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1、Chapter3BulkDeformationForming-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)ExitzonepisafunctionofhandϕForstrainhardeningmaterial,theflowstressYfinthe

6、expressionscorrespondstothestrainthatthematerialhasundergoneatthatparticularlocationintherollgapFromtheexpressions,wecanfindthatthepressureincreaseswithincreasingstrengthofthematerial,increasingcoefficientoffriction,andincreasingR/hfratio(notethattheR/hfratioisequivalenttoth

7、ea/hrationinupsetting)PressureDistributionintheRollGapTheneutralpointshiftstowardtheexitasfrictiondecreases.Ifthefrictionapproachestozero,therollsbegintoslipinsteadofpullingthetripinPressuredistributionintherollgapasafunctionofcoefficientoffriction.Theareaunderthecurveisther

8、ollseparatingforceperunitwidthofstrip.Notethat,asfrictionincreases,theneutr