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1、Chapter3 BulkDeformationForming-RollingRollingProcessAprocessofreducingthethicknessorchangingthecross-sectionalofaworkpiecebycompressiveforcesexertedbyapairofrotatingrollsFlat-andShape-RollingProcessesFlatRollingProcessDevelopedinthelate1500sStartwithslablikeingotPassthroug
2、htworollsseparatedbyadistancelessthanthethicknessoftheingotKeeppassingthroughsuchrollsuntilthefinalthicknessisachievedFrictionforceactsasdrivingforceThefinalproductsincludeplate,sheetandfoil(plate:t>8mm,sheet:t=0.2-4mm,Foil:t<0.2mm),andcanbeusedinavariousoffieldsFlatRollingP
3、rocessRotatingrollsreducethethicknessoftheincomingingotFlatRollingProcess(a)Schematicillustrationoftheflat-rollingprocess.(b)Frictionforcesactingonstripsurfaces.(c)Therollforce,F,andthetorqueactingontherolls.ThewidthwofthestripusuallyincreasesduringrollingNeutralPointApointw
4、heretherearenoslipbetweentheworkpieceandtherollerThefrictionoftwosidesopposeeachotherattheneutralpointThefrictionontheentrysidemustbehigherthantheexitsideThenetfrictionforceandthesurfacevelocitymustbeinthesamedirectionForwardslipisdefinedas:ForwardslipForceandStressThestress
5、stateissimilartothatinupsettingThecalculationinmoreinvolvedthanthatofupsettingduetothecurvedcontactsurfaceTheflowstressattheexitishigherthanthatattheentryStressonanelementinflatrolling.(a)EntryZone,(b)Exitzonepisafunctionofhand?Forstrainhardeningmaterial,theflowstressYfinthe
6、expressionscorrespondstothestrainthatthematerialhasundergoneatthatparticularlocationintherollgapFromtheexpressions,wecanfindthatthepressureincreaseswithincreasingstrengthofthematerial,increasingcoefficientoffriction,andincreasingR/hfratio(notethattheR/hfratioisequivalenttoth
7、ea/hrationinupsetting)PressureDistributionintheRollGapTheneutralpointshiftstowardtheexitasfrictiondecreases.Ifthefrictionapproachestozero,therollsbegintoslipinsteadofpullingthetripinPressuredistributionintherollgapasafunctionofcoefficientoffriction.Theareaunderthecurveisther
8、ollseparatingforceperunitwidthofstrip.Notethat,asfrictionincreases,theneutr
