机械制造技术基础课件-新第2章课件(1)

Chapter2BasicrulesinthemetalcuttingprocessandtheirapplicationsIntroduction2.1Basicrulesinthemetalcuttingprocess2.2ApplicationofthebasicrulesinmetalcuttingIntroductionFourbasicrulesinthemetalcuttingprocessandseveralaspectsofapplicationinproductionwillbediscussedinthischapter.Inthecuttingprocess,aseriesofphenomenasuchasmetaldeformation,cuttingforce,cuttingheatandtemperature,toolwearetcoccur.Thischapterinvestigatedthecauses,effectsandrulesofthesephenomena.2.1.1Cuttingdeformation2.1Basicrulesinthemetalcuttingprocess2.1.2Cuttingforces2.1.3cuttingheatandtemperature2.1.4Toolwearandtoollife2.1.1CuttingdeformationmetalcuttingprocessVSthemetalcompression(orstretching)process：(a)compressed（b）Cutting(freeorthogonalcutting)themetalexperienceselasticdeformation,plasticdeformationandcrystallatticeslide,thenfracture.ifweignoretheeffectsoffrictionandtemperatureaswellasstrainspeed.Whenpressed,thecuttinglayergeneratesplasticdeformation.M刀具切屑OA终滑移线始滑移线：τ=τsΦ剪切角2.1.1CuttingdeformationFig2.2MetalcompressionandmetalcuttingDividethemetallayeragainstthetoolintothreedeformedregions,asshowninFig2.2(c):regionI:theplasticdeformationregioninthecuttinglayerclosetothecuttingedge;regionII:theplasticdeformationregioninchipbottomlayerclosetothetool-chipinterface;regionIII:theplasticdeformationregioninthemachinedsurfacelayerclosetothecuttingedge.（c）Threeregionsofdeformation2.1.1CuttingdeformationⅠⅢⅡ2.1.1Cuttingdeformation2.1.1Cuttingdeformation2.1.1.5Lawsofvariationforcuttingdeformation2.1.1.1Chipformation2.1.1.2measurementofdegreeofdeformation2.1.1.3Chiptypes2.1.1.4Frictionintool-chipinterfaceandbuilt-upedge(1)Shearingslide(剪切滑移）inthefirstregionofdeformationThemetalinthecuttinglayerpassesthroughthefirstregionofdeformationandthenbecomesachip.Thefollowingisanexampletoanalyzetheformationoftypicalcontinuouschips.(a)TheslidingofapointFig2.3Chipformation2.1.1.1Chipformation①pointPinthecuttinglayerisgraduallyapproachingtothecuttingedgeandreachesposition1,plasticdeformationtakesplace.②thepointmovesforwardcontinuouslytopoint1′,andslidesalonglineACtopoint2simultaneously.thedistance1—2′istheslippage③thepointslidestopoint3andpoint4inturn,afterleavingpoint4,itflowsoutalongtherakeface(b)ChipformationmodelFig2.3ChipformationAsshowninFig2.3(b):thecuttinglayermovesforwardtotheshearplaneAB,thenitslidesandbecomesinthechip.TheprocesstakesplacecontinuouslymnnmTheincludedangleφbetweentheshearplaneABandthedirectionofcuttingspeediscalledtheshearangle;TheincludedangleωbetweenforceFrandthedirectionofcuttingspeediscalledtheactingangle.RegionIiswherechipformsandShearingslideoccursinthecuttinglayerofdeformation2.1.1.1Chipformation(2)DeformationcausedbypressinginregionIIofdeformationAsthechipmovesawayalongthetoolsurfaceitmustovercomethefrictioncausedbythepressingofthetoolrakesurfacesothatitdeformsfurther(deformationinthesecondregion),andthethinmetalatthebottomofthechiparefiberizedalongtherakesurface.Thefartherawaytherakesurface,thelessfiberized.2.1.1.1ChipformationⅠⅢⅡ(3)DeformationcausedbypressinginregionIIIofdeformationthemetalonthemachinedsurfacearepressedbytheroundedcuttingedgeandminorflank,thenthecrystalsofmetalareelongatedandhardened.2.1.1.1ChipformationⅠⅢⅡ(1)Relativeslideε)tan(cot'''0yCBCBys2.1.1.2measurementofdeformationFig.2.4Relativeslide(2.1)1Dchchchhhll(2.2)wherelc,hD—lengthandthicknessofcuttinglayerlch,hch—lengthandthicknessofchipFig.2.5Chipshrinkage（2）DeformationcoefficientΛhLchLD2.1.1.2measurementofdeformation2.1.1.2measurementofdeformationFromFig2.6weknowtheeffectofshearangleφonchipshrinkage:asφincreasestheshearplaneABshortens,hChdecreases,andthenΛhdecreases.Thereisthefollowingrelationbetweenthem:000sincoscotsin)cos(ABABhhDchh(2.3))tan(cot'''0yCBCBys2.1.1.2measurementofdeformationEq.2.1and2.3indicateshearangleφandrakeangleγoarethetwomainfactorsinfluencingcuttingdeformation.Ifγoandφincrease,εandΛhwoulddecreaseandthenthecuttingdeformationdecreases.RelationshipofεandΛh)tan(cot0ys00sincoscotDchhhh变形系数ΛhWhenγo=0~30,Λh1.5,εisclosetoΛh,itissimpleandstraightforwardtouseΛhtomeasurethedeformationdegree;Ifγoisnegative,εbecomesverybigwhilstΛhdecreases,orifΛh=1,Λhcannotbeusedtomeasurethedeformationdegree.Howaboutε?002cos1sin2hhh2.1.1.3Pressedfrictionintool-chipinterfaceandbuilt-upedge(1)Analysisofforceactingonchip.Fig2.6ForcesactingonchipFn-normalpressingforceFf-frictionunderFnFr-resultantforceonchipFsFnsFrFs-shearingforceFns-normalforceFr-resultantforceoncuttinglayerFz-drivingforcelongitudinallyFy-drivingforceperpendicularlyCanbemeasuredwithdeviceThesheardeformationisduetotheactionofFs.：Theshearstressτonshearplaneis：whereβ—frictionangleAD—cuttinglayerarea。)(cos'0rsFFsin)sin('cos)cos('00rrFFsincosyzsFFF(2.4)sin.sincossinDDyzDsbhFFAF(2.5)2.1.1.3Pressedfrictionintool-chipinterfaceandbuilt-upedge(1)Analysisofforceactingonchip.Fromtheforcebalanceonthechipandthefrictionallawwehave:μ＝tanβ＝Ff/Fn（2.6）frommeasuredvaluesofFzandFyandthefrictioncoefficientμorfrictionangleβ,we