机械制造技术基础课件-新第2章课件(4)

2.1.4Toolwearandtoollife2.1.4.1Typesoftoolwear2.1.4.2Toolwearprocessandcriteria2.1.4.3Causesoftoolwear2.1.4.4Toollife2.1.4.5InfluencefactorsoftoollifeEdgechoppingWearonrakefaceWearonrakeface2.1.4ToolwearandtoollifeMetallurgicalStructurebeforewearMetallurgicalStructureafterwear2.1.4Toolwearandtoollife2.1.4.1TypesoftoolwearToolwearcanbedividedintonormalwearandnon-normalwear.Thetoolwearincreaseswithtimeiscallednormalwear.Itcanbefurtherdividedintothefollowingkindsaccordingtothewornregion(1)normalwear①Flankwear②Wearontherakeface③SimultaneouswearonrakefaceandflankThenon-normalwearisnotgraduallyformedastimegoesby,butformedwhenthecuttingedgeissuddenlybroken,orthecuttingedgeiscurled,orthetoolbitiscrushedetc.(2)non-normalwearWearonrakefaceWearonflank2.1.4.1Typesoftoolwear2.1.4.1TypesoftoolwearToolWearCriteria：whenthetoolbecomessodullthatitcannotworkagain,thewearcausedinthislimitationiscalledtheWearCriteria.UsuallyitisjudgedbyobservationAsflankweariseasytomeasure,itisoftenusedastoolwearcriteria.ISOregulatesthatVBmeasuredonflanksurface,halfwayofthebackengagement，istakenasthetoolwearcriteria2.1.4.1TypesoftoolwearHomogeneouswearwithintheregionB—VB=0.3mm;InhomogeneouswearwithintheregionB—VB=0.6mm;DepthofcrateronrakefaceKT=0.06+0.3f(f—feed,mm/r).Table2.9WearcriteriaVB(mm)CuttingconditionCuttingprocessFinishturningPoorstiffnessTurningsteelTurningcastironLargeworkpieceofsteelorcastironFinishturning0.1～0.3Roughturning0.4～0.50.6～0.80.8～1.21.0～1.5InISOstandards,thetoolwearcriteria(highspeedsteelandcarbideinsert)frommetalcuttingresearchare:ThewearcriteriaforcarbideturningtoolsobtainedinpracticearelistedinTable2.9.ToolWearCriteria：2.1.4.1Typesoftoolwear2.1.4.3CausesoftoolwearCuttingtoolweartakesplaceunderconditionsofhightemperatureandpressure,therefore,thecausesoftoolwearareverycomplicated,involvingmechanical,physical,chemicaleffectsandphasevariation.1Abrasivewear2Adhesivewear3Diffusionwear4Phasechangewear5Oxidizingwear2.1.4.4Toollife(1)DefinitionoftoollifeToollifeisdefinedasthetimethatthewearlanddevelopsfromzerotothewearcriterionatwhichthetoolisregardedas“dull”,andisdenotedbyT.ToollifecanalsobeexpressedasthecuttingdistancelmorthenumberNofmachinedpartsbeforethetoolreachesthewearcriterion.Toollifeisanimportantindextojudgethetool’scuttingproperty.Itisconvenienttojudgewherethetoolisdullornotbyusingtoolliferatherthaninspectingthewidthofthewearland.vc＝mTA(a)CuttingspeedWhereA—coefficientrelatedtotheexperimentcondition,m—influenceindexofvconT,forHSStool:m=0.11,forCarbidealloytool,m=0.2~0.3,forceramicsm=0.4nTBTc(b)Feedandbackengagementf—Tandap—Thavethesimilarrelationship,f＝,ap=(2)Factorsaffectingtoollife2.1.4.4Toollife(3)Selectionofrationaltoollifetherearetwomethodstocorrectlyselectthetoollife:①ToollifeTpofthemaximumproductiverate,ortheminimumtimerequiredtomachineapart.Thetotaltimerequiredtoperformanoperationis:tpr＝tm＋tl＋tctm/Twheretm—cuttingtime;tl—supporttime(non-cuttingtime);tc—timepertoolchanging(min/change);T—toollife.2.1.4.4ToollifeToolLifeTpforMaximumproductiveratecptmmT)1(2.1.4.4ToollifeTheaveragecostCprforeachworkpieceinanoperationis:.②ToollifeTcoftheminimumproductivecostM—theunitexpenses,includinglabor,machineandetcCt—toolcost,includingresharpeningandlaboretcTtCTtMtMtMtCmtmclmpr2.1.4.4ToollifeDifferentiatetheequationandletittobezero,thetoollifeTcforminimumproductivecostis:lmtmcmprMtTKCTKMtKMTC11)(1MCtmmTtccNotice:TcTpCouldyoutellwhy?Thedetailedvaluesoftoollifecanbeselectedfromtechnicalinformationandhandbooks.2.1.4.4Toollife2.1.4.5Influencefactorsofthetoollife(1)Influenceofcuttingparameters;(2)Influenceoftool’sgeometricparameters;(3)Influenceofworkpiecematerials;(4)Influenceoftoolmaterials.(1)CuttingparametersvvyxpcvmfavCTAnexperientialformulaoftoollifeAllowableCuttingspeedvyxpmvTkfaTCvvvQuestion:inwhatsequencetoselectthecuttingparametersinordertoraisethemachineefficiency?2.1.4.5Influencefactorsofthetoollife(2)CuttingtoolgeometryRakeangleReliefangleMaincuttingedgeangle,minorcuttingedgeangleandnoseradius(3)MaterialofworkpieceStrength,hardness,elongation,heatconductivity(4)MaterialofCuttingtoolHothardness,impacttoughness2.1.4.5Influencefactorsofthetoollife