Construction and Tooling of CNC Machines.pdf

CNC Tooling

1. Construction and Tooling of CNC
Machines

2. CNCTechnologyand
Tooling
⚫Introduction,
⚫ConstructionandworkingofCNC,
⚫DNCandmachiningcenter.
⚫CNCaxes&drives.
⚫AutomaticToolChanger(ATC) andAutomaticpalletchanger
⚫NewtrendsinToolMaterials,
⚫Turningtoolgeometry,
⚫Toolinserts(anduncoated),
⚫ModulartoolingsystemforTurning.Millingtoolingsystems,
⚫Toolspresetting,Workholding.

3. 1.IntroductiontoCNC
machine
CNC=ComputerizedNumericalControl

4. HistoryandDevelopment
of Technology
ConventionalM/C
CNCM/C
NC M/C
(1948USAirforce,)
19971
stcommercialNCm/c
“CINCINNATICHYDROTELVERTICAL-SPINDLEMACHINE“

5. HistoryandDevelopmentof
Technology

6. Conventionalvs.CNC
machine
⚫MachineStructure
TheCNC machinetoolsarebasicallybuiltinthesame
wayasconventionalmachinetools.Thedifferencelies
inthefactthatthemachinecomponentsrelevantfor
turningandmillingprocessesarecontrolledby
computers.

7. Conventionalvs.CNCmachine
⚫Function

8. Conventionalvs.CNC
machine

9. Conventionalmachine
CNCmachine

10. DifferencebetweenConventional
M/C& CNCM/C
Item
Conventional
machine
CNC
machine
1.Movement Acmescrew Ballscrew
2.Feed manual motor
3.measurementmanual Linearscale

11. AdvantagesofCNC
⚫Flexible,highaccuracy
⚫Shortproductiontime
⚫Complexshapes
⚫Shortsettingtime
⚫Noskill requirement(programmingskillisrequired)
⚫Shortinspectiontime/highqualityproduct
⚫Lowcost

12. DisadvantagesofCNC
⚫Highmachinecost
⚫Complicatedmaintenance
⚫Skill&trainingarerequiredforprogrammingand
maintenance.
⚫Hightoolingcost
⚫Temperature,humidity&dustmustbecontrolled.

13. WhyCNC?
HUMANLIMITATION

14. 2.ComponentandFunctionof
CNC
⚫Feeddrive
⚫MeasuringsystemDirect/Indirect
⚫Workspindlehydraulic
⚫Coolingsystemreduceheat
⚫Toolturret
Construction

15. Feeddrive

16. Measuring
System

17. Toolchange
facilities

18. DNC
⚫Directnumericalcontrol(DNC)–controlofmultiple
machinetoolsbyasingle(mainframe)computer
throughdirectconnectionandinrealtime
⚫1960stechnology
⚫Twowaycommunication
⚫Distributednumericalcontrol(DNC)–network
consistingofcentralcomputerconnectedtomachine
toolMCUs,whichareCNC
⚫Presenttechnology
⚫Twowaycommunication

19. DistributedNumericalControl
Machine
ControlUnit
Machine
ControlUnit
Machine
ControlUnit
Central
Computer NCPgms
BTR BTR BTR
ComputerNetwork

20. 3.CoordinateSystem
3.1CNCAxes

21. CNCAXESAND
DRIVES

22. AxesonaCNC
lathe

23. AxesonaCNCmilling
machine

24. Zeroandreferencepointson
CNC

25. ZeroPointofmachineonaCNClathe

26. MachineZeroPointandWorkpartzeropoint
on CNCmillingmachine

27. CNCDRIVES
⚫BasicfunctionofaCNCmachineistoprovide
automaticandprecisemotioncontroltoitselements
suchworktable,toolspindleetc.
⚫Drivesareusedtoprovidesuchkindsofcontrolled
motiontotheelementsofaCNCmachinetool.Adrive
systemconsistsof drivemotorsandballlead-screws.
⚫Thecontrolunitsendstheamplifiedcontrolsignalsto
actuatedrivemotorswhichinturnrotatetheballlead-
screwstopositionthemachinetableorcauserotation
ofthespindle

28. Sr.
No
Feature HydraulicDrive Pneumatic
Drive
ElectricDrive
1Powertoweightratio Highest Lowest Moderate
2 PayloadCapacity Heavy Low Medium
3 ControllingDeviceHydraulicPowerPack Pneumatic
controlsystems
Control systems
needed.
4 Size&stiffness VeryHigh VeryLow LowStiffness
5 Compliance Low Good Better
6Leakage,Cleanliness Worst Better Nil
7ReliabilityofCompo. Low Higher High
8Accuracy&Response Good Bad High
9 Maintenance Needed More Low Less
10PressureTorqueat
actuator
High Medium MediumtoHigh
11OperationalSpeeds Wide VeryLittle Low-High
12 Sparkgeneration No No Possible
27

29. ⚫InCNC,usuallyAC,DC,servoandstepperelectrical
drivesareused.ThevariousdrivesusedinCNC
machinescanbeclassifiedas:
⚫a.Spindledrivestoprovidethemainspindlepowerfor
cuttingaction.
⚫b.Feeddrivestodrivetheaxis.

30. ⚫Thespindledrivesareusedtoprovideangularmotiontothe
workpieceoracuttingtool.Figureshows thecomponentsofa
spindledrive.
⚫Thesedrivesareessentiallyrequiredtomaintainthespeed
accuratelywithinapowerbandwhichwillenablemachining
ofavarietyofmaterialswithvariationsinmaterialhardness.
⚫Thespeedranges canbefrom10to20,000 rpm.The machine
toolsmostlyemployDCspindledrives.Butasoflate,theAC
drivesarepreferredtoDCdrivesduetotheadvantageof
microprocessor-basedACfrequencyinverter.
⚫Highoverloadcapacityis alsoneededforunintendedoverloads
on thespindledueto an inappropriatefeed.

31. FeedDrives
Fig.Typicalfeeddrive

32. Therequirementsofanidealfeeddrive
⚫•Thefeedmotorneedstooperatewithconstant
torquecharacteristicstoovercomefrictionand
workingforces.
⚫•Thedrivespeedshouldbeextremelyvariablewitha
speedrangeofabout1:20000,whichmeansitshould
haveamaximumspeedofaround2000rpmandata
minimumspeedof0.1rpm.
⚫•Thefeedmotormustrunsmoothly.
⚫•Thedriveshouldhaveextremelysmallpositioning
resolution.
⚫VariablespeedDCdrivesareusedasfeeddrivesinCNC
machinetools.However now-a-daysACfeed drivesare
beingused.

34. AutomaticToolChanger(ATC)andAutomatic
palletchanger(APC)
⚫Machiningcentersare used tocarryout multipleoperations
likedrilling,milling,boringetc.inonesetup on multiplefaces
oftheworkpiece.
⚫Theseoperationsrequireanumberofdifferenttools.Tool
changingoperationistimeconsumingwhichreducesthe
machineutilization.
⚫Hencethe toolsshouldbeautomaticallychangedtoreducethe
idletime.This canbeachievedby usingautomatictoolchanger
(ATC)facility.Ithelpstheworkpiecetobemachinedinone
setupwhichincreasesthemachineutilizationandproductivity.
Largenumbersoftoolscanbestoredintoolmagazines.Tool
magazinesarespecifiedbytheirstoragecapacity,toolchange
procedureandshape.Thestoragecapacityranges from12 to
200.

35. Fig.CNCtoolchanger

36. ⚫Thetoolsfromthemagazinesandspindleare
exchangedbyatoolchangerarm.Thetoolchange
activityrequiresthefollowingmotions:
⚫a.Thespindlestopsatthecorrectorientationforthe
toolchangearmtopickthetoolfromthespindle.
⚫b.Toolchangearmmovestothespindle.
⚫c.Toolchangearmpicksthetoolfromthespindle.
⚫d.Toolchangearmindexestoreachthetool
magazine.

37. ⚫e.Toolmagazineindexessothatthetoolfromthe
spindlecanbeplaced.
⚫f.Thetoolisplacedinthetoolmagazine.
⚫g.Thetoolmagazineindexestobringtherequired
tooltothetoolchangeposition.
⚫h.Toolchangearmpicksthetoolfromthetool
magazine.
⚫i.Toolchangearmindexestoreachthespindle.
⚫j.Newtoolisplacedinthespindle.
⚫k.Toolchangearmmovesbacktoitsparkingposition.

38. Advantagesof automatictool changer
⚫Increaseinoperatorsafetybychangingtools
automatically
⚫•Changesthetoolsinsecondsformaintenanceand
repair
⚫•Increasesflexibility
⚫•Heavyandlargemulti-toolscaneasilybehandled
⚫•Decreasestotalproductiontime

39. Toolmagazines
⚫ToolmagazinesaregenerallyemployedinCNCdrilling
andmillingmachines.Comparedtotoolturretsthetool
magazinescanholdmorenumberoftoolsthereforeproper
managementoftoolsisessential.Duplicationofthetools
ispossibleandanewtoolofsametypemaybeselected
whenaparticulartooliswornoff.Thepowerrequiredto
movethetoolsinatoolmagazineismoreincomparison
withthatrequiredintoolturrets.Thefollowingaresome
ofthetoolmagazinesusedinautomation.
⚫1Discordrumtype
⚫2Chaintype
⚫3Racktype type

40. 1 Discor drumtype
⚫Thedisctypetoolmagazinerotatestogetthedesired
toolinpositionwiththetoolchangearm.Largerthe
diameterofthedisc/drummorethenumberoftoolsit
canhold.Ithaspocketswheretoolcanbeinserted.In
caseofdrumtypemagazinewhichcanstorelarge
amountoftools,thepocketsareonthesurfacealong
thelength.Itcarriesabout12to50tools.Ifthe
numberoftoolsarelessthediscismountedontopof
thespindletominimizethetraveloftoolbetween the
spindleandthedisc.If thetoolsaremorethen,the
disciswallmountedormountedonthemachining
centercolumn.Ifthedisciscolumnmountedthen,it
needsanadditionallinearmotiontomoveittothe
loadingstationfor toolchange.

41. Fig.Drummagazine

42. 2Chaintype
⚫Whenthenumberoftoolsismorethan50,chaintype
ofmagazinesareused.Themagazineismounted
overheadorasaseparatecolumn.Inchainmagazines
thetoolsareidentifiedeitherbytheirlocationinthe
toolholderorbymeansofsomecodingonthetool
holder.Thesetypesofmagazinescanbeduplicated.
Therecanbetwochainmagazines:oneisactivefor
machiningandthesecondmagazineisusedwhenthe
duplicatetoolisneededsincetheactivetoolisworn
out.

43. Fig.Chainmagazine

44. Racktypemagazine

45. ⚫Rack magazinesarecost-efficientalternativetousual
toolmagazinesystemsSet-uptimecanbeoptimized
byutilizingtheracks’capacityofupto50tools.The
highstoragecapacityofupto400toolspermitsalarge
productioncapacityofvaryingworkpieceswithout
toolchanges.Theycanalsobeusedtostorework
pieces.