互换性与测量技术(汉英双语).ppt

Tolerancesandfits Thisbookincludestablesandcalculationsforeasyoptionoffitsofmachinepartsanddeterminationoftheirdimensionaltolerancesanddeviations Usingthistoolthefollowingtaskscanbesolved SelectionofsuitablefitsofmachinepartsaccordingtotheinternationalstandardISO286 DeterminationofdimensionaltolerancesanddeviationsofmachinepartsaccordingtotheinternationalstandardISO286 SelectionofpreferredfitsofmachinepartsanddeterminationoftheirdimensionaltolerancesanddeviationsaccordingtoANSIB4 1 Determinationofnon prescribedlimitdeviationsoflinearandangulardimensionsaccordingtoISO2768 Automaticdesignofafitforthegivenclearanceorfitinterferencerespectively Basicterms Itisnecessarythatthedimensions shapeandmutualpositionofsurfacesofindividualpartsofmechanicalengineeringproductsarekeptwithinacertainaccuracytoachievetheircorrectandreliablefunctioning Routineproductionprocessesdonotallowmaintenance ormeasurement ofthegivengeometricalpropertieswithabsoluteaccuracy Actualsurfacesoftheproducedpartsthereforedifferfromidealsurfacesprescribedindrawings Deviationsofactualsurfacesaredividedintofourgroupstoenableassessment prescriptionandcheckingofthepermittedinaccuracyduringproduction DimensionaldeviationsShapedeviationsPositiondeviationsSurfaceroughnessdeviations MoreTerminology NominalSize Generalidentificationinfractions ex 1 1 2for1 500 BasicSize Generalidentificationindecimal ex 1 500 d D basicsize ActualSize Measuredsize Limits Maximumandminimumsizesindicatedbythetolerancedimensions Dmax Dmin limitsofsizeforthehole dmax dmin limitsofsizefortheshaft ES holeupperdeviationEI holelowerdeviationes shaftupperdeviationei shaftlowerdeviationES Dmax DEI Dmin Des dmax dei dmin d Toleranceisthetotalamountaspecificdimensionispermittedtovary differencebetweenthemaximumandminimumlimits Th Dmax Dmin ES EITs dmax dmin es ei es 14 996 15 0 004ei 14 993 15 0 007Ts dmax dmin es ei 0 003Thedimensionbelowhasatoleranceof0 003 MaximumMaterialCondition Whenspecifyingtolerancedimensions themaximummaterialcondition MMC meanstheproductorpartcontainsthemaximumamountofmaterialspecifiedbythetolerance TheheaviestpartDM DmindM dmax LeastMaterialCondition Whenspecifyingtolerancedimensions theLeastmaterialcondition LMC meanstheproductorpartcontainstheleastamountofmaterialspecifiedbythetolerance ThelightestpartDL DmaxdL dmin tolerancezones ZeroLineAbovePositiveBelowNegativeDrawupperdeviationandlowerdeviationinthezoneMarktheBasicdimensionontheleft Dependingonthemutualpositionoftolerancezonesofthecoupledparts 3typesoffitcanbedistinguished ClearancefitTransitionfitInterferencefit ClearancefitXmax Dmax dmin ES eiXmin Dmin dmax EI esXav Xmax Xmin 2 Transitionfit Ymax Dmin dmax EI esYmin Dmax dmin ES eiYav Ymax Ymin 2 Interferencefit Xmax Dmax dmin ES eiYmax Dmin dmax EI esXav或Yav Xmax Ymax 2 FitTolerance Clearancefit Tf Xmax Xmin Interferencefit Tf Ymin Ymax Transitionfit Tf Xmax Ymax Tf ES ei es EI ES EI es ei Th Ts FitSystem Hole basicsystemoffit shaft basicsystemoffit Practise Thestandardtoleranceseries IT figureIT01 IT0 IT1 IT2 IT18Accuracy fromhightolow PrecisionDegradation tolerance value fromlowtohighmanufacture fromhardtoeasy standardtolerancetable basicdeviation 26Englishletterseliminatei l o q waddcd ef fg js za zb zcintotal28seriesLowercaseexpressshaftCapitalexpressholeforexample 25f6 30T7 80js7 CharacteristicsandApplication A Hlowerdeviationisbasicdeviation itispositivea hupperdeviationisbasicdeviation itisnegativeEI esP ZCupperdeviationisbasicdeviation itisnegativem zclowerdeviationisbasicdeviation itispositive IT7ES ei IT7ES ei ITn ITn 1 K M Nupperdeviationisbasicdeviation IT8ES eiIT7 otherisIT3 IT7 Basicsize0to500mmbasicdeviationofshaft Basicsize0to500mmbasicdeviationofhole 一 Generalconceptsofgeometricaltolerances1 FormerrorFormerroristhevariationofthetrueformofasinglefactortoitsperfectform Makeasmallshaftfoundtobedistortionandnotcylindrical orthesectionisoutofround ortheaxesisbended ormakeaplanefoundtobewarp GeometricalTolerances 2 PositionerrorPositionerroristhevariationoftheactualpositionofrelatedfactorstoitsidealpositionform Whilemachiningasteppedshaft theaxialcordofeachstepmaynotbeThesame namely concentricityandcoaxialityerror Surfacesexpectedtobeperpendiculararenotperpendicularafteritmachined 二 Codesofgeometricaltolerances 1 Geometricaltolerances 2 Codeofgeometricaltolerance Thecodeofthegeometricaltoleranceisreprsentedbytheformandpositionframes 3 Referencecode Thereferencecodeismadeupofthecapitalletterwithasmallcircleconnectedbyfinelinesandshortthicklines Inordertoavoidmisunderstanding generally E I J M O Pandsuchlettersarenotadopted 二 Methodofmarkinggeometricaltolerances 1 Iftheelementbeingtestedwithatolerancerequirementisacontourlineorsurface pointthearrowanddatumsymboltothecontourlineorsurface andkeepitawayfromthedimensionline 2 Iftheelementbeingtestedwithtolerancerequirementsisanaxis centrelineorsymmetricalplane thearrowanddatumsymbolshouldbealignedtothedimensionlineofthatelement 3 Iftheelementbeingtestedisasurfaceonthedrawing onecandrawareferencelinewithadotendandpointthearrowordatumsymboltothereferenceline Exercises Markgeometricaltolerancesinthedetaildrawing 1 30k6cylindricaltoleranceisnotlargerthan0 01 2 20H7straightnesstolerancetoleranceisnotlargerthan0 04 3 Thecoaxiatolerance 30k6to 20H7isnotlargerthan0 05 4 Pplaneto 30k6perpendicularityisnotlargerthan0 02 5 Pplaneflatnesstoleranceisnotlargert