供应链管理(第112讲)

©2007PearsonEducation10-1Chapter7ManagingEconomiesofScaleintheSupplyChain:CycleInventorySupplyChainManagement©2007PearsonEducation10-2OutlineRoleofCycleInventoryinaSupplyChainEconomiesofScaletoExploitFixedCostsEconomiesofScaletoExploitQuantityDiscountsShort-TermDiscounting:TradePromotionsEstimatingCycleInventory-RelatedCostsinPractice©2007PearsonEducation10-3第7章获取供应链规模经济的手段：循环库存一、循环库存在供应链中的作用二、利用固定成本获取规模经济三、利用数量折扣获取规模经济四、短期折扣：商业促销五、在实践中估测与循环库存相关的费用©2007PearsonEducation10-4循环库存产生原因——规模经济大批量生产与采购订购与运输数量折扣与促销©2007PearsonEducation10-5RoleofInventoryintheSupplyChainImproveMatchingofSupplyandDemandImprovedForecastingReduceMaterialFlowTimeReduceWaitingTimeReduceBufferInventoryEconomiesofScaleSupply/DemandVariabilitySeasonalVariabilityCycleInventorySafetyInventoryFigureError!NotextofSeasonalInventory©2007PearsonEducation10-6RoleofCycleInventoryinaSupplyChainLot,orbatchsize:quantitythatasupplychainstageeitherproducesorordersatagiventimeCycleinventory:averageinventorythatbuildsupinthesupplychainbecauseasupplychainstageeitherproducesorpurchasesinlotsthatarelargerthanthosedemandedbythecustomer–Q=lotorbatchsizeofanorder–D=demandperunittimeInventoryprofile:plotoftheinventorylevelovertime(Fig.7.1)Cycleinventory=Q/2(dependsdirectlyonlotsize)Averageflowtime=Avginventory/AvgflowrateAverageflowtimefromcycleinventory=Q/(2D)©2007PearsonEducation10-7RoleofCycleInventoryinaSupplyChainQ=1000unitsD=100units/dayCycleinventory=Q/2=1000/2=500=AvginventorylevelfromcycleinventoryAvgflowtime=Q/2D=1000/(2)(100)=5daysCycleinventoryadds5daystothetimeaunitspendsinthesupplychainLowercycleinventoryisbetterbecause:–Averageflowtimeislower–Workingcapitalrequirementsarelower–Lowerinventoryholdingcosts©2007PearsonEducation10-8RoleofCycleInventoryinaSupplyChainCycleinventoryisheldprimarilytotakeadvantageofeconomiesofscaleinthesupplychainSupplychaincostsinfluencedbylotsize:–Materialcost=C–Fixedorderingcost=S–Holdingcost=H=hC(h=costofholding$1ininventoryforoneyear)Primaryroleofcycleinventoryistoallowdifferentstagestopurchaseproductinlotsizesthatminimizethesumofmaterial,ordering,andholdingcostsIdeally,cycleinventorydecisionsshouldconsidercostsacrosstheentiresupplychain,butinpractice,eachstagegenerallymakesitsownsupplychaindecisions–increasestotalcycleinventoryandtotalcostsinthesupplychain©2007PearsonEducation10-9循环库存在供应链中的作用循环库存指供应链中建立的平均库存量Q：订购批量R：单位时间需求量（假设需求量不变）循环库存＝批量库存/2＝Q/2循环库存平均周转时间＝循环库存/需求量＝Q/2R为减少市场波动，公司理想循环库存一般较小TQ©2007PearsonEducation10-10EconomiesofScaletoExploitFixedCostsHowdoyoudecidewhethertogoshoppingataconveniencestoreoratSam’sClub?Lotsizingforasingleproduct(EOQ)©2007PearsonEducation10-11EconomiesofScaletoExploitFixedCostsAnnualdemand=DNumberofordersperyear=D/QAnnualmaterialcost=CDAnnualordercost=(D/Q)SAnnualholdingcost=(Q/2)H=(Q/2)hCTotalannualcost=TC=CD+(D/Q)S+(Q/2)hCFigure7.2showsvariationindifferentcostsfordifferentlotsizes©2007PearsonEducation10-12FixedCosts:OptimalLotSizeandReorderInterval(EOQ)D:AnnualdemandS:SetuporOrderCostC:Costperunith:HoldingcostperyearasafractionofproductcostH:HoldingcostperunitperyearQ:LotSizeT:ReorderintervalMaterialcostisconstantandthereforeisnotconsideredinthismodelDHSnHDSQhCH2*2*©2007PearsonEducation10-13利用固定成本获取规模经济单一产品批量规模Q（经济订购批量）R＝产品年需求量S＝每次订购固定成本C＝单位产品购买价格成本H＝每年存储成本年原料价格成本＝CR年订购次数＝R/Q年订购成本＝（R/Q）*S年存储成本＝（Q/2）H=(Q/2)hc年总成本TC＝CR+（R/Q）*S+（Q/2）hc©2007PearsonEducation10-14年总成本TC＝CR+（R/Q）*S+（Q/2）hc等式右边对q一阶求导，等于0时，得最佳订购批量Q*=注：h和R必须要有相同时间单位n＝R/Q*＝2RChS2RSCh©2007PearsonEducation10-15批量规模成本总成本储存成本订购成本原材料成本Q*©2007PearsonEducation10-16Example7.1Demand,D=12,000computersperyeard=1000computers/monthUnitcost,C=$500Holdingcostfraction,h=0.2Fixedcost,S=$4,000/orderQ*=Sqrt[(2)(12000)(4000)/(0.2)(500)]=980computersCycleinventory=Q/2=490Flowtime=Q/2d=980/(2)(1000)=0.49monthReorderinterval,T=0.98month©2007PearsonEducation10-17Example7.1(continued)Annualorderingandholdingcost==(12000/980)(4000)+(980/2)(0.2)(500)=$97,980SupposelotsizeisreducedtoQ=200,whichwouldreduceflowtime:Annualorderingandholdingcost==(12000/200)(4000)+(200/2)(0.2)(500)=$250,000Tomakeiteconomicallyfeasibletoreducelotsize,thefixedcostassociatedwitheachlotwouldhavetobereduced©2007PearsonEducation10-18Example7.2Ifdesiredlotsize=Q*=200units,whatwouldShavetobe?D=12000unitsC=$500h=0.2UseEOQequationandsolveforS:S=[hC(Q*)2]/2D=[(0.2)(500)(200)2]/(2)(12000)=$166.67Toreduceoptimallotsizebyafactorofk,thefixedordercostmustbereducedbyafactorofk2©2007PearsonEducation10-19例：bestbuy公司采购电脑，月需求1000台，固定成本每次4000，进价每台500，零售商库存成本占20％，求Q*解：年需求量R=1000*12=12000每批订购成本S=4000单位采购成本C=500年存储成本h＝0.2Q*=（（2*12000*4000）/（0.2*500））1/2＝980循环库存＝Q*/2=490年订购次数＝R/Q*=120000/980=12.24订购和存储成本＝（R/Q*）S+（Q*/2）hC=97980平均周转时间＝Q*/2R=490/1200=0.041年＝0.49月©2007PearsonEducation10-20拓展：A、如果批量规模1100，而不是980，则：订购次数＝12000/1100＝10.9总成本＝10.9*4000+1100/2*0.2*500＝43600+55000＝98600批量规模从980到1100，增加10％，总成本从97980到98600，仅增加0.6％。©2007PearsonEducation10-21B、假设月需求增加到4000每月（增长4倍），最佳规模批量和订购次数各自增加2倍，平均周转时间减少至1/2。Q*=年订购次数＝R/Q*平均周转时间＝Q*/2R结论：如果批量规模最佳，需求量增