供应链管理(第13讲-1)

1、CHAPTER 8Managing Uncertainty in a Supply Chain: Safety Inventory9-2LearningObjectivesTodeterminethe costs of holdinginventory.Toidentifythecostsassociatedwith astockout.Tounderstand theEOQconcept.Todifferentiate thevarious inventoryflow patterns.Toappreciate thecontemporaryapproachestomanaginginven

2、tory.9-3OverviewofInventoryManagementInventoriesarestocks of goods andmaterialsthataremaintainedformanypurposes,the mostbeingtosatisfynormaldemand patterns.Inventorymanagementisa keycomponentofsupply-chain management, in partbecauseinventorydecisionare often astartpoint, or driver,for other business

3、 activitiessuchaswarehousing,transportation, andmaterialshandling.Differentfunctionalareashave differentinventoryobjectives.Marketingtendstowant to ensurethat sufficientinventory is availableforcustomerdemand in order to avoid potentialstockoutsituations higher inventorylevels.Finance groupgenerally

4、seekstominimizethe costs associatedwithholding inventorylowerinventory levels.Oneofthe mostprominent concerns aboutinventoryisitscost, which is presentedingreater detaillaterinthis chapter.Finishedgoodsinventoriesaremuchmore expensivetohold thanraw materialsorwork in process.Thefocusoninventory cost

5、s hasintensifiedinrecentyearsbecauseofconcernwithinventoryturnover.9-7Inventoryturnoveristhenumber of times thatinventory is soldina1-yearperiod.Inventoryturnover: costofgoodssolddivided by averageinventory at cost.cost of goods sold=inventoryturnoveraverage inventory$200,000=inventoryissold4 times

6、peryear.$ 50,000Inventoryturnoverfigurescanprovideimportantinsightsaboutanorganizationscompetitivenessand efficiency.9-8Compare withcompetitorsorbenchmarkedcompanies.Lowinventory turnover =highinventorycarryingcosts, little(orno)stockoutcosts.High inventoryturnover= lowinventorycarryingcosts, highst

7、ockoutcosts.Its easytosay thatorganizationsshouldstrive fora properbalance of inventory; actually achievingitcanbequitedifficult becauseoftrade-offsthat areinvolved.Managingthetradeoffisimportant to maintain servicelevels.9-10InventoryClassificationsIts importanttoknow thekeyclassifications of inven

8、torybecause theclassificationinfluences thewaythatinventoryismanaged.Inventoryismostfrequently classifiedasPsychic stock ;Cycleorbasestock;Safety or bufferstock;Pipelineorin-transitstock;Speculativestock.Whileinventorygenerally existstoservice demand,insomesituations inventoryiscarriedtostimulatedem

9、and, alsoknownaspsychic stock. Retailstores stock hugeamountsofcertain merchandise.Cycle,orbase,stockreferstoinventory thatisneededtosatisfy normaldemandduring thecourseofanordercycle. We useoneegg perdayand we buyeggs every 12 days.Safety, or buffer,stockreferstoinventory thatisheldinadditiontocycl

10、estocktoguardagainst uncertainindemandand/or leadtime. making athree-egg omelet;buying eggsevery14days.Pipeline,orin-transit,stockisinventorythatisenroutebetween variousnodes(i.e.,fixedfacilitiessuch as aplant, warehouse,store) in alogistics system. eggsintransit betweenthe retailstoreandyourkitchen

11、.Speculativestockreferstoinventory thatisheldforseveralreasons,includingseasonaldemand,projectedpriceincreases,andpotential shortagesofproduct. SpringFestival, tends to cause an increase in demandforeggs.9-17Inventory-RelatedCostsInventory-relatedcostsaremostfrequently classifiedasInventorycarrying(

12、holding) costs;Stockoutcosts.Inventorycarrying(holding) costsincluding:ObsolescenceInventoryshrinkageStorage costs andhandlingcostsTaxesInterestchargesOpportunitycostIngeneral,inventorycarryingcostsare expressedinpercentage terms,andthis percentageismultipliedbytheinventorysvalue. However, thecalcul

13、ationofa carrying costpercentagecanbequiteunstructured.Stockoutcosts: Suchcostscan accrueduringstockouts, whencustomers demanditemsthat arentimmediatelyavailable.Althoughcalculationofstockcostscanbedifficult andinexact,itisimportantfor organizationtodosobecause suchknowledge canbebeneficial whendete

14、rmininghow muchinventory to hold.Estimating thecostsorpenalty forastockoutinvolvesanunderstanding ofcustomerreactiontoa companybeingout of stock whenacustomerwantstobuyanitem.(Page 273)9-23Table9-1:Determination of theAverage CostofaStockoutAlternativeLossProbabilityAverage Cost1. Brand-loyal custom

15、er$00.00.10 $00.002. Switches and comes back$37.00.65 $24.053. Lost customer$1,200.25 300.00Average cost of a stockout1.00$324.05Thesearehypothetical figuresfor illustration.Asa generalrule,thehigher theaverage costofastockout, thebetteritisfor thecompany to holdsomeamountofinventory (safetystock)to

16、protect againststockouts.Thehigher theprobabilityofa delayedsale, thelowertheaveragestockoutcostsandthelowerthe inventorythat needs to be heldbyacompany.9-25Trade-offs exist betweencarryingandstockoutcosts.Marginalanalysisfocuses on thetrade-offbetweencarryingandstockoutcosts,allowacompany to determ

17、ineanoptimum level of safetystocks.Marginalanalysishelpsdefinethe point at whichthecostsofholdingadditional safetystockareequaltothe savingsinstockoutcostsavioded.9-26Table9-2:Determination of SafetyStockLevelNumber of Units of Safety StockTotal Value of Safety Stock ($480 per Unit)25% Annual Carryi

18、ng CostCarrying Cost of Incremental Safety StockNumber of Additional Orders FilledAdditional Stockout Costs Avoided10$4,800$1,200$1,20020$6,481.0020 9,600 2,400 1,20016 5,184.803014,400 3,600 1,20012 3,888.604019,200 4,800 1,2008 2,592.405024,000 6,000 1,2006 1,944.306028,800 7,200 1,2004 1,296.2070

19、33,600 8,400 1,2003 972.159-27When to OrderFixedorderquantitysystem; Fixed order interval system(Page276)Reorder point (ROP)(Page276)ROP=DDx RCundercertaintyROP=(DDxRC)+SSunderuncertaintyWhereDD= daily demandRC= lengthofreplenishment cycleSS= safetystock9-28HowMuchtoReorderThetypicalinventoryordersi

20、zeproblem,referredtoastheeconomicorderquantity(EOQ),dealswith calculating theproperordersizewith respecttotwo costs:thecostsofcarryingthe inventoryandthecostsoforderingthe inventory.EQQdetermines thepointatwhichthesum of carrying costs andorderingcostsisminimized, or thepointatwhichcarryingcostequal

21、orderingcost.9-30Figure9-1:DeterminingEOQ by Useofa GraphEconomicorderquantity(EOQ)indollarsEOQ=2AB/C(Page278)WhereEOQ=themosteconomicordersize,indollarsA =annual usage,indollarsB =administrativecostsper order ofplacing theorderC =carryingcostsofthe inventory(%)9-32Economicorderquantity(EOQ)inunitsE

22、OQ=2DB/IC(Page278)WhereEOQ=themosteconomicordersize,inunitsA =annual demand,inunitsB =administrativecostsper order of placingthe orderC =carryingcostsofthe inventory(%)I= dollarvalueoftheinventory,perunit9-33Table9-3:EOQCostCalculationsNumber of orders per yearOrder size ($)Ordering cost ($)Carrying

23、 cost ($)Total cost (sum of ordering and carrying cost) ($)11,000 251001252 500 50 501003 333 75 331084 250 100 251255 200 125 20145Thefiguresfrom thefixedorderquantity(e.g.,EQQ)andthe safetystockcalculationscan be usedtodevelopaninventoryflowdiagram, which graphically depictsthe demandfor, andreple

24、nishment of,inventory.InventoryFlows9-35Figure9-2:Inventory FlowDiagram9-36Safetystockcan preventagainsttwoproblemareas.IncreasedrateofdemandLonger-than-normalreplenishmentWhen fixed order quantity systemlike EOQisused,time betweenorders mayvary.When reorderpointisreached,fixedorderquantityisordered

25、.9-37ContemporaryApproachestoManagingInventorySeveral of themore prominentapproaches arepresentedinthissection:ABCAnalysis; Just-inTime(JIT)Approach;Vendor-ManagedInventory (VMI);InventoryTracking.ABCAnalysisofinventoryrecognizesthatinventoriesarenot of equal valueandthatallinventory shouldnotbemana

26、gedinthesameway.Measuresused to determineABCstatus includesalesvolume, thefastest-sellingitems, itemprofitability,oritemimportance.Intermsofitem importance, ABCmightbeoperationalizedasfollows:A thehighest criticality;B moderate criticality;C lowcriticality.Just-in Time(JIT)Approach:From an inventory

27、perspective,the JITapproachseekstominimizeinventorybyreducingsafety stock, as wellasbyhaving therequiredamountofmaterials arriveattheproductionlocationattheexacttimethat theyare needed.TheJIT approach hasa numberofimportantimplications forsupply-chainefficiency.Collaboration among supply-chainpartic

28、ipantsiskey to successfulJIT initiatives.Vendor-ManagedInventory(VMI):UnderVMI, thesize andtimingofreplenishmentordersare theresponsibilityofthemanufacturer.VIMsbenefitsfordistributors andretailerstendtoinvolve areducednumberofstockoutsandhigher inventoryturns,whilemanufacturer benefits includeimproveddemand forecas