机械制造技术基础课件-chapter3-section5-2012

3.5ClampingoftheworkpieceInordertosecuretheworkpieceinthelocatedpositionwhilstundertheactionofthecuttingforce,inertialforceandgravityforce,aclampingdevicemustbeincorporatedintojigsandfixtures.Asthemachiningqualityandproductionefficiencyaredirectlyrelatedtotheclampingdevicedesignandselection,therefore,thefollowingrequirementsmustbeensuredinclampingdevicedesign,namely:accurate,rapid,secureandsolidclamping,easyandlighthandling,simplestructureandeasymanufacturing.2021/9/181SCUT2021/9/18SCUT2Concern：ClampingforceForcemagnitudeClampingdirectionClampingpositionThreeimportantaspects2021/9/183SCUT3.5.1TheclampingdirectionIndetail,thefollowingthreeaspectsshouldbetakenintoaccount：（1）Whentwoormorethantwosurfacesareusedasthelocationdatum,iftheworkpieceislarge,theclampingforceshouldbedirectedtowardseachofthelocationdatumfacessoastokeepthecorrectpositionoftheworkpiece；Iftheworkpieceissmall,aswellasthecuttingforce,theclampingforceonlyneedstobedirectedtowardsthemainsupportsurfacesoastoensurethatthereisenoughcontactareabetweenthemaindatumsurfaceandthelocationelements,andthereafter,tomakesuretheworkpieceisstableandclampedsafely.2021/9/184SCUT（2）Theclampingdirectionshouldbeeasyforsetupandtogetalowclampingforce.Fig.3-5-1showssomecombinedrelationshipsbetweentheclampingforce,gravityandthecuttingforceQuestion:whichoneneedstheleastclampingforce?Fig.3-5-12021/9/185SCUT（3）TheclampingdirectionshouldbechosentoreducetheclampingdeformationoftheworkpieceAstheworkpiecemayhavedifferentstiffnessesindifferentdirections,theclampingdeformationmayalsobedifferentunderdifferentclampingdirections.Fig.(a)showsthatathreejawchuckisclampingathinsleeveworkpieceintheradialdirection.2021/9/186SCUT2021/9/187SCUT(a)(b)3.5.2TheclampingpositionAftertheclampingdirectionisdecided,theclampingpositionandnumberwilldirectlyaffectthestabilityanddeformationoftheworkpiece.Usually,thefollowingaspectsshouldbetakenintoaccountindecidingtheclampingpositionandnumber：（1）theclampingpositionshouldsecurethelocationinsteadofmakingtheworkpiecemoveorrotate.andclosetothegeometricalcenterofthesupportsurface,anddistributetheclampingforceuniformlyinthecontactsurface.InFig.(a)and(b),theclampingforceQwouldbebetterreplacedbyQ1.2021/9/188SCUT8-368-372021/9/189SCUT（2）Theclampingpositionshouldbeintheplacewheretheworkpiecehasalargerstiffness,andthenumberofclampsshouldbesufficienttominimizetheclampingdeformation.inFig.(c)and(d),theclampingforceQwouldbebettercedbyQ1.（3）Theclampingpositionshouldbeascloseaspossibletothecurrentmachinedsurfacetoreducethecuttingtorquecausedbythecuttingforce,aswellasthevibration.2021/9/1810SCUT3.5.3ThemagnitudeofclampingforceEnsuringthattheworkpiececankeeptheoriginallocationpositionduringmachiningisnotonlyrelatedtotheclampingdirection,theclampingpositionandnumber,butalsomorerelatedtothemagnitudeoftheclampingforce.Thepracticalclampingforceshouldbe：Q＝K•Q’Here，safecoefficientK，itisbetween1.5~2.；desiredclampingforceQ’Forsomeveryimportantjigsorfixtures,itisusuallyachievedbyexperiment.2021/9/1811SCUTAppendix.1--TheCommonlyusedclampingdevices1.Wedgeclampingdevice(斜楔夹紧）PQPQ2021/9/1813SCUT)tan(tan12PQForcetransmittingcoefficient:ip=Q/P=1/[tgφ2+tg(α+φ1)],Pistheactualclampingforcegenerated.Application:wedgeclampingdeviceisusuallyusedinpoweredclampingdevicestoclampworkpieceswithsmalldimensionaltolerance.Shortcoming:requirealongworkingdistanceforthewedgesurface,whichwillmakethestructureloose,anddecreasethespeedofclampingvelocity.2021/9/1814SCUT2.ScrewclampingdeviceScrewclampingdeviceisoriginatedfromthewedgeclampingdevice,asitworkswiththesameprincipleofawedgeclampingdeviceinthat,thewedgehasbeenwrappedaroundacylindricalcolumn,soscrewdownthescrewandclamptheworkpiece.2021/9/1815SCUT2021/9/1816SCUT(1)ThecalculationofscrewclampingforceWhentheworkpieceisclamped,showninFig.6-40,thefollowingformulaistenableaccordingtothetorquebalanceprinciple,M=M1+M2whereM----theoriginaltorqueimposedonthescrewM1----thereactedtorqueimposedonthescrewbythescrewnutM2----thereactedtorqueimposedonthescrewbytheworkpiece.中螺母图5-40螺旋夹紧计算Q1RRRP'RQFFRPLr1rF22021/9/1817SCUT中螺母图5-40螺旋夹紧计算Q1RRRP'RQFFRPLr1rF2PQPQ11200r()24mPLQtgrtg螺旋升角（）自锁条件：122021/9/1818SCUTQ=R1ywhileR1x=R1y·tg(α+φ1)=Q·tg(α+φ1)F2=Q·tgφ2•Therefore,211)(rtgrtgPLQmα----thescrewascendingangle，generallyα=2~4°;φ1---thefrictionalanglebetweenscrewnutandscrew；φ2----thefrictionalanglebetweentheworkpieceandthescrewhead2021/9/1819SCUT2021/9/18SCUT20Advantages：simplestructure,goodmachinability,longclampingdistance,largerforcetransmittingcoefficientandgoodlockperformance。disadvantage:slowclampingandlowefficiency.ScrewclampingdeviceStandardfloatingclampingblockThecompoundclampingdeviceformedbyscrewandclampingplate2021/9/1821SCUT2021/9/1822SCUT3.EccentriccylindricalclampingdeviceTheeccentricclampingdevicealsocomesfromthewedgeclampingdevice,orinotherwords,itworkswiththesameprincipleasthewedgeclampingdeviceinthat,thewedgeiswrappedaroundacylindricaldisk,andtheworkpiececanbeclampedbyrotatingthedisk.观看动画.Eccentricc