中小企业精益生产路径探析(中英文翻译).doc
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中小企业精益生产路径探析(中英文翻译).doc
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QuantifyingEnergySavingsfromLeanManufacturingProductivity
Therationalforclaimingenergysavingcomesfromcomparingthebaselineenergyustothepost-eventenergyuse.Inthebaselinscenario,productionisincreasedbyaddinmanufacturingequipmentorbyextendinoperatinghours.Assuch,inthebaselinscenario,energyuseincreasesfromexistingusduetoadditionalequipmentoroperatinghours.
Alternately,inthepost-eventscenario,LeaManufacturingtechniquesenableproductiongainswithoutincreasingoperatinghoursoaddingmanufacturingequipment.Henceinthpost-eventscenario,energyuseisnotmucdifferentthatexistingenergyuse,andmuchlesthaninthebaselinescenario.
Currently,claimingenergysavingsfroproductivityimprovementsisnotwidespreadamongenergyefficiencyprogramsorLeaconsultants.Indeed,littlehasbeenpublishedohowenergysavingsshouldbequantifiedfrotheseimprovements.Inthispaperwepresentbriefreviewoftheexistingalgorithmsusedtcalculateenergysavingsfromproductivityimprovements.Furthermore,weproposetwnewapproachestocalculatingenergysavingeachwithexamples.
EXISTINGAPPROACHESTOCALCULATINGPRODUCTIVITYRELATEDENERGYSAVINGSDepartmentofEnergyIndustrialAssessmentCenters
TheDepartmentofEnergy’s(DOE)OfficeofEnergyEfficiencyandRenewableEnergy(EERE)IndustrialTechnologiesprogramsponsors26IndustrialAssessmentCenters(IAC)locatedatuniversitiesthroughoutthenation.TheIACsprovideenergy,wasteandproductivityassessmentsfreeofcosttoqualifyingsmallandmediumsizedmanufacturingfacilities.EachIACmustreportexpectedenergy,wasteandproductivitysavingsfromitsassessmentrecommendations.IACsmayclaim“effective”energysavingsfromproductivityrecommendations.Theapproachtocalculatingenergysavingsisbasedoncomparingpreand
post-implementationenergyintensityandmultiplyingthedifferencebypost-implementationproductionrates(Papadaratsakis,etal.,2003.).Whilethisapproachhasbeenpublishedindetail,wewillpresentanabbreviatedexamplehere.Forexample,aproductionprocesscurrentlyuses10kWh/unit.AfterimplementationofLeanManufacturingrecommendations,theprocessonlyuses8kWh/unit,andproductionhasbeenincreasedtofrom1,000to1,200units/year.Equation1presentstheeffectiveenergysavingsfromthisexample:
(1,200units/year)x(10–8)kWh/unit=2,400
Kissock(2005)oftheUniversityofDaytonIACdevelopedasimilarbutmoredetailedmethod.WhilePapadaratsakisetal.onlyconsideredunitizedenergyuse,Kissockdiscussedunitizedenergyuse(energyintensity)andnetenergyuse.Kissockalsousedinversemodelingofregressionmodelsbasedonrealdatatodeterminetheunitizedenergyforproductionquantity-dependent,temperature-dependentandoperatinghoursdependentcomponentsofenergy
use.Kissockalsorecognizedtheinfluenceofproductdemandonenergysavings,showingdifferentnetandunitizedenergysavingsdependentwhetherproductionquantityactuallyincreasinglyornot.NortheastUtilitiesProcessReengineeringImprovementforManufacturingEfficiency(PRIME)NortheastUtilities(NU)sponsorsthePRIMEprogramthroughtwoofitsmemberutilities,ConnecticutLight&Power(CL&P)andWesternMassachusettsElectricCompany(WMECO).ThePRIMEprogramissolelyfocusedonproductivityimprovementtoachieveenergysavings.LeanManufacturingconsultantsarecontractedtoprovidethreetofourday“Leanevents”.AstheLeanconsultantsdonotnecessarilyhaveenergyefficiencyexpertise,energysavingsarecalculatedwithageneralizedalgorithm.TheNUsavingsalgorithmreliesonasmallnumberofeasilyobtainedandunderstandableinputs,whichinfluencesavingscalculationsandwillvarysignificantlyfromsitetosite.Otherfactorsthatarenoteasilyobtainedmaybetimelierandcostlyassessmenttocalculate,maynotvarysignificantly,andarethussubstitutedwithgenericassumptions.NU’salgorithmrequiresthefollowinginputs:
1.Annualplant-wideelectricityuse
2.Percentaffectedelectricityuse:
ManyofthePRIMEeventsdonottargettheentiremanufacturingfacility,butperhapsjustoneproductionline.Assuch,determininghowmuchofthetotalannualelectricityuseisattributabletotheproductionlinesinquestionisanimportantestimate,typicallybasedonproductionvaluesorsales.
3.Pre-andpost-eventproductionquantity.Inadditiontothesethreeinputs,standardassumptionsappliedtoeachsiteinclude:
1.10-yearmeasurelife:
Thisvalueisusedtoonvertannualsavingsasdeterminedbythesavingsalgorithmtolifetimesavings.2.85%/10%/5%energydistributionassumption:
Thesavingsalgorithmassumesthatoftheaffectedelectricityuse,5%isattributabletoequipmentwithnoclaimablesavings.10%ofelectricityisattributedtooperating-hourdependentmanufacturingequipment.Theremaining85%ofaffectedelectricityuseisattributedtoproductionquantitydependentmanufacturingequipment.
3.Savingsonincrementalproduction:
Thealgorithmassumesthat6%energysavingsareachievedonlyonincrementalenergyuseofproduction-dependentequipment.Theexisting,baselineandpost-eventelectricityuseiscalculatedforindependent,hours-dependentandproduction-dependentcomponents.Officeelectricityuseisassumedconstantfortheexisting,baselineandpost-eventscenarios.Hours-dependentelectricityuseisassumedtoincreaseproportionallywithproductionfromtheexistingtobaselinescenarios.However,inthepost-eventscenario,hours-dependentelectricityuseisassumedtobeequivalenttotheexistingscenario.Finally,production-dependentelectricityuseincreasesproportionallywithproductionfromtheexistingtobaselinescenarios.However,post-eventelectricityuseiscalculatedassumingthatincrementalproductionis6%lessenergyintensethaninthebaselinescenario.
NEWAPPROACHESTOCALCULATINGPRODUCTIVITYRELATEDENERGYSAVINGS
LeanManufacturingTechniquesandImprovementTypes
ThereareavarietyoftechniquesreferredtoasLeanManufacturing.ALeanManufacturingprojectmayutilizeanynumberofthesetechniques,withthedifferenttechniquesaffectingproductivityandthusenergyuseindifferentways.WhiletheimplementationofaLeantechniqueoftenimprovesproductivity,however,itdoesnotguaranteeaproductivityimprovement.
LeanTechniquesthatmayincreaseproductioninclude5S,VisualManagement,StandardizedWork,ValueStreamMapping(VSM),Cellularflow,kanban,PokaYoke,Point-of-Use(POU)systemsandKaizenevents.LeanTechniquesthatdirectlytargetproductionincreasesincludeQuickChangeoverandTotalProductiveMaintenance(TPM).Seryaketal.(2006)brieflydescribedtheseLeanimprovementtypesandtheirrelationshiptoenergyuse.
TheLeanManufacturingtechniqueslistedaboveimproveproductivityinseveralways,whichmayormaynothaveimpactsonenergyuse.Additionally,LeanManufacturing
techniquescanalsoimproveenergyuseinwaysthathavenorelationtoproductivity.
Improvementtypesthataffectenergyuseincludereducedchangeovertime,reduceddowntime,reducedsetuptime,reducedcycletime,increasedthroughput,rework/scrapreduction,parttravelreduction,spacereductionanddirectequipmentefficiencyimprovement.Improvementtypesthatdonottypicallyaffectenergyuseincludeinventoryreduction.BasisforBothAlgorithms
Bothofournewapproachesbeginwiththesamegeneratingequation(Eq.2):
EnergySavings
Thisgeneralequationcanbeusedwithstatisticalregressionmodels,whichwewillrefertoasthe“EnergySignature”method.Thesameequationisthebasisforconsideringtheenergyuseofthespecificindustrialequipmentinvolved,whichwewillrefertoasthe“EnergyBreakdown”method.Examplesofbothmethodsarepresentedbelow.EnergyBreakdownMethodTheEnergyBreakdownmethodinvolvescalculatingtheenergysavingsforeachpieceofelectricity-usingequipment.ThemainstepsusedintheEnergyBreakdownmethodare:
1.Developaninventoryofenergyusingequipment.
2.Determinehoweachpieceofequipmentusesenergy.
3.Quantifyexistingenergyuseforeachpieceofequipment,basedonpre-Leaneventproduction.
4.Calculatebaselineenergyuseforeachpieceofequipment,basedonpost-Leaneventproductionandpre-Leaneventprocesses.
5.Calculatepost-eventenergyuseforeachpieceofequipment,basedonpost-Leaneventproductionandpost-Leaneventprocesses.
6.Comparepost-eventtobaselinescenariostocalculateenergysavings.Thedetailsofenergysavingscalculationsusingtheenergybreakdownmethoddifferdependingonwhichimprovementtypeisinquestion.Assuch,likemethodswillbeexploredfortheEnergyBreakdownmethod.Therelationshipbetweenequipmentenergyuseandproductiondiffersbasedonthetypeofequipment.Therearefourmaincategoriesofequipment:
Equipmentwithenergyuseindependentofproduction(includesofficeequipment),Equipmentwithenergyusedependentonproductionquantity,Equipmentwithenergyusedependentonoperatinghours,Equipmentwithenergyusedependentonbothproductionquantityandoperatinghours.
Forexample,anexhaustfanthatoperates24hours/dayforatwo-shiftoperationwillusethesameamountofenergynomatterifproductionquantityorproductionhoursincrease.Theexhaustfanisanexampleofequipmentwithenergyuseindependentofproductionfactors.Next,imaginededicatedproductionpressesthatullyshutoffduringidlecycletimes.Thisequipmentusesenergydirectlyproportionaltoproductionquantity,regardlessoftheoperatinghours.However,lightingequipmentforthissameoperationmayb
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