供应链管理(第13讲-1)

CHAPTER8ManagingUncertaintyinaSupplyChain:SafetyInventory9-2LearningObjectivesTodeterminethecostsofholdinginventory.Toidentifythecostsassociatedwithastockout.TounderstandtheEOQconcept.Todifferentiatethevariousinventoryflowpatterns.Toappreciatethecontemporaryapproachestomanaginginventory.9-3OverviewofInventoryManagementInventoriesarestocksofgoodsandmaterialsthataremaintainedformanypurposes,themostbeingtosatisfynormaldemandpatterns.Inventorymanagementisakeycomponentofsupply-chainmanagement,inpartbecauseinventorydecisionareoftenastartpoint,ordriver,forotherbusinessactivitiessuchaswarehousing,transportation,andmaterialshandling.Differentfunctionalareashavedifferentinventoryobjectives.Marketingtendstowanttoensurethatsufficientinventoryisavailableforcustomerdemandinordertoavoidpotentialstockoutsituations―higherinventorylevels.Financegroupgenerallyseekstominimizethecostsassociatedwithholdinginventory―lowerinventorylevels.Oneofthemostprominentconcernsaboutinventoryisitscost,whichispresentedingreaterdetaillaterinthischapter.Finishedgoodsinventoriesaremuchmoreexpensivetoholdthanrawmaterialsorworkinprocess.Thefocusoninventorycostshasintensifiedinrecentyearsbecauseofconcernwithinventoryturnover.9-7Inventoryturnoveristhenumberoftimesthatinventoryissoldina1-yearperiod.Inventoryturnover:costofgoodssolddividedbyaverageinventoryatcost.costofgoodssold=inventoryturnoveraverageinventory$200,000=inventoryissold4timesperyear.$50,000Inventoryturnoverfigurescanprovideimportantinsightsaboutanorganization’scompetitivenessandefficiency.9-8Comparewithcompetitorsorbenchmarkedcompanies.Lowinventoryturnover=highinventorycarryingcosts,little(orno)stockoutcosts.Highinventoryturnover=lowinventorycarryingcosts,highstockoutcosts.It’seasytosaythatorganizationsshouldstriveforaproperbalanceofinventory;actuallyachievingitcanbequitedifficultbecauseoftrade-offsthatareinvolved.Managingthetradeoffisimportanttomaintainservicelevels.9-10InventoryClassificationsIt’simportanttoknowthekeyclassificationsofinventorybecausetheclassificationinfluencesthewaythatinventoryismanaged.Inventoryismostfrequentlyclassifiedas――Psychicstock;Cycleorbasestock;Safetyorbufferstock;Pipelineorin-transitstock;Speculativestock.Whileinventorygenerallyexiststoservicedemand,insomesituationsinventoryiscarriedtostimulatedemand,alsoknownaspsychicstock.――Retailstoresstockhugeamountsofcertainmerchandise.Cycle,orbase,stockreferstoinventorythatisneededtosatisfynormaldemandduringthecourseofanordercycle.――Weuseoneeggperdayandwebuyeggsevery12days.Safety,orbuffer,stockreferstoinventorythatisheldinadditiontocyclestocktoguardagainstuncertainindemandand/orleadtime.――makingathree-eggomelet;buyingeggsevery14days.Pipeline,orin-transit,stockisinventorythatisenroutebetweenvariousnodes(i.e.,fixedfacilitiessuchasaplant,warehouse,store)inalogisticssystem.――eggsintransitbetweentheretailstoreandyourkitchen.Speculativestockreferstoinventorythatisheldforseveralreasons,includingseasonaldemand,projectedpriceincreases,andpotentialshortagesofproduct.――SpringFestival,tendstocauseanincreaseindemandforeggs.9-17Inventory-RelatedCostsInventory-relatedcostsaremostfrequentlyclassifiedas――Inventorycarrying(holding)costs;Stockoutcosts.Inventorycarrying(holding)costsincluding:ObsolescenceInventoryshrinkageStoragecostsandhandlingcostsTaxesInterestchargesOpportunitycostIngeneral,inventorycarryingcostsareexpressedinpercentageterms,andthispercentageismultipliedbytheinventory’svalue.However,thecalculationofacarryingcostpercentagecanbequiteunstructured.Stockoutcosts:Suchcostscanaccrueduringstockouts,whencustomersdemanditemsthataren’timmediatelyavailable.Althoughcalculationofstockcostscanbedifficultandinexact,itisimportantfororganizationtodosobecausesuchknowledgecanbebeneficialwhendetermininghowmuchinventorytohold.Estimatingthecostsorpenaltyforastockoutinvolvesanunderstandingofcustomerreactiontoacompanybeingoutofstockwhenacustomerwantstobuyanitem.(Page273)9-23Table9-1:DeterminationoftheAverageCostofaStockoutAlternativeLossProbabilityAverageCost1.Brand-loyalcustomer$00.00.10$00.002.Switchesandcomesback$37.00.65$24.053.Lostcustomer$1,200.25300.00Averagecostofastockout1.00$324.05Thesearehypotheticalfiguresforillustration.Asageneralrule,thehighertheaveragecostofastockout,thebetteritisforthecompanytoholdsomeamountofinventory(safetystock)toprotectagainststockouts.Thehighertheprobabilityofadelayedsale,thelowertheaveragestockoutcosts―andthelowertheinventorythatneedstobeheldbyacompany.9-25Trade-offsexistbetweencarryingandstockoutcosts.Marginalanalysisfocusesonthetrade-offbetweencarryingandstockoutcosts,allowacompanytodetermineanoptimumlevelofsafetystocks.Marginalanalysishelpsdefinethepointatwhichthecostsofholdingadditionalsafetystockareequaltothesavingsinstockoutcostsavioded.9-26Table9-2:DeterminationofSafetyStockLevelNumberofUnitsofSafetyStockTotalValueofSafetyStock($480perUnit)25%AnnualCarryingCostCarryingCostofIncrementalSafetyStockNumberofAdditionalOrdersFilledAdditionalStockoutCostsAvoide