非圆齿轮与机械压力机运动学优化毕业论文外文翻译Word格式.docx
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非圆齿轮与机械压力机运动学优化毕业论文外文翻译Word格式.docx
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OptimizedKinematicsofMechanicalPresseswithNoncircularGears
E.Doege(l),M.Hindersmann
ReceivedonJanuary8,1997
Abstract:
Thequalityofpartsmanufacturedusingmetalformingoperationsdependstoalargedegreeonthekinematicsofthepressram.Non-circulargearsytoobtainthosestroke-timebehavioursweaimatasanoptimumforthevariousmetalformingopewitharotational-angle-dependentspeedratiointhepressdrivemechanismofferanewwarationsintermsofmanufacturing.ThepaperexplainstheprincipleusingaprototypepresswhichwasbuiltbytheInstituteforMetalFormingandMetalFormingMachineToolsatHanoverUniversity.Itwillpresentthekinematicsaswellastheforcesandtorquesthatoccurintheprototype.Furthermore,thepaperdemonstratesusingoneexampleofdeepdrawingandoneofforgingthatthepressdrivemechanismwithnon-circulargearsmaybeusedadvantageouslyforvirtuallyallmetalformingoperations.
Keywords:
Press,Gear,Kinematics
1lntroductior
Increasingdemandsonqualityinallareasofmanufacturingengineering,insheetmetalformingaswellasinforging,gohandinhandwiththenecessitytomakeproductioneconomical.Increasingmarketorientationrequiresthatbothtechnologicalandeconomicrequirementsbemet.Theimprovementofquality,productivityandoutputbymeansofinnovativesolutionsisoneofthekeystomaintainingandextendingone'
smarketposition.Intheproductionofpartsbymetalforming,weneedtodistinguishbetweentheperiodrequiredfortheactualformingprocessandthetimesneededtohandlethepart.
Withsomeformingprocesseswehavetoaddtimefornecessaryadditionalworksuchascoolingorlubricationofthedies.Thisyieldstwomethodsofoptimization,accordingtothetwoaspectsofqualityandoutput.Inordertosatisfybothaspects,thetaskistodesignthekinematicstakingintoaccounttherequirementsoftheprocessduringforming;
alsotobeconsideredisthetimerequiredforchangingthepartaswellasforauxiliaryoperationsinlinewiththepriorityofashortcycletime.
2PressingMachineRequirements
Onemanufacturingcycle,whichcorrespondstoonestrokeofthepressgoesthroughthreestages:
loading,formingandremovingthepart.Insteadoftheloadingandremovalstagesweoftenfindfeedingthesheet,especiallyinsheercutting.Forthis,thepressrammusthaveaminimumheightforacertaintime.Duringtheformingperiodtheramshouldhaveaparticularvelocitycurve,whichwillbegoneintobelow.Thetransitionsbetweentheperiodsshouldtakeplaceasquicklyaspossibletoensureshortcycletime.Therequirementofashortcycletimeisforbusinessreasons,toensurelowpartscostsviahighoutput.Forthisreasonstrokenumbersofabout24/minforthedeepdrawingoflargeautomotivebodysheetsand1200/minforautomaticpunchingmachinesarestandardpractice.Increasingthenumberofstrokesinordertoreducecycletimeswithoutdesignchangestothepressingmachineresultsinincreasingstrainrates,however.Thishasacleareffectontheformingprocess,whichmakesitnecessarytoconsidertheparameterswhichdeterminetheprocessandareeffectedbyit.
Indeepdrawingoperations,thevelocityofimpactwhenstrikingthesheetshouldbeaslowaspossibletoavoidtheimpact.Ontheonehand,velocityduringformingmustbesufficientforlubrication.Ontheotherhand,wehavetoconsidertheriseintheyieldstresscorrespondingtoanincreaseinthestrainratewhichcreatesgreaterforcesandwhichmaycausefracturesatthetransitionfromthepunchradiustothesidewallofthepart.
Inforging,shortpressuredwelltimeisdesirable.AsthepressuredwelltimedropsthediesurfacetemperaturegoesdownandasaresultthethermalwearThisiscounteractedbytheenhancedmechanicalwearduetothegreaterformingforce,buttheincreaseduetothestrainrateiscompensatedbyloweryieldstressbecauseofthelowercoolingofthepart.Theoptimalshortpressuredwellcannowadaysbedeterminedquantitativelyusingthefiniteelementmethod[3].Inadditiontocostavoidanceduetoreductioninwear,shortpressuredwelltimeisalsoanimportanttechnologicalrequirementfortheprecisionforgingofnearnetshapeparts,whichhasapromisingfuture.
Therequirementsofhighpartqualityandhighoutputwillonlybemetbyamachinetechnologywhichtakesintoaccountthedemandsofthemetalformingprocessinequalmeasuretothegoalofdecreasingworkproductioncosts.Previouspressdesignshavenotsimultaneouslymetthesetechnologicalandeconomicalrequirementstoasufficientextent,ortheyareverycostlytodesignand
manufacture,suchaspresseswithlinkdrives[6].Thismakesitnecessarytolookforinnovativesolutionsforthedesignofthepress.Itsdesignshouldbelargelystandardizedandmodularizedinordertoreducecosts[6].
Fig1.Prototypepress
3PressDrivewithNoncircularGears
3.1Principle
Theuseofnon-circulargearsinthedriveofmechanicalcrankpressesoffersanewwayofmeetingthetechnologicalandeconomicdemandsonthekinematicsofthepressram.Apairofnon-circulargearswithaconstantcenterdistanceisthuspoweredbytheelectricmotor,orbytheflywheel,anddrivesthecrankmechanismitself.Theuniformdrivespeedistransmittedcyclicallyand
non-uniformlytotheeccentricshaftbythepairofnoncirculargears.Ifthenon-circulargearwheelsaresuitablydesigned,thenon-uniformdriveofthedrivengearleadstothedesiredstroke-timebehaviouroftheram.InvestigationsattheInstituteforMetalFormingandMetalFormingMachineTools(IFUM)ofHanoverUniversityhaveshownthatinthissimplemanneralltherelevantuninterruptedmotionsoftheramcanbeachievedforvariousformingprocesses[2].
Apartfrom,theadvantagesofthenewdrive,whichresultfromthekinematicsandtheshortenedcycletime,thedriveconceptisdistinguishedbythefollowingfavourablepropertties.Becauseitisamechanicalpress,highreliabilityandlowmaintenancemaybeexpected.Incomparisiontolinkagepressesthenumberofpartsandbearingsisclearlyreduced.Aboveall,abasicpresstypecanbevariedwithoutfurtherdesignchangesbyinstallingdifferentpairsofgears,designedaccordingtothedemands
ofthecustomer.Unlikelinkdrives,bearinglocationsandinstallationsdonotchangewithinoneload
classasaresultofdifferentkinematics.ThustheabovementionedrequirementofmodularizationandstandardizationistakenintoaccountReductionsintimeandcostsarepossibleforthedesignandpressmanufacture.
3.2Prototype
AttheInstituteforMetalFormingandMetalFormingMachineTools(IFUM)aC-framepresshasbeenremodeledandapairofnon-circulargearswasinstalled.Thepreviousbackgearswerereplacedbyaplanetarygearsetforthispurpose.Theworkcarriedoutshowsthatremodelingofexistingpressesforthenewdriveispossible.Thestateofthepressattheendoftheremodellingisshowninfiqure1.Thepressisdesignedforanominalramforceof1,000kNand200kNofthediecushion.Thecenterdistanceofthenon-circulargearsis600mm.Thepairofnon-circulargearshasanaveragetransmissionratioof1.Eachgearwheelhas59gearteeth,straight-toothed,module10mm(fiaure2).Thefacewidthis150mm.Thegearshaveinvolutegearteeth.Weassumeanon-circularbasecurveforthedesignoftheflankgeometry.Asaresultthetoothgeometryofanon-circulargearvariesalongthecircumference.Inspiteofthis,itcanbederivedfromthewell-knowntrapeziumrack,however[4,51.Analgorithmforthecomputation,whichtakestheaddendumanddedendumintoaccountexactly,hasbeendeveloped.
Fig.2Viewofthegearsfromtherear
Thepressisdesignedfordeepdrawingofflatpartsinsinglestrokeoperationmode.Themaximumramstrokeis180mm,thenumberofstrokes32/min.Atastrokeof140mmtheramvelocityalmostremainsconstant71mmlsfrom60mmbeforelowerdeadcenteruntillowerdeadcenter,seefiqure3.Thusthevelocitycorrespondstotheworkingvelocityofhydraulicpresses.Thevelocityofincidenceofacrankmechanismwiththesamenumberofstrokeswouldbe220mmls,incomparison.Inordertokeepthesameaveragevelocitywithacrankpress,thenumberofstrokeswouldhavetobehalved.Theshort
cycletimeoftheremodelledmachineresultsfromthefastupwardmotion.Becausethepressisruninsinglestrokeoperationmode,noparticularrequirementsweremadeconcerninghandlingtimeduringdesign.
Thedrivemechanismoftheprototypewithnon-circulargearshasinadditionafavourableeffectontheramforcesandthedrivingtorques(ficlure4).Foracrankpressthenominalforceisnormallyavailableat30"
rotationofthecrankshaftbeforethelowerdeadcenter.Thiscorrespondstoasectionundernominalforceofonly75%relativetothestroke.Toreachthenominalforceof1,000kN,thedrivehastosupplyatorqueof45kNmatthecrankshaft.Theprototypeonlyrequires30kNmonaccountoftheadditionaltransmissionofthenon-circulargears.Theyaretransmittedtoacyclic.non-uniformcrankshafttorque,resultinginanominalforcerangefrom60"
tothelowerdeadcenter.Thiscorrespondsto27.5%ofthestroke.Wealwaysfindsimilarconditionsifthepairofnon-circulargearsissteppeddownintheoperatingrangeofthepress.Thiswillalmostalwaysbethecasewithsheetmetalformingandstamping.Itisthuspossibletodesignsomemachinepartsinaweakerformandtosavecoststhisway.
4FurtherDesignExamples
Usingtheexamplesoftwostroke-timebehavioursthedesignisillustratedinthefollowing.Arange
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