机械制造技术基础英文课件CHAPTER6

Chapter6MachiningAccuracyAbstractThemachiningaccuracyofmachinepartsisthequalityfoundationofthewholemachine.Itisusuallymeasuredwithtwoindices:machiningaccuracyandsurfacequalityandtheirvaluesizewilldirectlyaffecttheperformanceandlifeofthewholemachine.Thischaptermainlyinvolvesthemachiningaccuracy.Thebasicconcepts,factorsthatarerelatedwiththemachiningaccuracy,thecomprehensiveanalysisofmachiningerrors,andthemethodsofraisingthemachiningaccuracyarediscussedinthischapter.Index7.1Basicconceptsofmachiningaccuracy7.2factorsaffectingthemachiningaccuracy7.3statisticanalysisofmachiningerrors7.4methodsofraisingthemachiningaccuracy6.1Basicconceptofmachiningaccuracy6.1.1MachiningaccuracyandmachiningerrorMachiningaccuracy：Thedegreeofthepracticaldimensionsaftermachiningconformstothedesiredgeometricalparameters.Thehigherthedegreeconforms,thehigherthemachiningaccuracy.Machiningerror：Thedegreeofthepracticaldimensionsaftermachiningdeviatesfromthedesiredgeometricalparameters.Thesizeofthemachiningerrordenotesthesizeofthemachiningaccuracy.“Machiningaccuracy”and“Machiningerror”aretwodifferentconceptstoevaluatetheaccuratedegreeofthepartgeometries.Inproductionpractice,theaccuracyisensuredbycontrollingthemachiningerrororactiveadaptingmethod。6.1.2ThemethodtostudythemachiningaccuracyTherearetwomethodstostudythemachiningaccuracy.Oneisthesinglefactoranalysismethod,inwhichthemachiningaccuracyisanalyzedbycalculation,experimentorinspectionsoastodecidethesinglefactor’sinfluencinglawtothesingleerror.Anotheroneisthestatisticmethod,inwhichthestatisticaltheoryisusedtoprocesstheinspecteddataofabatchofworkpiecefromthepracticesoastocontroltheprocessrunninginnormalcondition.Thesetwomethodsareoftenusedtogetherinpractice.Generally,thestatisticmethodisfirstusedtofindoutthelawoftheerror,andjudgethecauses,thenfactoranalysismethodisusedtofindoutthekeyfactorswhichinfluencethemachiningaccuracy.6.2FactorsaffectingthemachiningaccuracyPartmachininghappensintheprocessingsystemcomposedofmachinetools,fixtures,cuttingtoolandworkpiece.Allthefactorsinthesystemthatmaycausemachiningerrorsarecalledtheoriginalerrors.Theexistenceoftheoriginalerrorsmakesthepositionalormotionalrelationshipdeviatedfromitsdesiredstate,andbringsaboutthemachiningerror.Iftheoriginalerrorsexistedbeforemachining,orinanotherword,itiscausedwithoutthecuttingforce,itiscalledthestaticprocessingerror,otherwise,itiscalledthedynamicprocesserror.ClassificationoforiginalerrorOrigianlerror(原始误差）BeforemachiningInmachiningAftermachiningPrincipleerrorAdjustmenterrorSetuperrorMachinetoolerrorFixtureerrorCuttingtoolmanuerrorDeformationunderforceThermaldeformationCuttingtoolwearDeformationbyinnerstressInspectionerrorDynamicerrorStaticerrorDeformationundercuttingforceGeometricaccuracyofthemachinetoolToolwearWorkpieceaccuracyControlsystemaccuracyLocationandclampingaccuracyWeightdeformationThermaldeformation7.2.1ErrorofmachiningprincipleMachiningprinciplereferstotheformingprincipleofthesurfaceontheworkpiece.Theerrorofmachiningprincipleiscausedbysimilarcuttingmotionofformingorsimilarcuttingedgegeometry.Thepurposeistosimplifythedesignandmanufacturingofthemachinetoolandcuttingtool,reducethemanufacturingcost,raisetheproductionefficiencyandfacilitatetheuse.7.2.2ErrorofthemachinetoolErrorofthemachinetoolreferstothemanufactureerror,setuperrorandwearcomefromthemachinetoolwithoutcuttingforce.7.2.2.1spindlerotationalerror（1）conceptofspindlerotationalerrorTheoretically,thepositionoftherotationalaxisofthespindleinthespaceisfixed,orinanotherword,theinstantspeediszero.Butinpractice,therearealotoffactorsinfluencethepositionofthespindleandmakethespindlepositionchangeinstantly.Wecallthemaximumfloatingvalueinthesensitivedirectionoftheerrortherotationalerrorofthespindle.Pureangularmove：Thepracticalaxismovesinclinedtothedesiredaxiswithaconstantamplitude,andthejointpointkeepsconstant.Pureradialjump：Thepracticalaxisisparalleltothedesiredaxis,butjumpinconstantamplitudePureaxialjump：Thepracticalaxismovesalongthedesiredaxiswithconstantamplitude.Therearethreetypesofspindlerotationalerror,shownbelow：movieFig.1thethreetypesofthespindleerrorofthemachinetool(a)Pureradialjump(b)pureaxialjump(c)pureangularmove（2）influenceofthespindleerroronmachiningaccuracyDifferentrotationalerrorofthespindlehasdifferentinfluenceonthemachiningaccuracy,eventhesamerotationalerrorhasdifferentinfluencewhenthemachiningmethodisdifferent,shownasFig.6.5、6.6、6.7、6.8andtable6.1.moviemovie(a)Turninginfluencedbyradialjump(b)BoringinfluencedbyradialjumpmovieEndsurfaceinfluencedbyAngularmoveBoringinfluencedbyAngularmovementerrorTable1influenceofthespindleerroronthesurfacesunderdifferentmachiningmethod6.2.2.2ErroroftheguidewayTheguidewayofthemachinetoolisthemainreferencedatumfortherelativepositionandmotionofthemaincomponentswiththeothercomponents.Itwillinfluencethemachiningaccuracydirectly.（1）linearerrorintheverticalplanemovieThelinearerrorintheverticalplaneoftheguidewayonahorizontallatheorexternalcylindricalgrindingmachinecanbeomittedbecausetheerrorisinthenon-sensitivedirectionwhi