Secrets of 5-Axis Machining

KarloApro

I S B N 9 7 8 - 0 - 8 3 1 1 - 3 3 7 57

ttn ril llillffill

Secrets ot S-Axis

Machining by KarloApro

IndustrialPress,Inc. NewYork

Libraryof CongressCataloging-in-Publication Data Apro, Karlo. Secretsof s-Axis lvlachining/ Karlo Apro. p. cm. Includesindex. rsBN 978-0-8311-3375-7 1. l4achinetools--Numerical control.2. Machining.I. Title. IL Title: Secretsof 5-AxisMachining. TJ11B9.A68 20OB 671.3'5--dc22 2004027254

IndustrialPress,Inc. 989 Avenueof the Americas New York,NY 10018 FirstPrinting,August,2008 SponsoringEditor: lohn Carleo lnteriorText and CoverDesign: PaulaApro Developmental Editor: RobertE. Green ProductionI\4anagen lanet Romano

Copyright O 2009 by Industrial PressInc., New York. All rights reserved.This book, or any parts thereot may not be reproduced,stored in a retrieval system, or transmitted in any form without the permissionof the publisher. All trademarks and registeredtrademarks, including Mastercam@ and Vericuto, are property of their respectiveowners. All rights reserved. STATEMENTOF NON-LIABILITY No liabilityis assumedby the author or publisherwith respectto use of information contained herein, includingfor any loss of profit or other commercial,special, or incidental damages.While every reasonableprecaution has been taken in preparing this book,the author and pubiisherassumeno responsibility for errorsor omissions. Publicationof any data in this book does not constitute a recommendationor endorsementby the authoror publisherof any patent,proprietaryright, or product,

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Dedication Thisbookis dedicated, in lovingmemory/to my motherPiroska. Shetaughtme the meaning of hardworkandperseverance. Althoughshepassedawaybeforethe completion of this book,her spiritcontinues to livewith me.

Acknowledgements I wouldlike to thank Yavuzlvlurtezaoglu for giving me the inspirationto write this DOOK.

A specialthanksto LauraNortonfor her humblinginsights. And aboveall, I would like to thank PaulaApro, my hard-workingwife, friend,editot designer,and manager.For without her this book would neverhave come to be.

All the imagesin this book, includingthe virtual machines,were modeledusing (CNCSoftware,Inc.). The virtual machineswere broughtto life using f4astercamo (l"loduleworks) the machinesimulationcapabilitiesof 14achSim and VERICUT6 (CGTech). Formore informationon these productsor companiespleasecontactl Machsim/Moduleworks CGTech/VERICUT CNC Software/Mastercam ModuleworksGmbH 9000 ResearchDrive 671 Old Post Road Ritterstr,12 a Irvine, California 92618 Tolland,CT 06084 52072Aachen,Germany 949.753.1050 860.875.5006 +49.241.4006020 www.cgtech.com www.mastercam.com

www.moduleworks.com

Formore informationon the author,Dleasevisit www.multiaxissolutions.com

Table of Contents Introduction

... ....., . . .1

Chapte1 r : H i s t o r y o fs - A x i s M a c h i n e.s. . . . . . . 3 C o m m ol n4 i s c o n c e p .t .i o . .n, s R e a s o nt o s l J s eM u l t i a x li \s4 a c h i n e s .

.... .......4 ,,,....,B

C h a p t e r 2 !K n o w Y o u r M a c h i n e . . . . . . , , , . , . . 1 3 l4ultiaxisl\4achineConfigurations .........74 T a b l e / T a b l e M u l t i a x i sf l44ai cl lhi ni nge s . . . . . . . . . . . . . . 1 8 I \ 4 a c h i nReo t a r yZ e r oP o s i t i o(nl v l R Z P ) N e s t i nPgo s i t i o n s ,

......21 ............26

RotaryTableDynamicFixtureOffset . . . , , , , , , , . . . . . 27 H e a d / T a b l e M u l tl i4ai xl liisnl vg l a c h i n e s . . . . . . . . . . . . . . 3 1 H e a d / H eM a du l t i a x i s l v l il l4l a i ncgh i n e s . . . . . . . . . . . . . . 3 6 F i n d i ntgh e P i v o D t istance 4 - A x i ls\ 4 a c h i n e s

......37 .............3S

Genemll4aintenance & Issuesfor 14ultiaxis lYachines. . . 40 I\4illing l4achinesWith Five-or l.4ore-Axes. . . . . . . . . . . . 43

C h a p t e r 3C: u t t i n g S t r a t e g i e s . . . . . . . . . . . . . . 4 5

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Chapter4r Indexing MultiaxisToolpaths . . . , .49 I n d e x i nl vgl e t h o d s

........,,.51

H o wC A D / C A |SVyI s t e m sH a n d l eI n d e x i n gW o r k . . . . . . . .

56

MachineCoordinateSystems. . lulachine Home Position . . ActiveCoordinateSystem . . ,

60

I\4achine RotaryCenterPoint , .

60

CAD/CAMSystemOrigin . . . SynchronizinglYachineand CAD/CAMcoordinateSystems .

Chapter 5: SimultaneousMultiaxis Toolpaths. ,65 T h eO p t i m uW m o r kE n v e l o p e Feedrates. I n v e r sTei m eF e e d r a,t.e P o sPt r o c e s s o r s .

............70 .......,,72 .......,,,...74 ....,........76

Chapter6: Commonsimultaneous Multiaxis cAM ,.....79 Toofpath C o n t r o l s. C uP t atterns. T o oAl x i sC o n t r o l .

.......79 ............

86

T o oTl i pC o n t r o l .

.............90

C o l l i s iCoonn t r o l

.............93

A d d i t i o nMaLl r l t i a x i s I s s u e s a n d C o n t r o l s . . . . . . . . . . . . , 9 8 D o v e tE a fi lf e c t . C u t t i nDgi r e c t i o n I v l u l t i aRx o i su g h i n g .

....,.......98 ..........100 ........101

C h a p t e r TM r achineSimulation....,..,,..,1O3 G - c o d e S i m u l a t i o n V e r s u s C A M S i m u l a t i o n . .1. 0. ,5. . . . . C o n f i g u r i n g V i r tM La r ac lh i n eFso r S i m u l a t i o n . . . . , . . . . 1 0 5 VirtualMachineBuilding...,,......,...106 T h eS k e l e t o n C o m p o n e nv tss.l t 4 o d e. l.s.

.....106 ...,......I07

M a c h i nSei m u l a t i Ionnt e r f a c e. s

.........116

U s i nM gachin S ei m u l a t i .o, n. .

...,,....7I7

Chapter 8: Selecting The Right Machine For your Application ...........119 Head/Head Machines (with long X or y - axis linear travel, b u tl i m i t e d r o t a r ya x e st r a v e l ). . ......,.I21 Head/Tablel4achines(with long X-axis travel) . . . . . . . I23 H e a d / T a bl l4ea c h i n e .s

,......126

R o t a rT y a b l e- T i l t i n gH e a dC o m b i n a t i o n. .s. . . , . . . . 1 2 8 T a b l e / T a bl vl ei a c h i n e s . . G a n t r yT y p eH e a d / H e aldv l a c h i n e s . .

..,....I32 .,....

L34

Chapter 9! Choosing a CAD/CAM System For your A p p fi c a t i o n . ..,,.,..,,,tg7 SpeciP a lu r p o sSeo f t w a r .e. .. . C A D / C AT Io4o l b o x .

... ..,,..

.,......,,139

MultiaxiscAD/CAlvlConsiderations .,..... M u l t i a xCi sA f 4 . l 4 u l t i a xCi sA D / C ATI 4. a i n i n.g. , ,

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139

.,...I4O ....,,..I44

Behindthe Scenes:CAD/CAMSoftwareDevelopment. . 145 GeneralGuidelinesfor ResearchingCAD/CAMSoftware. . 146

Chapter 10: Putting ItAII Together, . , , . . . . .149 W h y U s e l 4 u l t i a x i s l v l a c h i n i n g T e c h. n . .i.q. .u.e. .s. ? W h a ti s a S t a n d a rsd- A x i sl \ 4 a c h i n e ?

152

......153

W h a t i s t h e S t a n d a r d A x i s C o n v e n t i o. .n. ? . ........

154

What are the ThreeMajor Multiaxisf4achineTypes?. . . 154 What are the l'.lajorBuildingBlocksof a CNCl4achine?. 1 5 6 What are the 14ostImportantPhysicalPositionsof a [4ultiaxis14achine?

157

What Toolsare Neededto FindMRZP?.. .

159

Description of Indexing/Rotary Positioning Work. . . . . . 1 5 9 Whal i5 a PostProccessor?.

159

DefiniLion of an Axis

160

Defininga Simultaneous 5-axisToolpath

160

Whatare the ThreeCommonSimultaneous lYultiaxis CAM ToolpathConLrols. 161 14ultiaxis MachineOffsels.. .

167

FindinglYachineRotaryZero Posilion.. .

162

Findingthe PivotDistance

164

I n d e x i n g / R o t a r y P o s i t i o n W o r k O v e r v i .e. w . . .. .. .

166

Pickinga CAD/CAMSystem for Multiaxis Work . . . . . . . 166 14achine Simulation.

167

Conclusion

767

Introduction Are you utilizing5-axismachining?Couldyour shop benefitfrom the efficiency and powerthat 5-axismachiningoffers?The majorityof peoplenot embracingthis technologylacka true understanding of 5-axispractices.Thereare many common misconceptions on the subject,and the intent of this book is to demvstifv5-axis machiningand bring it within the reachof anyoneinterestedin usingthe technology to its full potential.The informationpresentedin this book was gatheredduring 30 yearsof hands-onexperiencein the metal-workingmanufacturingindustrybridgingcountries,continents,and multiplelanguages(both human and G-code.) The authorworkedin Hungart Germany,Canada,and the USA,specializing in multiaxissolutions,He spent many yearssettingup, programming,and reparnng CNCequiprnent,and has used a number of different CAD/CA|Ysystems. He has workedas a self-employed multiaxisconsultant,as well as djrecuyfor CGTech(the makersof VERICUT@) and CNCSoftwareInc. (the makersof ttastercamo.) The authorhas instructedcountlessmultiaxistrainingclassesover the past decade, Theseclassescoveredtopicssuchas operatingCNCequipment,programming CNCequipment,both manuallyand with CAD/CAMsystems,and bujldingvirtual machineswith differentverificationsystems.Throughthe years,the author has met many professionals aroundthe world and has come to a realizationthat they atl havethe same questions,misconceptions, and concerns,when it comesto 5-axis machining.The needfor unbiasedinformationon the subjectbecameapparent. Up to this point,the best way to get informationon 5-axismachiningwas to talk to peersin the industry in the hopethat they would sharewhat thev had learned, Visitingindustrialtrade showsand talkingto machinetool and CAD/CAI4 vendors are other options- exceptthat these peopleall give their individualpointsof view and will promotetheir own machineor solution.Everybodvclaimsto havethe best mouse-trap,and it is left to the individualto choosethe right one. This book is not a trainingmanualfor any particularmachineor CAD/CAMsystem. Rather,it is an overviewof multiaxismachinetyDesand the commoncontrol methodsthat CAD/CAMsystemsuse to drivethe machines.The book will guideyou throughthis realm,from basicto complexconcepts,and will provideinformation to helpyou choosethe right tools, includingthe machine,work-holdingmethod, CAD/CAMsystem,and machinesimulationpackagethat will best suit your specific application. The bookcontainsnumerousillustrations to help you to precisely implementthesetools.

History of S-Axis Machines LongbeforeCNCcontrollersappeared,4-5-6-12-and more-axismachines,referred to as multiaxismachines,were beingused.Ihe individualaxeswere controlled mechanically through leversridingon cam plates.Some machineshad more than 12 cam plates,controllingnot onJytool/tableand rotary motions,but also clamprngand unclampingof work-holdingfixtures.Thesemachineswere cumbersomeano atme consumingto set up, but they were perfecUysuitedfor mass production. The first NC (numericalcontrolwithout internalmemory) machineswere cumbersometo set up and operate,but they also were great for massproduction.At first, only the most affluentand establishedshopscouldaffordthem. programm,ng was a lengthy,error-proneprocess.Soon,machinebuildersaddedintern;l memory to their controllers,then they addedthe abilityto executesimplebranchinglooping logic,and to calJsubroutinesfrom other subroutines.It was possibleto us; these macrolanguagesdirectlyon the machineand to quicklychangeset_Lrps, especially for familytype parts. Differentmachinebuildersdevelopedvarioussoluiions,which createda numberof CNC(computernumericalcontrolwith internalmemory) programmrng tanguages.Companieswith familiarnameslike Fanuc,Acramatjc, Heidenhein, Siemens,I\4azatrol, etc., all developedtheir own languages,but thesequicklybecamean issue.Some shopsran ten machineswiih eigfrtOifferent languages.If a repeatjob came in, and the originallyprogrammedmichine was bus, a new programwould haveto be re-writtin from sc-ratch becauseof the languagedifferences. N.ext,-the first.rudimentary CAD(ComputerAidedDesign)/CAM (ComputerAided lYanLrfacturing) systemswere devejoped.At first, these softwaresoluiionswere introducedby the same companiesthat developedthe controllers.Soonafter, enterprisingindividLrals wrote their own CAD/CAI4 software.Thisjump in tecnnorogy was huge becauseit allowedengineersto draw their parts in a CADprogram, generatea toolpathin the CAMsystemt genericlanguage,and then translateit into multipleG-Codelanguagesquickt, usingthe appropljatepost processor. This progressmeantthat CNCmachineswere no longerthe exception,and tney startedto becomethe norm. They were no longerusedonly for mass_production and they becameversatile,accurate,and affordable. Ivlultiaxis machineswent througha similarprocess,but becausethev were more complicaled,this processlook longer.First,Ihe machineswere expensiveto

purchaseand maintain, and harder to program,Only large aerospacecompanies had the need, the money,and the personnelto handle multiaxisapplications.Some companieskept their own processescloselyguardedin order to gain an advantage, Many softwarepackageswere born out of necessity- in order to solve specific applicationchallenges.Software,in general,is alwayson the very leadingedge of technology- pushingthe limits of softwarepossibilitiesand hardwarerestrictions. Today,there are many machinebuildersofferinga variety of multiaxisequipment in a wide range of configurations,quality,and price. Computershave becomevery affordable,and CAD/CAMsystems now offer excellentmultiaxiscutting strategies with great tool control and large post-processorlibraries.As a result, even smaller shopscan, and do, implementmultiaxismachining. Mostmachinebuildersare expandingproductionand embracingnew technology, Many believethat it is imperativeto competein the global market, especially againstcountrieswith abundantcheap labor.This attitude has resultedin increased multiaxismachinesalesand some machinebuildersnow havewaitinglistsof customersfor multiaxismachines,Multiaxismachiningis a constantlyexpanding field,with almostendlesspossibilities.

Common Misconceptions Most peopleassociatethe word "s-axis" with complicatedmotions such as those for the inductionpump illustratedin Figures1-1 and 1-2, and the programming techniquesneeded,This view is reinforcedby visits to any industrialtrade show to see both machinebuildersand CAD/CAMvendorsshowinooff their most complicatedcreations.

Figures 7-7 Exampleof inductionpump set-up Secretsof s-Axis Machining

Figure I-2 Exampleof induction pump design. In reality,the majorityof s-axisusersdon,tevermakean impeller,or finish portsfor a.racing-engine cyrinderhead.Mostof them machineparisusingsimpre 3-axisdrilling,contouring, and pocketmillingroutines,whileroiatingthe-part' occasionally in a rotaryindexingmechanism, as illustratedin Figurei1-3 and 1-4. very elaboratepartscanarsobe machinedby apprying3D surfa-cing toorpathsand engagingthe partfrom differentanglesby indexinga rotarytable.-

Figures t-g and l-4

Examptesof positioning work.

Usinga multiaxismachinewill greatly simplify the motions required,the programmingeffort, and the amount of fixturing neededfor machiningcomplex workpieces.other benefitsincludethe eliminati-onof multiple set-upsf increased accuracy,and better surfacefinish.

Historyof s-AxisMachines

common MisconceptionrI don't ilo enough S-axis work to warrant a S-axis machine.

Manyshopsare currentlymakingparts by movingthem manuallyto different fixtures on 3-axis machines.Comparedwith this procedure,productioncan be increasedgreatlywithoutmuch effort by usinga 4- or a 5-axismachine.If simplya single-or dual-rotaryindexingtablewas added,only slighteditswould be needed files.ExamDles to the CNC-code are shownin Fiqures1-5 and 1-6.

Figures 7-5 and 7-6 Third-party rotary mechanisms. Movingto multiaxismachiningrequiresthinkingin spaceinsteadof in a flat plane. Dedicatedmultiaxismachineshave beendevelopedfor the kind of indexingwork Figures1-7 and 1-8, usingtombstonetype fixtures. shownin the accompanying

Figure 7-7 Example of tombstone fixture. Secretsof s-Axis Machinino

Figure 7-8 Example of 4-axis positioning. Onceyou enterthe multiaxisrealm,new doorswill be openedfor your shop.your companywill quicklybecomemore adeptand ableto tacklemore comDlexwork. Beforetoo long,your shopwill start takingon more and morejobs, and will need to be exoanded. Common Misconception: S-axis CAD/CAM is too expensive and is hard to use, The abovestatementswere true in the past, but not any more. If you currenfly own a CAD/CAMsystem, there is a good chanceyou already have s-axis positioning capabilities. MostcAD/cAMsystemsincludethesecaDabilities in their basepackage.Manytimes, it is just a matter of trainingthat is neededto get up a n d r u nni n g . When you are shoppingfor a CAD/CAMsystem, make sure to chooseone from a reputablecompanywith a commitmentto trainingand localsupport.Remember that a CAD/CAMsystem is just another tool in your tool belt. you can buy fancy tools that are very capable,but they are worthlessif Vou don,t know how to use them. Great localsupport may very well be the most important feature of vour new tool.

Historvof s-AxisMachines

If you do a lot of simultaneousmultiaxiswork, the price of the CAD/CAMwill be only a smallfactor.Moretrainingwill be needed,but you will be ableto charge almostdoublefor your hourlymachinetime. The'hardto use'paft alwayscomes down to training - was it easy to learn how to operateyour first CNCmachine? job. If Don'tenterthe multiaxisworld by startingwith a complex,simultaneous you alreadyown a 3-axismachine,start with a single-or dual-rotarytableand apply indexingtechniques.You will make parts faster and more accurately,and you will be ableto investin more equipment.Whenyou decideto buy new equipment, see if you can bundlea CAD/CAMpurchasewith the machine'spurchaseorder. This is also a good time to make sure your CAD/CAMsystem speaksyour specific machine'slanguage- in other words, that it has the correct post processor. Somecompaniesbuy equipmentwith a turn-keysolution,whichensuresthat their specificjob will run on the machineupon deliveryfrom the manufacturer.Many engineers,who in machinetool buildersemploycapableteamsof applications turn, work closelywith CAD/CAMdevelopers,Together,the teams determinethe most efficientway to machineany specificpart, basedon many factors such as; and toolingavailability. material,quantity,tolerancerequirements,

Reasonsto Use Multiaxis Machines Reduced Set Up work One important reasonto use multiaxismachinesis to reduceset-up time for parts such as those shown in Figures1-9 and 1-10. Extra custom fixturing for secondary operationsis very costly and time-consuming.Most parts can be manufacturedin one or two set-ups, eliminatingthe need for extra fixturing and time.

Figure 7-9 Example part requiring positioning multiaxis machining. Secretsof s-Axis Machining

Figure 7-7O Part requires two separate set-ups for machining. Accuracy Everytime you move a workpiecefrom one fixture to another,there is a risk of misalignment- either during the set-up itself or during operation.It is easy to build up (stacked)errors betweenmachinedsurfaceswhen they are milled in multipleset-ups.The use of indexingrotary tables, or dedicatedmultiaxis machines,as shownin Figures1-11 and 1-12, allowsprecisemovementof short, rigid, high speedcutters for the best cutting engagement.More aggressivecuts can then be taken, with higher RPMand feed rates, while the highestlevelsof accuracy are maintained.

Figurc 7-17 Dedicated dual-rotary machine set-up. Historyof s-AxisMachines

Figure 7-72 Dedicated dual-rotary machine set-up. Better Surface Finishes Usingshortertoolswill causelesstool deflection,whichwill minimizevibrationand producesmooth, precise,cuts. When using ball-nosecutters it ls recommended that the contact point be moved away from the tip of the cutter that isn't spinning. By tiltingthe tool, as shownin Figures1-13 and 1-14,the workpiececan be engagedby a desiredcutter area, which will not only improvethe surfacefinish and repeatability,but will also greatly improvetool life.

Figures 7-73 and 7-74 Machiningparts such as fhese requires simultaneous cuttino motions.

10

Secretsof s-AxisMachining

Open New Possibilities some partsare impossibre to cut on a 3-axismachine.other partswourdtake too many set-upson a 3-axismachineto be profitable.Onceyour shopgets comfortable with indexingwork, you will be able to start machiningpart; suchas thosein Figures1-15, 1-16, and 1-17, usingsimurtaneous murtiaxismotions,and openyour buslnessto many new possibilities.

Figures 7-75, 7-76, and l-t7

More examples of parts that require simultaneous cutting motions.

A word of caution: Simultaneousmultiaxiswork is inevitablyJess accuratethan indexingwork becausethe machinemust be run in a loose mode with the rotary drives unlocked.It is recommended that all possibleroughingoperationsbe done by indexinqthe rotariesto optimum angles,becausethe machinein lockld mode is much more rigid.This type of work is also called2+3 machining.The two rotary axes are first positionedand locked into the optimumattack position,then a standard3-axisprogramis executed.

Historyof s-Axisl\ilachines

11

Know Your Machine Whatdo you picturewhen you see the words"standards-axismachine?,, lvany industrybuzzwordsare usedwhen describings-axismachines.Someof them include:staggeredgulde-ways,constantdynamiccontrol,digitalAC servomotors with pre-tensioned permanentpositioningmonitoringsystem,maximum ball-screws, utilizationlayout,long-termaccuracy, and so on. To simplifythings,we will say that thereare three major buildingblocksto thesetypesof machines.

The physical properties of the machine The physicalpropertiesof the machinedescribethe wav tne axes are stacked,the rigidityand flexibilityof the iron,the horsepower, torque, and maximumRPMof the spindlemotor,the qualityand workmanshipof the guides/slides, and the rotary bearings. The CNCdrive system The drivesystemis the musclesor the components that makethe machineslidesand spindlesmove.The systemincludesthe servo motors,drivesystem,ball screws,the way positioningis controlledand monitored,and the rapid-traverse and feed capabilities. CNCcontroller capabilities The controlleris the brainof the machine.Data handling,availableonboardmemorysize,and dynamicrotarysynchronization controls,are someof the thingscontrolledhere. The perfectcombination of the abovecharacteristics will builda fast, accurate,easyto-programand operate,s-axisCNCmillingmachine.lvanymanufacturers have spentmany yearstryingto come up with the perfectcombination, and as a result there are manVvariationsand solutions. The lllustrations in Figure2-1 showsomeof the varietythat existsin the machines that make up the CNCmanufacturing industry.

13

Figure 2-7 Typical arrangements of multiaxis CNCmachines.

Multiaxis Machine Configurations The arrangementsshown in Figure2-1 are all very popularconfigurations,but none of them is "standard."There is no such thing as a standardS-axis machine. First, let's establishthe definitionof an axis. Any motion controlledby the NC controller,either linear or rotationalis consideredan axis. For instance,in the iflustration in Figure2-2, both the spindleheadand the quill are capableof moving in the same direction,but are controlledby two separatecommands,Movementsof the head are controlledby Z and those of the quill by W.

TU

Figure 2-2 The spindle head and the spindle quill move along parallel axes. 14

Secretsof s-AxisMachinino

The terms multiaxisand s-axisare often usedinterchangeably and theseterms can be confusing.The widelyrecognized term in the industryis 5-axis,but it is misleadingbecauseg-axisstandardpossibilities exist - withoutaddingadditional sub-systems. In addition,a 4-axismachineis alsoconsidered to be a multiaxis machine.Despitethe title of this book,the more accurateterm multiaxiswill often oe useo. The followinglist providesthe industrystandardnomenclature for the basicg-axis designationsand directions.

XYZ are linearaxeswhereZ is alignedwith the spindleof the machine. ABC are rotary axes rotating aroundXyZ respectively. UVW are parallellinear axes along XyZ respectively.

KnowYourMachine

15

Unfortunately,different machinebuildersabide by this standardin differentways. Some buildersallow the end user to changethe machine'srotationaldirections or behavioron the fly. Third-party rotary devices,as shown in Figure2-3 and elsewhere,can be purchasedand mounted on a machinein a variety of ways, The end result of this flexibilitycan causetwo machines,of the same make and model, to have completelydifferent S-axisbehavior. Everymachineis a compromiseof some sort. Rotationaldirections,start positions, and limits, will be differentfrom one machineto another.The effectivework envelopeis greatly modifiedby changingthose variables,Some rotary axes can rotate in both directions.Some axes will choosethe rotary directionbasedon the existingposition- shortestdistanceversus clockwise(CW) or counter-clockwise (CCW).Some machinesthat are equippedwith dynamic rotary fixture offset mode will move the linear axis while rotating the rotary one basedon a rotary command. To understandthese machinescompletely,it is necessaryto look at every machine as a uniqueentity, to look under the skin and understandhow the skeletonis constructed,You need to know where all the joints are, where the rotary axes are, where the rotary zero positionsare, what makesthem move, and how the whole unit functionsin unison. Differentmanufacturersand CAD/CAMsystemshave many different namesfor the same things. Let's establishsome commonterms that will be used in this book in order to avoid assumptionsand confusion. Machine Home Position (MHP) - Most machinistsrecognizethe home position as the placeto whichall the axes movewhen you initiallyturn the machineon and selectZero return.

Figure 2-3 Machineat Home PositionX0. Y0. 20. A0. 80. 16


MachineRotary Zero Position (MRZP)- On multiaxismachines, machinerotary zeroshownin Figure2-4, is at the intersection of the rotary/pivoting axes.This pointmaybe unreachable by the machine.

Figure 2-4 Close-upshowing MachineRotary Zero position. lrogram Zero Position (PZP) CAMsystem.

- programZeropositionis the part datumin the

Figure 2-5 Another view showing the relationship between Machine Rotary Zero Position and program Zero position.

KnowYourMachine

17

Whensettingup/ operating/and programmingmultiaxismachinesit is essentialto maintainthe properrelationship betweenthe machinezero position(MRZp) and the programzero position(PZP). If the machinedoesnot havespecialfeaturesthen the PZP must coincidewith the MRZP. lYultiaxis millingmachinescan be organizedfurtherinto 3 major machinetypes:

Table/Table multiaxis machines execute the rotary motions by the dual rotary table, The primary rotary table carries the secondary rotary table, which in turn carries the fixture and the part. Head/Table multiaxis machines execute the rotary motions by the table, which carries the work piece, The spindle head articulates the tool with tilting motions. Head/Head multiaxis machines execute all rotary/pivotang motions by articulating the spindle head of the machine, The work piece is stationary.

Keepin mind that the focusof this book is milling,althoughthe line betweenthe mill and the latheis blurringmore and more everyyear.Thereis a new breedof multi-taskingmachinesavailablethat can do millingand turning,and thoseare calledMill/Turnmachines. Forthe sakeof simplicity,we will focusonly on multiaxismillingmachines.

Table/Table Multiaxis Milling Machines Table/Table multiaxismillingmachinescan be vefticalor horizontal.All the rotarymotionsexceptthe spindleare done by the tablesof these machines.The main rotarytable carriesa secondrotarytable,as shownin Figure2-6, to whichis fastenedthe fixtureand the Dartto be machined. Toollengthoffsetswork the sameway hereas with anv conventional 3-axis machine.The tool lengthcan be changedwithoutthe needto re-postthe NCdata. On thesemachines,the part is physicallyrotatedaroundthe tool. The machine's rotarydevicesneedto be capableof handlingthe weightof the part and the fixture,and this capabiiityis an impodantfactorwhen rapidmovementsare considered. Anothervariationis seenin Figure2-7. The examplesshownrepresentonly a smallfractionof the availableTable/Table variations.Mostof thesemachineshaveminimumand maximumrotarv limitson 18


oneof the rotaryaxes.somewill haveunlimitedrotary motionon the otheraxis. Someevenhavethe capabilityto spinthe work,as a lithe woutd. Table/Table machinesare the mostcommontypesof murtiaxismachines.Most peoplewill enterthe s-axisworldby purchasing-a single-or dual-rotarydeviceand boltit to their3-axismillingmachine

Figure 2-6 Simulation of a dual rotary mechanism fastened to the tabte of a standard 3-axis CNC milting machine.

Figure 2-7 A third-partyrotary mechanismfastenedto the tabteof a standard 3-axis CNCmilling machine.

KnowYourMachine

19

Figure 2-8 Third-pafty single rotary mechanism and tailstock, fastened to the table of a standard 3-axis CNC milling machine. After machiningone side of the work piece it is possibleto index the rotary unit to machinethe secondside, and so on. This type of work is called indexingor positioningwork. Some manufacturersuse specializeddual rotary mechanisms. such as the one shown in Figure2-9, which is designedfor machininginternal combustionenginecomponents.

Figure 2-9 Specializeddual rotary mechanismusedin enginemanufacture. 20

Secretsof s-Axis Machining

Dedicated Table/Table machinesare very capableof doingindexing/position ing work and are equarrycapabreof simurtaneous work. The inherentdiflerences betweenthe two are worth mentioning. The rndexing method hordsthe workpiecemuch more rigidrythan it is herdfor simultaneous machiningwork becausethe rotaryaxesare-rocked when machining. when rotatingan axis,the rotaryaxis must firsl be unrockedwith a designateJ M-code.The axis is then rotated,and it is rockedwith anotherM-Codeb-efore machiningis resumed.This sequenceallowsmachiningto be done in the machine,s most rigidstate. when usingsimurtaneous mi||ingtechniques, aI the brakesmust be disengaged, whichwill put the machinein its roosemode.Forthis reasonit is arwaysu g-ooi ideato use (when possible)indexing/position ing millingtechniques foi roujhing cuts.

Machine Rotary Zero position (MRZp) Commonly,MRZP representsthe intersectionpoint of the rwo rorary axes, althoughsometimesthe two rotaries may be offset by a specificdisfance.This distancemust coincideor be relativeto the part datum pZp (program Zero Point) of the CAMsystem. To accuratelyset up, operate,and programthesemachines,it is necessary to find the intersection of the rotarycentersof the machineaxes.some. but not ali, manufacturershave the varuesstampedon their rotary devices.However,those numbersare not to be trusted,and must be recalibrated regularly.

Finding the precise center of rotation is the foundation of accurate work.

Evensmalldiscrepancies will magnifyerrors.furtherawayfrom this machinerotary zero point.

KnowYourl\.4achine

21

Here are the steps to be taken: 1. Level the table by "zeroing" the indicator on either side of the table, as shown in Figures 2-1O and 2-11

Figures 2-7O and 2-77 Method of checking the level by dial-indicating both sides of the workholding table

Figure 2-72 Setting the dial indicator to zero before checking the level of the table.


2. Find the XY zero, using the dial indicator, Zero xy and A at this point, as shown in Figure 2-13,

Figure 2-73 ZeroingXY and A positionson the work-holdingtable. 3. RotateA+9O degrees and touch the OD of the table as shown in Flgure 2-t4,

Figure 2-74 After rotating the A axis through 90 degrees, touch the outside diameter of the table with the dial indicator.

KnowYourMachine

4. Rotate A-axis through 18Odegreesfrom the previous position and make sure the indicator reads zero on the other side.

Figure 2-75 After rotating the A axis through-90 degrees,touch the outside diameter of the table with the dial indicator' 5. Move the Z-axis in minus direction the radius of the rotary table and set up a gage tower. The gage tower is used to set all the tool length offsets

to z=o.

Figure 2-76 A gage tower is built to represent the MRZPto allow tool length offsetsto be set. 24


This location is the machine's rotary zero position (MRzp), as illustrated in Figure 2-17,

Figure 2-77 The rotary zero position of the machine, as establishedby the outlined procedure. Note that the intersectionof the dual rotary center lines is abovethe table in the examplegiven.This locationwill be differentfor every machine,even from the same manufacturer.It is imperativethat this positionbe checkedregularry, especially aftera heavyworkloador a crash,Smallmisalignments can causeiarqe errors becausethe tool positionis measuredfrom this intersectionpoint. All the Active coordinate systems also referredto as Nesting positions or Locaf Coordinate Systems, for example G54 - Sg, are relativeto the Machine Rotary zero Point (MRZP) position.It is good practiceto set one of the nesting positionshere, so that it will be capturedin the Registry allowingit to be recalle-d quickly,usingMDI (Manual Data Input). F o re x a m p l ec: 9 0 c 5 4 x 0 . y 0 . A 0 . c 0 .

The PZP(Program Zero point) of the CAMsystemsmustbe set exac v to the MachineRotary Zero point, as seenin Fiqure2-19.

Know Your Machine

Figure 2-78 Relationshipbetween the MRZPand the PZP. Some CAMsystemscall this positionthe World Zero, Master Zero, or the Origin. The main thing to remember is to draw the part in the same specificposition relativeto this World Zero as it sits on the machine,relativeto Machine Rotary Zero Point.

Nesting Positions Nestingpositionsare widely used for positioningwork. These positions,shown in Figure2-19, are temporaryActive Coordinate Systems and are typically set in relationto different faces of the part or fixture face, tooling ball, or dowel pin.

Figure 2-19 Sketchshowingsomeofthe many localcoordinatesystemsusedin CNCprogramming. Secretsof s-AxisMachining

The advantageof using these Locar.coordinate systems is that you can easiry followthe programon the controller,s displaysc.eenbecausethe absojute valuesshown there will reflectthe valuesrelativeto each locally-nestedposition. Z+1.000,for examplewill be 1.000(inch)abovethe part face. Despitethe fact that cAM systemsa use different naming conventionsfor their coordinatesystems/they alr handrethe rocarcoordinatesystemin a simirarway. Some.ofthe names used by_CAD/CAMsystems include:p'art Datum, Active Coordinate System, Local Coordinate System, System View, and Tool plane with an Origin. The disadvantageof using a number of different rocarcoordinatesystems is the potentiarfor misarignment when pickingup thesepositionsmanuairywith a dial indicator.Many programmersus_eonly _onecoordinatesystem for S_axiswort<.itrey usethe MachaneRotary zero point (MRzp) as the pirt datum and ret either the cAN4system or the machine'scontroler carcuratethe speciarrou"r"nt. nui"iruiy. If a part is placedin the same positionin the cAM and in the machine,the ciM i;' very capableof generatingthe correctcode. The advantageof using a singrecoordinatesystem is that the part needsto be indicatedonly once.The disadvantage is that it is harderto visuallvfollowthe programon the controller'sdisplayscreen.The system will have to be switched over to Distance to Go for safer operation. using a real s-axis machineas a verificationsystem is inefficient,cumbersome, -' and very dangerous. Thereare many machinesimulationsoftwaiet;.k;&; availablethat can savea rot of time and money,and theseare coveredin another chaDter.

Rotary Table Dynamic Fixture Offset The Problem cAM generates,code for a given positionof the programzero point (pzp) rerative to the centerof rotationmachinezero point, (MRZF). The machineoperito,.may th: c.ogglater,on the night shift, at a differenttocationApZp (Actual part lun Zero Point). He or she may not be able to placethe part exacflywhere the CAD/ cAM programmerintendedit to be. If the operatordoes not havethe accessor tire abilityto make the change,then the job wiri haveto wait for a repostedcodeto be supplied. ModernCAD/CAMsystemscan easilycalculatenew code if the part is moved. But as previouslymentioned,the part will have to be moved to exacflythe same positionin the cAM system and then the code wil have to be recarcurited. The Solution If the operatordoesn't have accessto the cAM system/ and is unableto match the cAl4's part positionon the machine,an option on the machinewi[ be needed to compensate for the discrepancy betweenthe two positions.This optionis called KnowYourl\y'achine

Rotary Table Dynamic Fixture Offset (RTDFO). When the Rotary Table Dynamic Fixture Offset function is activatedon the controller,the Program Zero Point (CAM datum) is offset to correspond with the set fixture offset amount, as shown in Figure2-20. This offset is the distancebetweenthe center of rotation (MRZP) and the Part Zero Point (PZP) and it must also take into accountthe angle of the rotary table. This function is convenientbecausemultiple-facemachiningcan be executedby setting one point as the referencewhen machininga complexworkpiece.

Figure 2-2O Potentialproblems in establishingthe rotary table dynamic fixture offset (RTDFO). Thereare 2 wavsto use RTDFO: 1. Set the fixture offset amount manually on the Fixture Offset screen of the machine,illustrated in Figure 2-21,

28


reyE (oFFSET) E-1grylo1selection --+ IFIXTUREOFFSETI

Figure 2-21 A Fixture Offset Screenon a CNCmachine. 2. Specify the values in the machining program (G-Code). The fixture offset amount is the distancebetweenthe rotationaicenter (MRZp) and the workpiecezero point, used by the CAMprogram as the programZero (PzP).

GlO L21 Pn X_Y_Z_B_C_ n

Fixture offset number (1_g)

X_Y_Z_B_C_

Fixture offset amount for each axis

When usingthe c90 mode/the specifiedvaluesare set. Whenusingthe G91 mode,the sums of the specifiedand the previousvaluesare set.

KnowYourlvlachine

29

ActivatinoRTDFO: G54,2 Pn;

RTDFO- ON

G54,2 PO,

RTDFO- OFF

Fixture offset number (1-8)

n

The G-Codebelowshowsan examDle: 00001 { P,ROGT?Ar, ZERO ) ( D]TE A2 ]i A7 TINE G21 c0 G17 G40 cac c90 G94 G9a

00001 { P.eoGr?Ai,- cLoNE2 ) ( DA?a O2-i1-07 TIME A7:22 )

07:22 )

G0 c17 G40 G80 G90 c94 G98 c28 XO. YO, BO,

3) D.aa. oii. I rooL ( G13.4 G5 Pl0O00 ) T3t M6

- 3.1

,,rN_

3)

Dra.

c90 Go 2500. s0. co_ c 43 . 4 ! 3 1 2 2 s 0 .

( laoL 31 Dra. a!F. ( c43.1 G5 P1A0O0 ) T3t M6

3:L

LEN-

31

G54

090 60 2s00. B0. c0. c 43 , 4 f l 3 1 2 2 5 0 . G05 P10000 G54

M69

M69

c90 G0 x13?.043 y3.53? C-31.266 818.001 St'ttat t\13

G 9 0 G 0 x l 3 7 . 0 S 3 v 3 . 5 3 7 c - e l . 2 6 6 8 1 E . 0 8 1 s L 0 a i : ; ar ' 1 3 2 1 8 8, 4 ? l 2 9 ' . .j 4 1 1 Gt 244.471 ?2n14. x135.846 y3.258 ZA3.??5C 41.64 814.209 Fri0trC_ x , L 3 4 , 6 3 9y 2 . 9 2 3 2 8 ! . 0 3 ? C - e 1 , 9 9 7 B 1 8 , 3 2 3 tt33.464 v2-526 2a9.244 C-32.331 B18.4!3 x l 3 2 . 3 2 1 y 2 . 0 6 1 z A 9 . i 3 s c 3 ? . 6 3 9B 1 3 . 4 7 6 x130.983 y1.606 ZA9.?33C 82.946 B13.652 . A 1 2 9 . 4 61 7 , 3 4 2 2 9 0 . 4 2 4 C - 8 3 . 3 1 5 8 1 8 . 9 3 4 xt21.722 r1.54 291,:24 C-83.869 819.31. tL2a.73a v2.796 292,504 C-S1,591 B19,874 tr24.061 v3-421 29t.492 C-45.439 824.334

293.4 ,-1 G 1 5 3 3 . 4 r 7 F : ' : 0r . . . , 1 3 5 . 3 4 6 y 3 . 2 5 3 2 8 3 , ? ? 6 C 3 1 . 6 4 A 1 3 . 2 0 9F ; 0 0 D . " < t 3 4 . 6 3 9v 2 , 9 2 3 ? 8 9 - 0 3 ? C - € 1 . 9 9 ? 8 1 9 , 3 2 4 x133.464 y2.526 289.:,!4 C-82.331 818.413 xt32.321 12.061 239-335 c 32-639 Bla.4t6 x l 3 0 . 9 8 3 y l . 6 0 5 2 3 9 . ? 3 4C 3 2 - 9 4 6 8 1 8 . 6 5 2 r1,29.46y1-382 290.424 c 83.335 816.934 x!2).122 y7,54 ?91,324 C-83,869 319.316 x125.t38y2.196!92-504C-!4.591B19,€?4 x124.06? y3.421 293,492 C-E5-439B20.334

Figure 2-22 Example of G-Code data for setting RTDFO. If the machinedoesnot havethe optionmentionedabove,the CADgeometrywill haveto be moved,and the G-Codere-postedin the CAMsystem. Notethat the aboveexamDleis for Fanuccontrollers. Othercontrollershavea varietyof namesfor this and similarfunctions.

30

Secrets of s-AxisMachining

Head/Table Multiaxis Milling Machines As their name suggests,these machineshavea rotarytableand a tilting head.

Figures 2-23, 2-24, and 2-25 Example of Head/Table multiaxis milling machines, which have rotary tables and tilting spindle heads.

KnowYourl\y'achine

Head/Table machinesare arguablythe most capableof the three groups illustratedand can machinelarge,heavyparts.On some machines,the rotarvtable can be supportedby a steady rest and it rotatesthe paft only around its own axis. The pivotingspindleheadcarriesthe weightof the tool. It needsto be capableof handlingthe cuttingpressuresas it is manipulating the tool. Thesemachinesare also well suitedfor both indexingand simultaneous work. Some havethe capabilityto calculateaxis substitutioninternally,enablingthe user to programparts in the 2D flat planeand then wrap the planearounda specified fourth-axis diameter, How does axis substitution

work?

Axis substitutionis shown in Figure2-26, and is effectedby the following orocedu re. lYeasure the A-axisdiameterand multiplyit by pi to find the circumference. Drawa rectanglewherethe Y side is the circumference and the X side is the lengthof the part. Createthe cuttinggeometryinsidethis rectangle. Createa 3-axis toolpath, XYZ, and activateaxis substitutionby first defining the A-axisdiameter. On a Bostomaticcontroller, for example,this resultis achievedby addingtwo lines of code. G25 A3.OOO

A-axis diameter

G131

Axis substitution Y to A active

Figure 2-26 A part produced by means of axis substitution. After these blocksare read, all Y-axismoves will be replacedby instructionsfor A-axisrotarymotions.If the machinedoesn'thavethis capability, this same processcan be achievedwith any modern CAD/CAMsystem. The rotaryaxeson thesemachinesusuallyhaveunlimitedrotarymotion.Some machinescan evenspin the workpieceas in a lathe.The secondarypivotingaxis has an upperand lowerlimit. In orderto accuratelyset up, operate,and program 32


these machines,it is necessaryto find the intersectionof the rotary and the pivotingaxes. Some examplesof machinesat the Zero positionare shown in Figures 2-27, 2-28, and 2-29

Figures 2-27, 2-28, and 2-29 Examples of machines with spindles at the zero Dosition, Notethat withoutconsidering the tool, all these machinesalignthe spindleface with the center of the rotary axis while the pivotingcenter point is some distance away from center.This distanceis commonlycalledthe Pivot Distance. The Gage Length is the distancefrom the spindleface to the tool tip. The sum of the Pivot Distance and the Gage Length is the Rotary Tool control Point (RTCP), which has to be triangulatedfor every s-axis positionof the toolpath.Figures2-30 and 2-31 show examplesof B90 rotation with and without RTCP.

Figure 2-3O Example of 890 rotation without RTCP,and Figure 2-37 890 with RTCPactive. KnowYourMachine

The machine'slinearaxesalso haveto movealongthe X and Z axes in orderto keep the tool tip stationaryin spaceas it executesthe pivoting B90 motion. CAM systemswill makethe necessarycalculations during"post processing.,,Some machineshavethe abilityto calculatethe necessarymotionsautomatically, based on the offsetsshownin Figure2-31, capturedin the machinecontroller,s reqistries.

PIVOT

= TANCE

COMPOFFSET

rbor-rr'rerrt

Figure 2-32

Multiaxis offsets.

Fanucexamole: G43.4, G43,5 s-AXIS ROTARYTOOL CENTERPOINT CONTROT(RTCP) If the Rotary Tool Control Point (RTCP)function is used in the Fanuc program,the spindlepositionis automaticallyadjusted in synchronywith all rotations,as shown in Figure2-33 and the listed code lines beneaththe figure. As a result, the relationshipbetweenthe tool center point and the workpiecewill alwaysstay fixed.

34

Secretsof 5-Axis lvlachining

Prog.am-Specifed

between the tool center point and the workpiece stav constant, G90 G54 c00 x0 Y0 B0 cot S-MO3; G00 G43.4 Z_H_; X_Y_B_C_t

G49; G43.4 . . . x,l ,z,

Toolcenter point function (Type 1) ON

(G90) The coordinatevalueof the end pointof the tool . . . center movement (G91) The travel amount of the tool center (G90) The coordinatevalue of the rotary axes end point

B,C . .

(G91) The travel amount of the rotary axes H . . . c49 .

Tool length offset number .

Toolcenter point control function (Type 1) OFF

Example: G90G00G54x0, Y0.80.

C0.;

. M o v e sX , t ,

B, C to PzP

s5000M03 G43. 4 zL . H01; . Activate RTCP. Positionsthe tool tip at Z+ 1.000 while Z axis positionis offset by offset data set for tool length offset number 1.

Know Your l\y'achine

Some Head/Table machineswill use both RTCP(Rotary Tool Control Point) and RTDFO(Rotary Tool Dynamic Fixture Offset) simultaneously.While RTCPis offsettingthe tool positiona combineddistancefrom the head'srotary point (pivot distance+ gage length), RPCP is compensatingfor the relativedistanceof the part from the MRZP (Machine Rotary Zero Point) to the actual fixture position. If the machinedoesn't have RTCP,to avoid repeatedre-postingwhen tools are changed,it is common practiceto pre-set all tools to the same length when Dossible.

Head/HeadMultiaxisMilling Machines All the rotary/pivotinomotions are executedby the spindlehead of the machine. These machinescan be both verticaland horizontal,and they have limited motion. Some machinescan changeheads,not just tools. Headscan be straight, g0-degree,nutating,or continuously indexing.Someexamplesare shownin Figure z- 5+.

Figure 2-34 Examplesof Head/Head machines. 36


All Head/Head machineshavedifferentbehavior;basedon indlvidualinstallation settings.Rotarydirections,limits,retractions,rotarywind-up,and handling singularitiescan all be alteredfrom factory settings.The most impoftant basic dimensionneededis the rotary/pivot center pointr which is measuredfrom the spindlefaceto the head'srotaryposition.Machinemanufacturers sometimes providea nominalvalue,but it is essentialthat the manufacturer's value be double-checked/ especiallyif it is a nice roundnumber,for instance,10 inches.The roundnessis a good lndicationthat the numberis not accurate. "Close" is not good enough. Knowing the exact dimension is vital if precision work is to be done.

Finding the Pivot Distance 1. First,makesure that the machinehead is in a perfectverticalorientationby touchingthe machine'stable with a dial indicatolthen rotatingthe indicator. The indicatorshouldreadzeroaroundthe wholecircleas shownin Fioure 2-35.

Figure 2-35 Indicating vertical position. 2, Placea 1.000diameterdowelpin into the mastertool holderwith a known Gage Length (GL). 3. Touchthe dial indicatorplungeras shownin Figure2-36. A flat attachment helpshere.Set the indicatorto zeroand recordthe Z valueon the controller's screen.Let'scallthis valueZ maximum.

KnowYourl\,4achine

37

Figure 2-36 Touching the dial indicator plunger is eased by having a wide, flat top on the plunger. Do not move the machineon the X axis. Moveonly on the Y and Z axes. Move to a safe point on the Z axis, and rotate the A axis through 90 degreesinto a horizontalorientation.Next, move on the Y axis in the plus and on the Z axis in the minusdirectionsuntil you get to the positionshownin Figure2-37.

Figure 2-37 Z minimum position. Recordthis Z valueon vour controller's screenand let'scall this Z minimum.

38


Youshouldhavethe followingvalueshandy: Z maximum Z minimum GL - Gage Length R - Dowel pin radius = .5OOO Formula to calculate Pivot Distance: PD=Zmax-Zmin-GL+R

This distance(PD). will be used by the post processor.Most CAMsystemswill drive the Pivot Point and they will have to calculatethe tool tip locationfor every programmedposition.The tool tip locationis the Pivot Distance plus the Gage Length away from the Pivot Point at all times, and must be triangulatedbasedon the rotary/pivotingangles.Evensmall discrepanciesin the Pivot Distance will be magnifiedinto largetool positionerrorsin the final program.

4-Axis Machines If a third-pafty,singlerotary mechanismis placedon a 3-axismillingmachine,it becomesa 4-axismachine.The most oopulardedicated4-axismachinesare the horizontaltypesshownin Figure2-38.

Figure 2-38 4-axis horizontal machining center.

Know Your Machine

Thesemachinesare mostlyusedfor tombstonework, wherepartsare clamped to all sidesof the tombstonefixture and machinedby rotating them into different positions, The chipsdon't collecton the work-piecebecausethey fall away by gravity and are cleanedoff by strategically-placedcoolantnozzles. The examplein Figure2-38 showsa palletchanger,whichis positionedoutsidethe machine'senclosure,allowingthe operatorto loadworkpieces and unloadfinished partsduringthe machinecycle.Elaboratepalletchangerassemblies are also available,with multipletombstoneson whicha varietyof differentjobs can be preto a loadedand made ready-to-run. This arrangementallowsfor quickchangeover job new withoutstoppingthe machine.

General Maintenanceand Issues for Multiaxis Machines It is recommended that all machinetoolsbe kept cleanand free of objectsthat can causedamage,and this rule is even more importanton s-axisequipment. Realigning routinesshouldbe done at regulartime intervals,and most certainly after heavywork, overloads,or a crash,A log shouldbe kept of the machine'svital statisticsand operatorsshouldbe instructedto listenfor any new soundscoming from the spindle(s)or rotary mechanisms. Somecommonoroblemsinclude: .

Sometimesthe rotary brakeswill fail and they won't disengage,The rotary mechanismwill then work extra hard to rotate from positionto position,and if simultaneous work is in hand,the unit will eventuallyfail.

.

Somedual rotarytablecenterlinesdo not intersect.Someof theseapparent discrepancies are by design,as shownin Figure2-39, and some are not. If the apparenterror is by design,it is usuallya largenumberthat can be seenby It must not be assumedthat eye. If it is not by design,it won't be noticeable. can be the centerlines are in line,and they must be checked,Misalignment compensatedfor by inputtingthe relevantvalue into the post processor,

Figure 2-39 Example of rotary mechanismsplaced in offset positions by design.

40

Secretsof 5-Axis l\4achinino

Figure 2-4O These rotary mechanisms appear to be intersecting. Some Head/Head types of machineswill not run true. To checkthis aspect, arrangethe machinewith the secondaryaxis pointingdown verticallyas shown in Figure2-41. Then, rotate the primary axis through 360 degrees.The dial indicatorshould read zero throuqhoutthis motion.

KnowYourMachine

41

Figure 2-47 Indicating run-out. The machinetypes describedin this chapter are built by many different machine buildersin a variety of sizes,shapes,qualities,and prices.The quality of a machine will be best highlightedwhen fast. simultaneous, multiaxismotionis beingused. A good-qualitymachinewill executethese motions quickly and repeatedly,in a smooth synchronizedway, without one rotary axis waiting for anothel and without backlashor vibration.The rotarymechanisms will haveminimalrun-out,and the rotary centerlineswill align precisely.Cheapermachinesmay execute positioning movementswell, but will executesimultaneous motionspoorly. Many manufacturerswill list "positionalrepeatability"in their specificationsbecause it is a good measureof the machine'squality.One way to do a quick check of repeatability is to set up an indicatoron the machinetable,engagingthe tool holder at zero.Then a ten-minuteroutineinvolvingall the machineaxeswith multiple rotationalmoves should be executed,terminatingwith returningto the start Dosition.The indicator'sreadout retativeto zero is the measurementof the Dositional repeatability. It is not necessaryto buy the most expensivemachine,but only to take a good look at current and potentialfuture needswhen consideringpurchaseof a multiaxis machine.

42


Milling Machineswith Five or More Axes lVostmachineswith more than five axes are built for specificmanufacturing applications,Some examplesincludethose shown in Fioure2-42:

Figure 2-42 Some examples of more than s-axis machine designs, It is possibleto assemblemultiple 9-axis subsystems,and some manufacturers have built machineswith over 100 axes. Many of these axes are part of elaborate work-holdingsystems,and have parts that need to be rotated out of the wav of other machinecomponentsduring some manufacturingprocesses.Many such machinesare controlledwith dedicatedM-codes,which activate pre-set subroutines.

KnowYourMachine

E A simpleexampleof sucha subroutineis an M06,whichcausesa tool change. Observecloselywhat happenson any machinewith an automatictool-changer: the machineslidestravel to pre-determinedlocations;the tool-changecarousel advancesthe chosentool; a little trap door may open, dependingon the machine;then a swing-armwill exchangethe tool betweenthe spindleand the carousel. This whole choreographyis just one of many internal macros,ready to be activatedby a simple code like M06. On multiaxis machines,many more of these internal macrosare available.Most of the time, the macrosneed to work in svnchronization,

44


Cutting Strategies If drawingsof the same multiaxispart were givento five differentCNC programmers,chancesare good that they would come up with five different methodsto machinethe part. This variabilityis a productof experience,available multiaxisequipment,availableCAD/CA[4 systems,tooling,fixturing,material,and quantities. What doesevery CNCprogrammerdo when askedto write a programfor a new part? He or she will createa mental imageof the part, and basedon the above factors,go througha varietyof differentscenariosto determinehow to machine it. Thesedecisionswill includehow to hold the part, and whichsideto start on. The programmerwill then mentallygo throughthe whole processof removingall the excessmaterial from the starting stock in order to free the desired part from within it. Mostprogrammerswill brainstormrepeatedlyand come up with multiple solutions,eliminatingthe weakestones,addingnew ideas,and then makingthe final decision.This whole processhappenslong beforethe creationof the actual toolpath.This pre-workmeditationis the singlemost importantpart of the whole manufacturingprocess. The processdescribedaboveis the same,whether3-axisor multiaxiswork is beingconsidered. The big differenceis usuallywith the fixturing.Work holdingis amongthe first decisionsto be made when programminga 3-axismachine.Many multiaxisprogrammerswill placethe part data on a virtual machine.This process lets them levitatethe part in the air and simulatethe machine'smotions,without a fixture present,to see if all motionsare possiblewithoutviolatingthe machine's work envelopeboundaries. The part will be movedin spaceto achieveoptimized, synchronized motions.Finalfixture placement,or design,might be one of the last steps, Of coursethis procedureis not alwayspossible,but when a fixture is predetermined, additionaleffort will be neededto make sure there are no collisions betweenthe fixture,tool, shank,arbor,or tool holder.Avoidingcollisionsis a big part of multiaxisprogramming.Collisionscan occurnot only duringcutting,but also duringtool changes,palletchanges,or manualretractionmovesafter an abrupt programstop. Forexample,after a powerfailure,the tool couldbe in a positionwherethe onlVsafe retractionmove is simultaneousmultiaxismotions.

The singlemost importantpart of mu tiaxis programmingis the initialtime that is spenton decidinghow to tacklethe job. I\4achining sequencesshouldbe kept just becausethe shop has the latestequipment,the simple,not made complicated most powerfu CAD/CA[4 system,or an unlimitedbudget.Hereare some questions that needto be considered: How many parts are needed? How much time is available? what is the material? What machine is available? How good is the CAD/CAM system? How well do you know CAD/CAM? what tooling is available? Do you have to use existing fixtures or can you make your own? Ar€ there any special requir€ments?

Limitationsapplyto every too in the shop.The trick is to work aroundthose limitations.The differencebetweena good multiaxisprogrammerand an average one is that the good one is industrious.If one approachdoesn'twork, anotherone will be tried Lrntilthe best solLrtion appears.Regardless of the CAD/CA|4systemin use, many times extra geometrywi I haveto be createdto achievethe best resuts. Do the Prep Work in the ong run. once a The time investedin preparingthe work will be invaluabLe decisionhas been madeon how the job wil be handled,it is importantto organize the work. Divideup the operationsin the CAD/CAMsystemand move necessary geometryto easily-recognizable named layers/levels. This preparationwill make it possibleto isolateindividLral featuresand allow a focusedworkflow. Make a Tool List It is very importantto make a tool list for any job. Start by analyzingthe part geometrydiligently.Findthe smallestfillets.Measurehow much room there is betweenfeaturesto determinethe minimumand maximumtoo diametersthat can be used.Checkwhat tools are readiy availablein the shop to see if any of them can be used,especiallyif you are a readyfamiliarwith their performance.If you must ordertools,do some researchon their performanceand availability.

46

Secrelsof 5 Axis Machining

Determine Fixturing Checkon availablefixtures,vises,and clamps.Useexistingvisesand fixtures wheneverpossible,to keepthe costsdown. The equipmentshouldbe modeledin the CAD/CAMsystemand organizedinto librariesthat can be readilyaccessedand loadedfor virtual simulationwhen checksare madefor possiblecollisions.

CompareMachines If more than one machineis availablefor the job, some comparisonsshouldbe made.Amongessentialchecksare: work envelopelimitations,maximum RPIY, feed-rates,and controllercapabilities.

Know Your Stock Options l'4aterial stocksmust also be considered.If the materialis unfamiliar,some researchwill be neededon differentcuttingcharacteristics. The originalform may be a billet,a cylinder,a casting,or a forging,and may requiresome preparatory work beforemachiningcan start.

CuttingStrategies

Indexing Multiaxis Toolpaths Set-upsusing indexingor indexedwork are rigid and precise.Other common names usedfor such set-upsare 2+3 machiningor positioning,and fixed rotary work. With indexingwork, the rotary/pivotingaxes are used only for positioning,and cutting (machining) takes placewith only the three linearaxesmoving,Indexingwork is the "bread and butter" of the multiaxismachiningindustry.Many parts are massproducedby this method, and it is the most basicmultiaxisconcept.It is an easy transitionfrom multiple set-up, 3-axis work to a single set-up indexingone, The graphicsin Figure4-1 show how one part can be cut from many differentangles without being removedfrom the fixture.

Figure 4-7 Images showing how one part can be cut from many different angles, without being removed from the fixture.

49

Figure 4-7a Images showing how one part can be cut from many different angles, without being removed from the fixture.

Figure 4-2 Part of an aircraft landing gear machined with an indexing set-up.


The conceptmay be simple, but it allows for the manufactureof very complex parts with precision,like the samplesshown in Figures4-2 and 4-3.

Figure 4-3 An aerospacecomponent machined with an indexing set up.

Indexing Methods There are many different indexingmethods,and they can pedormed with equipmentas simple as a manually-operated,custom indexingfixture. Third-party autonomousrotary devicesalso are available,which will executepre-programmed indexingsequencesat every cycle.The cyclescan be activatedmanuallyor through a dedicatedM-Code.If one of these methods is used, great care must be taken to synchronizethe manual operationswith the Nc-code,Ample opportunitiesexist to make a mistakewith these methods. Figures4-4 and 4-5 show two examplesof custom indexingfixtures.

Figures 4-4 and 4-5 Two examples of custom-built, indexing fixtures. IndexingMultiaxisToolpaths

5'l

The best method is to use fully-integrated. third-party, rotary devices,which will executerotary commandsdirectly from the Nc-code.For these methods,the rotary pivot center must be preciselylocated(as describedin Chapter2). Figures4-6 and 4-7 show some examplesof dedicatedthird-party rotary mechanisms.

Figures 4-6 and 4-7 Examples of dedicated third-pafty rotary mechanisms. The best approachis to use a dedicatedmultiaxismachine,if one is available. Thesemachineshave brakeson their rotary/pivotingaxes, which provideextra rigidity during cutting. Typically.these brakesare releasedwhile positioning changesare made,but oncein position,they are re-engagedso that the machine can stay in its most rigid state for cutting. Some machinesare not numerically controlledbut are capableof indexingonly in certainincrements(for example, 1 degree),and they often operate by lifting away from a serrateddividing plate duringindexing.

52


Figures4-8 and 4-9 show some examplesof dedicatedmultiaxismachine,rotary mechanisms.

Figures 4-8 and 4-9 Some examples of dedicated rotary machine components. On some machines,spindleheadscan be changedrepeatedlybetweenoperations. The examplesshown in Figure4-10 can be straight, set at a specificangle, or even adjustedsteplesslyto variousangles.

Figure 4-7O Spindle heads on some machines are designed to be straight, set at a specific angle, or even adjusted steplessly to various angles.

IndexingMultiaxisToolpaths

Othermachines,usedmainlyin the medicaland aerospaceindustries,are designed to indexand hold the part with grippingaxeswhile machining.Examplesof these types of machinesare shown in Figures4-LL and 4-I2.

Figures 4-77 and 4-12 Some machines are designed to index and hold the part during machining. Plainindexingis a very efficientway of moving parts into positionfor machining, especially when it is combinedwith pallet-cha nging.A palletchangercan be as simpleas a singlerotaryindexingmechanism.It can also be as complexas a multi-palletconveyer,with not just one, but multiplejobs, runningin a preorganizedsequence.Thesesystemsare so flexiblethat a brand new job can be introducedinto the queue without stoppingthe machinesequence,as shown by the examplesin Figures4-L3 and 4-L4.

54


Figures 4-73 and 4-74 Brand new jobs can be introduced into the queue without stopping the sequence with these pallet-changing machine designs. IndexingMultiaxisToolpaths

How CAD/CAMSystems Handle Indexing Work BeforediscussingCAD/CAMsystem applications,it is importantto establishsome core understanding of how CNCmachineswork. Priorto the inventionof CAD/CAMsystems,G-Codeneededto be generated"by job, the only hand."Indexingwork was handledjust like any other programming differencebeing that another one or two axes were sometimesadded to the mix. Most machinecontrollershave the ability to work in multiple local coordinate systems,also known as nestingpositions.These localcoordinatesystemswere, and still are, usedin a varietyof ways,One of the simplestways is to placemultiple fixtures and parts on the machine,establishthe part data for each individualpaft, and assignindividuallocalcoordinatesystems,as shownin Figure4-15.

tz

Figure 4-75 Positioning two fixtures with parts on a machine and assigning individual local coordinate systems. The aboveexampleshows only two positions.The part programswould be the same for both, except that the local coordinatesystem designationwould be provided at the beginningof the NC program (for example,G54 or G55 Fanuc).Different controllersuse different designationsfor these nesting positions,but they all work on the same principle.Dependingon the controller,numerousnesting positionscan be designated, This nestingconceptis one that many peoplestrugglewith, and its understanding is key to multiaxismachiningand programmingpractices.There are a variety of controllersand machinesavailablethat use this same concept,but they use different terminologyto describeit, 56


Machine Coordinate Systems Machine Home Position Simplyput, Machine Home Position is the centerof the machine'suniverse. Everyaxiswill travelto its Home (end of travel)positionand the machinewill stop there.At this Home position,in the machine'sAbsolute Coordinate System, all axesare reading/displayingzero. Everymovethe machineaxesmakefrom here will be relativeto this zero. Everypositioncaptured,suchas a nestingposition, will be a relativepositionin the Machine Coordinate System. Everytime a tool is changed,the machinewill go to the pre-determined positionspecifiedin this MachineCoordinate System. To establishthe nestingpositions,the first vise is loadedand checkedto make sure it is squareand securebeforeit is clampedin position.Thenthe workpieceis placedin the vise and the vise is tightenedto holdthe workpiecein place.Using an edgefinder,the centertop of the part is located,as shownin Figure4-15. The machine's absolutepositiondisplayshouldnow show how far the axesare from the Home position.This positionmust now be capturedand the machinemust be madeto rememberthis location.Machinesrememberby storingthe relative distances(from Home) in their registry.How nestingpositlonsare'captured' dependson the type of machineand controllerin use. Active Coordinate System Nestingpositionson a multiaxismachinecan be movedand rotatedin one plane. They can also be rotatedaboutthe machine'srotary/pivoting axes.

The Machine Home Position is the center of the machine's universe.


57

Figure 4-76 Multiplenestingpositionson a tombstonefixture. Therearetwo popularwaysto use nestingpositions, the first of whichis shownin Figure4-16, whichillustratesa tombstonefixturein use.Everypart datumon the Many tombstonefixtureshownhasits own localcoordinate systemassignment. programmers feelthat the arrangement shownin Figure4-16 is the bestway to usenestingpositions. Theotherway is to assignjust one centralcoordinate systemto the wholejob as shownin Figure4-t7 .

58


t/ Figure 4-77 Central coordinate system on a tombstone fixture. Both methodsare correct and it is simply a matter of personalpreferenceas to whichone is used. When it comesto machininga singleworkpiece,a preferredmethod is to use only one Active Coordinate System method, but this also is just a matter of oreference,

t

\

Figure 4-78 Central coordinate system on a single part. lndexingMultiaxisToolpaths

Usinga singleActive Coordinate System requiresthat only one positionbe indicatedon the machine.This approachsimplifiesthe processand lessensthe possibilityof error. Machine Rotary Center Point So far it has been establishedthat every machinehas its own Home Position, which is its center of the universe.Every localcoordinatesystem is a relative locationin that universe.Also, the intersectionof the rotary axis, commonly known as the Machine Rotary Center Point, is a relativelocationin that same universe. and its positionis stored in the registry.

CAD/CAMSystem Origin EveryCAD/CAMsystem also has its own universe.They all have a world zero, Master Coordinate System, System Origin, and so on. Just like machinetools, all these locationsare called by different names.One thing you can be sure of noneof them will havethe same Home Position as any other machine.The job of a CAD/CAMuserand CNCmachineprogrammeris to alignthe worldsof both the machinesand the CAD/CAMsystems. If the One Zero method - where the local coordinatesystem on the machine, which is the Machine Rotary Zero Point - is in use, it is possibleto simply match the CAD/CAMSystem'sWorld Zero with that location.The part must then sit in the same relative locationand orientationfrom the Machine Rotary Zero Point of the systemand the machine,as seenin Figure4-19.

Figure 4-79 TheRotaryZero Pointis wherethe two rotary centerlines intersect.

60


It on the otherhand,the multiplenestingpositionmethodis preferred,new Active CoordinateSystems must be createdin the CAD/CAM systemas shownin Figure4-20.

Figure 4-2O The relationship of the part zero to the Machine Rotary Zero point.

SynchronizingMachine and CAD/CAMCoordinate Systems TheseActive Coordinate Systems are the equivalentof the nesting positions (for exampleG54-59) on the machine.DifferentCAD/CAMsystemsestablishactive coordinatesin difterentways. as shown in Fig. 4-2L. For the sake of simplicity,the followingdescriptionwill be kept very general. An Active Coordinate System can be establishedby choosingan entity, such as a solid face, an arc, two lines, normal to a surface,normal along a line, or normal to a ptane,


61

,

"p{

ffe ,

Figure 4-27 Multiple local coordinate systems. one of the differences betweenprogramminga 3-axismachineand a multiaxis machineis the determination of wherethe fixtureand part will be locatedon the m a c h i n et a b l e . must be givenas to wherethe part On a multiaxismachlne,exact instructions shouldsit relativeto the Machine Rotary Zero Point. As always,a bit of preplanningwill go a long way.Avoidingcollisionsbetweentools,tool-holders, fixtures, and machinecomponents, for example,will be one of the major preoccupations. Creatingan accuratelibraryof the fixtureplates,vises,clamps,tools,and toolholdersin use in the plantwill help greatlyin avoidingthose potentialcollisions. Findthe Machine Rotary Zero Point (describedin Chapter2) for every machine in the shop,and placethe fixtureson thosevirtualmachinesin the CAD/CAIY to modelthe wholemachine,but at leastthe machine's system.It is not necessary tableshouldbe modeled.Extracareshouldbe taken that all the modelssit ln this and machine). aligneduniverse(CAD/CAM

Secretsof 5-Axis[,4achining

Figure 4-22

Complete Machine Simulation.

Dependingon the CAD/CAMsoftwareselected,it is also possibleto model and simulatethe whole machinelike those shown in Fiqwes 4-22 and 4-23.


Figure 4-23

Virtual -axis horizontal machine for simulation purposes.

It is vitallyimportantthat the "businessend" of the machinebe modeled accurately, if any simulationis to be useful,By the businessend is meantthe head, fixture, table - in other words, the parts that can actuallycollide.Simulationwill be discussedin more detail in a later chaDter.

o4


SimultaneousMultiaxisToolpaths f4anypeoplethink that simultaneous multiaxisis the true form of 5-axismachining, when in fact, it is not necessaryfor all the machineaxes to move at the same time for the machineto be considered s-axis.Evena simultaneous 2-axis,rotarycutting motionmay be considered to be a multiaxistoolDath. Simultaneous multiaxismachininqis also knownas Continuous s-axisor True 5-axismachining.

The illustration in Figure5-1 showsa 2-axismachinecuttinga patternonto a bowlingball.This machineonly has a tilting B and a rotatingC-axis.Thereis no Z axis. Instead,that motion is controlledby a softwareM code, which has an ON and OFFstate - either loweringthe tool onto the part, or lifting it to its reference Dosition.

Figure 5-7 Set-up on a 2-axis machine for engraving a bowling ball. The examplein Figure5-2 alsoshowsa simplemultiaxismotion- so simplethat it can be programmedby hand.The programcontainsthe followingcodes:

65

c01 22.0000 F90. x - 5 . 5 A 2 8 8 0 . 0 0 0 F 5 0. GOO25.

Figure 5-2 A simple multiaxis set-up.

Figure 5-3 Sketch of simultaneous cutting on a 4-axis machine -XYZA, Secretsof s-Axis l\ilachining

Figure 5-4 A 4-axis machine set-up for cutting a variable-pitch thread on an auger using motions on XYZ and A axes. Simultaneous cuttingon a 4-axismachineis shownin Figure5-3, and a set-up for cutting a variable-pitchthread on an auger using 4-axis motions XYZand A is shown in Figure 5-4. Figure5-5 illustratesa set-upon a similarmachine,combiningsimultaneous motions,and using a flywheelto producea knee-jointcomponentusing the 4-axis motionsXYZ and C.

Figure 5-5 The4-axis simultaneousmotionsXYZand C are showncutting a knee-joint, using a fly-cutter. Manypartswouldbe impossible to machinewithoutsimultaneous multiaxismotion. In.theearlydaysof multiaxis machining, manypartsweredesigned aroundmotion insteadof as freeformCADmodels.

SimultaneousMultiaxisToolDaths

An exampleis the spiralbevelgear shownin Figure5-6, whichwould normallybe producedon a specialgear-cuttingmachinein an automobileplant.

Figure 5-6

Spiral bevel gear produced on a s-axis CNCmachine.

Thisgearwas machinedwith the followingmanually-generated, motion-driven codes: o0001_ c20 c 9 0 c 0 0 x - 3 . 7 5 Y 0 .2 2 5 . B - 3 5 . C 0. T l M O6 s300M3 s3000M03 c4323.5 H1 2 3. 2 5 G 1 z 2. 9 F 2 4 0. M98 P3000 L30 c90G00225.M05 M30 02000 G91G1Z-.1E50. x2.22-.1C60.85. (4-axis simultaneous motion) x - 2 . 2 2 . 1 C - 6 0. B - 5 . M99 03000 M98 P2000 i,3 G91G002.3

zr. c72. lt-L.

M99


This last exampleis very simplistic,but with somecreativeuse of branching/looping logic.Someshopshave usedthis techniqueto producevery complexparts. There has always been a separationbetweendesignand manufacturing.Typically, paft designersare not CNCprogrammersor operators.As a result, many designs don'ttake accountof cleantool motion,or theV includefeaturesthat are hard to machineand requireadditionaloperations.In well-runshops,designersand productionengineerswork in conjunction, from the designprocessthroughto manufacturing. This is an idealsolution,but unfortunately not the norm. Working in conjunction, engineerscan savemany hoursof valuablemanufacturing time, tooling,fixturedesignand building. CADsystemshaveevolveddrastically and, as a result,it is possibleto designand manufacture ever-morecomplexparts like the examplesshownin Figure5-7.

Figure 5-7 Examplesof parts produced on multiaxis milling machines, including turbine blades and rotors, impellers, pump components, brackets, and manifold covers.

Simultaneous MultiaxisToolpaths

69

Figure 5-7 Examples of parts produced on multiaxis milling machines, including turbine blades and rotors, impellers, pump components, brackets, and manifold covers. Developingcutting strategiesfor these multiaxis parts entails more than just creatingtoolpaths.The strategy is all about control.The goal is to create a toolpath that causesthe smoothest,most efficient,machinemotion insidethe machine's "sweet spot" (the optimum work envelope),while avoidingnear-missesand collisionsbetweenmachinetool components,fixtures and holders.

The Optimum Work Envelope The optimum work envelopeis the spacein which the machine'srotary axes rotate aboutthe same diameters.The followingis an example.

70


Figure 5-8 A vertical milling machine with a trunnion-type duat rotary tabte, set up to machine a model of a human head. Machiningof a modelof a human headon a trunnion-typedual rotarytable is shown in Figure5-8. The head is high abovethe Machine Rotary Zero point, measuredalong the Z-axis, but it is very closeto the C-axiscenter point of the rotarytable, measuredalongthe X and Y axes. In programmingsuch a job, it is best to avoid creatingsimultaneousrotary cutting motionsinvolvingthe full rangeof the tilting B-rotaryaxis (-15 and +105 degrees) while the C-axisis being rotated around its axis. Doing so will create uneven motions betweenthe rotarv mechanisms.

Figure 5-9 Example of part being placed far away from MRZP. Simultaneous MultiaxisToolDaths

71

In Figure5-9 it should be noted that the B-axis move is much longerthan the C-axismove, even though the angularvaluesare the same. The reason,of course, is that the circumferencesare widely differentfor the B and C motions. Highquality machineshandlethese kinds of unevenrotary motions better than lowerquality machinesbecausethey synchronizethe two rotariesto arrive at the same point, while maintaininga constantfeedrate.CAD/CAMsystemscan also control feedratesby using Inverse Time Feedrate output. A more detailedoverviewof these controlsis includedin the Feedratessectionof this chapter.At this point, it is sufficientto know that it will be much better to placethe workpiececloserto the same rotarydiametersof the specificmachine.as shownin Figure5-10, especially if a third-partydual-rotarytable,or a lesserqualitymultiaxismachineare in use.

Figure 5-7O The part is placed close to the Rotary Zero Point of the machine. Placingthe workpiececloseto the same rotary diametersof any particular machine,as shownin Figure5-10, might not alwaysbe possible.But when it is, take advantageof this simple techniqueto better control motion.

Feedrates On a 3-axis (non-rotary) machine,there is no need to specifya feedratemode becausethese machinesall operatein the units/time mode. Forexample,if you designatea positionas G9L G1 x7 .07f07 Y7.07107 rl-0, your machineslideswill move the workpiecein a coordinatedlinear motion from destinationof x7.07107 Y7.07107 at 10 its currentDositionto an incremental inchesa minute. The machinewill move the workDieceexactlv 10.000 inchesin a straightdiagonalline.

72


Figure 5-77 A diagonal groove is machined by moving both tabte stides simultaneously using linear interpolation, With linear interpolation,the workpiecewon't get to 10 inches/perminute instantlybecausethe slidesneed to acceleratefrom zero. Once a sDeedof 10 inchesa minuteis reached(if the machineis capable),it won,t instantlystop at its destination.Instead,the slideswill decelerateto that position,but for this example,those losttimes are negligible. We can calculatethe time of this 10.0000 inch movewith this equation:10 inches/minute = I minute.

Figure 5-72 Circular interpolation is used to move the workpiece in a circutar path. SimultaneousMultiaxisToolDaths

A planarcirclecut usinga c3 r-5. F10. commandis illustratedin Figure5-12. The resultingmotionappearsto be a true circle,but it is not. Any machinethat has the standardthree XYZlinearaxescannotcut a true circle;only an approximate one.The slideson these machinescan move only in straightlines.Therefore,in orderto generatea circularpath,the controllerwill haveto interpolatea circular move by breakingthe programmedcircleinto a numberof straight-line segments. On most machines,the circulartolerancecan be set from insidethe control parametersettings.The largerthe sizeof straight-line segments,the lessaccurate the circleswill be. A smaliernumberwill resultin more accuratecircularcuts. Changingthe circulartoleranceaffectsnot only the circularaccuracy,but alsothe feedrateusedfor the cut. The machinewill haveto slow down in orderto maintain the accuracyset, and the feedratewill changebasedon the sizeof the arc. Large arcs can be cut with a faster feedratethan small ones. Everyquadrantof an arc includesa peakerror area.whichconsistsof the points where the linear axes intersectthe arc at 0, 90, 180, and 270 degrees.As the machineinterpolatesthe circle, it needsto reversethe slide motion of its linear axisto travelin the oppositedirection.Evenif a high feedrateis programmed,the machine'scontrollerwill limit the executedfeedratebasedon the circulartolerance set in the controllerand the arc sizecurrentlybeingexecuted.Forthis reason, calculating cycletimes is not an exactscience. Multiaxismachineswork with two types of feedrates: . Standard (G94 units/time),as describedabove . Inverse Time feedrate(G93)

Inverse Time Feedrate Duringsimultaneous multiaxisrotarymotions,both rotaryand pivotingaxes must ideallyarriveat a specifiedrotarydestinationat the sametime. Otherwise, movementon one axis will stoDto wait for the other rotarv axis to arrive. This wait will causethe tool to dwell in one position,whichin turn, will changethe cuttingpressureand deflection.In the best casescenario,this delaywill cause an unwantedtool mark on the part surface.In the worst case scenario,the pause can evengougethe part. CAMsystemshandlethis problemby linearization, which breaksup these movesinto smallersegmentsand appliescontrolledInverse Time feedratesto them. The feed/minuteis specifiedwhen the tool needsto move at a specifiedfeedrate to maintainthe necessaryfeed per tooth to cut the material consistently.To move the tool with that feedrate,the rotary center points need to move much faster in space,especially if longertoolsversusshorteronesare beingused. The exampleshownin Figures5-13 and 5-14 has only one rotary motioncombined with X and Z linearmoves. 74

Secretsof 5-Axis l\ilachining

Figure 5-73 The start position for machining a complex parc.

Figure 5-74 Destination of motion from start point in Figure S-13.

Simultaneous Multiaxis Toolpaths

in Figures5-13 and 5-14, it is possibleto observe Lookingat the two illustrations and imaginethe differencein travel distancesbetweenthe tool tip and the rotary centerpoint of the head.To maintainthe programmedfeed/minuteon the tool tip, the center of the rotary spindlehead needsto move very quickly.This scenario can be comparedto runnerson a track. Runningin the insidelaneof the track coverslessdistancethan runningon the outsidelaneof the track.The tool tip is the runneron the insidelane,and the centerofthe rotaryis runningon the outside t an e . In short, the machineshould not be instructedto move from the current positionto the destinationat X units per minute.Instead,it shouldbe told to movefrom start motion,on all the to destination,in X amountof time, in a smoothinterpolated axes involved.On Fanuctype controls,G93 signifiesthe staft of the inversetime mode.Theremust be an F commandat the end of every line containinga G1, G2 and G3 code.The Inverse Time mode will not affect rapid G0 moves, In Inverse Time Feedrate mode, an F signifiesthat the move betweenthe currentpositionand the destinationshouldbe completedin (1 dividedby the F number)minutes.For example,if the F numberis 2.0, the movewill be completed in half a minute. Inverse Time Feedrates were widely used in the early days of NC, but today many modern CNCcontrollersare capableof parsingstandardfeedratesinto inversetime and vice-versa.(A parseris a compileror interpreter).Usually,an into this featureand it can be inversetime smoothingalgorithmis incorporated parametersetting. enabled,or disabled,in the controller's

Post Processors CAD/CAMsystemsgenerates-axis vector lines along 3D paths.The 3D paths representthe tool motion as it followsthe pattern being cut. The vectors represent the individualtool axis directions(IlK vectors)as the tool followsthe 3D (XYZ) pattern. Everyvector is representedby a line of code, and during toolpath creation, a resolutionof these vectors can be specified,either by definingthe minimum angulardifferences,or the linear distancesbetweenvectors,This informationis on the CAD/CAMsystem,the language writtenin a genericlanguage.Depending may be calledAPT,CLS,NCI,and others.Machinetool controllersdo not speakor howeverthey do understandmany different understandthesegenericlanguages, languages and dialects. language, The genericCAD/CAMcodemust be translatedinto a machine-readable a processthat is called post processing.A post processorwill calculatethe axis motions neededon a specificmachineto reproducethe CAMvector sequence.The post processorincludesdetailedinformationaboutthe specificmachine'sphysical and computingpropertiesthat allows it to generatethe requiredaccurateG-Code. This code,in turn, will governthe axis movementsof the machinethat are needed

76


to machinethe part. A different post processorwill be neededfor every type of multiaxismachinein the shoD. Postprocessorshave built-in intelligencedesignedto detect rotary limits and automaticallyretract and repositionmachineaxes. Rotary moves are treated with a bias (not applyinga neutral point of view correctionto the process),basedon the layout, as well as the primary and secondaryrotary axes of the machine.post processorswill stay away, or warn of 5-axis instabilities,and they can output rotary rapid motionsas programmedhigh feedratesto better control every aspectof a machine'smotions. There are alwaystwo possiblesolutionswhen a post processormaps a s-axis tool orientationto a s-axis machinetool's kinematics.The post processorswill choose the bestsolutionof the two. Considerthe exampleshownin Figure5-15. The currentpositionis xyz A+80.000 BO.0O0.In theory.the tool couldalso reachthis same positionat xyz A-80.000 8180.000, but that would be impracticalbecausethe part would be hiddenfrom view and the oDeratorwould see the back side of the rotary device.Also, there is not enoughy-axis travel capabilityon this specificmachine.

Figure 5-75 Oneof the two possiblesolutionsfor a S-axisposition. selectingthe bests-axispositionis the taskof the postprocessor writer.Another task of a postwriteris to solves-axisinstabilities, alsoknownas polesingularities. Thesefaultsoccurwhenthe tool is verticalor almostvertical.Mostoostswill generateretractmovesalongthe tool axisin thesesituations.Goodpostswill avoid erraticretractand largerepositioning movesby trackingthe possibleanglepairs, anglechangelimits,andmachine mechanical travellimits. Simultaneous MultiaxisTooloaths

lYanyCAMsystems handle safe motions betweentwo subsequent.toolpath operationswith post processors.Thesecontrols retract the tool into a safe area, and a s-axis machinerepositionsfrom one operationto the next. Instead of simply retractingto the MachineHome Position,safety volumes (box, hemisphere,cylinder)can be used for efficienttool retraction.Keepin mind that an efficienttoolpath doesn't make erratic and unnecessarymotions - it retractsthe workpieceonly to a minimum safe distance,and keepsthe cutterengaged,while maintainingall machineaxesin optimumpositions.. EveryCAD/CAMdeveloperhas dedicateddepartmentsdevotedto writing and supportingtheir post processors,and there are many consultantsmaking a living doing the same work. There is a great need for post processors becauseno two machinesor operatorsare the same' Postprocessorscan be customized,not only to suit individualmachines,but alsoto suit the individual user's preferences.If a companywishesto attempt to modify its own post processor,most developerswill providetraining and documentation. lot of effort, Developinga post processorfor multiaxismachinestakes a "hackers" who are talent, professionalism,and perseverance.There are many managingto "make it work,"but a high-qualitypost processoris suppliedwith detaileddocumentationand user-definedswitches. An exceptionalpost processorwriter visits corporatemachinebuildersto get informationdirectly,and then developsand tests the post processoron all the machinetypes in use, The post processoris thus tried, tested, and certified by both the CAD/CAMcompanyand the machinetool builder.

78


Common SimultaneousMultiaxis Toolpath Controls A good CAD/CAMsystem is one of the most importanttools in a modern machine shop,and will provideenoughcontrolto confidentlydrive any multiaxisCNC equipment.The three major thingsthat needto be controlledare:

Cut Pattern - Thispatternguidesthe tool'scuttlngdirections. Tool Axis Control - The orientationof the tool'scenteraxisin 3D spaceas it followsthe cut pattern. to Tool Tip Control - Thegeometrythat the tool tip is compensated follow.

In additionto those three major controls,which are definedin more detail in this nce. systemsalso provideadditionalcollision-avoida chapter,good-quality CAD/CAN4 This insurance will recognize the tool'scutteLshank,and holder.Differentavoidance behaviorscan be invokedwhen any of thesecomponentscomesinto proximitywith the work-pieceor a fixture. Differentnear-misstolerancescan be assignedto each of these tool comDonents.

Cut Patterns Cut Patterns guide the tool along specifiedpaths.These patternscan be simple 2D or 3D wireframe,or solidprimitives(for example,box, cylinder,and sphere.)Cut grids. Patterns can also be complexmulti-surface Someexamplesof cut patternsare shownin Figures6-1 through6-17

79

Figure 6-7 Tool motion following a 3D curve projected on to the face of a workpiece.

Figure 6-2 Tool motion following the rib's bottom edge.

Figure 6-3 A Cut Pattern is selected to slice the part in any given plane, for example, patterns 3 or 4. Secretsof s-Axis Machining

Figure 6-4 Impeller floor surfaces that use a Cut Pattern that morphs between the two blade surfaces.

Figure 6-5 Cut Pattern that is parallel to the bottom hub sutface, while cutting individual blades.

Figure 6-6 The Cut Pattern for producing a cylindrical-spiral tool motion. Common SimultaneousMultiaxisToolpathControls

Figure 6-7 Cut Pattern produced by morphing between the two edge curves of the floor surface.

Figure 6-8 This Cut Pattern is shown by the red 3D curve projected on to multiple

surfaces,

Figure 6-9 Floor sufface being cut by morphing between two 3D curves formed by the floor's outer edge curves, Secretsof s-AxisMachinino

Figure 6-7O Cut Pattern parallel to the floor surface as it spirals down each blade.

Figure 6-77 Racing engine intake and exhaust ports machined with a spiraling Cut Pattern.

Common Simultaneousl\4ultiaxisToolpathControls

'l

Figure 5-72 Path following a spherical Cut Pattern.

Figure 6-73 Path following a box-shaped Cut Pattern.


Figure 6-74 Axial Cut Pattern on a turbine blade.

Figure 6-75 Radial Cut Pattern on a turbine blade.

Figurc 6-76 Turbine blade's foot sufface cut by morphing the Cut Pattern between the outer edge of the foot sufface and the blade surface.

Common SimultaneousMultiaxisToolDathControls

Figure 6-77 Cut Pattern following the natural flow of the surface - the grid lines.

Tool Axis Control The examplesshown in Figures6-1 through 6-17 were designedto illustrate the results producedby tool motions on variousparts. It is necessaryto control the directionof the tool axis as the tool followsthe Cut Pattern. The Tool Axis Control allows orientationof the tool's center axis to be manipulatedas it follows the Cut Pattern. The sketchesin Figures6-18 through 5-25 illustratethese conceDts

o

Figure 6-78 The Tool Axis can be locked normal to a plane. In this example, the Tool Axis will be maintained normal to the bottom floor surface of each individual inseft Docket, Secretsof s-Axis Machining

Figure 6-79 The Tool Axiscan be lockedso that it always intersectsany definedDointon the holderside.

Figure 6-20 The Tool Axis can be Iocked so that it is always aligned with a defined point at any distance as it follows the Cut Pattern.

Figure 6-27 The Tool Axis can be forced to remain normal to one sur-faceor to multiDle surfaces.

Figure 6-22 The Tool Axis can be forced to fo ow a chain, while spiraling down an intake or exhaust channel. Common SimultaneousMultiaxisToolpathControls

6-23 The Tool Axis is controlled by the curves of the top and bottom surface edqes.

Figure 5-25 A Tool Axis can be forced to rotate about anv other axis. Figure 6-24 Lines can be drawn that will guide the Tool Axis as it follows a Cut Pattern.


In additionto the previouslydescribedTool Axis Control Methods, more controls are availablethat allow the tool to be rotated around its tip by specifyinglead, lag, and sidetilt angles,as shownin Figures6-26 through6-30.

Figure 6-26 Tool axis normal to a surface.

Figure 5-27 Tool axis at a lead angle.

Figure 6-28 Tool axis at a lag angle.

Figure 6-29 Tool with side-tilt angle.


Newersystemseven allowdynamicchangesto be madeto the side tilt, or the lead/lagangles,whilecutting.The examplein Figure6-30 showsturbineblade machiningin whichthe Tool Axis is dynamically controlled.With this control,the tool can be providedwith optimum accessto all the featureson the blade in all staoesof the cut.

Figure 6-30 Dynamic side-tilt angle changes.

Tool Tip Control In summarywhenCAD/CAM systemscreates-axistoolpaths,they will: .

90

Firstgeneratea numberof tool positionsalongthe user'schosencut Pattern as shownin Fioure6-31.

Secretsof s-Axisl\4achining

Figure 6-37 Generating tool positions on the cut pattern. The systemsthen assigntool vectorsto every one of those positions,basedon the Tool Axis Control method chosenby the usen as shown in Fiqure6-32.

Figure 6-32 The generated tool axis vectors. Next, they will move the tool to a desireddepth along the ToolAxis, basedon the Tip Compensation method.

CommonSimultaneousMultiaxisToolDathControls

Forexample,surfacesgeneratedto controla toolpathfor the humanheadshownin Figure 6-33.

Figure 6-33 Human head sculpted under computer numerical control. The surfaceswere generatedby a scanner,and thereforethey are not the best quality.The file may havegonethrougha few translations. The modelmay have beenscannedinitiallyand savedas an IGESfile, then sent to someonewho saved it as a STEPfile. Next,it couldhavegoneto anothershopwhereit was saved again as an IGESfile. Everytime a file gets translatedbetweendifferentCAD/CAM systemsthere is a toleranceissue.It is very easy for errors to be compoundedand producea poor qualityCADmodel.The modelmay consistof thousandsof surfaces and there may be gapsbetweenthem. The Tool Axis wouldflip radicallyif it tried to stay normalto all the surfacesas it traveled.Fixingthe gapswould be very time-consuming. A good,cleanmodelwill alwaysproducea nicerCut Pattern, stabletool axis orientatlon,and cleanercuts.

A handy5-axistrick is to createa cleancore underthe poorqualitysurfaces. This clean core is used to generateboth the Cut Pattern and the Tool Axis is appliedto the tool tip in cuttingthe outerControl. Then,compensation skin surfaces.followinothe cleanoattern.

92

Secretsof s-Axis l\y'achining

Figure 6-34 A clean core was created under the poor-quality surfaces and the tool was moved to positions at the set depth.

Figure 6-35 The clean core was used to generate the Cut pattern.

CollisionControl It is a giventhat collisions or gougesare alwaysto be avoided,so why is collision control needed?Why aren't all CAD/CAN4 Systemsdesignedto avoid them automaticallv? That first sentenceabove is not alwaystrue. In some instances,there is a need to gougethe drivesurface!Whenwouldthis applicationbe useful?Engineheadporting is a good example.The shapesof the intake and exhaust ports are very complex.Traditionally theseshapeswere carvedby hand,with carvingtoolssimilar to the instrumentsused by dentists. Reproducingthese complexshapeshas always beena challenoe. CommonSimultaneous MultiaxisTooloathControls

The CNCprocessis very good at reproducingshapesand comes in handy for this application.The challengeis getting these hand-carvedshapesinto the CAD/ CAMsystem. Probingis a common method usedto reproduceports, A probe is a sphericalinstrumentthat is used to touch the part and record a point in space, Touchingmany pointswill recordwhat is knownas a pointcloudwhichis a group of pointsthat roughly representsthe part's shape.If a probe of the same diameter as the tool to be used is employed,the tool can be guided along the points in this point cloud to cut the part. An exampleof a shapeto be reproducedis shown in Figure.5-36, and a close-upof the probe in contactwith the surfacesin Figure 6-37.

Figure 6-36 Probe being used to generate points over the part's surfaces.

Figure 6-37 Close-upshowing contact of the probe with the partb surface. 94


In some instances,it may be advisableto use a tighter cutting grid to obtain a better finish, or to use a different size of tool. In these conditions,it may be necessaryto transform the point clouds into workablesurfaces.Thesesurfaces would exist relativeto the center of the probe and, in this situation,it would be necessaryto lead the tool center on the surface,(the same place where the probe center was) thus gougingthe surface.

Figure 6-38 Theseport surfaces were generated on the probe's centerline. The tool center is led on to the surfaces, Most engine builderstoday use either a more sophisticatedscanningmethod that compensatesautomaticallyfor the probe diameter,or laserscanners/as shown in Figure6-39, that read the exact shapesof the ports,

CommonSimultaneous Multiaxis ToolpathControls

vc

Figure 6-39 This probe sutface was generated with a laser scanner that can represent the true shape of the port, Collisionavoidancemust be usedwhen cuttingthesecomplexsurfaces.Collision control permits monitoringof the cutter'sengagementwith the sudace, while ensuringthat noneof the other featuresof the tool (shank,holdeqetc.) come in contactwith any surfaces.Better CAMsystemsallow a choiceof ways to avoid collisions,and even permit "near-miss"distancesto be set for different parts of the tool, The impellerexampleshownin Figure5-40 has twistedand warpedblades, whichwouldbe impossible to cut with the side of a tool. TheseshaDesneedto be generatedby steppingdown on each individualbladewith a ball-nosecutter.The bottomfillet is smallcomparedto the bladeheight,and althougha long and skinny ball nose cutter is needed,it is not practical.A tapered-shankball-nosecutter is preferred,Becausethere is very little room betweenthe blades,there is great dangerof gouging,both the bladebeingcut, and the neighboringblade.Cautionis also neededat the hub surfaceto ensurethat it doesn't qet violated bv the nose of the cutter.

96

Secretsof s-Axisl\rachining

Figure 6-40 A warped impeller. Some CAD/CAMsystems providecontrol by allowingmultipleavoidancestrategies to be specifiedin the same path. For instance,in the aboveexampleit is possible to: .

Specifycutting with multiple, spiralingcuts.

.

Specifythat cuts should start from the top and work down toward the bottom of eachblade.

.

Specifyuse of a tapered-shankball-nosecutter.

.

Specifythe sidetilt anglethat is to be maintained.

.

If the cutter's shank comes within a certain distancefrom the blade,the tool is instructedto tilt away, either in the lead/lag,or the side tilt directions.

.

If the tool nosecomes in contact with (or within a near-missdistance)of the hub surface,it is instructedto retract along the tool's axis.

o

If the tool holder comes within a near-missdistancefrom the toD surfacesof the blades,the machineis stoppedso that the tool can be moved out from the holder(longertool is needed).

This level of control allowscreationof a clean,smooth cut with a rigid taperedshankball-nosecutter,as shownin Figure6-41.

Common Simultaneousl\ilultiaxisTooloathControls

Figure 6-47 A Clean Cut Pattern with dynamic tool axis control. Not all CAD/CAMsystems providethis amount of control. Some will only allow the definitionof check surfacesto be avoided,but will not orovidethe meansto avoid them. Keepin mind that thesecontrolsfocuson collisionsbetweentools.holders, fixturing,and work-pieces. They will not avoidpotentialcollisions on the machine. To avoid collisionsbetweenmachinecomponents,like rotary headsor tables. machinesimulationis needed.That subiectwill be coveredin the next chaoter.

Additional Multiaxis Issues and Controls Dovetail

Effect

Even4-axis,and especiallys-axis,motionwill introducesome uniquechallenges. Forexample,if a straighttool is plungedinto the centerline of a cylinderand then the cylinderis rotated, a dovetailshapewill be left betweenthe start and end positionsof the tool, as shown in Figure6-42.


EOVETAIL

Figure 6-42

The dovetail effect.

If the intentionis to cut a spline with parallelwalls, the tool should be moved off center,as illustratedin Figure6-43.

Figure 6-43 For cutting a spiral sptine, the tool must be moved off center. The offset amount must changefor each side of the spline,and the offset amount will dependon the pitch of the spline. Note also that the bottom center of the tool face cannot be in contact with the minor diameter.

CommonSimultaneous MultiaxisToolDath Controls

Cutting Direction lYostcutters are very sensitiveto the cutting direction.In the 3-axis world, it is easy to see and define cuts that are conventionalor climbing,but this is not true when cuttinga multiaxispart.

Figure 6-44 lllustration of Lead Lag in milling operations. Whentakinga light cut, simplychangingthe lead/lagangleof the tool changesthe cutting directionat the tool contact point, as illustratedin Figure6-44. The tool engagementareaalsochangesdrasticallyin deepor heavycuts, suchas thoseusingleadand lag cut engagementshownin Figures6-45 and 6-46.

100


Figure 6-45 Lead cut engagement in milling.

Figure 6-46 Lag cut engagement in millino. The examplesin Figures6-45 and 6-46 show differentengagementsduring the samecut, but changingthe leadangleto a lag angle.The tool contactarea changesfrom the side to the bottom of the tool, Extra attention must be paid to this aspect,especiallyif inserted,hollow-center,non-bottomcutting tools are in use. Multiaxis Roughing There are many instanceswhere it is necessaryto use long tools for roughing,as seen in Figure6-47. This is usuallydictated by the part features.Impellersare a good exampleof this problem.Tall bladeswith small gaps betweenthem force the use of a long cutter, and these cutters don't perform well with side-cutting pressures,As the side-loadincreases,these tools will deflect,causingvibration, chatter,poor surfacefinish, and drasticallyshorter tool life. Multiaxisplunge roughingis a good way to remove material in these circumsrances.


101

Figure 6-47 Plunge roughing Plungecuts should not be made to the final depth all at once. Instead, it is best to plungeonly to a manageabledepth, plungeout one layer,then pick away on the next one. The cutting pressurewill be along the tool axis. This procedurewill eliminatetool deflectionand all its negativeside effects.A typicaljob produced with this procedureis shown in Figure6-48. Some CAD/CAMsystems also have the ability to look at the shapeof the stock model and eliminateall air-cutsfrom the toolpath.This ability,combinedwith plungeroughing,can shaveoff hoursfrom high-volumeroughingoperations. Plungeroughing is not a simultaneousmultiaxiscut and therefore is a more rigid cut.

Figure 6-48 This part was cut out of "green ceramic" which gets fired after milling. The finished component is resistant to abrasive chemicals in hightemDerature environments. 102


MachineSimulation Machinesimulationis the safestand most cost-effectiveway to prove out multiaxis toolpaths.Usinga multiaxismachineto proveout programsis time-consuming and dangerous,both for the machineand for the operator!Runningprogramsblindly on a real machine,basedon a wireframebackplotin a CAD/CAMsystem, is just as oangerous. WhenCAD/CAMprogrammersconverseabout programminga multiaxismachine, they typicallyuse a specialsign languageinvolvingrotatingarms and torsos,while holdingup two fingersand a thumb, signifyingthe right-handcoordinatesystem in all kindsof differentorientations. They visualizethe part and the machineas it performsan imaginarychoreography. This visualization is not easyto do, especially if there are many different machinetypes in the shop, Wireframebackplotsportray the tool motion as it moves around a stationarypart. This movementis later post-processedinto machinemotion and is differentfor every differenttype of machine.The CD includedwith this bookcontainsa numberof examplesshowingthe same part beingcut on variousmachines.it will be clearthat eventhoughthe CAD/CAMbackplotmotionsare the same,the machinemotionsare comDletelvdifferent. With machinesimulation,a machine'svirtualreplicacan be shownon the comDuter screenwhere the cutting processcan be simulatedsafely.This try-out will ensure that the programcontainsthe most effectivecut, the part is locatedin the machine's"sweet spot". and no fixtures, tools, or any machinecomponentswill meet unexpectedly. It must not be assumedthat machinesimulationis only to be usedfor prove-outs with the soleaim of findingerrorsin the code.Instead,it must be lookedat as an additionaltool to help make clean,efficient,and accurateprogramsevery time. With simulation,differentapproachesand differentcutting strategiescan be tested on different machines,without leavingthe desk. And there is no need to tie down a machinefor prove-outs.Nobodylikesto see an expensives-axismachinesittingidle whileprogramsare beingtested, Peoplemake mistakesunderpressure.Evensmallmistakeson multiaxisequipment can quickly add up to catastrophicproportions.Damageto the part, machine,downtime for repairs,repaircosts,and penaltiescan reallyruin a business.Running 103

a newrunproven/5-axisprogramblindlyon a machine,is Iike playingRussian roulettewith the gun chambersfully loaded.UsingmultiaxisCNCequipmentas a verificationsystemdoesn'tmake sense,and is much more expensivethan using simulation.But with that said,nothingcan substitutefor the real thing, Evenafter simulationtests,the first run will alwaysbe exciting.The sights,the sounds,the Machinesimulationis not a magicbullet,but used feel of the cuts are irreplaceable. properly,it is an extremely helpfultool. Old School Samulation Manv shopsstill cut foam or wax for prove-outs.Some will even replacethe cuttingtool with a flexiblepipecleaner,and run the programon a finishedpart to see if there are any interferences.They will slow down, overrideboth the rapid movementsand the feedrates,and keepa closeeye on all possiblecollisions. If there are any closecallsthey will stop, makechangesin the program,either and repeatthe process.On a complexpart, this manuallyor in a CAD/CAM, processcan take days.On a complex,state-of-the-art, multiaxismachine,this process prove-out couldcostthousandsof dollarsin downtimealone.Only a highly-qualifiedoperator/programmershould attempt this type of prove-out,even if it costs more in wages. Realities many peoplestill manuallyedit Evenwith today'sadvancesin CAD/CAMcapability, the code created by their CAMsystem.There are various reasonsfor this and some of those reasonsincludethe followinq: Post processors are not configured properly' For example,during rotary positioningmoves,the rotary brakesshouldbe disengaged, and engagedagain duringcutting.This brakeapplicationis governedby M codesthat vary with different machines.If the post processoris not configuredproperly,these M codeswill needto be insertedmanually. A repeating pattern on the part can be called up, using subroutines. For example, an impeller has repeatingfeatures.Instead of letting the CAD/ CAMwrite long extensivecode, it is sometimeseasierto take the CAM-created code for one feature and repeat it using subroutinelogic.This procedureis particularlyuseful when there is a lack of memory in the machine'scontroller. No matterwhat the reasonis for usingthis method,you will find that this more efficientprogram is alwayseasierto prove out. Manually-programmed probing routines are introduced' For example, a branching/loopingprobing routine using system or user-definedvariables might checkthe part for alignmentat the beginning,or betweentool changes. Then, basedon the results,the probing routine would adjust the NC code to alignwith the part. Experiencedprogrammerstend to do more G-codeediting than new programmers, New programmerstend to embraceand trust the technologymore, and many are in earlierchapters,CAM As was established unfamiliarwith G-codelanguages. 104

Secretsof s-Axis l\.4achining

systemsfirst generategenericintermediatecode (APl NCI, CLS)and then post processthat code into the machines'specific G-codelanguage.All NC machines understandG-code,and when they readthat code,they translateit into machine motions.Everyword in that code, regardlessof where it comesfrom - the CAM systemor manualediting- will be recognized withoutdiscrimination. The most commonquestionis whetherto simulatethe intermediatecodeor the G-code.

G-code Simulation Versus CAM Simulation Onlya handfulof CAMsystemshaveintegratedmachinesimulation.Mostof those only simulate postedtoolpath code (XYZABC),not the postedG-code.Some have post processorsthat will post two streamsof code at once - a simplifiedone for simulationand the controllingG-codefor the machine.If these post processors are configuredcorrectly,the virtual machineand the real one will behaveexactlvthe same. Thereis currentlyonly one machinesimulationsoftwareprogramthat can run true G-codeand that is Vericut@ by CGTech. This programhas multiplemachine controllersavailable,and can be configuredto realistically simulateall known G-codelanguages, includinglooping/branch ing logic,probingroutines,and G and lY codes.If configuredproperly,the program'svirtual machineswill behaveexactly like the real ones.Notethat both methodswill only work if they are properly configured. If the shopis programmingmanually,or doesmassiveeditsto the postedcode, it will needsimulationthat is properlyconfiguredto simulatereal G-code.On the other hand, if the CAMt post processoris properlyconfiguredto drive an on-board simulation,no other simulationis needed. In eitherinstance,the questionto ask is "Who will do this configuration?,, Configuring multiaxismachinesimulationrequiresan intimateknowledgeof each machine,the simulationsoftware,and the post processor.

ConfiguringVirtual MachinesFor Simulation Softwarecompanieshave teams of dedicatedprofessionalswho spendall their time testing and applyingthe software. EveryCAMdeveloperhas a post department whichwritestranslators(post processors) for every machines'language. The departmentis constantlymonitoringnew developments in the machine-building industryand is in closecontactwith the machinebuilder'sapplications teams. Togetherthe teams developfactory-approvedpost processors.Without the efforts of the post writers, all CAMsoftwarewould be useless.The ultimate end Droduct of CAMsoftwareis not creatinggreat toolpathson a computer screen,but creating codethat will govern the movementson specificCNCmachines.

MachineSimulation

105

is the best If true G-codemachinesimulationis the goal,Vericutby CGTech, years has hundreds of of combinedhandsteam solutionbecausetheir apDlications type of CNC machine, and is capableof configuring any on G-codeexperience processing, The company specializes in reverse-post even entiremachiningcells. just it to machine movements, meaningthat they start with G-codeand convert like a machine'sCNCcontrollerwould. SomeCAMsoftwarepackagesoffer multiplemachinesimulationinterfaces. A few havedirectinterfaceswith Vericut.Anotherpopularchoiceis Machsim in post Moduleworks team specializes The equally-capable by Moduleworks. produce processors and the G-code output. both the simulation configuredto EveryCAlvland simulationsoftwarecompanyprovidespost processingtraining and/orvirtualmachinebuilding.Thesecoursesare typicallya few days long. can opt to sendemployeesto one of thosecoursesor just leavethe Companies configurationwork to the professionals. The followingis an overviewof the generalstepsin virtualmachinebuilding.

Virtual MachineBuilding It is not necessary to virtuallybuildan entiremachineincludingthe chip conveyor, coolanttank, and so on. Sucha processmakesfor slicksimulation, NC controller, but the only crucialpart that needsto exactlyresemblethe real machineis the area nearthe workingenvelope.Thesemotionsmust exactlyreplicatethe real machine.The remainderof this chapterwill coverthe processinvolvedto virtually buildall the major machinesthat were coveredin Chapter2. The stepsare very of the simulationsoftwarebeingused. similar,regardless The Skeleton The first step is to buildthe skeletonof the machine.The skeleton,or kinematic structureof the machine,describeshow the machine'slinearand rotary/pivoting axesare connected.Everymachinewill havea BASE,TOOL, and STOCK component.The best way to see the skeletonof the machineis to stand by the machineand jog everyaxis.Try to imaginethe machinenaked,withoutthe covers. Observethe examplein Figure7-1.

Everymachinewill have a BASE,TOOL, and STOCKcomponent.

106


C "€,tor,,-.

a z _E MoDELS B-

EBrrrooels

TOOL

eY_^ {JMODELS

a x__

I+IMODELS

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€BMoDELS Figure 7-7 Kinematic component tree.

The baseof the machinein Figure7-1 is hidden,to allowa betterview of the "business-end"of the machine, The kinematiccomponenttree (shownto the left in Figure7-1) describesthe machine(shownto the right in Figure7-1). The BASE is the first component.The Z-linear axis is attachedto the BASE,The B-rotary axis is connectedto Z. The indentationsignifiesthe axis priority,meaningthat if you move the Z-axis, the B-axis will move with it, becauseit is carried by the same slide.The last componenton this branchis the TOOL. carriedby, or attachedto, the B-axis. The secondbranchis also attachedto the BASE' starting with the y-linear axis component.Observethat Y is at the same indentationas Z. The y-axis is carrying the x-linear axis component.X is carryingthe A-rotary axis component,which in turn is carryingthe STOCK,or workpiece.This kinematiccomponenttree is the most basicdescriptionof a machine,and is a stripped-downskeletonof the machine.There are no modelsattachedto this skeleton,but you can tell by a glancewhich bonesare connectedtogether. Manyother componenttypescan be attachedto this basicstructureincluding, fixture, tool changer,pallet changer,and robots. Components

vs Models

Dependingon whichsimulationsoftwareis in use, multiplemodelscan be attached to every one of the main components.This ability to attach modelsenables

MachineSimulation

107

different propertiesto be assignedto each of the models.Uniquetolerancevalues, colors,translucency,visibility,and reflectivitycan be assignedto each model, and individualmodelscan also be includedor excludedon the collision-detection settings. Most machinesimulationsoftware uses STL modelsas a default,and some can also use solid primitives(block, cylinder,cone, sphere,or torus). Other softwarecan use its native solid models,or a mixture of all the above models. Somepopularmachineexamplesare illustratedin Figures7-2 through7-10.

.'

BASE

3x

>B a srocK $ rool

Figure 7-2 Horizontal 4-axis machining center, The horizontal4-axis machiningcenter configurationshown in Figure7-2 is very popularfor high-volumetom bstone-fixture type manufacturing,Note the pallet changer,which can be adaptedto servicean entire pallet center.With this capability,multiple differentjobs can be introducedinto the manufacturingprocess withoutstoppingthe machine.

108


ar BASE 3Y

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Figure 7-3 Vertical 3-axis machine, converted to s-axis with a third-party dual rotary device. The modifications shownin Figure7-3 can be adaptedto sult most 3-axisvertical machiningcenters.The dual rotary device bolts to the machine'stable, instantly transformingit into a 5-axismachine.Some room will be lost in the Z-axisworkinq envelope,but the multiaxiscapabilitywill be gained.

MachineSimulation

109

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Figure 7-4 Verticat s-axis machine with a dual, rotary, nutating table' The machinein Figure7-4 is a dedicateds-axis Table/Table vertical machining ."nt"r- f,lot" the rigid machinebase. Such a machinecan handle heavy work with Drecisionand confidence'

110


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Figure 7-S Vertical s-axis machine with a trunnion-type dual rotary table. Trunnion-typedual rotary configurations,as shown in Figure7-5, are very popular in the industry.This may be becausethey are competitivelypricedand easy to set up and ooerate,

MachineSimulation'l'l'l

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Figure 7-6 Vertical s-axis machine with a dedicateddual rotary table. Figure7-6 showsanotherexampleof a sturdy,dual-rotary,s-axisvertical machining center. Thismachine alsohasthe abilityto spinthe C-axisas a spindle, allowing for turningworkto be done.

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Figure 7-7 Horizontal/vertical s-axis Head/Table machining center. The machinein Figure7-7 is calledVH - Verticaland Horizontal.It is a s-axis Head/Table machine,and its design allowsfor exceptionalflexibility in additionto formidablerigidity.

lvlachineSimulation113

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Figure 7-8 Vertical s-axis Head/Table machining center. The vertical S-axis,Head/Table machinein Figure7-8 providesan amazing combinationof speedand precision.

114

Secretsof s-Axis Machinino

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Figurc 7-9 Vertical s-axis profiler, with a dual rotary head. Many manufacturersoffer variationson the type of Head/Head configuration shown in Figurc7-9, commonlyknown as a profiler.Typicallythese machineshave limited rotary range combinedwith long bed travel.

Machine Simulation 115

'BASE

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Figure 7-7O Vertical s-axis laser machine, with a dual rotary head. The verticals-axis machineshownin Figure7-10 is usedfor laser-machining, but this kind of Head/Head configurationis also very popularfor milling and water-jet machining.

Machine Simulation Interfaces A GUI (GraphicalUser Interface), or form of text file, can be used to build virtual machines.With such a program, models,or whole componentbranches,can be manipulatedindividually. For example,the virtualmachinecan be usedto translate,rotate, or set dependencies,translucencies,or reflectivity. Oncethe virtualmachineis built,all its axescan be movedindividually with MDI (ManualData Input) commands,or slider bars, to check if the correct modelsare assignedto the correct axes. Thesecommandscan also be used to check if the positiveand negativemotions are correct. Rememberthat all simulationsoftware is uselessif it is not emulatingthe movementsof the real machine.The models representingthe real machinemust be accuratein relationto the businessend of the machine.This area is nearthe work envelopeand includesthe spindle, fixturing, and rotary devices. Oncethe physicalmodel of the machineis built, the virtual controllermust be configured.In a CAMsystem this work is done with the post processor.In Vericut, configurationis achievedwith a reversepost processor.This configurationprocess is criticalin emulatinothe behaviorof the real machines. 116


Using MachineSimulation Thesedays, very few peopleprogram exclusivelyby hand. Most peopleuse a CAD/ CAlvlsystem to generatecode.The palt is typicallyeither designedor imported, and then toolpathsare generatedusingtoolsfrom an internalor an external library.Machinesimulationcan be run at any time duringor at the end of this process,providedthe groundworkhas beenlaid down and the machineshavebeen b uilt. The processof settingup machinesimulationis very similarto settingup a real machine.The part must be placedon the machinein the correctorientationand then the Local Coordinate System needsto be set relativeto the Machine Rotary Zero Position. The tools then need to be loadedinto the magazineand the Tool Length Offsets must be set correctly.This work can be time-consuming if there is no direct interfacebetweenthe CAD/CAMand the simulationprograms. If there is a well-configuredinterface,or if the simulationis an intricate part of the CAD/CAM, then settingup will take only a few secondsof processing time. NativeCAD/CAMsimulationloadstools from its libraries.Vericutuses its own tool managerfor it will builda tool libraryautomatically if it is integratedwith a CAM system.Oncethe part, tools,and toolpathsare loaded,the simulationis ready to be run, eitheras singleblocks,or continuously. The simulationcan be slowed down or sped,and the modelcan be dynamicallyrotated.Somesystemsallow movementsforward or backwardat any time, but others don't offer this option. Somesystemswill show materialremovalwith simulation,and somewill permit analysisand measurementof the virtualpart. Mostsystemswill signalif there is a near-missor collisionbetweenany configuredcomponents. They will also display an alarm if the limit switchesare hit by over-travelling on any of the motionaxes. Operatorsare ableto see throughmodelsby makingthem invisible,whichallows examinationof the cuttingprocessin waysthat are not possibleon a real machine. Thereare many benefitsto machinesimulation,whichallowsdifferentideasto be tested out without pressure.Estimatedprogram cycletimes can be accessed,to helpdeterminethe bestone. Crashinga machineon the computerscreenis not a big concern,whereascrashinga real one is a catastrophe. But not usinga multiaxis machineto its full Dotentialis a shame.Simulationallowsthe best ideasfrom different cutting strategies,and the most efficientmotion for any specificmachine to be combined.

The processof setting up machinesimulationis very similar to setting up a real machine.The part must be placedon the machinein the correct orientationand then the Local Coordinate System needsto be set relative to the Machine Rotary Zero Position.

l\ilachine Simulation

't17

SelectingThe Right Machine For Your Application Makinga multiaxisequipmentchoicedecisionis similarto choosinga car make and model.The decisionneedsto be basedon the intendeduse, budget,and personality, alongwith many other considerations. The multiaxis\\garage"includes the equivalents of racecars,all-terrainvehicles,buses,and luxuryvehicles.There are general-purpose machinesand there are machinesmadefor specificapplications. This chapter may help narrow the searchbasedon the specificparts being manufactured. Mostsmallshopsenterthe multiaxisarenaby addinga single-or dual-rotaryunit to their existing3-axisverticalmachiningcenter.The additionof the single-or dualrotary unit allows pafts to be manufacturedmore quickly and makes it possibleto machinemore complexpartsthat were previouslyout of reach.Thisadvancemay causea chain reaction.When shops get better at producingcomplexparts, they start to chargemore for those parts. They then seek out even more challengingwork to make more money.In turn, these ventureswill stretch the limits of capabilityof the equipment,promptingconsideration of purchasing more new equipment. The availablebudgetis alwaysthe big consideration. The priceof any machinewill reflect its quality, but as with cars, the price may also be affectedby the name brand. However,budgetaryconsiderationsare outsidethe scopeof this book. Machinemanufacturers spenda great deal of time developingmachines.They also spendtime on their salesand marketingefforts. Reputablemanufacturershave applications teamswho installnew equipment,train new customers,and provide ongoingtechnicalsuppoft.They alsoemploydedicatedapplications specialists who can preparebenchmarks,or turnkey solutions,for prospectsand customers. Regardlessof the specificmachinetype under consideration,it is smart to research the reputationearned by the support servicesprovidedby different manufacturers. MostCNCequipmentis sold by a dealernetwork.Not all dealerswill maintain the same quality of service.It is wise to visit local shopsthat have different CNCequipmentand talk to them abouttheir experiences. Ask them how their equipmentis performing,what the serviceis like when there is a problem,and if the manufacturerprovidedgoodtraining.It may also be wiseto ask if the suppliers deliveredon all their Dromises.

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tr criteria,and then take a Selecta machinemanufacturerthat suitsthe applications good look at the variety of pafts currently being manufacturedin your plant. Also considerthe partsyou intendto manufacturein the future.Considerthe following scenarios. How many parts are typically run after each set-up? If your shop produces500,000of the same parts per year,it would be wiseto look for a dedicatedmachineor machinesto producethat part. Investigatethe possibility of a turnkeysolutionfrom the machinebuilder.Sucha solutionmay includea completemachiningcell,possiblywith multitaskingmachinesand roboticloaders. Does your shop/company thrive on challenging jobs and have a reputation for producing complex work? Some shoos like to take on work that others considerto be too difficult.These companieslearn from every challengeand becomebetter and better with every job. Takingon difficultjobs may be risky, but it can pay great dividends.Before contracting for suchdemandingjobs, ensurethat your multiaxisequipmentis precise, flexible, and adaptableenoughfor the challenge. Are your existing CNC machines waiting for programs, or are your CNC programmers waiting for a free machine? If existingequipmentsits idle waiting for programs,then the workflow,CAD/ CAMsystem capability,and programmers'andoperators'proficienciesneed to be If programmersare waitingfor free machines,it is againa good idea scrutinized. to checkthe CAD/CAMsystem'scapability.Couldthe cutting strategy be improved? Are the right tools beingused?Imaginerunningold style high-speedsteeltools on a modernCNCmachinecapableof 40,000 RPMand 1500 IPM - the limitationsof cheaptoolingcouldhold backa very capableand very expensivemachine.In the same way, if your CAD/CAMsystem is obsolete,you won't be able to use your CNC equipmentto its full potential. Are you happy with the performance of your CAD/CAM system, and are you using it to its full potential? Makesure that your CNCprogrammers are up-to-datewith their trainingon your CAD/CAMsystem to ensure it is being used to its full potential.It is much cheaper and easierto get organized,trained, becomeefficient,and promote teamwork, than it is to buy a brandnew machineand put it into production. Is your shop/company dedicated to a single manufacturing field, for instance automotive, aerospace, mold & die, medical or oil? field you are workingin will alsoaffectyour choiceof machine The manufacturing type. There are differenttorque, speed,and precisionrequirementsin every field.

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Secrets of s-AxisMachining

New Possibilities After determiningthat your shop is runningfull out and needsadditional equipment,it is time to considernew possibilities. The first obvious consideration is the physicalsizeof the machine,and that is dictatedsimply by the sizeof the partsthat will be machinedand the sizeof your shopfloor. The next consideration is the materialthat will be used,whichwiil determine the rigidityneeded.The qualityrequirements of the machinewill be affected by the expectedtolerancesyou want to hold, and budgetaryrestraintsmust also be kept in mind. Asidefrom theseproperties,keepin mind that some multiaxisequipment is better suited for certain types of work than others,

Head/Head Machines (with long X- or Y-axis linear travel, but limited rotary axis travel) The manufactureof airplanewingsand fuselagepanelsis a goodfit for Head/ Head machines.The panelsare designedfor strength,but are kept as light as possible. Thereare severaltapered-wallpocketingmachinesthat are perfectly suitedfor swarf-typetoolpaths.Typicallythesepartsare madefrom solidbilletst n two set-ups,as shownin FigureB-1.

Figure 8-7 A vertical mill set-up for machining an aerospacepanel. SelectingThe RightMachineFor YourApplication

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An airplanewing stringeris a goodexampleof a part that is long,but very slim. Partslike this are typically machinedfrom specialextrusions,which can be over parts likethesewere madeon machinessimilarto the ones 40 feet long.Typically, shownin Figures8-2 and 8-3, usingmultipleset-upsand elaboratefixturing.

Figure 8-2 Gantry-type Head/Head machine.

Figure 8-3 Bridge-type Head/Head machine. The Dartswould tend to deform betweenset-ups becausematerialwould be removedunevenly,first from one side, then from the other, in a secondsetup,The machineshownin Figure8-4 solvesthis problem.


Figure 8-4 Dedicated extrusion milling machine. The machinein Figure8-4 is well suitedfor machininglong extrusions.It is a s-axis machinewith X, U, Y, Z and A-axes.The U-axismoves parallelwith the X-axisand it has two sets of rotary jaws that are usedto clamp and traversethe extrusionpast the cutting tool. Cutting takes place in a narrow but rigid corridor in successivesections,The overall lengthsof the parts are limited only by the support systemsat eitherside of the machine.

Head/Table Machines (with long X-axis travel) Long parts, similar to the examplesshown in Figure8-5, requiresevererotary motions in the primary axis and limited rotary motions in the secondarvaxis.

Figure 8-5 Typicalrotary parts. SelectingThe RightMachineForYourApplication

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These Dartswould be best manufacturedon the Head/Table machine configurationshown in Figure8-6.

Figure 8-6 Head/Table type milling machine' The rotary pivotingconfigurationshown in Figure8-6 is very suitablefor manufacturinglong rotary parts. The weight of the part is supportedby a tail stock, and the part is rotated around its center of mass. Ineftia is an important for when usingmultiaxismachines'Considerthe configuration consideration in machine the differences porting and imagine in Figure 8-7, shown engine head movementswhen comparedwith Figure8-8.

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Figure 8-7 Head/Table engine head-port milling.

Figure 8-8 Dedicated Table/Table port milling dual rotary attachment.

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The machinepicturedin Figure8-7 is designedto rotate the head around its center unwantedcenfrifugalforces' The machinein Figure8-8 of mass without generating "nock-and-Roll" dual-rotarydevice.It is designedespecially nas sometningcitted a for machining-portson engine heads.The entire fixture holdingthe part is rocked una |.ori"athioughout thelutting processto presentthe work to the cutter.These fixtures need to be carefullybalancedto ensuresmooth motion'

Head/Table Machines

suchas thoseshownin Figures8-9, 8-10' and 8-11' are Head/Table configurations urnon6tn" most virsatile choicesfor a variety of other multiaxisapplications.This ""rr"t]f ii'l"ri"es from the fact that the steady rest can easily be removedand the spa."canbeusedformountingadditiona|fiXtures.CustomizedfiXturescana|sobe built to suit specialjobs.

Figures 8'9.and 8-7O Additionat versatility using multiple fixtures'

Figure 8-77 Machining an auger feed spira! for an injection molding machine' 126

Secretsoi s-AxisMachining

Figure 8-72 Machining a rotary windmill unit.

Figure 8-73 An impeller. Figures8-12 and 8-13 representexamplesof veftical machineswith long X-axis travels,but Head/Table machinesare built in many forms and shapes.

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Rotary Table- Tilting Head Combinations Theexampleshownin Figure8-14 blursthe linesomewhatbetweenthe vertical and horizontaldefinitions.

Figure 8-74 This Head/Table machine is available in both vertical and horizontal configurations, The rotary-tableand tilting-headconfigurationsshown in Figures8-15 through 8-18 are not suitablefor long parts, but can readily be adaptedfor a variety of multiaxisapplications.

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Figures 8-75 and 8-76 Head/Table aerospacetand Head/Table automotive applications.

Figures 8-77 and 8-78 Two Nutating Head/Table configurations. SelectingThe Right Machine For YourApplication

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All rotary-table,tilting-headmachinestend to rotate the workpiecesaround their centersof mass while maintainingthe capabilityto reachall their featuresby tilting the head.Thesemachinesare built in many sizesand are widelyusedin many different industries,from manufacturingsmall medicalparts (Figure8-19) where precisionand speedare the main requirements.to manufacturinglarge earthmovingequipmentparts (Figure8-20), whererigidityand horsepower are the focus.

Figures 8-79 and 8-2O Typical medical part, and heavy equipment component manufacturing. In the mold and die industry,most of the roughingoperationsare done on 3-axis, verticalor horizontalmachiningcenters.In this manufacturing field,one of the challenges is cuttingdeep cavitiesor tall cores,The deep cavitiesare designed with steepsidewalls,usuallyat anglesof 1 or 2 degrees,and often requireuneven floors with small fillets along the intersectionof the wall and floor surfaces,as shownin Figure8-21. Cuttingthesefilletson a 3-axismachinewould requirelong, ball-nosecutters. Small steps need to be taken, causinglong cycletimes. The tool is often deflectedby the high cutting forces,causingvibration, excessivecutter weaq and poorsurfacefinish.

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Figure 8-27 Typical plastics-mold cavity. Usinga s-axis machineallowstapered ball-nosecutters to be used for this work. The taperedconfigurationmakes the ball-nosetool much more rigid for the same diameter,and the ability to tilt the tool also allows use of a shorter cuttet as shown in Figure8-22. More aggressivecuts can then be taken, shorteningthe cycletime. Deflectionof the rigid tool is less, and vibration is eliminateddue to the reduced deflection.Tool life is increased,and a precise.good-qualitysurfacefinish is achieved.

Figure 8-22 Multiaxis machining allows for the use of shorter, tapered cutters, SelectingThe RightMachineForYourApplication

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Table/Table Machines Figures8-23 and 8-24 show the most commonconfigurationsof Table/Table machines,The partsto be machinedare clampedto a dual-rotarytable and are rotated around the tool, Inertia is a consideration.The dual-rotarytable is either mounted on the machinetable or is a dedicateddual-rotarycomponentof the machine.These machinesare not suited for manufacturinglong parts' The work envelopeis fairly limited, especiallywhen some tool changerlimitationsare considered,Despitethe limitations,this configurationis very popular.

Figure 8-23 A populartrunniontype setup.

Figure 8-24 A dual rotary "rock and roll" fixture. 132


Table-mountedunits are not completelyrigid, but dedicateddual rotariescan be both agile and rigid. They are equally well suited for 3+2 indexingwork, and for simultaneousmultiaxiswork. Some applicationsare shown in Figures8-25 through 8-28.

Figures 8-25 and 8-25 Machiningan aerospace bracket, and a fixture component.

Figures 8-27 and 8-28 Machining rotor blades, and machining a medical comDonent.

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Gantry Type Head/Head Machines cantry type Head/Head machines,as shown in Figure8-29, arc used for large parts, mostly in the aerospace,oil, and wood industries,This configurationpermits long lineartravels.Some machinesare designedto allowchangesof heads in additionto tools. Rigidityand precisionmay not be the strong suit of these machines,but long reach capabilityis.

Figure 8-29

Water-jet/milling combination machine.

Some more machinevariationsare shown in Figures8-30 through 8-33. However' it is impossibleto describeall the different machineconfigurationsthat are available,especiallybecausethis is a constantlyevolvingfield.

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Figure 8-3O A s-axis laser cuttinq machine.

Figure 8-37 This machine presentsa good compromise between lonq reach and rioiditv.

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Figures 8-32 and 8-33 A 6-axisindustrialrobot, and a 7-axisindustrialrobot. Thischapterhasonly coveredthe mostpopulardesigns,and somesuggested spend It is recommended that engineers applications basedon experience. sometime on initialresearchwhenchoosinga machine,researchnot only of the machine, but alsothe intended use.

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Choosinga CAD/CAMSystem For Your Application Choosingthe appropriateCAD/CAMsystem is as important, if not more important, than choosingthe most suitablemultiaxismachine.Thereare many specialized machinesthat are dedicatedto specifictypes of work, howeverone CAD/CAMsystem will driveall the CNCequipmentin the shoD. It is importantto make sure that the selectedsystem can handlenot only all the differenttypes of work the shop does now, but will also be capableof taking on futurechallenges. CAD (ComputerAided Design)/CAM(ComputerAided Manufacturing)is always referredto as one combinedsystem becausemost CAD/CAMsystemsoffer both designand manufacturingcapabilities.Be aware, however,that very few excel in both CADand CAM. Systemswith heavy CAD emphasishave their roots in CAD and are better at solid modelingso that they can handle large assemblieswith ease.Thesesystems have associativitybetweenall the componentsso that when a changeis made to one feature on one part in an assembly,it will propagatethroughoutthe entire assembly. Thesesystemsare very good at managingCAD data, but their CAMcapabilitymay have been added later and it often does not have the same deDth. Systemswith heavy CAMemphasisare good at everythingrelatedto toolpath creation,from simple2D drilling,contouring,and pocketingto multi-surface and multiaxismachining.Toolpathscan be generatedfor all kindsof CNCequipment includingwire- and other- EDM,water-jets, lasers,lathes, mills, and multitasking machines.These systemshave intelligenttool librarieswith associatedfeeds and speedsfor different materialsand cutter types. Instead of heavy CADcapability, these systemsare very good at importing CADdata from any system, with the main goal of generatinga toolpath from that data.

Special Purpose Software Many specializedCAD/CAMsystems have been designedfor specificpurposes.For example,some shops in the mold and die industry use CAMsvstemsthat have virtually no CADcapability,but they can import large, complex,multisurfacefiles quickly.The user only needsto choosethe tools and selectfrom a short list of

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A toolpathis soongenerated,posted,and readyautomatedcuttingstrategies. changes to-go.The trade-offfor this speedand easeis realizedwhen engineering are necessary,Those changesneed to be made on a separateCAD system and imported back into the CAMsoftware.Also, these specializedCAIYsystemswill not suppoftany other kind of CNCmachines(lathe,EDM,plasma,waterjet,etc,) and many won't even supportsimplecontour,drill, or pocketroutines.Thistype of specialpurposeCAMsoftwareonly makessensefor shopsthat are machining to purchasea separate largemold cavitiesday in and day out. It may be necessary programmingseat of CAD,and maybeeven anotherseat of generalpurposeCAl4. Softwarethat can dynamicallychangethe feedratethroughoutthe cutting process is anothergood exampleof a specialized CAMfeature.Thisfeaturemimicsan operatorstandingat the machineand overridingthe programmedfeedratesby manuallymanipulating the feedrateoverridedial. In mold and die manufacturing, largeamountsof materialneedto be removed.The topographyof multisurface moldsis often so complexthat it is impossible to maintaina constantstep-over,or even a constantdepth of cut. Cuttingforceson the tool vary greatlythroughoutthe processof machininglargemoldsand dies,and the work can take hours,days,and to standby the machineand anticipateevery evenweeks.It would be impossible motion of the axes, and overridethe correspondingfeedrates,but with feedrate This optimizationtakes optimization, the softwarewill vary the rate automatically. place before any cutting is done, basedon constantsfor volume removal rate, chipload, surfacespeed, and other factors. Feedrateoptimizationproducesconstant cutting forcesthat are designedto lengthentool life, increaseaccuracy,and shoftencycletime. dramatically Softwarethat is specificallydesignedto generatetoolpathsfor lathes is one more CAD/CAM. ThissoftwareofferslimitedCADcapabilityand exampleof specialized only turning-specifictoolpaths.The softwareis often built in to the controllers on certainmachines,and only generatestoolpathsspecificto that machine's conversationallanguage.With this type of softwarethere is no need for a post processor.The approachis very direct, and that can be an advantage.Howevet it can also be a disadvantage becausethesetoolpathscannotbe transferredto any other machines.Grinders,lasers,water-jets,plasmacutters,and other specialized machinescan all operatein this samefashion. In additionto CAD/CAMsystems,othertoolsare availablethat can closethe loop Simulationsoftwarepackagescan help check betweendesignand manufacturing. generated the results by CAMsoftware,and are a very importantlink and optimize betweenthe virtualand physicalworlds.Ensuringthat toolpathsare bulletproof in the virtualworld will savethe shoptime and moneyin the long run. Thesetools shouldnot be overlookedwhen the shoo is beinooutfittedfor multiaxiswork.

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CAD/CAM Toolbox Buyinga CAD/CAN4 system is like buying a fully stockedtoolbox, but care must be takento ensurethat it containsthe right toolsfor the job. All tradesmenhave their own ideaof the perfectset of tools.A perfectset of sharp,high-qualitychisels wouldbe uselessto an electrician. At the sametime, it would be cumbersometo usea SwissArmy knifeas a screwdriverall day long. Very few CAD/CAMsystems can do everythingwell. They all have their strengths and weaknesses. On the other hand,very few companiesneedall the power affordedto them by a modern CAD/CAMsoftwaresystem.The trick is findinq the right balance. Some CAD/CAMcompaniesprovidefor the capabilitiesof their softwareto be increased as the companygrowsand demandsmore functionaiitv. Mostfirst time CAD/CAI4userswill start off with softwarethat can perform only simple 2D drilling, contouring,and pocketingtoolpaths.Oncethe users becomeproficient,they can take on more complex,3D, multi-surface machining,or multiaxis3+2 indexing work. Fromthat point,userscan move into complex,simultaneous, multiaxis milling,or evenoperationof multi-taskingmilling/turning machines.

Multiaxis CAD/CAMConsiderations Multiaxismanufacturingrequiressoftwarethat is very strong in CAlv.CAD capabllityis needed,but mostlyto import CADfilesfrom all the major CAD systems,in all the popularCADdata formats.On top of that requirement, additionalCADcapabilityis neededto createsuppoftinggeometryfor tool axis control,fixturedesign,or virtualmachinebuilding. High-endCAD/CAMsystemsare fully associative. If a designchangeis made,the changewill propagatethroughthe entiredatabaseand will modifythe necessary movementsin the toolpath.This featureis helpfulif one softwarepackageis used for the entiredesign-to-manufacturingprocess.If a single,all-encom passing packageis not used, then extra cost is being incurredfor associativitythat cannot be used. Unfortunately,most geometry associativityonly works with native geometry. Most multiaxisshops import files from a variety of customers.Thesefiles could havebeendesignedin any numberof CADsystems,so it is crucialto be able to readand write in multipleCAD/CAMlanguages. Oncethe modelis imported,it is criticalto havegoodanalysistoolsto analyzeit and then separateits major featuresinto organizedlayersor levels. After the modelhas beenanalyzedand organized,someadditionalgeometry creationmay be needed.This geometrycouldincludeadditionalwireframe,edge curves,lines,arcs,points,non-trimmingsurfaces,or evensomesolidmodel creation.This work will requirelight-dutyCADcapability.

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Multiaxis CAM The categoryof 3+2 indexingwork requiresthe ability to quicklyand easilychange the work planes,which are alwaysperpendicularto the spindle/toolaxis. The creationand manipulationof these work planes,also known as Active Coordinate Systems, should be intuitive and easy-to-use'Some systemswork interactively by allowingthe user to simply pick a solid face, an arc, two lines,three points, and such. to definethe orientationof a new Active Coordinate System. This selection is a light-duty capabilityfor most CAMsoftware. Heavy-dutyCAMcapabilityis neededfor tacklingsimultaneousmultiaxis applications.This capabilityhas to be a delicatebalancebetweencontrol,flexibility, and ease of use, A shotgun approachdoesn't work well here - the precisionof a rifle is needed. consider mold and die work as an example.This work is one of the most demandingand accuratefields in manufacturing.Moldscannot be mass-produced but are made one or two at a time, and they have predictablefeatures,either a core, or a cavity,or a little of both. A good 3-axis roughingstrategy will always work well here. Some CAMsystemscan quickly and automaticallyanalyzethe featuresand then automaticallygeneratea toolpath to machinethem' In this shotgun approach,a wide field of targets can be coveredwith one shot. Precisecontrol is neededwhen it comes to driving simultaneousmultiaxis machines.The followingis a list of must-havetools from a well-rounded,multiaxis, CAMsoftwaretoolbox. Pleaserefer to Chapter6 for detailedexamples. Cut Pattern Control It is important to have a variety of ways to define and control the pattern that will be followed by the cutting tool. These patterns can be anythingfrom a simple wireframeto complexsurfacepatternssuch as that shown in Figure 9-1.

Figure 9-7 Spiraling cut pattern on a turbine blade. 140


Tool Axis Control Toolaxis control providesthe ability to set and manipulatethe center axis alignmentof the tool duringthe cuttingprocess,as illustratedin Figure9-2. Thesecontrolscan be dynamic or static, but it is essentialthat they work in a predictable,stable way.

Figure 9-2 Positions of tool axis controlled by lines. Tool Tip Control The tool tip control targets the precisearea of the tool tip's engagementwith the part, as shownin Figure9-3.

Figure 9-3 Tool tip compensated to follow the outer surfaces of the work. Choosinga CAD/CAMSystem For YourApplication

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Collision Avoidance Measures Care must be taken to avoid potentialcollisionsbetweenmoving components/ and betweenmoving and stationarymachinepads when multiaxistoolpaths are being generated,As illustratedin Figure9-4, this particularcontrol focuses on meansto avoid collisions,particularlybetweenthe cutter,arbor, holder,and the workDiecefixture assembly.

Figure 9-4 Dynamic shank collision avoidance. Stock Recognition Roughing Strategies duringroughingwill savetime. Illustratedin Figure9-5, Stockrecognition stock recognitiontrims the toolpath to the stock size.This stock can be the initial CAD data or the in-processmaterialcreated by previousmilling operations.Multiaxisroughingcan be a time-consumingaffair and this feature is a must-havein creatingefficientroughingtoolpaths.

Figure 9-5 Plungeroughing,usingstock recognition.

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Machine Simulation Machinesimulationeliminatesthe guessworkand the needto prove-outnew machiningprocesseson real machines,Usinga real machineto prove-outa toolpath wastesvaluableproductiontime and risks potentialcollisions.Userfriendly and powerfulvirtual machinesimulations,as shown in Figure9-6, can improve productivitytremendously,but care must be taken to configurethem properlyfor each machine.Pleaserefer to Chapter7 for detailedexamples.

Figure 9-6 Properly configured virtual s-axis machines emulate the movements of real machines, Post Processor A good post processor is the most important part of any multiaxis CAD/CAM software. Without post processing,parts can be cut only in the virtual world and not on real machines.The role of anv CAMsoftwareis to generatecode that will drive the movementsof the axes on a CNCmachineso that a part can be machined,The native CAMlanguagemust be translatedto matchwith eachmachinet specificlanguage.Customized multiaxispostsare usuallyan extra charge,It is importantto find out if they are availablefor each specificmachineand how much they will cost. A professionalpost processoris usuallydeliveredwith supportingdocumentationthat explainsits featuresand all the availableswitchesto activatethem. CAMsoftwaretypicallycomes with a set of genericpost processors,which are user-configurable. Ask if postdevelopmenttrainingis available.

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Multiaxis CAD/CAM Training that Becauseof the complexityof multiaxismachining,it is not recommended multiaxisprogrammersbe self-taught.Trainingis a very important part of getting the most out of the softwarepurchase,and the best training is hands-on throughoutthe entire process.Trainingshould includeimportinggeometry,creating and simulatingthesetoolpathson a virtualmachine, toolpaths,post processing, Thesesteps representhalf the job. The next step is to learn how to set up a real machine,find the machine'sRotary zero Point, set the tool locations,load the toolpath into the machine'scontrollel and then cut the real part. Nothingcan replacethe feeling of excitementassociatedwith running a new programon a real machine. It is essentialto find out if this kind of programmingtraining is offered by the CAD/CAMcompanythat respondsto your requestto quote. Many programmers take three- to five-day,cannedtraining courses,which use pre-arrangedtraining sessionsand step-by-stepinstructions.It is possibleto completethese training coursesby simplyfollowingthe carefullylaid-outsteps,but there is no requirement for the user to retain any insight into why they are followingthose steps.These user/traineeswill get back to work and not know where to start. Very specific questionsneed to be asked about the training optionsoffered. On-linetrainingcoursesare alsoan option.Someof thesecoursesare very good, offering narratedvideos, and hands-ontraining sessions.The appealof these coursesis that users can take them at home at their convenience. CAD/CAMcompaniesalso offer on-site training,This arrangementensuresthat the focus is on the operationand the parts for which the programswill be used. The Caremust be takento stay on course dangerwith on-sitetrainingis interruptions. at all times. companyshouldprovide What happensafter training?The chosenCAD/CAM applicationssupport after training is complete.It is very helpfulto have that support availableas a safety net for at least the first few jobs. How about update training?As mentionedearlier,CAD/CAMsoftwareis constantly evolving,and it is important to keep up with these changesby attending periodic updatetrainingsessions.Userforumsare alsoa very goodway of keepingup with changesand a good way to exchangeideaswith peers.

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Behind the Scenes: CAD/CAMSoftware Development The softwarethat is ultimately chosenwill have a profoundeffect on the business. Not only will the shopget the softwarefunctionality to run its machines,it will also be allying itself with a companythat can provideyears of experienceand invaluable support.Considerable thoughtshouldbe givento the companybehind the software.A well-established,reputable,companycan becomea valuableasset and partnerto the operation. Understandingthe developmentcycle of modern CAD/CAN4 systemscan be helpful when softwarecompaniesare being researched.The followingbehind-the-scenes look at the developmentcyclewill illustratewhy it is importantto selecta large, well-esta blishedcompanyas opposedto a fly-by-nightbusiness. CAD/CAMdevelopmentis a very dynamic process.A successfulCAD/CAMcompany consistsof many teamsof individuals workingtowardthe samecommongoal.The individualsall strive to make powerful,flexible,and user-friendlysoftwarefor the end-user.This task is difficult becausethe more adaptiveand powerfulthe software is, the more complex it becomes.Complexityand ease-of-useoften conflictwith each other,and writers of good softwarestrive to find a balancebetweenthe two. Imaginationis a very important and fundamentalpart of CAD/CAMdevelopment, but it can be tricky becauseit must be tempered with todayt (and tomorrow,s) hardwarelimitations.Theoreticalpossibilitiesare always restrictedbV current hardwarelimitations.CAD/CAMdesignis a long-term,ongoingproject,and hardwareadvancesmust be correctlyanticipatedand implementedinto the software. Softwaredevelopmentplanningis done by mixedgroupsof individuals who includesoftwareengineers,mechanical engineers,applications engineers,sales, and marketingpeople.Thesegroupsare also heavilyinfluencedby feedbackfrom existing users. Existingusers help these groups make up the "wish list,,of new tools, as well as the recommendedimprovementsslotted for the next software release.The softwaredeveloperstake a close look at the.'wish list.,and determine what can be done,when,and how. Oncethe softwaredevelopmentteam has producedthe first usableproduct, they will make it availableto the rest of their teams,includingqualitycontrol, applications, and post development. All thesegroupswill conducttheir own usabilitytests and providefeedback.The developerswill use this feedbackto fix bugs,improvethe interaction, and make performance enhancements. This cvcleis repeatedcontinuously, until a stable,predictable, user-friendly Betaversionofthe softwareis created. The Betaversionis distributedto a specialgroupof end-userswho will conduct their own tests. At the same time, the softwaremanufacturer,sapDlications departmentwill conduct more tests by cutting real parts on real machines.

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Throughoutthis developmentprocess,everythingis carefullydocumented. groupwritesHelpfiles,and trainingmanualsare The technicaldocumentation developedand tested for each product. process, At the very end of this planning,development, testing,and documentation a new versionof the softwareis launchedand monitoredat every step. At that point,a dedicatedtechnicalsupportteam is readyto assistcustomerswith any issuesthat may a rise. But this point is not the end of the developmentprocess.The planninggroupkeeps on dreamingand makingnew plans.The softwaredevelopment team staysbusy workingon those plans,and so on. A goodsoftwarecompanyhas largeteams in orderto be ableto continuallydevelopnew and improved of professionals softwaretools.The work is neverdone becauseit is literallyon the leadingedge of technology.

General Guidelines for Researching CAD/CAM Software Start CAD/CAMresearchonline.This approachcan be a greatway to comparethe featuresand benefitsof severaldifferentsoftwarepackages.Many sites include demo video files, which can providea good feel for the software'sinterfaceand will often illustratethe software'snewestfeatures.The web site will also indicate detailsof any localresellerin your area. Conversations with peersor with companieswith whom the shopwill work are usefulto learn what kind of softwarethey are using and why. Ask peopleif they are happywith the localsupport,and was the softwareeasyor hardto learn?Can filesfrom outsidesourcesbe importedand exportedeasily?Werethere any hidden costs?Is the local resellerreDutable?Wouldthev recommendthe softwarethev are using? Visitsto tradeshowsare stronglyrecommended. Tradeshow demonstrations are short and are gearedto show off the latest hot featuresof the software.Visiting softwarecompaniesat tradeshowsalso providesthe opportunityto talk directlyto their corporatestaff, and the staff can includepeoplefrom all the different groups responsible for the softwaredevelopment. Chancesare that the localresellermight also be on handto explainspecificfeaturesand services.Suchvisitsare a prime opportunityto learnwhetheryou would like workingwith the firm's employees,and to see if they are genuinelytrying to helpyou or just trying to make a sale. lvlostof today's modern CAD/CAMpackageshave very similar features,making it extremelydifficultto comparethem with each other.Another problem is that the packagesare alwayssubject to development,and thereforeare constantly changing.Bewareof anyonewho makescomparisons betweencompetingCAD/ CAIYsystems,and bewareeven more of peoplewho are trying to make a sale by puttingothersdown.A tradeshowis a great opportunityto meet the peoplewho developand supportthe software.In additionto lookingat the latesthot features 146


tr of the software,take the time to assessthe peopleyou wouldbe workingwith if you decidedto purchasethe software.Are they enthusiastic abouttheir product?Are they behavinglike a team, or are they shifty.disinterested and unhelpful? The following are among important questions that should be asked when visiting software companies: .

Can you start smalland then increasefunctionality as your business grows?Many softwarecompaniesoffer different levelsof the software, Findout if you can buy only the functionality you needtoday,and add to it lateras the businessdeveloos.

.

Findout whereyour localreselleris located,and try to meet someone from the company.Ask questionsregardingtraining,support,post processors/and other aspectsof purchase.Makesure you are comfortable with the resellerbecausethe supportyou receivecan make or breakyour softwareexDerience. How establishedis the softwaremanufacturer?It is a good idea to find a reputablecompanywith a largeuser-baseand supportnetwork.Findout how many programmingseatsare usedworldwide.Is use of the particular softwareat which you are lookingtaught at trade schoolsor colleges?You may want to considerhow easy or difficult it may be to find employees that already know how to operateyour softwareof choice

The next importantstep is to set up a demonstration at your plant.The localsales representative shouldvisit your shop,Iookat your operation,and basedon what kind of work you do, evaluatewhetherthe softwareis the right fit for you. If it is, he/ she can also recommendthe propersoftwarefunctionality you need.Bewareof sales representatives who start with "Do I havea solutionfor you!" even beforethey see the type of work you do.

Choosinga CAD/CAMSystemForYourApplication

Putting It AII Together By now, readersshouldhavea good graspof the multiaxismachiningprocess,with a clearunderstanding of the differenttypes of machines,multiaxistoolpathtypesand machiningtechniques,multiaxisCAD/CA|Y controls,simula on options,and how they all fit together.To test your new knowledge,try to answerthe followingquestions. Answeringthe questionssuccessfully meansthat you are readyto bre;k lnto the fast growingmultiaxismachiningworld. AIIquestionswill be answeredon subsequentpages.and rneseanswerscan serveas a quickreferenceguidefor the most importantlessonslearnedin this book.

QUrZ 1.) Name three benefits to using multiaxis machining techniques, 1.

2.) Describe a standard s-axis machine?

149

3,) which of the following is the standard axis convention?

B

A 4.) what are the three major multiaxis machine types? 1. ') 3.

5.) what are the three major building blocks of a cNc machine? (Circlethree.) . Machinetable servo drive system

. CNCcontrollercapabilities

. SpindleRPMand horsepower

. CNCdrive system

. Physicalpropeftiesof the machine

. Lineartable limit switches

. Chipconveyorunit

150


i 6,) What are the most important physical positions of a multiaxis machine? .

Centerof gravity, Home Base ProgramHome Base,IncrementalZero Position,Spindletype

.

MachineHome Position,MachineZero Position,ProgramZero Position

7.) What tools are needed to find the Machine Rotary Zero Position (MRZP)? (Circle two.) .

level

.

edgefinder

.

dial indicator

.

maintenance manual

.

hammer

8.) Describe indexing/rotary positioning work,

9.) What is a post processor?

Puttinglt All Together

't5t

ANSWERS 1,) Why use multiaxis machining techniques?

't52

.

partsmoreefficiently Multiaxismachiningtechniques are usedto manufacture and accurately by eliminatingextraset-upsand fixturing.

.

Standardshortertoolingcan be used,whichresultsin the abilityto rough moreaggressively, whileincreasing tool life.

.

A moreprecisesurfacefinishcan be achievedby avoidingcontactwith the non-spinning deadcenterof the tool.

Secretsof +Axis Machining

Figure 7O-7 Multiaxis machining manufacturesparts more efficiently, increases tool life, and producesa more precise surface finish, 2.) What is a standard S-axis machine? This is a trick question!Thereis no suchthing as a standards-axismachine. Multiaxismachinesare availablein many shapesand forms. Figure10-2 shows examplesof the varioustypes of s-axis machines.

Figure 7O-2 Examplesof the varioustypes of 5-axis machines.

Putting lt All Together

153

3.) What is the standard axis convention?

Figure lO-3

The standard axis convention,

The X, Y Z linear axes shown in Figure10-3, representingthe Cartesiancoordinate system,move in straightlines,in plusand minusdirections. The A, B, and C rotary axes rotate about the X, Y and Z axes respectively.The U, V and W axes move in straight lines, parallelwith the X, Y and Z axes respectively. 4,) What are the three major multiaxis machine types?

TABLE/TABLE HEAD/TABLE HEAD/HEAD

154


Table/Table Multiaxis Machines

Figure 7O-4 Table/Tablemachines can be configured vertically or horizontally. Table/Table multiaxis machinescan be configuredverticallyor horizontally,as shown in Figure 10-4. The rotary motions are executedby the dual rotary table of the machine.The rotary table carriesanother rotary table, which in turn carriesthe fixture and the part. With these machinetypes, the part is physicallyrotated around the tool. The weight of the part and fixture need to be handledby the machine's rotary devices,so inertia will be a factor when consideringfast movements. Head/Table Multiaxis Machines

Figure 7O-5 Head/Table machines are very capable and versatile.


155

Head/Table machinesare arguablythe most capableof the three groups.They can machinelarge, heavy parts. On some Head/Table machines,the work piece is held by a rotarytable and is supportedby a tailstock,as shownin Figure10-5. The work piece rotates around its own axis. The pivoting head only carriesthe weight of the tool and it handlesthe cutting pressuresgeneratedas it articulates aroundthe work Diece. The rotary axis on these machinesusuallyhas unlimitedrotary motion, Some can even spin the rotary as a lathe would. The secondarypivotingaxis has an upper and lower rotary/pivotinglimit, Head/Head Multiaxis Machines

Figure 70-6 Head/Head machines can be both vertical and horizontal. On Head/Head machines,an exampleof whichus shownin Figure10-6, all rotary/pivotingmotions are executedby the head of the machine.Head/Head machinescan be both vertical and horizontal,where one axis has limited motion. Somecan changeheadsin additionto tools.Headscan be straight,90 degree, nutating,or continuously articulating.In additionto milling,these machinescan also be outfitted to manipulatea water-jet or a laser. 5.) What are the three major building blocks of a CNC machine? 1. The physical properties of the machine The physicalpropertiesof the machineare representedby the machine'sskeleton. Everymachineis built on a uniquebase.The qualityof the iron givesthe machine its rigidity.The linear and rotary axes are stackedfirst onto the base,then onto eachother.The qualityof the linearslidesand rotarybearingsgive the machine

156


its flexibilityand potentialaccuracy.The spindlemotor'storque and horsepower further definethe characterof the physicalmachine. 2. The CNC drive system The CNCdrive system representsthe muscles of the machine.The CNCdrive system consistsof componentsdesignedto move the machine'slinear and rotary axes. These componentsincludethe servo motors. drive system, and ball screws, which are responsiblefor moving the machine'slinear and rotary componentsin a smooth, preciserand rapid manner, 3. CNC controller capabilities The CNCcontrolleris the brain of the machine.Data handling,availableon-board memory size, and dynamic rotary synchronizationcontrols,are some of the things controlledhere. 6.) What are the most important physical positions of a multiaxis machine? Machine Home Position - Most machinistsrecognizethis positionas the placeto which all the axes move when the machineis initiallyturned on and Zero return is selected,as shown in Figure 10-7.

Figure 7O-7 Machine at Home Position.


157

Machine Rotary Zero Position - MachineZero Positionis the intersectionof the rotary/pivotingaxes shown in Figure 10-8. This point may be unreachableby the machine.

Figure 7O-8 Machine Rotary Zero Position. Program Zero Position - This position,shown in Figure10-9, is also the part datum locationin the CAMsvstem.

Figure 7O-9 ProgramZero Position.

158


7.) What tools are needed to find the Machine Rotary Zero position (MRzP)? The tools neededto find MRZPare a level and a dial indicator. 8,) Description of indexing/rotary

positioning work

Most CAD/CAMsystems let the user define multipleActive Coordinate Systems in space,and then create toolpathsusing the orientationof each individual coordinatesystem.As shown in Figure10-10, the Z-axesof these coordinate systemswill align with the spindle,signalingthe post processorto output rotary indexingcommandsinto the NCcode.

Figure 7O-7O Multiple Active Coordinate Sysfe/.ns. 9,) What is a Post Processor? CAD/CAMsystemsgenerates-axis vector lines along 3D paths.The 3D paths representthe tool motion as it followsthe cut pattern. The vectorsrepresentthe tool axis direction(IJK vectors) as the tool followsthe 3D (XyZ) pattern. Every vector representsa line of code,This informationis written in a genericlanguage. The genericCAD/CAMcode must be translatedinto a machine-readable language. This processis called post processing.A post processorwill calculatemotions neededon a specificmachineto reproducethe CAMvector model, which will govern the machine'smotions in order to cut the part. A different post processoris neededfor every type of multiaxismachine. Puttinglt All Together

159

1O.) Definition of an axis Any motion controlledby the NC controller,either Iinearand/or rotational consideredan axis.

Figure to-t7 In this examplethe spindleheadand the quill move in the same direction,but are controlledby two separatecommands,z and W respectively. 11,) Defining a simultaneous S-axistoolpath multiaxistoolpathsmust moveall 5 False.Mostpeoplebelievethat simultaneous whilecutting,whenin fact a singlerotary axesof the machinetool continuously multiaxis cuttingmotion. to be simultaneous is considered andlinearcombination Figures 10-12 and 10-13. in areillustrated multiaxis toolpaths Typical simultaneous

Figures 70-72 and 7O-73 Examplesof simultaneous multiaxis toolpath motions' Secretsof s-AxisMachining

12,) What are the three common simultaneous multiaxis CAM toolpath controls? 1. Cut Pattern - Guidesthe tool along cutting directions. 2. Tool Axis Control - Controlsthe orientationof the tool's center axis as it followsthe Cut Pattern. 3. Tool Tip Control - Controlsthe geometryto which the tool tip is compensateo. In additionto the abovethree major controls,quality CAD/CAMsystemsalso offer additionalcollisioncontrol. Even near-misscollisionavoidanceof the cutter, shank, and holder can be checkedagainst any part of the workpiece,fixture, or machine comDonents, Pleaserefer to Chapter6 for more detail.

More in Review: Multiaxis Machine Offsets

PIVOT

= TANCE

COMPOFFSET LENGTH'

Figure 70-74 In addition to Tool Length compensation,multiaxis machinesuse other offsetsincludingGageLengthand RotaryPivotDistance.TheRotaryTool ControlPointDistanceis the sum of Pivot Distanceplus GageLengthOffset. PuttingltAll Together

161

Quick Reference:How to Find Machine Rotary Zero Position For Table/Table Machines:

Figure 7O-75 Step 1: Level the A-axis.

Figure 70-77

162


Figure 1O-16 Step2: Findx,Y center.

Step 3: RotateA+90 and set dial indicator to Zero.

Figure 70-78

Step 4: RotateA-90. Dial indicator should read Zero

Figure 70-79 Step5: log Z minus the radiusofthe rotary table diameter,and adjust gage tower height to match.

PuttingltAllTogether 163

Finding the Pivot Distance For Head/Table and Head/Head Machines: First,makesurethat the machineheadis in a perfectverticalorientationand that the spindleis runningtrue.

Figure 7O-2O Step 1: Use a dial indicatorto checkfor verticalalignment.

164


Figure 7O-27 Step2: Checkif spindleis runningtrue.

Figure 70-22 Step 3: Record Z max.

Figure 70-23

Step 4: Record Z min.

Z max Z min GL - Gage Length R - Dowel pin radius = .5OOO Formula to calculate Pivot Distance: PD=Zmax-Zmin-GL+R

ltAllTogether 165 Putting

Indexing/Rotary Positioning Work Overview Also known as 3+2 machining,indexing/rotarypositioningwork, illustratedin Figure 10-24, is the most basicmultiaxisconcept.The rotary/pivotingaxes are used only for positioning,and the cutting takes placewith only the three linear axes moving.Indexingwork is rigidand precise,It is recommended that all possibleroughingoperationsbe performedin this rigid state.

Figure 70-24

Indexing/rotary positioning work is the most basic multiaxis concepL

Picking a CAD/CAMSystem For Multiaxis Work When selectinga CAD/CAMsystem for multiaxiswork, make sure it is CAM oriented,and has a powerfulCADtranslator.The CADtranslatoris very important becauseit's likely that files will be receivedfrom many different sources.Makesure the CAMsystemhas all the multiaxiscontrols,pluscollisionchecking.Havingan onboard,easy-to-use.machinesimulationis a big plus, especiallywhen project planning.Machinework envelopeand machinecomponentcollisioncheckingare reouired. In additionto the abovefeatures, it is also very important to researchthe CAD/ CAMsystem developerand the local dealer.Do they providequality training and support, and do they have post processorsfor your machine? Pleaserefer to ChaDter9 for more detail.

'166


Machine Simulation Do not assumethat machinesimulationis usedonly for prove-outswith the sole aim of findingerrorsin the code.Instead,machinesimulationshouldbe regarded as an additionaltool to help make clean,efficient,and accurateprogramsevery time. Machinesimulationpermitstesting of differentapproaches,differentcutting strategieson different machines,without leavingthe desk. There is also no need to tie down a machinefor VourDrove-outs. Machinesimulationiets you builda replicavirtualmachineon the computer screen,where cutting processescan safely be simulatedto make sure that the most effectivecut has been created,that the part is locatedin the machine's "sweetspot,"and that no fixtures,toolsor any machinecomponents are meeting unexpectedly.

In Conclusion Congratulations on the commitmentto becomemore informedaboutmultiaxis machining!Multiaxismachiningis a dynamic,constantly-evolving field,full of possibilities. lYultiaxis machinetoolswill becomemore complexand capable,and CAD/CAM systemswill developadditionalcapabilities to controlthem. Userswill continuallylook for more capability, combinedwith easeof use,and this demand will pressurethe machinebuildersand CAD/CAlvl developers to combinetheir effoftsin buildingmachine/controller combinations with built-inintelligence. As pasttrendsshow,thesedevelopments will open yet more possibilities, addingmore complexity. Creativitydoesnot fit into a box, but knowingthe basicconceptswill allow engineersto think outsidethe box. Hopefullythis book has demystified this field and inspiredyou to take the next step in training yourselfto becomemore proficientand competitivewith all the toolsavailable. The best measureof competencyin any field is mastery of the availabletools. Mere possession of more powerful tools doesn't make one more capable, but knowledge does. The manufacturing industryin general,and multiaxismachiningln padicular,is bestsuitedfor thosewho can think outsidethe box.Thereare alwaysmultiple ways to solve any problemand that solutionalwaysstarts with oneself.The biggest secretof s-axismachiningis the realization that all the expensiveCNCmachinery, CAD/CAM, and simulationsoftwareare meretools.Withoutthe knowledgeto use them properly,nothingcan be accomplished. With the availabletoolsand the right knowledge,all you haveto do is imagine- by applyingyourself,your imagination will becomea realitv.


167

Index Cuttnrg

A ABC lineara{es.l5 system.5? Absolutecoordinate Activecoordnrabsystems,25 2'7, 57,59-61, 140 Acturl part zeropoint, 27 Aligneduniversc,62 Avoidingcollisions.45 Automaticlool changing,16.423

dircciion,l00 strategies, 45.70. 103,117,138.167 variablepitchthread,67

D 9, 10 Dedicated multiaxismachnrcs. anddirections of multiaxismachine Designations

B

Desiredcutterarea.engaging,l0 Dovetail effecl. 98 Dynanic contol of tool axis,90,98 robry fixtureoffset.16.27-8,36

Bal]-nose cutters,10,96,130 Bettersurfacelinishes.l0

E

dcfined,l4 substitution,32

(3,7. 27, CAD/CAMsystems, capabilities.l39 I 39 multiaxiscoDsiderations, origin,60 selecting,137 145 softwaredevelopmcnt, rcsearching,146 tmining,l4,l pivotdisiance(PD),33,37-8,169 Calculating CAM, multiaxis,139 multiaxismachines,3 Can-operated 53 spindleheads, Changeable repeatibjlity.'12 Checkingpositioning Circular 73 interpolation, Cleancore,92 CNC 3, 76 controllers. capabilities,l3,157 l3 drivesystems, (seeAvoidingcollisioDs) Collisionavoidance 4, 6. 7 misconccptions, Common of rvork, 120 Complexity Computernunericalcontrol,3, 92 Crashirg,I I 7 94, 140,161 Cutpattem,79,86

Effectivcwork envelope.16 Engagingdesiredcutterarea,l0 Extrusionmillingmachine.123

F Fanucprogritn,34 Fcedrate,T2 138 dynanicchanges. inversetime,74 6 optimizaiion,l3S standardlime. 74 Findingthe ccnterofrotation.21.27'8 pivotdistance, 33,36-9.l6l. l6,l XYzero,23 5'axis nachineierms,13 vectorInres,76,159 nachines,39 positioning,T

G Gage length(GL),36-9. 161 tower,24,163 122,134 machines, Ganrrytypehead/head G codes,29.30.56, 104'106 169

sinulntion.105 G 90code.29.30 G-91code.29.30 ll6 Gaphicaluscrnrtel1ace,

H nrultiaxismachines. 18.367. ll5 6. Head/head l2l 2. 13,t.156,i64 bridgeiype. 122 ganlry1ype,122.13,1 lasercuttingmichnre,116.135 warcrjer miling machnre.ll6. 134 18,31.36.113,1 Headltablenrultiaxisnrachnrcs, 123,1.155 129,133 aerospace, automotive applications, millingenginchcadports,125 nilling longrotarypafts.124 mdd anddic applications, 130 nuiatingheadconbinations,129 rotafylxble,rilthg head.12830 1249 variousconligurations, with longX'axis tavel. 123 work,56 Ho\vCNCmachines Historyof 5 axismachining.3

I I n d e x n r g , 2 l , 4 4 , 5 11 , 5353. lixtures,5l methods.5l toolpaths.49 wirh rotar)devices.52 wo*.:19.55 Indusrrial robots.135 Interpolation circular,T3 linear,73 Inversetnncleedrate, 72-4.76

L Leadandlag jn milling.100 Lnnihlions,,16 Linear .txis,14 6,34.,19.74, 106.121,166 73 interpolation. Localcoordinate systems.25 7.56 8.61 2,117

170

Secrets of s-Axlsl\,4achining

M Machine 7.57 61.140,15' aclivccoordirrte system.25 4, 167 1136,116-7,139.1,13 bxildingvirtual,64, cnd,6,l,107.125 busnrcss 159 7,56-7.61'2.1,10. coordinate systems,25 157 homeposidon, 16,57.60.78. slstcns,25,26. 6l localcoordinate

hone positior(MRHP),l7 zeropoint,21,25-7,36.60 2,1 1 2, 1M (MRZP).I 6 '7,21,25.21.36, zeroposition 1 1 7 , 1 5 8 ,r96.2 1036. 143.1657 simulrtion,27,63-4,98. graphicaluserinlefaccs.I l6 using.tl7 Machirlnlg centcrconJigul"tion. 108 I l0 complexworRpicccs,5 cngnrccomponents.20 profiling. ll5 progrrn,29 104.138 routines.5. spnd bevelgears.68 Machsimsoftwxlc,106 Maintenance issues.40 Manualclrt.tinpur(MDl),25.1l6 Master system,60 coordinalc zero,26 M-code.2l,43,60 Milling nachineswith nvc or moreaxes.4:l \ 4 o , r e l i n2-r. ., ' 1 . u l . l l ' . I n - P l l 6 l 1 - - r ) 159 6. 8, 17-9,40,7,1. 124.153 Multiaxis machines.3 140 camtype.3. dedicated,6. 9 10.21.39,52-3,110,l2l) anddirections.l5 designilions physicalpropeties,13.156 rorghing. 21.101.130,1402, 166 58. 61 Multiplenestnrg,

N 25.26,56 8, 61 NeslingpositioDs. Newpossibilities, 11.121 parts, Nunbersof 120

Nunerical conlrol. 3

o Old schoolsimulatifl. 104 One zero meihod,60 Optimum rvork envelope.70 Odgin,26,60

P Palletchargers, 40, 54, 107-8 datum,17,21.27,58,158 zeropoirt (PZP),27 8 Plungeroughing,101-2,142 Probesandprobing,94-5,103',1 I'hysicalproperties of5-axismachines, 13 Pivot distance.33 point,379 Pivonngspindleheads,18,32-6,38. 124.156.lbo Pockct nrilling.5.86, l2l, ll7 9 $ork. 5, 7, 8. 13,20-l, 26. 42,49,52, Positioning

R pxltcrns,l0,l Rcpcating Rotary andpivotingaxcs,32.74 axis,16,21,33.,12.60.71.7.1, 107.i21, 156 d c v i c c1 s ,6 , 1 8 . 2 1 . 521, l l 6 . 1 5 5 xrdexingnechanisns,5, 54 mcchanisns. 6, 19,20.39.403. 52 3. 7l tool cortrolpoint(RTCP).33'4.36.l6l Rotarytables,5. 8.9. 18,21,278.31 2. 130-2.

r 5 56 .r 6 3 brakes,21,.10, 52.l0,l d e v i c e1s 6. ,1 89 , 2 1 , 5 12 . 7 7 .1 0 9 1. 1 6 ,1 2 61. 5 5 dynxnicfixlurcoft.\cl(RTDFO).16,27 8.36 sinsleanddual. 6, 8. 18.39.ll9 Roughnrg. 11,21,101'2,130,140'2,152,166 Routnrcs,5.40,42, 1045 S Secondrotart table,18 Selecfirgnachnlcs,I l9 Selecting software.137 Stullrlaftrn, 19,27,47.63 4.98.10317.I38,1667

r 5 9r,6 6 processing,3.4.8.34,40,76 8. 103-6,138, 1 4 37 , 1 5 9 r, 6 6 processor,3,4, 8,39,40,769. 10zl6, I16,138. 1 4 3 1, 4 7 , 1 5 9 Probingroutines.1045 Program nnnurleditnrg. 104 subloutines. 9, ,13-4. 10.1 (PZP).l6 8,25.32.117.158-9.162 zcroposition P r o g r d m n r i l gq...118 . 2 4/ 5 . 6 .5 4 . 6 ) . l . l 0 : . 105.138,144.147 .onsiderations, 46 languages,3 limitrtions.46

a

46. I 44. I 41. 119 Qucstbnsandanswers, physicalpositions,151,157 standard axisconvention. 150.154

cutlingmotions,10,71 millingte.hniques.2l muhiaxistoolpathconirols,79,101,152.161 toolpaths. 5.48.65.78. 103,105,107.l2l Special-puryose softlvare,137 heads. Spindle changeable. 31.53 Spil"l splines,99 Standard multiaxisnomenclature. 15 Slock(natcrial)option1.47.102 rccognition,1,12 104 Subroutines.3.43. Surlacelinishes.better,5,10 origin.60 view,27

T Txblc/lxblc multiaxis machnrcs, l8 9.24.I10.125, 1 3 2 1, 5 5 . 1 6 2 wjth port-nillingaftachment, 125

'171

111,I32 honnionandrock andro11Iixtules,71. 133 variousapplications. 5 toolpaths, 3D surfacing Tiltingspindleheads,31 Tombstone lixtures,6, 40, 58-9,108 Tool 139,l4l, 161, axiscontrol,79,86,89,91-2,98, lengrhoffsets,18, 24, I 17 lists,46,140,145 for lathes.138 simultaneous,65 planewith odgin,27 tip control,79,90-91,l4l Tradeshows,146 Training,144 2 + 3 positioning,49

U UsingmotionsXYZ andC,67 Unlockedrotary drives, 11 U\r!V linear axes,15

v Vericutsoftware,1,95, 106,116-117 Verilication system,27, 104 1, 146-7 Visitingsoftwarecompanies, Virtualmachine,103,105 building,l06 components andmodels,107 configudngfor simulation,105 kinematiccomponenttlee, 107 skeleton,106

w wire franes,79,103,139-40 Worldzero,26,60

x 7,74 XYZ linearaxes,15.32,66

z Zeroingthe indicator,22 17,21,117.158,162 Zeroposition, Z-Maximum,37 Z-Minimum,38

172

secrclsof s-Axislrachining

Virtual MachiningCD Allthe imageson this CD, includingthe virtualmachines,were modeledusinglvlastercam@ (CNCSoftware,Inc.). The virtualmachineswere broughtto life usingthe machinesimulation capabilitiesof l4achsim (lYoduleworks)and VERICUT6(CGTech). Installation The enclosedCD should run automaticallywhen inserted into a CD-ROlqdrive. if the autorun feature does not work. please use File I\4anagerto navigateto the CD. Find the file called Index.htmland dolrble-click it.

System Requirements The CD was built to run ootimallvon a PCwith: . . . . . .

WindowsXP or Vista Internet Explorer(Version7) or higher 1024x 768 resolution(or higher) installed. (Go to http://www.adobe.com/downloads/to install a Adobe@ Acrobat Reader@ free version,) to installa AppleQuickTimeplug-ininstalled.(Go to hftp://www.apple.com/quicktime free version,) If you installthis cD on your hard disk.you will need650 l4Bfree space.

Virtual Machining CD Contents: . over 25 Interactive Machine simulations - self-extractingexecutablefiles launch interactivemachinesimulationsessions.Take control of all aspectsof the simulation, includingview manipulation, simulationspeed,and individualaxis control.Lookat the machiningprocessfrom various views impossibleto see on a real machjne.This offers a uniquevisualization to helpunderstanda varietyof multiaxismachiningconcepts, .

Real Machining videos - watch a real s-axis machine pefform several different 5-axisparts, multiaxiscuttingroutineson complexsimulLaneous

.

virtual Machine Siniulation Videos - WatchVERICUT in action;F it elecutesmachine simulationand verification on over a halfdozendifferentexamplesof complexmultiaxis parts.

.

Printable PDF Files - Quick Referenceguidesfor the most important aspectsof setting up a s-axismachineand commonmultiaxisconceptsall availableas easyprint-outs,

.

Image Gallery - See full colorexamplesof many of the partsand machinesfound throughoutthe book.

Technical Questions: or to the authorat Pleaseemailyour questionsto info@industrialpress,com and go to the link for FAQS. [email protected]. Or visit www.5axissecrets.wordpress.com

Secrets of 5-Axis Machining

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