpointcontrolmayberequired.

2. Straight-cutisakindofthemachinemotionswhichmovesthecuttingparalleledtooneofthemachineaxis,suchasXaxis.

3. Contouring is the most complex machine motion with the capability ofpoint-to-point and straightprecise control of more than one macinterpolation (movements between positions by straight lines) acircular interpolation (contouringcontrol.Thespeedofmachinemotioniscontrolledbythefeedrate(Fcode)inNCprogram.Someadditionalmotionsaredescribedasthecontrol of the operation spindle speed, the coolant supply, the toolchanges,andsoon.

AfteraNCprogrammerfinishesprogramming,andbeforeanoperatorbeginstomanufacture the part, it is very helpful for them to watch a graphicrepresentation of the pathsystem can be developed to generate automatically the optimal cutter path, tomove fromonemachiningNCtoolpathsimulationwiththeabilitytodisplaythecutterpathsuperimposedon the part geometry. CAD systemrather than in black and wsuggeststhatthegeometryasashadedimageisinonesetofcolor,andthenthetool path is in a contrasting color. Cutting paths are as solid lines and rapidmovements inairareseenasdotted lines.ThereCNCmanufacturingprocesssimulationmorepowerfulandclearthananyothersimulations.MACHINE TYPES Lathe Theenginelathe,oneofthemostproductivemachinetools,hasalwaysbeenanefficientmeansofproducingroundparts(Fig.ontwoaxes.

Fig. 5.1 The basic elements of a CNC.

ItisknownthattherearethreemajorNCmachinemotions.pointisthesimplesttypeofthemachinemotions.Itmovesatool

fromonespecifiedpositiontoanotherwhilesomeoperationsarecarriedbetweenthesetwopositionsisnottoosignificantto

be considered. For instance, during the drilling operation, only pointpointcontrolmayberequired.

cutisakindofthemachinemotionswhichmovesthecuttingparalleledtooneofthemachineaxis,suchasXaxis.

is the most complex machine motion with the capability ofpoint and straight-cut control. It also provides simultaneous

precise control of more than one machine axis. For exammovements between positions by straight lines) a

circular interpolation (movements as arcs or circles), are requiredcontouringcontrol.Thespeedofmachinemotioniscontrolledbythefeed

ode)inNCprogram.Someadditionalmotionsaredescribedasthecontrol of the operation spindle speed, the coolant supply, the tool

AfteraNCprogrammerfinishesprogramming,andbeforeanoperatorbeginstot is very helpful for them to watch a graphic

representation of the path superimposed on the part geometry. A CADsystem can be developed to generate automatically the optimal cutter path, tomove fromonemachining feature to thenext.Currentresearch focusesontheNCtoolpathsimulationwiththeabilitytodisplaythecutterpathsuperimposedon the part geometry. CAD system displays cutter location on a color screenrather than in black and white screen. Additionally, the CAD/CAM systemsuggeststhatthegeometryasashadedimageisinonesetofcolor,andthenthetool path is in a contrasting color. Cutting paths are as solid lines and rapidmovements inairareseenasdotted lines.Therefore,CAD/CAMsystemmakes

processsimulationmorepowerfulandclearthananyother

Theenginelathe,oneofthemostproductivemachinetools,hasalwaysbeenanproducingroundparts(Fig.5.1).Mostlathesareprogrammed

50

pointisthesimplesttypeofthemachinemotions.Itmovesatoolfromonespecifiedpositiontoanotherwhilesomeoperationsarecarried

betweenthesetwopositionsisnottoosignificanttooperation, only point-to-

cutisakindofthemachinemotionswhichmovesthecuttingtool

is the most complex machine motion with the capability ofcut control. It also provides simultaneous

hine axis. For example, the linearmovements between positions by straight lines) and the

movements as arcs or circles), are requiredcontouringcontrol.Thespeedofmachinemotioniscontrolledbythefeed

ode)inNCprogram.Someadditionalmotionsaredescribedasthecontrol of the operation spindle speed, the coolant supply, the tool

AfteraNCprogrammerfinishesprogramming,andbeforeanoperatorbeginstot is very helpful for them to watch a graphic

superimposed on the part geometry. A CAD/CAMsystem can be developed to generate automatically the optimal cutter path, to

feature to thenext.Currentresearch focusesontheNCtoolpathsimulationwiththeabilitytodisplaythecutterpathsuperimposed

displays cutter location on a color screenhite screen. Additionally, the CAD/CAM system

suggeststhatthegeometryasashadedimageisinonesetofcolor,andthenthetool path is in a contrasting color. Cutting paths are as solid lines and rapid

fore,CAD/CAMsystemmakesprocesssimulationmorepowerfulandclearthananyother

Theenginelathe,oneofthemostproductivemachinetools,hasalwaysbeenan.1).Mostlathesareprogrammed

CNC system and configuration

The X axis controls the cross motion of the cutting tool. Negative X (Xmoves the tool towards the spindle centerline; positive X moves the toolawayfromthespindlecenterline.

TheZaxiscontrolsthecarriagetraveltowardorawayfromtheheadstock.

Fig. 5.1 The main axes Milling Machine The milling machine has always been one of the most versatile machine toolsusedinindustry(Fig.5.2).Operationssuchasmilling,contouring,gearcutting,drilling,boring,andreamingareonlyafewofthemanyoperationswhichcanbeperformed on a milling machine. The milling machine can be programmed onthreeaxes:

TheXaxiscontrolsthetablemovementleftorright. TheYaxiscontrolsthetablemovementtowardorawayfromthecolumn. The Z axis controls the vertical (up or dow

spindle.

Fig. 5.2 The main axesThe diagram below shows a top view of the grid as it would appear on themachine tool. This view shows the X and Y axes

The X axis controls the cross motion of the cutting tool. Negative X (Xmoves the tool towards the spindle centerline; positive X moves the tool

centerline.TheZaxiscontrolsthecarriagetraveltowardorawayfromtheheadstock.

The main axes of a lathe or turning center. (Emco Maier Corp)

machine has always been one of the most versatile machine tools).Operationssuchasmilling,contouring,gearcutting,

,boring,andreamingareonlyafewofthemanyoperationswhichcanbeon a milling machine. The milling machine can be programmed on

TheXaxiscontrolsthetablemovementleftorright.TheYaxiscontrolsthetablemovementtowardorawayfromthecolumn.The Z axis controls the vertical (up or down) movement of the knee or

.2 The main axes of a vertical machining center. (Denford Inc.)

The diagram below shows a top view of the grid as it would appear on themachine tool. This view shows the X and Y axes as the operator faces the

51

The X axis controls the cross motion of the cutting tool. Negative X (X-)moves the tool towards the spindle centerline; positive X moves the tool

TheZaxiscontrolsthecarriagetraveltowardorawayfromtheheadstock.

center. (Emco Maier Corp)

machine has always been one of the most versatile machine tools).Operationssuchasmilling,contouring,gearcutting,

,boring,andreamingareonlyafewofthemanyoperationswhichcanbeon a milling machine. The milling machine can be programmed on

TheYaxiscontrolsthetablemovementtowardorawayfromthecolumn.n) movement of the knee or

of a vertical machining center. (Denford Inc.)

The diagram below shows a top view of the grid as it would appear on theas the operator faces the

CAD/CAM

machinetool.Toolmovesawaytotherightofzeroispositiveincrease;awaytotheleftofzeroisnegativeincrease.Toolmovesawayfromoperatorispositiveincrease along Y direction; and moves close to operator causing a nincrease.

Fig. 5.3. CoordinateTheworkzerointheZ-axisisusuallysetatthetopofthepartbe entered in the tool length offset as a negative value. Tool moves above thepartsurfaceispositiveincrease,otherwise,negativeincrease.PROGRAMMING SYSTEMSTwo types of programming modes, the incremental system andsystem,areusedforCNC.Bothsystemshaveand no system is either right ortoolstodayarecapableofhandlingeitherincrementalorabsoluteprogramming.

Incremental program locations are always given as the distancefromtheimmediatelyprecedingpoint(Fig.machinetomovethetable,spindle,millingmachineasanexample:

Fig. 5.5 A workpiece dimensioned in the incremental system mode.

machinetool.Toolmovesawaytotherightofzeroispositiveincrease;awaytotheleftofzeroisnegativeincrease.Toolmovesawayfromoperatorispositiveincrease along Y direction; and moves close to operator causing a n

.3. Coordinate system of TRIAC NC machine

axisisusuallysetatthetopofthepartbe entered in the tool length offset as a negative value. Tool moves above thepartsurfaceispositiveincrease,otherwise,negativeincrease.

PROGRAMMING SYSTEMS Two types of programming modes, the incremental system and

areusedforCNC.BothsystemshaveapplicationsinCNCprogramming,and no system is either right or wrong all the time. Most controls on machine

capableofhandlingeitherincrementalorabsoluteprogramming.

Fig. 5.4 program locations are always given as the distance

fromtheimmediatelyprecedingpoint(Fig.5.5).Commandcodeswhichtellthemachinetomovethetable,spindle,andkneeareexplainedhereusingavertical

anexample:

A workpiece dimensioned in the incremental system mode.

52

machinetool.Toolmovesawaytotherightofzeroispositiveincrease;awaytotheleftofzeroisnegativeincrease.Toolmovesawayfromoperatorispositiveincrease along Y direction; and moves close to operator causing a negative

system of TRIAC NC machine axisisusuallysetatthetopofthepartsurface;thiswill

be entered in the tool length offset as a negative value. Tool moves above the

Two types of programming modes, the incremental system and the absoluteapplicationsinCNCprogramming,

wrong all the time. Most controls on machinecapableofhandlingeitherincrementalorabsoluteprogramming.

program locations are always given as the distance and direction).Commandcodeswhichtellthe

andkneeareexplainedhereusingavertical

A workpiece dimensioned in the incremental system mode.

CNC system and configuration 53

A“Xplus”(X+)commandwillcausethecuttingtooltobelocatedtotherightofthelastpoint.

A“Xminus”(X-)commandwillcausethecuttingtooltobelocatedtotheleftofthelastpoint.

A“Yplus”(Y+)commandwillcausethecuttingtooltobelocatedtowardthecolumn.

A “Y minus” (Y-) will cause the cutting tool to be located away from thecolumn.

A“Zplus”(Z+)commandwillcausethecuttingtoolorspindletomoveuporawayfromtheworkpiece.

A“Zminus”(Z-)movesthecuttingtooldownorintotheworkpiece.In incremental programming, the G91 command indicates to thecomputer and MCU (Machine Control Unit) that programming is intheincrementalmode.Absolute program locations are always given from a single fixedzero or origin point (Fig.5.6). The zero or origin point may be aposition on the machine table, such as the corner of the worktableor at any specific point on the workpiece. In absolute dimensioningand programming, each point or location on the workpiece is givenasacertaindistancefromthezeroorreferencepoint.

Fig. 5.6 A workpiece dimensioned in the absolute system mode. Note: All

dimensions are given from a datum.

A “X plus” (X+) command will cause the cutting tool to belocatedtotherightofthezeroororiginpoint.

A“Xminus”(X-)commandwillcausethecuttingtooltobelocatedtotheleftofthezeroororiginpoint.

CAD/CAM

A “Y plus” (Y+) command will cause the cutting tool to belocatedtowardthecolumn.

A“Yminus”(Y-)commandwillcausethecuttingtfromthecolumn.

Inabsoluteprogramming,theG90commandindicatestothethattheprogrammingisintheabsolutemodePoint-to-Point or Continuous Path CNC programming falls into two distinct categories (Fig.betweenthetwocategorieswasonceverydistinct.units are able tohandle both pointknowledge of both programming methods is necessary to understand whatapplicationseachhasinCNC.

Fig. 5.7 Point-to-Point PositioningPoint-to-pointpositioning isusedwhen it isnecessary toaccurately locate thespindle,ortheworkpiecemountedonthemachinetable,atoneormorespecificlocations to perform suchpunching(Fig.5.8).Point-toone coordinate (XY) position or location to another, performing themachining operation, and continuing this pattern until all thebeencompletedatallprogrammedlocations.

Fig. 5.8 The path followed by pointprogrammed points

A “Y plus” (Y+) command will cause the cutting tool to belocatedtowardthecolumn.

)commandwillcausethecuttingtooltobelocatedaway

Inabsoluteprogramming,theG90commandindicatestothecomputerandMCUthattheprogrammingisintheabsolutemode.

Point or Continuous Path CNC programming falls into two distinct categories (Fig. 5.7betweenthetwocategorieswasonceverydistinct.Now,however,mostcontrolunits are able tohandle both point-to-point and continuous path

of both programming methods is necessary to understand whateachhasinCNC.

.7 Types of CNC positioning systems

Point Positioning pointpositioning isusedwhen it isnecessary toaccurately locate thertheworkpiecemountedonthemachinetable,atoneormorespecific

operations as drilling, reaming, boring, tapping, andto-pointpositioningistheprocessofpositioningfrom

coordinate (XY) position or location to another, performing themachining operation, and continuing this pattern until all thebeencompletedatallprogrammedlocations.

followed by point-to-point positioning to reach various

programmed points (machining locations) on the XY axis.

54

A “Y plus” (Y+) command will cause the cutting tool to be

ooltobelocatedaway

computerandMCU

7). The differenceNow,however,mostcontrol

point and continuous path machining.Aof both programming methods is necessary to understand what

pointpositioning isusedwhen it isnecessary toaccurately locate thertheworkpiecemountedonthemachinetable,atoneormorespecific

, reaming, boring, tapping, andpointpositioningistheprocessofpositioningfrom

coordinate (XY) position or location to another, performing themachining operation, and continuing this pattern until all the operations have

ing to reach various (machining locations) on the XY axis.


InFig.5.8point1topoint2isastraightline,andthemachinetheXaxis;butpoints2and3requirethattakesplace.Asthedistancewill reach its 15 position first, leaving X to travel in a straight line for theremainingdistance.Asimilarmotiontakesplacebetweenpoints3and4.CONTINUOUS PATH (CONTOURING)Contouring,orcontinuouspathon a lathe or milling machine, where the cutting toolworkpieceasittravelsfromoneprogrammedpositioning is the ability tosimultaneouslytokeepaconstantcutter

Fig. 5.9 Types of contour

TheprogrammedinformationintheCNCprogrammustaccuratelypositionthecuttingtoolfromonepointtothenextandfollowapredefinedprogrammed feed rate in order to produce the5.9) Interpolation The method by which contouring machine tools move from onepoint to the next is called interpolation.pointsintoapredefinedtoolpathfive methods of interpolation:contouringcontrolsprovidelinearinteof both linear and circular interpolation. Helical, parabolic, and cubicinterpolationareusedbyindustriesthatmanufacturepartswhichshapes,suchasaerospacepartsanddiesforcar Linear Interpolation Linear Interpolation consists of any programmed points linkedstraight lines, whether the points are close together orCurvescanbeproducedwithstraight-line segments. Thisnumberofpointswouldhavetobeprogrammedtodescribethecurveto produce a contour shape.

point1topoint2isastraightline,andthemachinetheXaxis;butpoints2and3requirethatmotionalongboththeXandYaxestakesplace.AsthedistanceintheXdirectionisgreaterthanintheYdirection,Y

position first, leaving X to travel in a straight line for thedistance.Asimilarmotiontakesplacebetweenpoints3and4.

TH (CONTOURING) ,orcontinuouspathmachining,involvesworksuchas

machine, where the cutting tool is in contact with theasittravelsfromoneprogrammedpointtothenext.Continuouspath

positioning is the ability to control motions on two or more machine axeskeepaconstantcutter-workpiecerelationship.

Types of contour machining (A) Simple contour; (B) complex

informationintheCNCprogrammustaccuratelypositionthecuttingtoolfromonepointtothenextandfollowapredefinedprogrammed feed rate in order to produce the form or contour required (Fig.

The method by which contouring machine tools move from onepoint to the next is called interpolation. This ability to merge individual axispointsintoapredefinedtoolpathisbuiltintomostoftoday’sMCUs.Therearefive methods of interpolation: linear, circular, helical, parabolic, and cubic. All

providelinearinterpolation,andmostcontrolsarecapablelinear and circular interpolation. Helical, parabolic, and cubic

interpolationareusedbyindustriesthatmanufacturepartswhichshapes,suchasaerospacepartsanddiesforcarbodies.

consists of any programmed points linkedstraight lines, whether the points are close together or far apart (Fig.Curvescanbeproducedwith linear interpolationbybreakingthemintoshort,

. This method has limitations, because a very largewouldhavetobeprogrammedtodescribethecurve

shape. A contour programmed in linear interpolation

55

movesonlyalongmotionalongboththeXandYaxes

intheXdirectionisgreaterthanintheYdirection,Yposition first, leaving X to travel in a straight line for the

distance.Asimilarmotiontakesplacebetweenpoints3and4.

machining,involvesworksuchasthatproducedis in contact with the

pointtothenext.Continuouspathcontrol motions on two or more machine axes

workpiecerelationship.

contour; (B) complex contour

informationintheCNCprogrammustaccuratelypositiontheaccuratepathata

form or contour required (Fig.

The method by which contouring machine tools move from one programmedThis ability to merge individual axis

mostoftoday’sMCUs.Therearelinear, circular, helical, parabolic, and cubic. All

rpolation,andmostcontrolsarecapablelinear and circular interpolation. Helical, parabolic, and cubic

interpolationareusedbyindustriesthatmanufacturepartswhichhavecomplex

consists of any programmed points linked together byfar apart (Fig. 5.10).

linear interpolationbybreakingthemintoshort,method has limitations, because a very large

wouldhavetobeprogrammedtodescribethecurveinorderA contour programmed in linear interpolation

CAD/CAM

requires thecoordinate positions (XYpositions in twoandfinishofeachlinesegment.Therefore,theendpointofonelineorbecomesthestartpointforthenextsegmprogram.

Fig. 5.10 An example of two Circular Interpolation The development of machine control unitinterpolationhasgreatlysimplifiedtheprocessofprogrammingarcsandcircles.To program an arc (Fig. 5(theXYaxes)ofthecirclecenter,theradiusofthecircle,point of the arc being cut, and the direction(clockwise or counterclockwisevarywithdifferentMCUs.

Fig. 5.11 For two-dimensional circular interpolation the MCU must be suppwith the XY axis, radius, start point, end point, and direction of cut. NC PROGRAMMING FORMATWord address is the most common programming format used forprogramming systems. This format contains a large number(preparatory and miscellaneous) that transferspartprinttomachineservos,relays,These codes, which conform to EIA (Electronic Industries Association)

requires thecoordinate positions (XYpositions in two-axis work) for the startfinishofeachlinesegment.Therefore,theendpointofonelineor

becomesthestartpointforthenextsegment,andsoon,throughouttheentire

An example of two-axis linear interpolation.

machine control unit (MCUs) capable of circularsimplifiedtheprocessofprogrammingarcsandcircles.5.11), the MCU requires only thecoordinate

)ofthecirclecenter,theradiusofthecircle,thestartpointandendcut, and the direction in which the arc is to be cut

(clockwise or counterclockwise) See Fig. 5.11. The information required may

dimensional circular interpolation the MCU must be suppradius, start point, end point, and direction of cut.

NC PROGRAMMING FORMAT Word address is the most common programming format used forprogramming systems. This format contains a large number

and miscellaneous) that transfers program information from thepartprinttomachineservos,relays,micro-switches,etc.,tomanufactureapart.

conform to EIA (Electronic Industries Association)

56

axis work) for the startfinishofeachlinesegment.Therefore,theendpointofonelineorsegment

throughouttheentire

axis linear interpolation.

capable of circularsimplifiedtheprocessofprogrammingarcsandcircles.

), the MCU requires only thecoordinate positionsthestartpointandend

in which the arc is to be cut. The information required may

dimensional circular interpolation the MCU must be supplied

radius, start point, end point, and direction of cut.

Word address is the most common programming format used for CNC of different codes

program information from theswitches,etc.,tomanufactureapart.

conform to EIA (Electronic Industries Association)


standards, are in a logical sequence calshouldcontainenoughinformationtoperformonemachiningWord Address Format Every program for any part to bemachine controlunitcan understand.The formatbuiltinbythemachinetoolbuilderthe machine. A variable-commonly used. Each instruction word consists of an address character,such as X, Y, Z, G, M, or S. Numerical data follows this addressidentifyaspecificfunctionsuchasthedistance,feedTheaddresscodeG90inaprogram,tellsthecontrolthatallintheabsolutemode.Thecotheincrementalmode. Codes The most common codes used when programming CNC machines tools are Gcodes (preparatory functions), and M codescodessuchasF,S,D,andTcutterdiameteroffset,toolnumber,etc.Codes Meaning

Common Alphanumeric Address Codes

in a logical sequence called a block of information. Each blockshouldcontainenoughinformationtoperformonemachiningoperation.

Every program for any part to be machined must be put in amachine controlunitcan understand.The format used on any CNC machine isbuiltinbythemachinetoolbuilderandisbasedonthetypeofcontroluniton

-block format which uses words (letters) is mostused. Each instruction word consists of an address character,

X, Y, Z, G, M, or S. Numerical data follows this addressidentifyaspecificfunctionsuchasthedistance,feedrate,orspeedvalue.TheaddresscodeG90inaprogram,tellsthecontrolthatallmeasurementsareintheabsolutemode.ThecodeG91,tellsthecontrolthatmeasurementsarein

The most common codes used when programming CNC machines tools are Gcodes (preparatory functions), and M codes (miscellaneous functions). OthercodessuchasF,S,D,andTareusedformachinefunctionssuchasfeed,speed,

offset,toolnumber,etc.Meaning

Common Alphanumeric Address Codes

57

led a block of information. Each blockoperation.

must be put in a format that thed on any CNC machine is

andisbasedonthetypeofcontrolunitonblock format which uses words (letters) is most

used. Each instruction word consists of an address character,X, Y, Z, G, M, or S. Numerical data follows this address character to

rate,orspeedvalue.measurementsare

controlthatmeasurementsarein

The most common codes used when programming CNC machines tools are G-(miscellaneous functions). Other

usedformachinefunctionssuchasfeed,speed,

CAD/CAM

G-codes are sometimes called cycle codes because they refer tooccurringontheX,Y,and/orThe G-codes are grouped into categories such as Group 01,G00,G01,G02,G03.whichcausesomemovementofthemachinetableorhead.Group03includeseitherabsoluteorincrementalprogramming,whileGroup09dealswithcannedcycles.

Fig. 5.12 The functions of a few common G

A G00 code rapidly positions the cutting tool while it is above thefromonepointtoanotherpointonajob.DuringtheeithertheXorYaxiscanbemovedsametime.Althoughtherateofrapidtravelvariesfrommachinetomachine,itrangesbetween200and800in./min(5and20m/min).TheG01,G02,andG03codesmovetheaxes

G01isusedforstraight G02(clockwise)andG03(counterclockwise

(circularinterpolation).

codes are sometimes called cycle codes because they refer toand/orZaxisofamachinetool.

codes are grouped into categories such as Group 01,G00,G01,G02,G03.whichcausesomemovementofthemachinetableorhead.

absoluteorincrementalprogramming,whileGroup09

The functions of a few common G-codes and tool path

A G00 code rapidly positions the cutting tool while it is above thefromonepointtoanotherpointonajob.Duringtherapidtraversemovement,eithertheXorYaxiscanbemovedindividuallyorbothaxescanbemovedatthe

therateofrapidtravelvariesfrommachinetomachine,itbetween200and800in./min(5and20m/min).

TheG01,G02,andG03codesmovetheaxesatacontrolledfeedrate.G01isusedforstraight-linemovement(linearinterpolation).G02(clockwise)andG03(counterclockwise)areusedforarcs(circularinterpolation).

58

codes are sometimes called cycle codes because they refer to some action

containing codesG00,G01,G02,G03.whichcausesomemovementofthemachinetableorhead.

absoluteorincrementalprogramming,whileGroup09

and tool path.

A G00 code rapidly positions the cutting tool while it is above the workpiecerapidtraversemovement,

canbemovedatthetherateofrapidtravelvariesfrommachinetomachine,it

feedrate.linemovement(linearinterpolation).

)areusedforarcsandcircles


Some of the most common GMormiscellaneouscodesareusedtoeitherturnONorOFFwhich control certain machine toolcategories,althoughseveralcodesasM03,M04,andM05whichcontrolthemachinetoolspindle.•M03turnsthespindleonclockwise•M04turnsthespindleoncounterc•M05turnsthespindleoff

Some of the most common G-codes used in CNC programming.

MormiscellaneouscodesareusedtoeitherturnONorOFFdifferentfunctionscertain machine tool operations. M-codes are not grouped into

categories,althoughseveralcodesmaycontrolthesametypeofoperationssuchM05whichcontrolthemachinetoolspindle.

•M03turnsthespindleonclockwise•M04turnsthespindleoncounterclockwise•M05turnsthespindleoff

59

codes used in CNC programming.

differentfunctionscodes are not grouped into

maycontrolthesametypeofoperationssuchM05whichcontrolthemachinetoolspindle.

CAD/CAM

Fig. 5.13 The functions of a few common M

Some of the most common M

The functions of a few common M-codes.

Some of the most common M-codes used in CNC programming.

60

codes.

codes used in CNC programming.


Block of Information CNC information is generally programmed in blocks of fiveEach word conforms to the EIA standards and they are written ona horizontal line. If five complete words are not included in eachblock, the machine control unit (MCU) will not recognize theinformation,thereforethecontrolunitwillnotbeactiv

Fig. 5.14 A complete block of information consists of five words.UsingtheexampleshowninFig.N001 representsthesequencenumberoftheoperation.G01 representslinearinterpolationX12345 willmovethetable1.2345in.inapositivedirectionY06789 willmovethetable0.6789in.alongtheYaxis.M03 SpindleonCW.PROGRAMMING FOR POSITIONINGBeforestartingtoprogramajob,itisimportanttobecomefamiliarto be produced. From the engineering drawingscapableofplanningthemachiningsequencesrequiredtoproducethepart.

Fig. 5.15 The first step in producing a CNC program is to take the information from the print and produce a program manuscript.

Reading Drawing

Programming

Inputting Program

CNC information is generally programmed in blocks of fiveEach word conforms to the EIA standards and they are written ona horizontal line. If five complete words are not included in eachblock, the machine control unit (MCU) will not recognize theinformation,thereforethecontrolunitwillnotbeactivated.

.14 A complete block of information consists of five words.

UsingtheexampleshowninFig.4.14,thefivewordsareasfollows:representsthesequencenumberoftheoperation.representslinearinterpolation

thetable1.2345in.inapositivedirectionwillmovethetable0.6789in.alongtheYaxis.SpindleonCW.

PROGRAMMING FOR POSITIONING Beforestartingtoprogramajob,itisimportanttobecomefamiliar

be produced. From the engineering drawings, the programmer should becapableofplanningthemachiningsequencesrequiredtoproducethepart.

The first step in producing a CNC program is to take the information from produce a program manuscript.

Reading Drawing

Programming

Inputting Program

Manufacturing

61

CNC information is generally programmed in blocks of five words.Each word conforms to the EIA standards and they are written ona horizontal line. If five complete words are not included in eachblock, the machine control unit (MCU) will not recognize the

.14 A complete block of information consists of five words.

,thefivewordsareasfollows:

thetable1.2345in.inapositivedirectionalongtheXaxis.

Beforestartingtoprogramajob,itisimportanttobecomefamiliarwiththepartprogrammer should be

capableofplanningthemachiningsequencesrequiredtoproducethepart.

The first step in producing a CNC program is to take the information from

CAD/CAM 62

Visual concepts must be put into a written manuscript as the first step indeveloping a part program. It is the part program that will be sent to themachine control unit by the computer, tape, diskette, or other inputmedia.The programmer must first establish a reference point for aligning theworkpiece and the machine tool for programming purposes. The manuscriptmustincludethisalongwiththetypesofcuttingtoolsandwork-holdingdevicesrequired,andwheretheyaretobelocated.

CAD

DIMENSIONING GUIDELINES The system of rectangular coordinates is very important to theoperation of CNC machines. Certain guidelines shoulddimensioningpartsforCNCmachining.Thethedimensioninglanguagethetechnician,theprogrammer,andthemachineoperator.1. Definepartsurfacesfromthreeperpendicularreference2. Establish reference planes along part surfaces which are

machineaxes.3. Dimensionfromaspecificpointonthepartsurface.4. Dimension the part clearly so that its shape can be understood

makingmathematicalcalculationsorguesses.5. Definethepartsothatacomputernumerical

programmed.

Fig. 6.1. Structure of a NC simulation software.

MACHINE ZERO POINT Themachinezeropointcanbesetbythreemethodsbyaprogrammedabsolutezeroshift,orbyfixtureortheparttobemachined.

CHAPTER SIX

CAD/CAM WORK STATION SETUP

DIMENSIONING GUIDELINES The system of rectangular coordinates is very important to theoperation of CNC machines. Certain guidelines should be observed whendimensioningpartsforCNCmachining.Thefollowingguidelineswillinsurethat

ensioninglanguagemeansexactlythesamethingtothedesignengineer,thetechnician,theprogrammer,andthemachineoperator.

Definepartsurfacesfromthreeperpendicularreferenceplanes.Establish reference planes along part surfaces which are

Dimensionfromaspecificpointonthepartsurface.Dimension the part clearly so that its shape can be understoodmakingmathematicalcalculationsorguesses.Definethepartsothatacomputernumericalcontrolcutter

.1. Structure of a NC simulation software.

intcanbesetbythreemethods-bytheoperator,manuallyabsolutezeroshift,orbyworkcoordinates,tosuittheholding

machined.

The system of rectangular coordinates is very important to the successfulbe observed when

followingguidelineswillinsurethatmeansexactlythesamethingtothedesignengineer,

planes.Establish reference planes along part surfaces which are parallel to the

Dimension the part clearly so that its shape can be understood without

pathcanbeeasily

.1. Structure of a NC simulation software.

operator,manuallyworkcoordinates,tosuittheholding

CAD/CAM workstation setup

MANUAL SETTING-TheoperatorcanusetheMCUcontrolstospindleoverthedesiredpartzeroandthensettheXontheconsoletozero.

Fig. 6.2 Relationship between the part zero and the machine system of coordinates.UnderG54...G59theactualmachinecoordinatesofpartstored zero offsets memory andactual machine coordinates are inserted andprogram. ABSOLUTE ZERO SHIFT-coordinate system by a command in the CNCsends the machine spindle toprogram. Then another command (G92 for absolute zero shift) tells the MCUhow far from the home zero location, the coordinate system originpositioned.Thesamplecommandsmaybeasfollows:N1G28X0Y0Z0(sendsspindletohomezeroposition)N2G92X4.000Y5.000Z6.000(thepositionthemachinewillzero)

TheoperatorcanusetheMCUcontrolstospindleoverthedesiredpartzeroandthensettheXandYcoordinateregisters

elationship between the part zero and the machine system of coordinates.

UnderG54...G59theactualmachinecoordinatesofpartzeroarestoredinthestored zero offsets memory and activated in the part program.actual machine coordinates are inserted and used on the G92 line of the part

Theabsolutezeroshiftcanchangethepositionoftheby a command in the CNC program. The pro

sends the machine spindle to home zero position by a G28 command in theanother command (G92 for absolute zero shift) tells the MCU

how far from the home zero location, the coordinate system origin

Thesamplecommandsmaybeasfollows:N1G28X0Y0Z0(sendsspindletohomezeroposition)N2G92X4.000Y5.000Z6.000(thepositionthemachinewillreferenceaspart

64

TheoperatorcanusetheMCUcontrolstolocatetheandYcoordinateregisters

elationship between the part zero and the machine system of coordinates.

zeroarestoredintheactivated in the part program. Under G92 the

used on the G92 line of the part

thepositionoftheprogram. The programmer first

home zero position by a G28 command in theanother command (G92 for absolute zero shift) tells the MCU

how far from the home zero location, the coordinate system origin is to be

referenceaspart

CAD/CAM

WORK SETTINGS AND OFFSETSAll CNC machine tools require some form ofsetting, and offsets (compensation) to place the cutter and work inthe proper relationship. Compensation allows the programmer tomakeadjustmentsforunexpectedtoolingandsetupconditions.

WORK COORDINATES In absolute positioning, wcorner of a part and all programming is generally takenFig.6.3,thepartzeroisusedforallpositioningforholelocations1,2,and3.

Fig. 6.3 In absolute programming, all dimensions must be tat the top left-hand corner of the part.

In incremental positioning, the work coordinates change becauseeach location is the zero point for the move to the next location,fig.6.4.

Fig. 6.4 In incremental programming, all dimensions are taken from the previous point

WORK SETTINGS AND OFFSETS All CNC machine tools require some form of work setting, toolsetting, and offsets (compensation) to place the cutter and work inthe proper relationship. Compensation allows the programmer tomakeadjustmentsforunexpectedtoolingandsetupconditions.

In absolute positioning, work coordinates are generally set on onecorner of a part and all programming is generally taken from this position. In

,thepartzeroisusedforallpositioningforholelocations1,2,and3.

absolute programming, all dimensions must be taken from the XY zero hand corner of the part.

In incremental positioning, the work coordinates change becauseeach location is the zero point for the move to the next location,

In incremental programming, all dimensions are taken from the previous

65

work setting, toolsetting, and offsets (compensation) to place the cutter and work inthe proper relationship. Compensation allows the programmer tomakeadjustmentsforunexpectedtoolingandsetupconditions.

ork coordinates are generally set on one edge orfrom this position. In

,thepartzeroisusedforallpositioningforholelocations1,2,and3.

aken from the XY zero

In incremental positioning, the work coordinates change becauseeach location is the zero point for the move to the next location,

In incremental programming, all dimensions are taken from the previous

CAD/CAM workstation setup 66

On some parts, it may be desirable to change from absolute toincremental, or vice versa, at certain points in the job. Inserting theG90(absolute)ortheG91(incremental)commandintotheprogramatthepointwherethechangeistobemadecandothis. R PLANE OR GAGE HEIGHT The word-address letter R refers to a partial retraction point in the Z axis towhichtheendofthecutterretractsabovetheworksurfacetoallowsafetablemovement in the X Y axes. It is often called the rapid-traverse distance, gageheight, retract or work plane. The R distance is a specific height or distanceabovetheworksurfaceandisgenerally.100in.abovethehighestsurfaceofthework piece, Fig. 6.5, which is also known as gage height. Some manufacturersbuildagageheightdistanceof.100in.intotheMCU(machinecontrolunit)andwheneverthefeedmotionintheZaxisiscalledfor,.100in.willautomaticallybeaddedtothedepthprogrammed.Whensettingupcuttingtools,theoperatorgenerallyplacesa.100in.thickgageontopofthehighestsurfaceoftheworkpiece.Eachtoolislowereduntilitjusttouchesthegagesurfaceandthenitslengthisrecordedonthetoollist.Oncethegageheighthasbeenset,itisnotgenerallynecessarytoaddthe.100in.toanyfuturedepthdimensionssincemostMCUsdothisautomatically.

Fig. 6.5 Using a .100 in. gage block to set the gage height or R0 on the work surface. TOOL LENGTH OFFSET Every tool loaded into the machine is a different length. In fact, if a tool isreplacedduetowearorbreaking,thelengthofitsreplacementwilllikelychangebecauseitisalmostimpossibletosetanewtoolintheholderinexactlythesameplaceastheoldone.TheCNCmachineneedssomewayofknowinghowfareachtool extends from the spindle to the tip. This is accomplished using a ToolLengthOffset(TLO).

CAD/CAM 67

Fig. 6.6: Tool Length Offset

The TLO is found by jogging the spindle with tool from the machine home Z-position to the toolsetting point onthe machine. This canbe the top of a toolprobe, or as shown in fig. 6.6, the top of a 1-2-3 block resting on the machinetable.Thedistancetravelledfromhometothetopoftheblockisrecorded,andthe value entered into the TLO register for that tool (called an H-register,becauseit isprecededby the letterH in theCNCprogram). Ifa toolwearsorbreaks, it can be replaced, the H-register reset to the new tool by touching offagainonthe1-2-3block,andtheprogramcontinuedwithnootherchanges.CUTTER DIAMETER COMPENSATION Cutter diameter compensation (CDC) changes a milling cutter’s programmedcenterlinepathtocompensateforsmalldifferencesincutterdiameter.OnmostMCUs, it is effective for most cuts made using either linear or circularinterpolationintheX-Yaxis,butdoesnotaffecttheprogrammedZ-axismoves.Usuallycompensationisinincrementsof.0001in.upto+1.0000in.,andusuallymostcontrolshaveasmanyCDCsavailableastherearetoolpocketsinthetoolstoragematrix.TheadvantageoftheCDCfeatureisthatit:1. allowstheuseofcuttersthathavebeensharpenedtoasmallerdiameter.2. permits the use ofa larger or smaller tool already in themachine’s storage

matrix.3. allows backing the tool away when roughing cuts are required

duetoexcessivematerialpresent.

CAD/CAM workstation setup

4. permits compensation for unexpected tool or part deflection, ifthedeflectionisconstantthroughouttheprogrammedpath

The basic reference point of the machine tool is never at themillingcutter,butatsomepointonitsperiphery.is used to machine the edges of akeepa.500in.offsetfromtheworksurfaceinordertoThe .500 offset represents the distance from the centerline of themachinespindletotheedgeofprogrammer must calculate an offset pathdiameter.

Fig. 6.6 Cutter-diameter compensation must be used when machining with various size cutters. Modern MCUs, which have part surface programming, automatically calculatecenterline offsets once the diameter of the cutter forprogrammed. Many MCUs have operatorcompensatefordifferencesincutteonethathasbeensharpened,canbeusedaslongasthecompensationvalueforoversizeorundersizecuttersisentered. WORK HOLDING Almost every part presents unique work holding challenges. Part geometry,materialtype,wallthickness,this present multiple challenges. Like a chess player, a machinist has to thinkahead several moves to visualize what the part will look like each step of the

permits compensation for unexpected tool or part deflection, iflectionisconstantthroughouttheprogrammedpath.

The basic reference point of the machine tool is never at thecutter,butatsomepointonitsperiphery.Ifa1.000in.diameterendmillto machine the edges of a workpiece, the programmer would have to

fromtheworksurfaceinordertocuttheedgesaccuratelyThe .500 offset represents the distance from the centerline of themachinespindletotheedgeofthepart.Wheneverapartisbeingmachined,theprogrammer must calculate an offset path, which is usually half the cutter

diameter compensation must be used when machining with various

, which have part surface programming, automatically calculatecenterline offsets once the diameter of the cutter for each operation isprogrammed. Many MCUs have operator-entry capabilities which cancompensatefordifferencesincutterdiameters;thereforeanoversizecutter,oronethathasbeensharpened,canbeusedaslongasthecompensationvaluefor

orundersizecuttersisentered.

Almost every part presents unique work holding challenges. Part geometry,materialtype,wallthickness,andfeaturesallinfluenceworkholding.Partslikethis present multiple challenges. Like a chess player, a machinist has to think

to visualize what the part will look like each step of the

68

permits compensation for unexpected tool or part deflection, if.

The basic reference point of the machine tool is never at the cutting edge of aIfa1.000in.diameterendmill

workpiece, the programmer would have tocuttheedgesaccurately.

The .500 offset represents the distance from the centerline of the cutter orisbeingmachined,the

which is usually half the cutter

diameter compensation must be used when machining with various

, which have part surface programming, automatically calculateeach operation is

capabilities which canrdiameters;thereforeanoversizecutter,or

onethathasbeensharpened,canbeusedaslongasthecompensationvaluefor

Almost every part presents unique work holding challenges. Part geometry,featuresallinfluenceworkholding.Partslike

this present multiple challenges. Like a chess player, a machinist has to thinkto visualize what the part will look like each step of the

CAD/CAM

way.Beforestartingthisproject,itisimportanttosequencing,workholding,andpotentialproblems.Clampsareusetosecuretheparttothetableasshowninwill be cut on the ends of the stock to hold and locate the part in subsequentoperations.Planningaheadisnecessaryrigid flanges and face the parandsetrapidheightstoeasilycleartheclamps.

Machine flangesonthepartendsasshowninpurposes.Thefirstistogripthepartwhilethetopsideismaistolevelthepartwhenmachiningtheleftandrightsides.

Beforestartingthisproject,itisimportanttoconsidermachiningmethods,sequencing,workholding,andpotentialproblems.

tosecuretheparttothetableasshowninfig.5.7will be cut on the ends of the stock to hold and locate the part in subsequent

Planningaheadisnecessary.Stocksthickenoughcanbeuserigid flanges and face the part onboth sides. Locate clamps clear of toolpaths

easilycleartheclamps.

Fig.6.7onthepartendsasshowninfig.6.8.Theseflangesservetwo

purposes.Thefirstistogripthepartwhilethetopsideismachined.Thesecondistolevelthepartwhenmachiningtheleftandrightsides.

Fig.6.8

69

considermachiningmethods,

fig.5.7below.Flangeswill be cut on the ends of the stock to hold and locate the part in subsequent

canbeusetoformt onboth sides. Locate clamps clear of toolpaths

.Theseflangesservetwochined.Thesecond

CHAPTER SEVEN

CAM/CNC PROGRAMMING AND OPERATION SAFETY FIRST Mostmachinistsgotheirentirecareerwithnoseriousinjuryeventhoughtheyworkwithmanydifferentmachinesthatexposethemtorisks.Machinistsare,bynature and training, careful and methodical. They learn from experience anattitudeofsafetyawarenessandrespectforequipment.Knowingthatignorancecanhurtyou isessential tocultivatinganattitudeofsafety. It is true thatCNCmachines are generally safer than manual machine tools. They are usuallycompletelyenclosed,whichreducestheriskofflyingchips,debrisfrombrokentools, or contact with a spinning tool. Yet machine shops are inherentlydangerousplacesthatareunforgivingofanycarelessness,ignorance,orneglect.Cutting tools, and the chips they produce, are sharp. Chips ejected from themachinecancauseeye injuries. CNCmachinescanmoveoverone foot in lessthan a second. Any physical contact with a spinning tool will result in seriouscuts or worse. Remember, if it can cut metal it can cut skin and bone just aseasily. Here are some examples where a failure to know or apply shop safetyrulescausedinjury: A person forgets to wear safety glasses and sustains an eye injury from a

metalchipthrownoverthetopcoverofaCNCmillastheywalkthroughtheshop.

Apersonleansagainstabenchwhereacuttingchiphasfallen,resultinginacuttotheirhand.

A person wearing open sandal shoes has a chip fall between their foot andshoe,causingacut.

Apersonleaningoveramachinesuddenlyraisestheirheadandbumpsintoatoolstoredinthetoolchanger,causingaseverecut.

A person reaches into the machine to remove a part, gets distracted andrakestheirarmagainstanendmill.

Apersongrindsapieceofaluminiumonabenchgrinderwithastonetypewheel. The aluminium embeds in the porous wheel and expands due toheating,causingthewheeltofailandthrowofffragmentsathighspeed.

PERSONAL CONDUCT & SHOP ETIQUETTE Itisimportanttofollowstrictofrulesofpersonalconductandetiquetteintheshop.Thiswillkeepyouandyourpeerssafeandpromoteahospitableandprofessionalenvironment: Knowwhereyourhandsareatalltimes. Movedeliberatelyandalwayslookwhereyourhandsaregoing.

CAD/CAM 71

Alwaysbeawareofwhatcouldhappenifyourhandslips.Forexample,whentightening a bolt, think about what would happen if the wrench slipped.Wouldyourhandorarmcontactatool?Apileofsharpchips?

Alwaysbeawareofwhatcouldhappenifyouslippedandlostyourfooting.Would your center of gravity cause you to fall into a sharp tool or otherhazard?

Nohorseplayorpracticaljokesareallowedintheshop. Beconsiderate.Donotengageinloudorunnecessarilytalk. Donotinterruptsomeoneworkingatthemachine.Thiscouldcausethemto

makeamistake. Neverborrowtoolsfromaprivatetoolboxwithoutfirstaskingtheowner.If

theyrefuse,acceptitgraciously. RespectprofessionalMachinists.Thereismuchyoucanlearnfromthem. Donotmakeunreasonabledemands(“Ineedityesterday”etc.). Cleanupafteryourself.Leavethemachineandsurroundingareaat leastas

leanasyoufoundit. Alwaysputtoolsandequipmentwhereyoufoundthem. SHOP CLOTHING Followtheserulesofpersonaldressfortheshop: WearANSIapprovedsafetyglassesorANSIsafetyapprovedglasseswithside

shields.Youmustwearsafetyglassesatalltimesintheshop,notjustwhenatthemachine.

Ifmachiningoperationsareloud,usehearingprotection. Donotwearflipflopsorsandals.Leathershoesarebest.Steeltoeshoesare

notnecessaryunlesshandlingheavyobjectsthatwouldcrushregularshoes. Donotwearlongsleeveshirtsbecausethesecouldgetcaughtinequipment.

WearshortsleevesorT-shirts. Removeringsandwatcheswhenatthemachine. Donotwearshortpants.Wearsturdylongpantslikebluejeansorwork

pants. Longhairshouldbetiedbackorunderahattopreventitbeingcaughtinthe

machinespindle. Neverwearglovesastheycanbecaughtinthemachine.Latexglovesare

acceptable.ThegeneralworkflowtogofromCADmodeltomachinedCNCpartis:1. BeginwithCADmodel.2. Establish Job parameters including CNC coordinate system and stock

shape/size.3. SelectCNCprocess.4. Selectcuttingtoolandmachiningparameters.5. SelectdrivingCADgeometry.

CAM/CNC programming and operation

6. Verifytoolpath.7. PostProcess.8. TransferG-codeprogramtoCNCmachine.9. SetupandoperateCNCmachinetomakepart. CNC TOOLS A wide range of tool types and configurations are available for CNC millingmachines. Discussing every type, variation and use is beyond the scope of thiscourse. This chapter introduces the most commonly used tools for prototypeand short run productionothers.•Endmills(Flat,Ball,BullandChamfer)Facemill•CornerRoundingtools•SlotTools•Spot-CenterDrill•TwistDrill•Tap•Reamer•Counterbore

CUTTING TOOL FUNDAMENTALSRotation DirectionAlltools(exceptleft-handedtaps)rotateclockwise(M3)whenviewedfromthemachinespindlelookingdownatthepart.

Fig. 7.1: Clockwise Tool Rotation

Chip Formation CuttingtoolsremovemetalbyshearingactionasillustratedinFigthetooladvances into thematerial it causesasmallamountof thematerial toshearaway,formingachip.

programming and operation

codeprogramtoCNCmachine.SetupandoperateCNCmachinetomakepart.

tool types and configurations are available for CNC millingmachines. Discussing every type, variation and use is beyond the scope of thiscourse. This chapter introduces the most commonly used tools for prototypeand short run production machining. Any tool supply catalog will list many

•Endmills(Flat,Ball,BullandChamfer)Facemill

CUTTING TOOL FUNDAMENTALS

handedtaps)rotateclockwise(M3)whenviewedfromthemachinespindlelookingdownatthepart.

Fig. 7.1: Clockwise Tool Rotation

removemetalbyshearingactionasillustratedinFigthetooladvances into thematerial it causesasmallamountof thematerial toshearaway,formingachip.

72

tool types and configurations are available for CNC millingmachines. Discussing every type, variation and use is beyond the scope of thiscourse. This chapter introduces the most commonly used tools for prototype

machining. Any tool supply catalog will list many

handedtaps)rotateclockwise(M3)whenviewedfromthe

removemetalbyshearingactionasillustratedinFig.7.2below.Asthetooladvances into thematerial it causesasmallamountof thematerial to

CAD/CAM

FigChip Load Thethicknessofmaterialshearedpertooth,orchipload.Asthechipisejectedfromtheworkareaitcarrieswithitsomeoftheheatgeneratedbytheshearingprocess.

Oneofthebestwaystovalidatecuttingspeedsancreatedbythemachiningprocess.Chipsshouldbecurledandmaychangecolordue to heating. After gaining some experience machinistscuttingspeedsandfeedsbasedinpartonthesize,shape,andcolorofchipsandonthesoundproducedbythecuttingprocess.Millingtoolscanadvancethroughthematerialsothatthecuttingflutesengagethe material at maximum thClimb Milling.Cuttingintheoppositedirectioncausesthetooltoscoopupthematerial, starting at zero thickness and increasing to maximum. This is calledConventional Milling. Conventionalmilling

Fig.7.2: Chip Formation Diagram

Thethicknessofmaterialshearedawaybyeachcuttingtoothiscalledthefeedthechipisejectedfromtheworkareaitcarrieswithit

someoftheheatgeneratedbytheshearingprocess.

Fig.7.3: Chip load waystovalidatecuttingspeedsandfeedsistoobservethechips

createdbythemachiningprocess.Chipsshouldbecurledandmaychangecolordue to heating. After gaining some experience machinists are able to adjustcuttingspeedsandfeedsbasedinpartonthesize,shape,andcolorofchipsandonthesoundproducedbythecuttingprocess.

Millingtoolscanadvancethroughthematerialsothatthecuttingflutesengagethe material at maximum thickness and then decreases to zero. This is called

Cuttingintheoppositedirectioncausesthetooltoscoopupthematerial, starting at zero thickness and increasing to maximum. This is called

Conventionalmillingisusedoftenonmanualmachines

73

awaybyeachcuttingtoothiscalledthefeedthechipisejectedfromtheworkareaitcarrieswithit

dfeedsistoobservethechipscreatedbythemachiningprocess.Chipsshouldbecurledandmaychangecolor

are able to adjustcuttingspeedsandfeedsbasedinpartonthesize,shape,andcolorofchipsand

Millingtoolscanadvancethroughthematerialsothatthecuttingflutesengageickness and then decreases to zero. This is called

Cuttingintheoppositedirectioncausesthetooltoscoopupthematerial, starting at zero thickness and increasing to maximum. This is called

isusedoftenonmanualmachines


becausebacklashinthemachineleadscrewscausesthetooltolurchwhenclimbcutting.ThisisnotaproblemonCNCmachinesbecausetheyuseballscrews.

Fig.7.4Conventional milling causes the tool to rub against the cutting surface, workhardeningthematerial,generatingheat,andincreasingtoolwear.Rakingchipsacross the finished surface also produces a poorer surface finish.Unless specifically recommended by the tool manufacturer for the materialbeingmilled,alwaysuseclimbmillingonaCNC.Climbmillingproducesfarlesscutting pressure and heat, leaves a better surface finish,toollife. CANNNED CIRCLE Canned cycles are special codes that act like a macro. They are used for holemaking and allow one compact block of code to command many moves. Forexample,aholecanbecreatedusingapeckdrillcyclewithtwolinesofcode(leftcolumn)whereasthesamemovewcodeifeachmotionwascommandedseparately(rightcolumn).

GeneratingthepartprogramforaCNCmachineisakeystepinthemachiningprocess. Every motion of the tool requires a block of programtheseblocksarewrittenmanually,programmingmaybecomeatimetask.Tosimplifyprograms,CNCcontrolsoffercannedcyclesthese referred to as fixed cycles. A canned cycle is simply aoperationsinitiatedbyasingleblockofcode.Cannedcyclesactasprogrammingshortcutsformachineoperationsthatarefrequentlyperformed.are valuable because they shorten the program, reduce programming errors,anddecreasethetimeittakestowritetheprogram.Thisclasswillteachyouthe



.7.4: Climb vs. Conventional Milling

causes the tool to rub against the cutting surface, workhardeningthematerial,generatingheat,andincreasingtoolwear.Rakingchipsacross the finished surface also produces a poorer surface finish.

ally recommended by the tool manufacturer for the materialbeingmilled,alwaysuseclimbmillingonaCNC.Climbmillingproducesfarlesscutting pressure and heat, leaves a better surface finish, and results in longer

ycles are special codes that act like a macro. They are used for holemaking and allow one compact block of code to command many moves. Forexample,aholecanbecreatedusingapeckdrillcyclewithtwolinesofcode(leftcolumn)whereasthesamemovewouldrequiremaybetwentyormorelinesofcodeifeachmotionwascommandedseparately(rightcolumn).

GeneratingthepartprogramforaCNCmachineisakeystepinthemachiningprocess. Every motion of the tool requires a block of programtheseblocksarewrittenmanually,programmingmaybecomeatime

Tosimplifyprograms,CNCcontrolsoffercannedcycles.Youmayalsoseethese referred to as fixed cycles. A canned cycle is simply aoperationsinitiatedbyasingleblockofcode.Cannedcyclesactasprogrammingshortcutsformachineoperationsthatarefrequentlyperformed.are valuable because they shorten the program, reduce programming errors,

decreasethetimeittakestowritetheprogram.Thisclasswillteachyouthe

74


causes the tool to rub against the cutting surface, workhardeningthematerial,generatingheat,andincreasingtoolwear.Rakingchipsacross the finished surface also produces a poorer surface finish.

ally recommended by the tool manufacturer for the materialbeingmilled,alwaysuseclimbmillingonaCNC.Climbmillingproducesfarless

and results in longer

ycles are special codes that act like a macro. They are used for holemaking and allow one compact block of code to command many moves. Forexample,aholecanbecreatedusingapeckdrillcyclewithtwolinesofcode(left

ouldrequiremaybetwentyormorelinesofcodeifeachmotionwascommandedseparately(rightcolumn).

GeneratingthepartprogramforaCNCmachineisakeystepinthemachiningprocess. Every motion of the tool requires a block of program instructions. Iftheseblocksarewrittenmanually,programmingmaybecomeatime-consuming

.Youmayalsoseethese referred to as fixed cycles. A canned cycle is simply a series of machineoperationsinitiatedbyasingleblockofcode.Cannedcyclesactasprogrammingshortcutsformachineoperationsthatarefrequentlyperformed.Cannedcyclesare valuable because they shorten the program, reduce programming errors,

decreasethetimeittakestowritetheprogram.Thisclasswillteachyouthe

CAD/CAM

most common canned cyclesused on the machining centerand turninganddescribefrequentapplications.TYPES OF CANNED CYCLESExperience with CNC machinecontrolhasitsowncharacteristics.Thisiscertainlytrueforcannedcycleslist of canned cycles available on any single type of CNC control most likelycontainsamixofthefollowing:

Standardcannedcycles Special canned cycles

machinecontrol. Customized canned cycles

machinetool.G codes activates canned cyclesrequirethesameGcodeonmostcontrols,keepinmindthateveryCNCcontrolisuniqueandmostlikelycontainsamixofstandard

Hole—making CyclesG73RapidPeckDrillingG74Left—handTappingG81 Drilling G82 Drilling with DwellG83PeckDrillingG84Right—handTappingG85BoringReamingG86BeringwithRapidRetract Hole-Making Cycles Probably the most universal canned cyclesConsequently, hole-making canned cycles are focontrol.Machiningcentersarecapableofperformingallof theseoperations.Abasiclatheiscapableonlyofmachiningaholeonthepartcenterline.turning center equipped with live tooling frequently will be used to machinevariousholepatternsaroundthecenterlineofcylindricalparts.

Fig.7.5. Common holeMosthole-makingcannedcyclesposition, machines the hole, backs out of the hole, and rapids to the nextposition.Asthetoolmovesfromoneholetothenext,ittravelsonanRlevel.

most common canned cyclesused on the machining centerand turninganddescribefrequentapplications.

TYPES OF CANNED CYCLES Experience with CNC machines eventually teaches you that every machine orcontrolhasitsowncharacteristics.Thisiscertainlytrueforcannedcycleslist of canned cycles available on any single type of CNC control most likely

owing:StandardcannedcyclesthatappearonalmosteveryCNCcontrol.Special canned cycles that the CNC control manufacturer offers with the

Customized canned cycles that have been added by the user of the

canned cycles in the program. While certain canned cyclesrequirethesameGcodeonmostcontrols,keepinmindthateveryCNCcontrol

containsamixofstandardandcustomizedcodes.

making Cycles Turning Cycles

1 Drilling G82 Drilling with Dwell

handTapping

BeringwithRapidRetract

G70FinishTurning/FacingG71RoughTurningG72RoughFacingG73RoughProfileTurningG75ThreadingG90BasicTurningG94BasicFacing

Probably the most universal canned cycles are those used to machine holes.making canned cycles are found on almost every CNC

.Machiningcentersarecapableofperformingallof theseoperations.Abasiclatheiscapableonlyofmachiningaholeonthepartcenterline.

center equipped with live tooling frequently will be used to machinevariousholepatternsaroundthecenterlineofcylindricalparts.

. Common hole-making operations performed on the mill.

makingcannedcyclesworkinasimilarfashion.Thetoolrapidsintoposition, machines the hole, backs out of the hole, and rapids to the nextposition.Asthetoolmovesfromoneholetothenext,ittravelsonanRlevel.

75

most common canned cyclesused on the machining centerand turningcenter

s eventually teaches you that every machine orcontrolhasitsowncharacteristics.Thisiscertainlytrueforcannedcycles.Thelist of canned cycles available on any single type of CNC control most likely

thatappearonalmosteveryCNCcontrol.that the CNC control manufacturer offers with the

that have been added by the user of the

in the program. While certain canned cyclesrequirethesameGcodeonmostcontrols,keepinmindthateveryCNCcontrol

andcustomizedcodes.

Facing

3RoughProfileTurning

are those used to machine holes.und on almost every CNC

.Machiningcentersarecapableofperformingallof theseoperations.Abasiclatheiscapableonlyofmachiningaholeonthepartcenterline.However,a

center equipped with live tooling frequently will be used to machinevariousholepatternsaroundthecenterlineofcylindricalparts.

making operations performed on the mill.

workinasimilarfashion.Thetoolrapidsintoposition, machines the hole, backs out of the hole, and rapids to the nextposition.Asthetoolmovesfromoneholetothenext,ittravelsonanRlevel.


Fig.7.6. On the mill, the R level is slightly above the part surface.This level is a predetermined safe distance from the part surface that permitsrapid tool travel. The R level is more commonly referred to as the clearanceplane. If clamps or part features obstruct tool movement, the clearance planecanbeincreased.

Fig.7.7. On the lathe, the R level is slightly in front of the part face. Drilling Themostcommoncannedcycleis thedrillingG81ismostoftenusedforgeneraldrilling.DuringtheG81cannedcycle,thetoolfirstrapidsalongtheX-axisandYtheclearanceplane.Next,thetoolfeedsintothepartuntilitreachesthedepthofthehole.Lastly,thetoolrapidsoutofthehole.Asthesecodesinthesameblock:

Fig.7.8.Toolmovementsduringthedrilling


. On the mill, the R level is slightly above the part surface.

This level is a predetermined safe distance from the part surface that permitsrapid tool travel. The R level is more commonly referred to as the clearance

features obstruct tool movement, the clearance plane

. On the lathe, the R level is slightly in front of the part face.

Themostcommoncannedcycleis thedrillingcyclesignalledbytheG81code.ismostoftenusedforgeneraldrilling.DuringtheG81cannedcycle,thetool

axisandY-axis.Then,thetoolrapidsdowntheZNext,thetoolfeedsintothepartuntilitreachesthedepthof

thehole.Lastly,thetoolrapidsoutofthehole.Asshowninfig.thesecodesinthesameblock:

The G81 drilling

duringthedrillingcycle.

76

. On the mill, the R level is slightly above the part surface. This level is a predetermined safe distance from the part surface that permitsrapid tool travel. The R level is more commonly referred to as the clearance

features obstruct tool movement, the clearance plane

. On the lathe, the R level is slightly in front of the part face.

cyclesignalledbytheG81code.ismostoftenusedforgeneraldrilling.DuringtheG81cannedcycle,thetool

axis.Then,thetoolrapidsdowntheZ-axistoNext,thetoolfeedsintothepartuntilitreachesthedepthof

.7.8,G81requires

The G81 drilling codes.

CAD/CAM

Milling Canned Cycles This is by far the most common canned cyclescycles and the multiple repetitive cycles used on the turningyou also may find on certain controls canned cycles for millingmachining center controls may be equipped with customized milling cannedcycles designed by the control manufacturer. Also, milling canned cycles arefound on controls designed for conversational programming. Examples ofcommonmillingcannedcyclesinclude:

A face milling cycle that automatically faces the top surface of a part(Fig.7.9).

Aninternalcircularmilling A pocket milling cycle that automatically mi

(Fig.7.10).

Fig.7.9. Tool movements during a face milling

Fig.710. Operators can machine a pocket with a milling

DependingontheCNCcontrolmanufacturer,othermillingavailable. Milling cycles, in addition to theholehighly valued for their ability to simplify CNC programming and improvemachining.

y far the most common canned cycles are the various holecycles and the multiple repetitive cycles used on the turningyou also may find on certain controls canned cycles for millingmachining center controls may be equipped with customized milling cannedcycles designed by the control manufacturer. Also, milling canned cycles are

n controls designed for conversational programming. Examples ofcommonmillingcannedcyclesinclude:

cycle that automatically faces the top surface of a part

Aninternalcircularmillingcyclethatmachinesacircularpocket.cycle that automatically mills a rectangular pocket

. Tool movements during a face milling cycle.

. Operators can machine a pocket with a milling canned cycle.

DependingontheCNCcontrolmanufacturer,othermillingcannedcyclesavailable. Milling cycles, in addition to thehole-making and turninghighly valued for their ability to simplify CNC programming and improve

77

are the various hole-makingcycles and the multiple repetitive cycles used on the turning center. However,you also may find on certain controls canned cycles for milling. Variousmachining center controls may be equipped with customized milling cannedcycles designed by the control manufacturer. Also, milling canned cycles are

n controls designed for conversational programming. Examples of

cycle that automatically faces the top surface of a part

tmachinesacircularpocket.lls a rectangular pocket

cycle.

canned cycle.

cannedcyclesmaybemaking and turningcycles, are

highly valued for their ability to simplify CNC programming and improve


Basic Turning Cycles Hole-makingcannedcyclescentersaswell.However,thereareadditionalcannedcyclesthatarespecifictotheturningcenter.TwoexamplesofbasiccyclesaretheG90turningcycleandG94facingcycle.BothcannedcyclesrequireXfeedrate. Consider theG90toolpattern inactivated,thetoolmustbeinthestartingposition.First,thetoolrapidstotheXaxispositionindicatedwiththeXcode.Then,thetoolfeedstotheZincludedintheZcode.

Fig7.12 Tool movements during the basic turningFinally,thetoolfeedsbackuptotheoriginalXtheoriginalZ-axisposition.G94issimilar,exceptthetoolpatternisdesignedforfacinginsteadofturning.Liketheholeotherwords,theycanberepeatedbysimplyincludinganewXorZcodeinthefollowingblock.

Fig7.13 Tool movements during the basic facing cycle.Fig.7.14showstheactualcodescontainedinthesecycles.Inaddition,bothG90and G94 are capable of machining tapers. On some controls, an R code is


makingcannedcyclesappearoneverymachiningcenterandmanyturning,thereareadditionalcannedcyclesthatarespecificto

theturningcenter.TwoexamplesofbasiccyclesaretheG90turningcycleandG94facingcycle.BothcannedcyclesrequireX-andZ-axispositions,aswellasa

Consider theG90toolpattern in fig.7.11.Before thecannedcycle isactivated,thetoolmustbeinthestartingposition.First,thetoolrapidstotheXaxispositionindicatedwiththeXcode.Then,thetoolfeedstotheZ

Tool movements during the basic turning cycle.

Finally,thetoolfeedsbackuptotheoriginalX-axispositionandthenrapidstoaxisposition.G94issimilar,exceptthetoolpatternisdesignedfor

.Likethehole-makingcycles,G90andG94aremodal.Inotherwords,theycanberepeatedbysimplyincludinganewXorZcodeinthe

Tool movements during the basic facing cycle.

showstheactualcodescontainedinthesecycles.Inaddition,bothG90and G94 are capable of machining tapers. On some controls, an R code is

78

appearoneverymachiningcenterandmanyturning,thereareadditionalcannedcyclesthatarespecificto

theturningcenter.TwoexamplesofbasiccyclesaretheG90turningcycleandaxispositions,aswellasa

.Before thecannedcycle isactivated,thetoolmustbeinthestartingposition.First,thetoolrapidstotheX-axispositionindicatedwiththeXcode.Then,thetoolfeedstotheZ-axisposition

cycle.

axispositionandthenrapidstoaxisposition.G94issimilar,exceptthetoolpatternisdesignedfor

makingcycles,G90andG94aremodal.Inotherwords,theycanberepeatedbysimplyincludinganewXorZcodeinthe

Tool movements during the basic facing cycle. showstheactualcodescontainedinthesecycles.Inaddition,bothG90

and G94 are capable of machining tapers. On some controls, an R code is

CAD/CAM

required to indicate the change in position from one end of the taper to theother.OthercontrolsusebotSomecontrolsalsoallowabsoluteXandZcodestodeterminethetaper.

Fig.7. MULTITASKING MACHINESMultitasking is a recent concept in CNC machines. Multitasking machinesincorporate several processes in a single work center. For example, if acomponent requires millingbedesignedtocarryoutalltheseoperations.Thistypeofmachinereducesthenumber of set upsand therefore reducescycle times. Accuracy is improved astherearefewersetups.Veryoftendesignersbreakdowncomplexcomponentsintoanumberofpartstofacilitatemachining.Multitaskingmachineseliminatethis need thereby increasing the integrity of the part. Another advantage ofmultitaskingisthepossibilityofcostreductionbecauseofreductioninsetups,eliminatingtheneedforseveralfix

Fig.

required to indicate the change in position from one end of the taper to theother.OthercontrolsusebothanIandKcodetoindicatetheamountoftaper.SomecontrolsalsoallowabsoluteXandZcodestodeterminethetaper.

Fig.7.14 G90 basic turning codes.

MULTITASKING MACHINES is a recent concept in CNC machines. Multitasking machines

incorporate several processes in a single work center. For example, if acomponent requires milling, turning and grinding, a multitasking machine cbedesignedtocarryoutalltheseoperations.Thistypeofmachinereducesthenumber of set upsand therefore reducescycle times. Accuracy is improved astherearefewersetups.Veryoftendesignersbreakdowncomplexcomponents

tstofacilitatemachining.Multitaskingmachineseliminatethis need thereby increasing the integrity of the part. Another advantage ofmultitaskingisthepossibilityofcostreductionbecauseofreductioninsetups,eliminatingtheneedforseveralfixtures

Fig. 7.15 CNC Turn Mill Centre

79

required to indicate the change in position from one end of the taper to thehanIandKcodetoindicatetheamountoftaper.

SomecontrolsalsoallowabsoluteXandZcodestodeterminethetaper.

is a recent concept in CNC machines. Multitasking machinesincorporate several processes in a single work center. For example, if a

, a multitasking machine canbedesignedtocarryoutalltheseoperations.Thistypeofmachinereducesthenumber of set upsand therefore reducescycle times. Accuracy is improved astherearefewersetups.Veryoftendesignersbreakdowncomplexcomponents

tstofacilitatemachining.Multitaskingmachineseliminatethis need thereby increasing the integrity of the part. Another advantage ofmultitaskingisthepossibilityofcostreductionbecauseofreductioninsetups,


CYLINDRICAL GRINDING InmanycasesCNCisprovidedonlyforwheelheadslidetocontroldiameters.Insome casesCNC is provided for longitudinal traverseand wheelhead traverse(2-axis) to control length of shoulders and diameter steps. Workpiece size isachievedbydressingthewheelwithreferencetofixeddressingpointorbyuseof an interactive size control unit. Such machines can generate solids ofrevolution involving tapers, circular arcs and curved surfaces. Similar controlsare available for internal grinders. Tablcylindrical grinding machines. FigCNCgrindingmachine.X-axisistheinlongitudinaltraverseofthegrindingwheelistheZtheS1axis.Ifthegrindingwheelrpmisprogrammable,itprovidestheS2axis.SwivelingofthewheelheadisBA-axis.C-axisisalsoprovidedonsomemachines.Figureshowsonlyaxes.Table7.1SpecificationsofaTypicalCylindricalGrindingMachine


InmanycasesCNCisprovidedonlyforwheelheadslidetocontroldiameters.Insome casesCNC is provided for longitudinal traverseand wheelhead traverse

axis) to control length of shoulders and diameter steps. Workpiece size isthewheelwithreferencetofixeddressingpointorbyuse

of an interactive size control unit. Such machines can generate solids ofrevolution involving tapers, circular arcs and curved surfaces. Similar controlsare available for internal grinders. Table 7.1 gives specifications of typicalcylindrical grinding machines. Fig. 7.16 shows the schematic arrangement of a

axisisthein-feeddirectionofthegrindingwheel.ThelongitudinaltraverseofthegrindingwheelistheZ-axis.ThespindlerotationistheS1axis.Ifthegrindingwheelrpmisprogrammable,itprovidestheS2axis.SwivelingofthewheelheadisB-axis.Swivelingaxisfordressingthewheelisthe

axisisalsoprovidedonsomemachines.Figureshowsonly

SpecificationsofaTypicalCylindricalGrindingMachine

80

InmanycasesCNCisprovidedonlyforwheelheadslidetocontroldiameters.Insome casesCNC is provided for longitudinal traverseand wheelhead traverse

axis) to control length of shoulders and diameter steps. Workpiece size isthewheelwithreferencetofixeddressingpointorbyuse

of an interactive size control unit. Such machines can generate solids ofrevolution involving tapers, circular arcs and curved surfaces. Similar controls

gives specifications of typicalshows the schematic arrangement of a

feeddirectionofthegrindingwheel.TheThespindlerotationis

theS1axis.Ifthegrindingwheelrpmisprogrammable,itprovidestheS2axis.axis.Swivelingaxisfordressingthewheelisthe

axisisalsoprovidedonsomemachines.FigureshowsonlyX,ZandS1

SpecificationsofaTypicalCylindricalGrindingMachine

CAD/CAM

Fig. 7.15

CNChasbeenappliedtocomplextoolandcuttergrindersinvolvingasmanyaseight axes. The control system working in anprogram residing in the memory leads the operator step by step reducing theprogrammingefforttotheabsoluteminimum.even on optical profile grinders. The control system has linear, circular andhelical interpolation to generate complex contours, and has provision to dressthe wheel and to compensate for wheel wear. Optics serves for tool setting,positioningtheworkpiece,checkingwheeldreswithoutremovingitfromthefixture.SPECIAL PURPOSE CNC MACHINESManySPM’sarenowdesignedwithcomputernumericalcontroltoprovidethenecessaryflexibilitytothemachine.AtypicalexampleisamovingcolumnSPMthatisdesignedforboringandreamingoperations.UndertheguidanceofCNCthetoolispositionedatadesiredpointorthetoolismadetofollowanycontourformachiningoperations.SwitchoverfromonetypeofmachiningoperationstootheriscompletelyautomaticthroughtheprovisionofAutomaticToolChanger(ATC).Thecolumntraverseandfixedtablemodulecontributetohighertransferefficiency and flexibility in line production. Hence these CNC special purposemachinescanbeintegratedwithothlineforgreaterflexibilityinproducingavarietyoftotallyfinished

7.15 Cylindrical Grinding Machine

CNChasbeenappliedtocomplextoolandcuttergrindersinvolvingasmanyaseight axes. The control system working in an interactive mode with the partprogram residing in the memory leads the operator step by step reducing theprogrammingefforttotheabsoluteminimum.CNChasbeenusedtoadvantage

grinders. The control system has linear, circular andhelical interpolation to generate complex contours, and has provision to dressthe wheel and to compensate for wheel wear. Optics serves for tool setting,positioningtheworkpiece,checkingwheeldressingandinspectionofworkpiecewithoutremovingitfromthefixture.

SPECIAL PURPOSE CNC MACHINES ManySPM’sarenowdesignedwithcomputernumericalcontroltoprovidethenecessaryflexibilitytothemachine.AtypicalexampleisamovingcolumnSPMhatisdesignedforboringandreamingoperations.UndertheguidanceofCNC

thetoolispositionedatadesiredpointorthetoolismadetofollowanycontourformachiningoperations.Switchoverfromonetypeofmachiningoperationsto

elyautomaticthroughtheprovisionofAutomaticToolChanger(ATC).Thecolumntraverseandfixedtablemodulecontributetohighertransferefficiency and flexibility in line production. Hence these CNC special purposemachinescanbeintegratedwithothermachinetoolsintoflexiblemanufacturinglineforgreaterflexibilityinproducingavarietyoftotallyfinished

81

CNChasbeenappliedtocomplextoolandcuttergrindersinvolvingasmanyasinteractive mode with the part

program residing in the memory leads the operator step by step reducing theCNChasbeenusedtoadvantage

grinders. The control system has linear, circular andhelical interpolation to generate complex contours, and has provision to dressthe wheel and to compensate for wheel wear. Optics serves for tool setting,

singandinspectionofworkpiece

ManySPM’sarenowdesignedwithcomputernumericalcontroltoprovidethenecessaryflexibilitytothemachine.AtypicalexampleisamovingcolumnSPMhatisdesignedforboringandreamingoperations.UndertheguidanceofCNC

thetoolispositionedatadesiredpointorthetoolismadetofollowanycontourformachiningoperations.Switchoverfromonetypeofmachiningoperationsto

elyautomaticthroughtheprovisionofAutomaticToolChanger(ATC).Thecolumntraverseandfixedtablemodulecontributetohighertransferefficiency and flexibility in line production. Hence these CNC special purpose

ermachinetoolsintoflexiblemanufacturinglineforgreaterflexibilityinproducingavarietyoftotallyfinishedcomponents.


SinceCNCmachineslidesarefittedwithfeedbackdevices,theycanalsobeusedfor post process metrology. Many of the prestouch trigger probes, which can be used for inspection of workpiece and forsettingthetooloffsets.Onmachiningcentrestheprobecanbestoredinoneofthe pockets of the tool magazine. Theprobe is inserted into the sprogramcontrolandthencanbeusedlikeacoinspect thecomponentbeingmachined.Theprobecanbe used tocompensatefor fixture offsets, thermal deformations etc. A similar probe located at a fixedreferencepointcanbeusedtosettheoffsetsofthetoolslocatedinthespindle.Such probes are also used on turning machines to set the tool offsets and formonitoringthesizeoftheworkpiece. MILLING AND DRILLING PROGRAMMINGCNCProgrammingHints–

Foraprogramtorunonamachine,itmustcontainthefollowingcodes:M03Tostartthespindle/cutterrevolving.SxxxThespindlespeedcodetosetther/min.Fxx Thefeedratecodetomovethecuttingtoolor position.ANGLES:TheXYcoordinatesofthestartpointandendpointoffeedrate(F)arerequired.Z CODES: •AZdimensionraisesthecutterabovetheworksurface. •AZ-dimensionfeedsthecutterintotheworksurface. •Z.100istherecommendedretractdistanceabovethe beforearapidmove(G00)ismadeto RADII / CONTOUR Requirements: •Thestartpointofthearc(XYcoordinates) •Thedirectionofcuttertravel(G02orG03) •Theendpointofthearc(XYcoordinates) •Thecenterpointofthearc(IJcoordinates)orthearc


SinceCNCmachineslidesarefittedwithfeedbackdevices,theycanalsobeusedfor post process metrology. Many of the present day machines are fitted withtouch trigger probes, which can be used for inspection of workpiece and forsettingthetooloffsets.Onmachiningcentrestheprobecanbestoredinoneofthe pockets of the tool magazine. Theprobe is inserted into the sprogramcontrolandthencanbeusedlikeaco-ordinatemeasuringmachinetoinspect thecomponentbeingmachined.Theprobecanbe used tocompensatefor fixture offsets, thermal deformations etc. A similar probe located at a fixed

pointcanbeusedtosettheoffsetsofthetoolslocatedinthespindle.Such probes are also used on turning machines to set the tool offsets and formonitoringthesizeoftheworkpiece.

MILLING AND DRILLING PROGRAMMING MILLING

Foraprogramtorunonamachine,itmustcontainthefollowingcodes:Tostartthespindle/cutterrevolving.Thespindlespeedcodetosetther/min.Thefeedratecodetomovethecuttingtoolorworkpiecetothedesired

TheXYcoordinatesofthestartpointandendpointoftheangularsurfaceplusa

•AZdimensionraisesthecutterabovetheworksurface.dimensionfeedsthecutterintotheworksurface.

therecommendedretractdistanceabovetheworksurfacebeforearapidmove(G00)ismadetoanotherlocation.

RADII / CONTOUR Requirements: •Thestartpointofthearc(XYcoordinates)•Thedirectionofcuttertravel(G02orG03)

pointofthearc(XYcoordinates)•Thecenterpointofthearc(IJcoordinates)orthearcradius)

82

SinceCNCmachineslidesarefittedwithfeedbackdevices,theycanalsobeusedent day machines are fitted with

touch trigger probes, which can be used for inspection of workpiece and forsettingthetooloffsets.Onmachiningcentrestheprobecanbestoredinoneofthe pockets of the tool magazine. Theprobe is inserted into the spindle under

ordinatemeasuringmachinetoinspect thecomponentbeingmachined.Theprobecanbe used tocompensatefor fixture offsets, thermal deformations etc. A similar probe located at a fixed

pointcanbeusedtosettheoffsetsofthetoolslocatedinthespindle.Such probes are also used on turning machines to set the tool offsets and for

Foraprogramtorunonamachine,itmustcontainthefollowingcodes:

workpiecetothedesired

theangularsurfaceplusa

•AZdimensionraisesthecutterabovetheworksurface.worksurface

anotherlocation.

radius)

CAD/CAM

Fig.7.15 A sample flat part used for CNC

ProgramNotesforfig.7.15above Programintheabsolutemodestartingatthe

leftcorneroftheprint. Thematerialisaluminum(300CS),feedrate10in/min. Thecuttingtoolisa.250in.diameterhighspeedsteel2 Millthe1in.squareslot. Drillthetwo.250in.diameterholes,

A sample flat part used for CNC programming and machining

ProgramNotesforfig.7.15aboveProgramintheabsolutemodestartingatthetoolchangepositionatthetop

Thematerialisaluminum(300CS),feedrate10in/min.Thecuttingtoolisa.250in.diameterhighspeedsteel2-flute

Millthe1in.squareslot.Drillthetwo.250in.diameterholes,.250in.deep.

83

programming and machining

toolchangepositionatthetop

fluteendmill.


Millthe.250in.wideangularslot,.125in.deep. Millthe.250in.widecirculargroove,.125in.deep. Afterthejobiscompleted,returntothetoolchangeposition. Programming:

Machining the square groove


Millthe.250in.wideangularslot,.125in.deep.Millthe.250in.widecirculargroove,.125in.deep.Afterthejobiscompleted,returntothetoolchangeposition.

Machining the square groove

84

Afterthejobiscompleted,returntothetoolchangeposition.

CAD/CAM

Hole Drilling

Machining the Angular Slot

Machining the Angular Slot

85


Machining the Circular Groove

FANUC COMPATIBLE PROGRAMMINGCNC Programming Hints

Foraprogramtorunonamachine,itmustcontainthefollowingcodes:M03Tostartthespindle/cutterrevolving.SxxxThespindlespeedcodetosetther/min.Fxx Thefeedratecodetomovethecuttingtoolor position. TAPERS/BEVELS/ANGLES• The X Z coordinates of the small diameter, the large feedrate mustbeprogrammed.• Z moves the cutting tool longitudinally away from the end workpiece.


Machining the Circular Groove

FANUC COMPATIBLE PROGRAMMING CNC Programming Hints – TURNING


Tostartthespindle/cutterrevolving.Thespindlespeedcodetosetther/min.Thefeedratecodetomovethecuttingtoolorworkpiecetothedesired

TAPERS/BEVELS/ANGLES The X Z coordinates of the small diameter, the large

mustbeprogrammed.Z moves the cutting tool longitudinally away from the end

86


workpiecetothedesired

The X Z coordinates of the small diameter, the large diameter, and a

Z moves the cutting tool longitudinally away from the end of the

CAD/CAM

• Z- moves the cutting tool along the length of the workpiece chuck(headstock).• Xmovesthecuttingtoolawayfromtheworkdiameter.• X-movesthecuttingTheprogramming for theFanuccompatiblecontrol is theoneusedinindustry.Althoughmanycontrolsarearesomedifferences.Afewof1. TheG28codeisusedtosettheprogrammedoffsetofthereferencepoint.2. Codesaremodalanddonothavetoberepeatedinevery3. Alldimensionsareenteredasdecimals.

Fig. 27 A typical round part used for CNC programming and machining.

Using the part illustrated in Fig.compatiblecontrolwouldbeasfollows: TURNING PROGRAMMINGProgramming Sequence

moves the cutting tool along the length of the workpiece

Xmovesthecuttingtoolawayfromtheworkdiameter.movesthecuttingtoolintotheworkdiameter.

Theprogramming for theFanuccompatiblecontrol is theoneusedinindustry.AlthoughmanycontrolsaresimilartotheFanuccontrol,therearesomedifferences.Afewofthemaindifferencesare:

susedtosettheprogrammedoffsetofthereferencepoint.Codesaremodalanddonothavetoberepeatedineverysequenceline.Alldimensionsareenteredasdecimals.


Using the part illustrated in Fig. 7.16 the programming for a Fanuccompatiblecontrolwouldbeasfollows:

TURNING PROGRAMMING

87

moves the cutting tool along the length of the workpiece towards the

Theprogramming for theFanuccompatiblecontrol is theonemostcommonlysimilartotheFanuccontrol,there

susedtosettheprogrammedoffsetofthereferencepoint.sequenceline.


the programming for a Fanuc


Rough Turning Cycle


88

CAD/CAM

Finish Turning

89

CHAPTER EIGHT

SIMULATION IN COMPUTER AIDED MANUFACTURING Simulation in manufacturing refers to a broad collection of computer basedapplications to imitate the behavior of manufacturing systems. A system is afacility or a process either actual or planned such as factory with workers,machine tools, materials handling devices, storage devices etc. Simulation isintendedtostudythemodelofthisrealworldsystembynumericalevaluationusing software. Simulation is carried out to evaluate the performance of asystem, product or process before it is physically built or implemented.Another type of simulation, which has become very popular of late, ismanufacturing or factory simulation. Factory simulation involves creating avirtualfactory.Here,insteadofsimulatingaprocessoraworkcentretheentirefactoryissimulatedtohaveaclearunderstandingoftheworkingoftheplantasa whole. Simulation technology holds tremendous promise for reducing costs,improvingquality,andshortening the time-to-market formanufacturedgoods.In the present context, simulation refers to the study of the performance of amanufacturing system or a factory. Simulation involves modeling andvisualization of the entire plant. There are several potential benefits fromsimulation.Butlackofunderstanding,costofsoftwareandexpertisehavemadesimulation not popular with manufacturing engineers, till recently. Thedevelopment and maintenance of simulation models of manufacturingequipmentcanbecostly.Forexample,letustakethecaseofamachineshop.Adetailedsimulationmodelofasinglemachinetoolmaytakeanengineerseveralweeks to create, and such customized models are required for each type ofmachine tool. However, standard reusable simulation model codes are nowavailable which reduces the time involved in creating the model. Today,computer-based simulation is inexpensive and effective. Simulation makes iteasier to evaluate production cells or systems before implementing them. Itallows errors or deficiencies to be identified and corrected before they areimplemented. Models can be built, tested and compared for different designvariations. ‘What-if’ analysis can then be carried out either to choose the bestdesignorlayoutorproductmix.Extensivesimulationstudiescanbecarriedouttoevaluatetheperformanceofamanufacturingsystem,undervariousinputandoperating conditions as well as under different plant configurations andcapacities. Simulation helps to meet the objective of bringing products to themarket faster because it does not require the time-consuming activities ofbuildingphysicalmodelsoftheplant.Insteaditusesthemodelsdesignedinthecomputer,whichwouldnormallybethebasisforbuildingthephysicalmodels.Buildingphysicalmodelsofplantsisnotpracticalandevenifmade,theyarenotsuitableforsimulationpurposes.Thus,timeissavedbecauseitisnotnecessaryto build the ‘physical’ model. In addition, even more time is saved asmodifications could be made to the computer-based model to improve theperformanceof theplantandthesimulation isrepeatedasa “what if”case. In

Simulation in computer aided manufacturing 91

addition to usual applications like system design and performance estimation,simulationcanalsobeusedforscheduling.Thesimulationsoftwareinthiscasegathers therequireddata frommanufacturingexecutionsystemandgeneratesmultipleschedulesfromwhichoptimumcouldbeselected. TYPES OF SIMULATION Simulationcouldbeclassifiedintothreetypes.

i. Static or dynamic simulation: Static or dynamic simulation: In staticsimulation time does not have a role. However, most of the manufacturingsystemsaretimedependentandarehencedynamic.

ii. Continuous or discrete: A continuous system is one which continuouslyvarieswithtime.Examplesarerefinery,thermalpowerplantandplateglassmanufacturingplantwhereproductioniscontinuousbutmayfluctuateovertime.Anautomotiveassemblyplantismoreorlessacontinuoussystem.Ontheotherhand,acompanymanufacturingmachinetools,motors,pumps,isadiscretesystem.AJobshopwherebatchquantitymayvaryfromonetomanyis another example of a discrete manufacturing plant. In some cases, themanufacturingsystemmaybeacombinationofbothdiscreteandcontinuoussystem. Such a system may be called mixed continuous-discrete system.Discreteeventsimulationisapowerfultoolinmanufacturing.Theadvantageofthesimulationmodelisthatitcanbereusedforadifferentproblemortoevaluateanotheroption.Intheglobalizationera,engineersshouldbecapableofrespondingfastertodynamicallychangingglobalmarketsandsimulationhelpstoreducethetimetomarket.

iii. Deterministic or stochastic: Systems which have no random inputs aredeterministic. A design bureau or a rapid prototyping shop may receiveorders at random. Several fabrication companies may also fall under thiscategory. A manufacturing system may also have both deterministic andrandominputs.

TECHNIQUES OF SIMULATION Simulationcanbecarriedoutinthreeways.

i. Programmingingeneralpurposesimulationlanguagesii. Simulationusingsimulationlanguages

iii. HighlevelsimulatorsSIMULATION USING GENERAL PURPOSE LANGUAGES SimulationprogramscanbewritteninhighlevellanguageslikeFORTRANorC.Thisapproachwaspopularwhensimulationlanguageswherenotavailable.Theadvantageofthisapproachistheopportunitytodesignthesystemtoaspecificapplication in a customized manner. However, the process is tedious, timeconsuminganderrorprone.

CAD/CAM 92

SIMULATION LANGUAGES General Purpose Simulation System (GPSS) is one language popularly used forsimulation. GPSS is a family of mostly-declarative languages designed fordiscrete-event simulation and system modeling. A GPSS simulation programconsistsofasetofblockswhichincludegenerators,queues,servers,selectorsorrouters,datacollectors,timingandcomputationalnodes.Datatypessupportedin simulation models vary between versions, but usually include integers, realnumbers,strings,andrecords.GPSSsystemsalwayshadsophisticatedrandomsample generators to model various probability distributions that to modelrealworld processes. SIMSCRIPT, SLAM, SIMAN etc were later developed andbecame popular with manufacturing industry. These are very flexible tosimulatevarietyofsystems.HIGH-LEVEL SIMULATORS Highlevelsimulatorsdifferfromthesimulationlanguagesasthelatterfeatureinaddition powerful graphics user interfaces, menus and dialog boxes. Standardconstructs enable the user to model a system quickly. This makes modelcreation faster. However, there is a trade off in flexibility. The facility fordynamicgraphicanimationgivestheusertovisualizetheactualworkingofthesystem.SIMULATION PROCESS FOR MANUFACTURING SYSTEMS ANALYSIS Theprocessofsimulatingamanufacturingsysteminvolvesthefollowingsteps.

i. Model design: In this step the issues to be addressed are identifiedbased on which the project is planned. Next step is to develop aconceptualmodel.

ii. Model development: The simulation engineer chooses a modelingapproachsuitablefortheproblem.Afterbuildingthemodelitistestedtoverifyandvalidatethemodel.

iii. Model deployment: The model is used to carry out experiments like‘What if” analysis. The results are then studied and used for makingdecisions.

SIMULATION SOFTWARE PACKAGES Thereareanumberofsimulationpackagesinusetoday.Someofthemarelistedbelow:•AutoDESKHSM•Fusion360•Automod•Autoshed•@risk•CrystalBall•eMPlant•EnterpriseDynamicSimulationSoftware

Simulation in computer aided manufacturing 93

•EnterpriseDynamicSimulationstudio•ExtendOR•ExtendSuite•FlexSim•GPSS•GoldSim•Lean_modeler•MAST•ProcessSimulator•ProModel•PSM+++•SAIL•ShowFlow2•SIGMA•SIMAN•SIMPROCESS•SIMSCRIPTII.5•SIMUL8•SLIM•SupplychainGuru•VisualSimulationEnvironment•WebGPSS•Witness2006•XLSim

Standardized interfaces, component model libraries, and modeling techniqueshave reduced the cost and increased the accuracy and accessibility ofmanufacturing simulation technology. Simulation is commonly usedmanufacturing system design and improvement methods such as leanmanufacturingandsixsigma. APPLICATION OF SIMULATION Simulationhasbeenwidelyusedinthemanufacturingindustrytooptimizethedesignoftheshopfloorsandtailorthefacilitytoyieldtherequiredoutput.Itisalso used to predict the output under various input and operating conditions.Automotive industry and aerospace industry are the major industries, whichmake use of simulation. The following sections give brief details of howsimulationisusedinindustries. SIMULATION IN AUTOMOTIVE INDUSTRY The automotive industry uses discrete event simulation to investigate thecapabilities of the different manufacturing shops involved in buildingautomobiles like body shops, paint shops, trim/chassis/final assembly shops,andengineassemblyshops,machiningshopsandstampingshops.Simulationof

CAD/CAM 94

bodyshopsystemsduringtheconcept,designandbuildphasesofaproductlifecycle allows an automotive company to investigate the impact of tooling,conveyor and material delivery systems on the throughput. There are twodifferent approaches adopted to analyze the performance of a body shop. Thefirst is to model the body shop at the station level. The second approach is tomodelthebodyshopatthelineorsubassemblylevelofdetail.Thestation-levelsimulationmodelisusedtoanalyzethestandalonecapabilityofasubassemblyarea.Stationcycletimesanddowntimesareenteredintoasimulationmodelandthesubassembly throughput isestimated.Thesubassembly throughputcanbecompared directly to the body shop target throughput. As a general rule, thesubassemblythroughputmustbegreaterthanthefullbodyshopthroughputornew design of the subassembly area would be needed. If complex manualoperationsoccuratastation,theseoperationscanbeaddedtothestationlevelmodel.Modeling the walk, pickup and set down times can identify if an individualstation can meet the required cycle time for the subassembly area. While thestation-levelanalysisofthesubassemblyareasisbeingcarriedout,a linelevelmodel can be developed. The throughput estimates from the individualsubassembly models are entered into the line level model and the conveyorsystemsaremodeled indetail.The interactionbetweenthesubassembliesandtheconveyorsystemscanbeusedtoidentifysetsofsubassembliesorindividualsubassemblies to identify the bottlenecks in the body shop. Sizing of theconveyor can be accomplished by increasing buffer between bottlenecksubassembly areas and reducing buffer between non-bottleneck areas. Thisprocesscontinuesthroughthedesignphase.Analternativetothisapproachistointegrateallofthesubassemblymodelsintoonelargedetailedmodel.Anytimeasubassemblychangesortheconveyorlayoutchanges,themodelisupdatedtoanalyze the full body shop system. The full body shop model is also used toinvestigatetheimpactthatoperationalparametershaveonthesystemonceitisimplemented. The operational parameters can include: preventativemaintenance,reducingmeantimetorepair,batchsizing,andovertime.Changing operational parameters and identifying their impact on systemperformancewillshowtheopportunitiesforincreasingsystemperformanceandwillaidintheprioritizationoffunding.Anadditionalanalysisthatoccursinthebody shop is the delivery of materials to the line locations. This analysisinvestigates the impact of the number of fork lift trucks, fork lift truckassignments, the amount of stock at the line, the location of storage areas, thelocations of docks, and the number of docks on delays caused by parts notpresentattheline.Intheconceptphase,thisanalysiscaninfluencethelocationof subassemblies and identify strategic locations for stock to minimize thematerialdeliverytimes.Whenautomotivepaintshopsaresimulated,thefocusisusuallyonthepowerand-freeconveyorsystemsthattransportpartsthroughthe

Simulation in computer aided manufacturing

paintingoperations.Powerandbecauseofcarriersthatfixthemselvestothemechanism called a dog. When two different speed chains merge, carriers canaccumulateandarepickedupbythedogsonthenewchain.Therearetwotypesofchains: lowspeedproductionchainsusedwhilepartsarebeinghigh speed transport chains, which move parts between different productionareas.During thedesign phase of a paint system, thepowerevaluated using simulation to determine if throughput targets can be met.Power-and-free systems may require kilometers of production and transportchaintoconnectdifferentsubdeterminethenumberofcarriersrequired,howchainmergesandtransferswilloperateandwhetheradequateaccumulathigher density empty carrier storage is required, carriers are rotatedaccumulation,whichiscalledbiasbanking.Thesizeofbiasbankbufferscanbedeterminedusingsimulation.Simulationisusedwhileoperatto determine the effects of adding different body styles and paint types toexistinglines.As new models with varied vehicle paint options are introduced, it becomesnecessary to modify paint lines to handle new requirements. Simulatiprovidesatestbedwherechangesinthepaintshoptomeetthenewproductionrequirement can be evaluated prior to making any changes to the existingsystem.Thisreducesnotonlythesystemdowntimeduringchangeoverbutalsoinstillsconfidenceinoperators,supervisorsandmanagers.PROCEDURE FOR SIMULATION USING SOFTWAREThe following section describes a simple example of simulation using Arena.This is almost a trivial case but is adequate to introduce the reader to theprocess of simulation. Thediameter inacentre lathefromapolishedC45rodof25mmdiameter.Figshowsthecomponent.Thebatchsizeis10andthemanualoperationtakes10minutesperpiece.Thefinishedpart is inspectedandthosecomponentswhichfallwithinthedimensionlimitsareaccepted.Therestarerejected.

Fig.

imulation in computer aided manufacturing

paintingoperations.Powerand-freesystemsaredifferentfromotherconveyorsbecauseofcarriersthatfixthemselvestothedrivechainbymeansofahookingmechanism called a dog. When two different speed chains merge, carriers canaccumulateandarepickedupbythedogsonthenewchain.Therearetwotypesofchains: lowspeedproductionchainsusedwhilepartsarebeinghigh speed transport chains, which move parts between different productionareas.During thedesign phase of a paint system, thepower-evaluated using simulation to determine if throughput targets can be met.

ystems may require kilometers of production and transportchaintoconnectdifferentsub-systemstotransportparts.Simulationisusedtodeterminethenumberofcarriersrequired,howchainmergesandtransferswilloperateandwhetheradequateaccumulation isprovided. Insomeareaswherehigher density empty carrier storage is required, carriers are rotatedaccumulation,whichiscalledbiasbanking.Thesizeofbiasbankbufferscanbedeterminedusingsimulation.Simulationisusedwhileoperatingapaintsystemto determine the effects of adding different body styles and paint types to

As new models with varied vehicle paint options are introduced, it becomesnecessary to modify paint lines to handle new requirements. Simulatiprovidesatestbedwherechangesinthepaintshoptomeetthenewproductionrequirement can be evaluated prior to making any changes to the existingsystem.Thisreducesnotonlythesystemdowntimeduringchangeoverbutalso

perators,supervisorsandmanagers.

PROCEDURE FOR SIMULATION USING SOFTWARE The following section describes a simple example of simulation using Arena.This is almost a trivial case but is adequate to introduce the reader to theprocess of simulation. The example taken is that of turningdiameter inacentre lathefromapolishedC45rodof25mmdiameter.Figshowsthecomponent.Thebatchsizeis10andthemanualoperationtakes10minutesperpiece.Thefinishedpart is inspectedandthosecomponentswhichfallwithinthedimensionlimitsareaccepted.Therestarerejected.

Fig. 8.1 Component to be Machined

95

freesystemsaredifferentfromotherconveyorsdrivechainbymeansofahooking

mechanism called a dog. When two different speed chains merge, carriers canaccumulateandarepickedupbythedogsonthenewchain.Therearetwotypesofchains: lowspeedproductionchainsusedwhilepartsarebeingpaintedandhigh speed transport chains, which move parts between different production

-and-free layout isevaluated using simulation to determine if throughput targets can be met.

ystems may require kilometers of production and transportsystemstotransportparts.Simulationisusedto

determinethenumberofcarriersrequired,howchainmergesandtransferswillion isprovided. Insomeareaswhere

higher density empty carrier storage is required, carriers are rotated beforeaccumulation,whichiscalledbiasbanking.Thesizeofbiasbankbufferscanbe

ingapaintsystemto determine the effects of adding different body styles and paint types to

As new models with varied vehicle paint options are introduced, it becomesnecessary to modify paint lines to handle new requirements. Simulationprovidesatestbedwherechangesinthepaintshoptomeetthenewproductionrequirement can be evaluated prior to making any changes to the existingsystem.Thisreducesnotonlythesystemdowntimeduringchangeoverbutalso

The following section describes a simple example of simulation using Arena.This is almost a trivial case but is adequate to introduce the reader to the

example taken is that of turning a pin of 16mmdiameter inacentre lathefromapolishedC45rodof25mmdiameter.Fig.8.1showsthecomponent.Thebatchsizeis10andthemanualoperationtakes10minutesperpiece.Thefinishedpart is inspectedandthosecomponentswhichfallwithinthedimensionlimitsareaccepted.Therestarerejected.

CAD/CAM 96

Thesimulationiscarriedoutinasystematicmannerasexplainedinsubsequentsections.

i. Modeling the process: During this stage the process is defined,documentedandcommunicated

ii. Simulation: The system is studied to understand its performance andexplorepossibilitiesofimprovement.

iii. Visualization: With the aid of graphics animation, the process isvisualized.(

iv. Analysis: The performance of the system can be studied to predict theperformanceofthesystemundervarious“whatif”conditions.

REFERENCES Amaitik,S.M.,&Kilic,S.E.(2005).STEP-basedfeaturemodellerforcomputer- aided process planning. International Journal of Production Research, 43(15),3087-3101.Arezoo,B.,Ridgway,K.,&Al-Ahmari,A.M.A.(2000).Selectionofcutting tools and conditions of machining operations using an expert system. ComputersinIndustry,42(1),43-58.Badiru, A. B. (1992). Expert Systems Applications in Engineering and Manufacturing.EnglewoodCliffs.NJ.USA:PrenticeHall.Baker, S. (1988). Nexpert object: mainstreaming AI applications. IEEE Expert. Winter.p.82.Balasubramanian, S., & Norrie, D. H. (1996). A multi-agent architecture for concurrentdesign,processplanning,routing,andscheduling.Concurrent EngineeringResearchandApplications,4(1),7-16Beg,J.,&Shunmugam,M.S.(2003).Applicationoffuzzylogicintheselectionof part orientation and probe orientation sequencing for prismatic parts. InternationalJournalofProductionResearch,41(12),2799-2815.Bo,Z.W.,Hua,L.Z.,&Yu,Z.G,(2006).OptimizationofprocessroutebyGenetic Algorithms.RoboticsandComputer-IntegratedManufacturing,22(2),180- 188.Brown,R.G.(2000).DrivingDigitalManufacturingtoreality.InProceedingsof WinterSimulationConference,Orlando,FL,USA.Campbell, M. I., Cagan, J., & Kotovsky, K. (1999). A-Design: An agent-based approach to conceptual design in a dynamic environment. Research in EngineeringDesign,11,172–192.Carpenter, I. D., & Maropoulos, P. G. (2000). Flexible tool selection decision support system for milling operations. Journal of Materials Processing Technology,107(1-3),143-152.Chan, F. T. S., Zhang, J., & Li, P. (2003). Agent- and CORBA®-based application integration platform for an agile manufacturing environment.

98

InternationalJournalofAdvancedManufacturingTechnology,21(6),460- 468.Chang,T.-C.,Wysk,R.A.,&Wang,H.-P.(1991).Computer-AidedManufacturing (PrenticeHall,EnglewoodCliffs,NJ).Chen,C.L.P.,&LeClair,S.R.(1993),Unsupervisedneurallearningalgorithmfor setup generation in process planning. In Proceedings of International ConferenceonArtificialNeuralNetworksinEngineering,(pp.663-8).Chen, Y. H., & Lee, H. M. (1998), A neural network system for 2D feature recognition.InternationalJournalofComputerIntegratedManufacturing, 11(2),111-7.Chen,Z.,&Siddique,Z.(2006).Amodelofcollaborativedesigndecisionmaking using timed Petri-net. In Proceedings of the ASME Design Engineering TechnicalConference.Chuang,J.H.,Wang,P.H.,&Wu,M.C.(1999),Automaticclassificationofblock- shaped parts based on their 2D projections. Computers & Industrial Engineering,36(3),697-718.Hwang, J.-L. (1991), Applying the perceptron to 3-D feature recognition, PhD ThesisArizonaStateUniversity,USA.Jain, P. K., Mehta, N. K., & Pandey, P. C. (1998). Automatic cut planning in an operativeprocessplanningsystem.ProceedingsofIMechE,PartB:Journal ofEngineeringManufacture,212(2),129-140.Newman, S. T., Allen, R. D., & Rosso Jr., R. S. U. (2003). CADCAM solutions for STEPcompliant CNC manufacture. International Journal of Computer IntegratedManufacturing,16,590–597.Park,S.C.(2003).Knowledgecapturingmethodologyinprocessplanning.CAD Computer-AidedDesign,35(12),1109-1117.Sormaz, D. N., & Khoshnevis, B. (1997). Process planning knowledge representationusinganobject-orienteddatamodel.InternationalJournal ofComputerIntegratedManufacturing.Yue, Y., Ding, L., Ahmet, K, Painter, J., & Walters, M. (2002). Study of neural network techniques forcomputer integrated manufacturing. Engineering Computations(Swansea,Wales).

INDEX A

Associativeconstraints,

27

Attributes,30,35,36

Auxiliaryholes,33

Axes,10,11,12,21,22,

42,49,50,51,55,56,

58,63,66

Axisymmetric,31

B

Batchquantity,32

binding,ii

blueprints,34

C

CAD,iii,3,4,7,8,9,21,25,

34,35,36,40,43,45,

49,50,63,71

CADsystem,3,5,7,9,34,

49,50

CAE,4

CAM,4,34,35,40,41,42,

43,44,45,46,49,50,

63,70

cannedcycles,58,74,75,

77,78

CAPP,4

CAPPS,4

CAQA,4

Cartesiancoordinate,21

CAST,4

CircularInterpolation,56

Clamps,69

CNCTOOLS,72

codestructure,33

CODEsystem,33

codingsystems,31

collinearconstraint,27

Colours,6

Commercialparts,33

compressivestrength,1

Conceptional design,4

conceptualmodel,92

Concurrent engineering,2

construction,1,2,12,15,

17

Contouring,50,55

Contouringmovements,

12

Coordinate,6,7,37,41,52

coordinatesystem,5,7,

10,12,27,43,46,64,71

counterclockwise,56,58,

59

curve,6,7,8,9,19,22,55

Cuttingtools,32,70,72

D

Datum,7,21,22,23,24,

25,26,30,53

DatumFrame,26

datum points,22,26

DCLASSsystem,33

Design assessment,4

Designdata,35

Detail design,4

Digitalrepresentation,33

Dimensionalspace,12

Discretemanufacturing,

91

DrawingExchangeFile,37

Drilling,4,41,50,51,54,

76

Dynamicsimulation,91

E

Electronicdrawings,3

Engineeringdrawings,3,

6,34,61

Engineeringgraphics,iii,1

Engineeringprojects,2

EnterpriseDynamic,92,

93

extrude,19,20,26

F

fillet,29,30

G

Geometricelement,7

Geometricmodels,14,35

Graphical

communications,1

graphics pipeline,6

Graphicsprimitives,5,6,7

grinding,41,79

Grouptechnology,30

GUI,21

H

Highlevelsimulators,91,

92

Hybridstructure,33

I

inertiaproperties,13

Interpolation,55

interpretation,33

K

KK-3system,33

L

linemodel,15

linesegments,13,22,55

Linearextrusion,15

LinearInterpolation,55

M

Machinists,70,73

Majordimensions,31

manualdrawingtools,3

100

Manufacturing,4,5,34,

40,41,43,45,49,50

Manufacturingattributes,

30,31,33

Manufacturingdata,35

Meshobjects,20

MICLASSsystem,33

milling,4,12,40,41,42,

44,45,51,52,55,67,

68,72,73,74,77,79

Minordimensions,31

Mirror,10,11,26,29

Model development,92

ModernMCUs,68

Multitasking,79

N

numericalcontrol,12,49,

63

O

OPITZsystem,33

Opticalprofile,81

Origin,11,12,13,27,53,

64

P

Parametric,3,4,6,21,36

Parametricequations,6

Partcoding,33

Partfamily,31

Path,12,19,20,40,45,46,

50,54,55,58,63,67,68

pixel,5

planarobjects,20

polylines,20

precisegeometries,2

Primitives,6

principal viewing planes,

21

Prismatic,31

Processplanning,4,31,

32,33,35,43

processingequipment,32

product concept,4

productdevelopment,4,

40

Productionflowanalysis,

31

Productionrate,32

Productiontime,32

Profile,20,22,27,28,29,

30,36

R

Randominputs,91

Rasterdisplay,5

Revolvecurves,19

Rotation,10,12,22,26

Rotationalsweep,15

S

scaling,9

sheetmetal,31

simulationmodels,90

Simulationprograms,91

SimulationSystem,92

Sixsigma,93

Snap,7

Solidmodelling,3,17,18,

34,35

Splines,20

Standard,iii,3,25,26,28,

35,45,46,75

Stochastic,91

Surfacefinish,31

Surfacemachining,33

Surfacemodel,15

Surfacemodeling,20

Sweep,15,16,19,20,26

Symmetrical,30

T

Tertiarydatums,26

Tolerancezone,25

Toolingcost,30

Topologicalinformation,

35

Transition,9

Translationalsweep,15

Turning,4,40,41,51,75,

77,78,79,95

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