机械制造技术基础课件-新第2章课件(2)

Theforcesactingonthetoolandtheworkpiecearecalledcuttingforces.2.1.2Cuttingforces2.1.2.1Sourcesofcuttingforces,resultantforcesaswellcomponentsofcuttingforces2.1.2.2Measurementofcuttingforceandestablishmentofempiricalformulas2.1.2.3Specificcuttingforceandspecificcuttingpower2.1.2.4Influenceofvariousfactorsoncuttingforce2.1.2.1Sourcesofcuttingforces,resultantforcesaswellascomponentsofcuttingforcesTheforcesactingonthetoolcomefromtwosources:①resistancetometalelasticandplasticdeformationinthedeformationregions;②frictionsbetweentoolandchipandbetweentoolandmachinedsurface.(a)freeorthogonalcuttingFig.2.21ResultantforcesandcomponentsofcuttingforcesResistanceFnyanti-plasticdeformationontherakefaceFrictionforceFfytangentialtotherakefaceTheresultantforceFrResistanceFnaanti-elasticandplasticdeformationnormaltotheflankfacefrictionforceFfatangentialtotheflankfaceFig.2.21Resultantforcesandcomponentsofcuttingforces（b）obliquecutting.Inordertomeasure,calculatecuttingforcesandanalyzetheeffectsofcuttingforces,usuallytheforceFrisdecomposedintothreecomponentsofforces:MaincuttingforceFzRadialthrustforceFyAxialthrustforceFx2.1.2.1Sourcesofcuttingforces,resultantforcesaswellascomponentsofcuttingforces（c）obliquecuttingFromFig2.21(b)thereistherelation:where,FxyisthecomponentofFrinthetoolreferenceplane,Fy=FxycosκrFx=Fxysinκr22222xyzxyzrFFFFFF(2.11)2.1.2.1Sourcesofcuttingforces,resultantforcesaswellascomponentsofcuttingforcesFig.2.22straintransducer-dynamometersl一transducer；2一circuitry；3一straingauge；4一recording2.1.2.2Measurementofcuttingforceandestablishmentofempiricalformulas(1)TheprincipleofdynamometersAsinglefactormethodandamulti-factormethodcanbeusedtoestablishempiricalformulaforcuttingforce.Theregularformsofempiricalformulaofcuttingforceareasfollows:—effectcoefficients,theirvaluesarerelatedtoexperimentconditions;—effectindicesofbackengagementofthecuttingedgeaponthecuttingforce;—effectindicesoffeedfonthecuttingforce;——correctioncoefficientsonthecuttingforceduetothedifferencebetweencalculationandpractice(2)EstablishmentofempiricalformulasforturningzzFzFzFyxpFzKfaCFyyFyFyFyxpFyKfaCFxxFxFxFyxpFxKfaCF(N)(2.12)(N)(2.13)(N)(2.14)zyXFFFCCC,,zyxFFFxxx,,zyXFFFyyy,,zyxFFFKKK,,2.1.2.2MeasurementofcuttingforceandestablishmentofempiricalformulasTakethebuildingoftheempiricalformulaofmaincuttingforceFzasexampleFig,2.25Straightlineinthedual-logarithmcharts(a)αp－Fz；（b）f－Fz(a)(b)Withaseriesofexperimentalvaluesforap-Fzandf-Fz,wecanconnectthesepointsinthedual-logarithmchartsandobtaintwostraightlinesshowninFig2.25.Cuttingdepthfeed2.1.2.2MeasurementofcuttingforceandestablishmentofempiricalformulasTheequationsfortwolinesare:lgFz＝1gCap十xFzlgap1gFz＝1gCf十yFzlgfTheaboveequationscanbechangedintothefollowingforms:Combiningequations(a)and(b)wegettheempiricalformulaforthemaincuttingforce—theslopeofstraightlineap-Fz,f-Fz.—theinterceptofstraightlineap-Fz,f-Fz—theevaluationfromthecombinationofequations(a),(b)FzyfzfCFzFpxpazaCF(a)(b)zFzFzyxpFzfaCF(c)zzFFyx,faCCp,zFC2.1.2.2Measurementofcuttingforceandestablishmentofempiricalformulas(3)Theprincipleofpiezo-electrictransducerFig2.26isapictureofapiezo-electrictransducerformeasuringforcesinthreeorthogonaldirectionsFig.2.26piezo-electrictransducer2.1.2.2Measurementofcuttingforceandestablishmentofempiricalformulas2.1.2.3Unitcuttingforceandcuttingpower(1)UnitcuttingforceUnitcuttingforcepmeansthemaincuttingforcerequiredintheremovalofaunitareaofcuttinglayer.Itiscalculatedwiththefollowingequation:Theformulashowsthatpisnotinfluencedbybackengagementofthecuttingedgeap,becausewhenapchangescuttingforceFz,andcuttinglayareaADalsochangeinthesameproportion.AlthoughADisincreasedwiththeincreaseoff,Fzincreasesslightly.ItismorestraightforwardtoutilizetheunitcuttingforcepforthecalculationofthemaincuttingforceFz.21/mmNfCfafaCAFpZFzzFzFzyFpyxpFDZ(2.15)（2）CuttingpowerCuttingpowermeansthepowerexpendedinthecuttingregion.Usuallythepowerexpendedbythemainmotioniscalculatedas.whereFz—themaincuttingforce(N);vc—thecuttingspeedofthemainmotion(m/min).ThepowerPErequiredbythemachinemotoris:PE=Pm/ηkW（2.17）whereη—machinetransmissionefficiency.kWvFPczm60103(2.16)2.1.2.3UnitcuttingforceandcuttingpowerUnitcuttingpowerPsmeansthepowerexpendedinaunittimefortheremovalofaunitvolumemetalZw.Ps=Pm/ZwkW/（）(2.18)Thefollowingrelationcanbedeveloped:Table2.1listssomeexperimentalvaluesofunitcuttingforcepandunitcuttingpowerPs.Intheexperimentacarbidetoolwasusedandfeedf=0.3mm/rwasfixed.Iffeedfischanged,thevaluesofpandPsinthetableshouldbemultipliedbythecorrectionalcoefficientsKfp、KfpswhicharelistedinTable2.2.13.smm)./(101010001363smmkWpfvafvpaZPPcpcpwms(2.19)（3）Unitcuttingpower2.1.2.3UnitcuttingforceandcuttingpowerTable2.1UnitcuttingforcesandcuttingpowersforvariousworkmaterialscutbyacarbideturningtoolWorkpiecematerialConditionsofexperimentUnitcuttingforceunitcuttingpowerNameMarkStateHardness（HB）CuttingtoolgeometryRangeofcuttingparametersP（N/）P[kW/()]StructuralcarbonsteelandstructuralalloysteelA3HotrolledOrnormalized134～137γ0＝15°kr＝75°λs＝0°br1＝0withbreake