机械制造技术基础课件-chapter3-section4-2012

2021/6/28SCUT1Areferenceisusedtodefinethepositionofotherpoints,linesorsurfacesofthepart.Itisalsocalledthepositioningreferencedatum.3.4selectionofreference(datum,基准)3.4.3Calculationoflocationerror•Inordertoensurethemachiningquality,thefollowingformulamustbeensured,•here,——thesumoferrorscausedbydifferentfactors.——thetoleranceoftheworkpiecetobemachined.TssT2021/6/282SCUT•Inthissection,onlythelocationerrorsrelatedwiththedesignofjigsorfixturesarediscussed，Therefore,aboveformulacanberewrittenas:where-----thelocationerror；------thesumoftheothererrorsexceptforthelocationerror,whichcanbefoundinhandbooksaccordingtotheeconomicmachiningaccuracy.Telel2021/6/283SCUT3.4.3Calculationoflocationerror3.4.4ThecomponentsoflocationerrorTheso-calledlocationerroristhepositionalerrorbetweenthemachiningsurfaceandtheoperationaldatumsurfacecausedbytheworkpiecelocation.Forabatchofworkpieces,thepositionofthecuttingtoolkeepsconstantafteradjustment,namely,thepositionofthesurfacetobemachinedinrelationtothedatumisconstant.therefore,thelocationerroristhemaximumvariationoftheoperationaldatuminthedirectionofmachiningdimensionTherearetwoaspectsmadeupofthelocationerror：2021/6/284SCUTbΔDWaTheoperationaldatumThelocationdatum3.4.4Thecomponentsoflocationerror2021/6/285SCUT①Thelocationerrorcausedbytheconflictionbetweenthelocationdatumandtheoperationaldatum.,alsocallednon-superpositionerrorn3.4.4Thecomponentsoflocationerror2021/6/28SCUT6②Thelocationerrorcausedbythemanufacturingerrorofthelocationelements(定位元件)andthelocationdatum(定位基准).Therefore：Thisformuladescribesanalgebrasuminthemachiningdirection.dnel＋dLocationerrorHOAO1O23.4.5ThecalculationoflocatingerrorsTheplane-locatederrorBBAALLBACF'FD'E'EDL222HL12021/6/287SCUT•（1）TheerrorwithplanelocationTheFig.showsthelocationsituationwhentwothoroughholesAandBinablockworkpiecearemachinedwithaboringmachine.Astheholesarethorough,thestoplocationdatumisnotnecessary.2021/6/288SCUT•①EnsuredimensionsA1BBAALLBACF'FD'E'EDL222HL1THedtan2(A1)THeeeeAdAdAnltan2)1()1()1((A1)01eAn）（3.4.5Thecalculationoflocatingerrors2021/6/289SCUTBBAALLBACF'FD'E'EDL222HL1②DimensionsA222LAne）（02eAd）（2222LAdAnALeee）（3.4.5Thecalculationoflocatingerrors2021/6/2810SCUT③EnsuredimensionsB1WhenholeB1ismachined,theoperationaldatumofdimensionB1issurfaceF，butthelocationdatumissurfaceD.thefollowingequationistenable:BBAALLBACF'FD'E'EDL222HL111BLn）（tg2H1B）（dtg2H1111LBdBnB）（）（）（e3.4.5Thecalculationoflocatingerrors2021/6/2811SCUTDimensionsB2:thelocationdatumissurfaceC，then：hence,④EnsuredimensionsB2Note:inmostcases,themanufacturingerrorisnotconsideredwhentheplaneisusedasthelocationelement.0)(2Bne0)(2Bde0)()()(222BdBnBleeeBBAALLBACF'FD'E'EDL222HL13.4.5Thecalculationoflocatingerrors（2）Thelocationerrorwhentheinternalcylindricalsurfaceisusedasthelocationdatum①Whentheworkpieceismountedinacenteringshaft,asboththeoperationalandlocationdatumisthecenterofthepart,thedatumisinsuperposition.then0n②Astheclearancefitisappliedbetweentheholeoftheworkpieceandthecentershaft,andthemanufactureerrorisalsoinvolved,thepositionofthecentrallineoftheholevaries.Thepositionalerrorofthedatumis:ddne2021/6/2812SCUT3.4.5Thecalculationoflocatingerrors2021/6/2813SCUTDDddThediameterdimensionoftheholeisThediameterdimensionofthecenteringisAndtheminimumfitclearanceiscminThesituationswillbeconsideredaccordingtothepositionofthecentershaft3.4.5Thecalculationoflocatingerrors①Whenthecentershaftisputintheverticaldirection•ShownasFig.a,thepositionalvariationoftheholeiscalculatedaccordingtothemaximumdimensionoftheholeandtheminimumdimensionofthecentershaft,whichis:maxminmin21)222(2CCTTCTTOOedDdDLFig.aDmaxdminOelO1O22021/6/2814SCUT3.4.5Thecalculationoflocatingerrors②Whenthecentershaftisputinthehorizontaldirection•shownasFig.(b)，theworkpieceisalwaysonthesamesideofthecentershaftbecauseofitsdead-weight，andthepositionalvariationofthecentrallineoftheholeisintheverticaldirection.Themaximumvalueis:Fig.aDmaxdminOelO1O22021/6/2815SCUTmaxmin12121C)CT(TOOedDL3.4.5Thecalculationoflocatingerrors(3)Thelocationerrorwhentheexternalcylindricalsurfaceisusedasthelocationdatum—V-shapedblocktolocatethecylindricalcenter2021/6/2816SCUTHBαOAOA=Sin(α/2)OB=Sin(α/2)dd(OA)=Sin(α/2)1d(d)－dd(Sin(α/2)2cos22sin4sin22dDWdTTen=IgnorethesmallhighorderitemandtheangularerroroftheV-shapedblock,then2sin2dDWTen=b）a）H2BOH1BOAC•Fig(a)andFig.(b)givetwosituationsthatthekeywayismarked.2021/6/2817SCUTQuestion:Whatisthedifferencebetween(a)and(b)?Howtocalculatethetotallocationerror?111122sin21122sin2dDWdDWTTel1el2el2=BB1=BE-B1E=(BA+AE)-(B1A1+A1E)=BA+AE-B1A1-A1E=d/2+d/[2sin(α/2)-(d/2-△d/2)-(d-△d)/[2sin(α/2)]=△d/2[1+1/sin(α/2)]设KB=1/2[1+1/sin(α/2)]el1=CC1=EC-EC1=(AE-AC)-(A1E-A1C1)=AE-AC-A1E+A1C1=d/[2sin(α/2)]-d/2-(d-△d)/[2sin(α/2)]+(d-△d)/2=△d/2[-1+1/sin(α/2)]设KC=1/2[-1+1/sin(α/2)]2021/6/2818SCUTExamplesforcalculatingthelocationerror•【Example5.1