机械制造技术基础课件-chapter3-section2-2012

3.3LocationprincipleofworkpieceInordertofulfillthemachiningrequirementofacertainjob,arelativelyaccuratepositionoftheworkpieceinamachinetoolinrelationtothecuttingtoolduringthemetalcuttingmovementmustbeensured.Thefollowingthreeconditionsmustbesatisfiedwhenfulfillingsuchapracticalfunction,whichare（1）Theaccuratepositionofabatchofworkpiecesinrelationtothejigsorfixtures；(2)Theaccuratepositionofthejigsorfixturesinrelationtothemachinetool;（3）Theaccuratepositionofthecuttingtoolinrelationtothejigsorfixtures.Inthissection,themainattentionisdirectedtotheaccuratepositioningofworkpiecesinjigsorfixtures.Relativepositionbetweenworkpiece,fixtureandmachinetool3.3Locationprincipleofworkpiece（1）movealongaxisX,denotedby•（2）movealongaxisY,denotedby•（3）movealongaxisZ,denotedby•（4）rotatearoundaxisX，denotedby•（5）rotatearoundaxisY,denotedby•（6）rotatearoundaxisZ，denotedbyXYZXYZ3.3Locationprincipleofworkpiece3.3,1The6-pointlocationprincipleoftheworkpiece3.3Locationprincipleofworkpiece•任一物体在空间都有六种宏观运动的可能性，称为六个自由，即沿X、Y、Z轴的移动和绕此三轴的转动，欲使工件在空间取得唯一位置，则必须限制六个自由度。这就是六点定位原理Thereare6possiblemovementsforanyobjectinspace,whichiscalled6-degreeoffreedom.Iftheonlyonepositionfortheobjectisdesignated,the6-degreeoffreedommustbelimited,whichistheprincipleof6-pointlocation.Principleofsix-pointlocationQuestion:Howtodecidethepositionoftheobjectinspace?cbaZYX,,,,,Answer:limitthe6degreesoffreedom3.3LocationprincipleofworkpieceThesix-pointlocationprincipleFig.3-4sixdegreesoffreedomcancelledforaworkpiece3.3LocationprincipleofworkpieceConcepts:•Completelocation(完全定位）：allthesixdegreesoffreedomhavebeencancelled.•Incompletelocation（不完全定位）：notallthe6degreesoffreedomhavebeencancelled,butstillsatisfytherequirement..•Redundantlocation（过定位）:twolocationelementshavebothcancelledthesamedegreeoffreedomforaworkpiece.•Insufficientlocation（欠定位）：thenumberoflocationpointsislessthanthedegreesoffreedomwhichmustbecancelled,theworkpieceisinsufficientlylocated.3.3LocationprincipleofworkpieceZYXa）ZYXb）ZYXc）Completelocationandincompletelocation3.3Locationprincipleofworkpieceb）BBBInsufficientlocation3.3LocationprincipleofworkpieceRedundantlocation3.3LocationprincipleofworkpieceRedundantlocationDefinition——adegreeoffreedom(orseveraldegreesoffreedom)islimitedbytwo(orabovetwo)points.Allowableornot?itmustbedecidedaccordingtothepracticalcondition:1）ifthelocatesurfacehasbeenmachined,anditsshape,dimension,positionhavehighaccuracy,thenredundantlocationisallowable.Sometimesitisnecessary,sincenotonlyitwouldnotinfluencethemachiningaccuracy,butalsoreinforcethestiffnessofthemachiningsystemandstabilityoflocation2）otherwise，itisprohibited,becauseitwillcauseinaccuratelocationorunstablelocation,orlocationinterference3.3LocationprincipleofworkpieceRedundantlocationandeliminationCasestudy:齿轮坯以内孔和一大端面定位，车削外圆和大端面。加工后检测发现大端面与内孔垂直度超差。试分析原因，提出改进意见。4A0.02A间隙配合刚性心轴Casestudy:redundantlocationDeformationcausedbyclamping橡胶垫a）YXZa1）YXZa2）YXZa3）YXZb）XZYXb1）XZYXXZb2）YXXZb3）YXAnalysisofredundantlocation3.3.2Thelocationwaysandelements•Ontheonehand,thedistributionofthelocationelementsinjigsorfixturesmustconformtothesix-pointprinciple.•Ontheotherhand,thedistributionenvelopeofthelocationelementsshouldbeaslargeaspossiblesoastomaketheweightoftheworkpieceandthecuttingforcefallwithintheareaformedbythesupportpoints.locationelementsFixedlocationelementsadjustablelocationelementsAuxiliarysupportelementfloatinglocationsupportsupportpostsupportplatelocationpincenteringshaftV-shapedblock3.3.2Thelocationwaysandelements•（1）Positionedwithplainsurfaceonworkpiece3.3.2ThelocationwaysandelementsSupportpinSupportplate（a)plainhead(b)sphericalhead(c)meshedhead3.3.2ThelocationwaysandelementsAdjustablesupportpin1—screwadjustable2---securenutsQuestion：howmanydegreesoffreedomarecanceledbyeachlocationelement?•（1）Positionedwithplainsurfaceonworkpiece•(1)Positionedwithplaneontheworkpiece3.3.2ThelocationwaysandelementsSelf-adjustablelocationpinQuestion：howmanydegreesoffreedomarecanceledbyeachlocationelement?•(2)Positionedwithcylindricalholesontheworkpiece3.3.2Thelocationwaysandelements(a)Fixedcylindricalpin(b)changeablepin©fulltaperedpin(d)3--segmentedtaperedpin(a)(b)©(d)Note:theselocationelementsarestandardized,andutilizedwithotherlocationelementsQuestion：howmanydegreesoffreedomarecanceledbyeachlocationelement?•(2)Positionedwithcylindricalholesontheworkpiece3.3.2ThelocationwaysandelementsThereare3typesofcylindricalpins,whicharelongpin(l/d0.8~1),shortpin(l/d0.4)andrhombicpin(削边销）Question：howmanydegreesoffreedomarecanceledforeachlocationelement?rhombicpin•(3)Positionedwithexternalcylindricalsurfaceontheworkpiece3.3.2ThelocationwaysandelementsQuestion：howmanydegreesoffreedomarecanceledforeachlocationelement?HBαOAintegrated-shapedblockdiscontinuousv-shapedblockSeparatedV-shapedblock3.3.3Symboloflocationandmarking3.3.3Symboloflocationandmarking3.3.3Symboloflocationandmarking3.3.3Symboloflocationandmarking3.3.3Symboloflocationandmarking(3)Cylindricallocationpin（圆柱形定位销）FittingtolerancebetweenpinandthefixturebodyisH7/r6,orH7/n6betweenthe