1、Chapter 7Aggregate Planningin the Supply Chain8-1Learning ObjectivesIdentify the decisions that are best solved by aggregate planningUnderstand the important of aggregate planning as a supply chain activityDescribe the information needed to produce an aggregate planExplain the basic trade-offs to co

2、nsider when creating an aggregate planFormulate and solve basic aggregate planning problem using Microsoft Excel2OutlineRole of aggregate planning in a supply chainThe aggregate planning problemAggregate planning strategies(三種戰(zhàn)略)Aggregate planning using linear programming Implementing linear program

3、ming for aggregate planning using Microsoft ExcelImplementing aggregate planning in practice3Role of Aggregate Planning in a Supply ChainCapacity has a cost, lead times are greater than zeroQuestionShould a company invest in a plant with large capacity that is able to produce enough to satisfy deman

4、d even in the busiest month?Should a company build a smaller plant but incur the costs of holding inventory built during slow period in anticipation of demand in later months?These are types of questions that aggregate planning helps companies answer4Role of Aggregate Planning in a Supply ChainAggre

5、gate planning (總體方案): process by which a company determines ideal levels of capacity, production, subcontracting, inventory, stockouts, and pricing over a specified time horizonThe goal is to satisfy demand while maximize profit供應(yīng)鏈綜合方案之上，是供應(yīng)鏈戰(zhàn)略；供應(yīng)鏈綜合方案之下，是企業(yè)資源方案；綜合方案介于之間。對(duì)上細(xì)化，對(duì)下驅(qū)動(dòng)內(nèi)部供應(yīng)鏈，驅(qū)動(dòng)“企業(yè)資源方案。5Ro

6、le of Aggregate Planning in a Supply ChainAggregate planning is an important supply chain issue To be effective, it requires inputs from throughout the supply chain, and its results have a tremendous impacts on supply chain performance. Collaborative forecasts are created by multiple supply chain en

7、terprises and are an important input for aggregate planningMany constraints in aggregate planning come from supply chain partners outside the enterpriseThe output from aggregate planning is also of value to both upstream and downstream partners6Role of Aggregate Planning in a Supply ChainThe main ob

8、jective of aggregate planner is to identify the following operational parameters over the specified time horizon:Production rate (消費(fèi)率): the number of units to be completed per unit time (such as per week or per month)Workforce (勞動(dòng)力數(shù)量): the number of the workers/units of capacity needed for productio

9、n.Overtime (加班量): the amount of overtime production planned. Machine capacity level (機(jī)器消費(fèi)才干): the number of units of machine capacity needed for production.7Role of Aggregate Planning in a Supply ChainSubcontracting (轉(zhuǎn)包合同): the subcontracted capacity required over the planning horizon. Backlog: dema

10、nd not satisfied in the period in which it arises but carried over to future period. Inventory on hand (現(xiàn)有庫存): the planned inventory carried over the various periods over to future periods. All supply chain stages should work together on an aggregate plan that will optimize supply chain performance8

11、The Aggregate Planning ProblemGiven the demand forecast for each period in the planning horizon (方案期), determine the production level (消費(fèi)程度), inventory level (庫存程度), and the capacity level (消費(fèi)才干程度) for each period that maximizes the firms (supply chains) profit over the planning horizonSpecify the p

12、lanning horizon (typically 3-18 months)Specify the duration of each period9Information Needed for in Aggregate PlanDemand forecast in each periodProduction costs (消費(fèi)本錢)labor costs, regular time ($/hr) and overtime ($/hr)subcontracting costs ($/hr or $/unit)cost of changing capacity: hiring or layoff

13、 ($/worker) and cost of adding or reducing machine capacity ($/machine)Labor/machine hours required per unitInventory holding cost (庫存本錢) ($/unit/period)Stockout or backlog cost (庫存缺貨或積壓本錢($/unit/period)Constraints: limits on overtime, layoffs, capital available, stockouts and backlogs. Constraints

14、from suppliers to the enterprise10Outputs of Aggregate PlanProduction quantity from regular time, overtime, and subcontracted time；Inventory held；Backlog/stockout quantity；Workforce Hired/Laid off；Machine capacity increase/decrease；A poor aggregate plan can result in lost sales, lost profits, excess

15、 inventory, or excess capacity11Fundamental Tradeoffs in Aggregate PlanningCapacity (regular time, overtime, subcontract)InventoryBacklog / lost salesBasic Strategies三種根本戰(zhàn)略Chase strategyTime flexibility from workforce or capacityLevel strategy12Aggregate Planning StrategiesThese strategies involve t

16、rade-offs among capital investment, workforce size, work hours, inventory, and backlogs/lost sales Chase strategy (追逐戰(zhàn)略 using capacity as the leverTime flexibility 彈性時(shí)間from workforce or capacity strategy using utilization as the leverLevel strategy (程度戰(zhàn)略 using inventory as the leverMixed strategy a

17、combination of one or more of the first three strategies13Chase StrategyProduction rate is synchronized with demand by varying machine capacity or hiring and laying off workers as the demand rate variesExpensive if cost of varying capacity is highNegative effect on workforce morale 聯(lián)想裁員案例，目前外企和銀行都采用

18、外包的方式應(yīng)對(duì)Results in low levels of inventoryShould be used when inventory holding costs are high and costs of changing capacity are low14Time Flexibility StrategyCan be used if there is excess machine capacityWorkforce is kept stable, but the number of hours worked is varied over time to synchronize pr

19、oduction and demandCan use overtime or a flexible work schedule很多企業(yè)采用這種戰(zhàn)略，比如四大Requires flexible workforce, but avoids morale problems of the chase strategyLow levels of inventory, lower utilizationShould be used when inventory holding costs are high and capacity is relatively inexpensive15Level Stra

20、tegyMaintain stable machine capacity and workforce levels with a constant output rateShortages and surpluses result in fluctuations in inventory levels over timeInventories that are built up in anticipation of future demand or backlogs are carried over from high to low demand periodsBetter for worke

21、r moraleLarge inventories and backlogs may accumulateShould be used when inventory holding and backlog costs are relatively low16Aggregate Planning Strategies進(jìn)一步的思索生活和學(xué)習(xí)中，我們都會(huì)不自覺的采用這幾種戰(zhàn)略，比如考試；哪種戰(zhàn)略更好？大家可以思索一下?！凹僭O(shè)每天針對(duì)某個(gè)領(lǐng)域純?nèi)蝿?wù)時(shí)間能有6個(gè)小時(shí)，10年以后一定在這個(gè)領(lǐng)域非常了不起。引薦的書籍和博客： blog.renren/blog/bp/QmMZyS1NQP blog.renre

22、n/blog/bp/QmmNlSZhEP blog.renren/blog/bp/QgVEhrQsIP17Aggregate planning using linear programming The limitations of spreadsheet based approaches for solving aggregate planning problems. A highly effective tool for a company to use when it tries to maximize profits while being subject to a series of

23、constraints is linear programming. Linear programming finds the solution that creates the highest profit while satisfying the constraints that the company faces. 18Aggregate Planning at Red Tomato Tools19Aggregate Planning at Red Tomato Tools20Aggregate Planning at Red Tomato Tools21Table 8.1 Demand

24、 Forecast at Red Tomato Tools22Table 8.2 Costs for Red Tomato23步驟一、確定決策變量Wt = Workforce size for month t, t = 1, ., 6Ht = Number of employees hired at the beginning of month t, t = 1, ., 6Lt = Number of employees laid off at the beginning of month t, t = 1, ., 6Pt = Production in month t, t = 1, .,

25、6It = Inventory at the end of month t, t = 1, ., 6St = Number of units stocked out at the end of month t, t = 1, ., 6Ct = Number of units subcontracted for month t, t = 1, ., 6Ot = Number of overtime hours worked in month t, t = 1, ., 624步驟二、建立目的函數(shù)Regular-time labor cost Overtime labor cost Cost of

26、hiring and layoffs Cost of inventory and stockout Cost of materials and subcontracting25步驟二、建立目的函數(shù) (8.1)26Subject to (8.2) (8.3) (8.4) (8.5) (*) (8.2): Workforce, hiring, and layoff constraints; (8.3): Capacity constraints; (8.4): Inventory balance constraints; (8.5): overtime limit constraints; (*)

27、: nonnegative constraints. 步驟三、識(shí)別約束條件27Average inventory = Average time in inventory =28Table 8.3 Aggregate Planning for Red TomatoPeriodHtLt WtOtItSt CtPt012345600000000150000080656565656565000000010001983156795001175000000267000000000258325832583258325832583Ht: No. Hired; Lt: No. Laid off; Wt: Wor

28、kforce size;Ot: Overtime; It: Inventory; St: Stockout; Ct: Subcontract; Pt: Production. 29步驟四、用EXCEL求解First Step is to build a table containing each decision variableABCDEFGHIJ123PeriodHtLt WtOtItStCtPtDt400080010000051000000001600620000000030007300000000320084000000003800950000000022001060000000022

29、00Aggregate Plan Decision Variables 30步驟四、用EXCEL求解Second step is to construct a table for the constraints in (8.2)(8.5)Constraints MNOP123Workforce Production Inventory Overtime 45-800-6000600-30000700-32000800-38000900-220001000-2200031步驟四、用EXCEL求解Cell Cell FormulaEquation Copied toM5 =D5-D4-B5+C58

30、.2M6:M10N5=40*D5+E5/4-I58.3B6:N10O5=F4-G4+I5+H5-J5-F5+G58.4O6:O10P5=-E5+10*D58.5P6:P1032Aggregate Planning in ExcelThe third Step is to create a cell containing the objective functionAggregate Plan CostsABCDEFGHI121314PeriodHtLt WtOtItStCtPt15100000000162000000001730000000018400000000195000000002060

31、00000002122Total Cost = $33步驟四、用EXCEL求解The Fourth Step is to use the Tools | Solver to invoke SolverSet Target Cell: C22Equal to: Select MinBy changing cell: B5:I10Subject to the constraints:B5:I10=0 All decision variables are nonnegativeF10=500 Inventory at the end of period 6 is at least 500G10=0

32、Stockout at the end of period 6 equals 0M5:M10=0 N5:N10=0O5:O10=0P5:P10=034ResultsTotal cost over planning horizon = $422275Revenue over planning horizon =Average seasonal inventory Average flow time = 35Scenarios-敏感性分析Increased demand fluctuation (Example 8.1)Increase in holding cost (from $2 to $6

33、) (Example 8.2)36Example 8.1All the data are exactly the same as in our previous discussion of Red Tomato, except for the demand forecast shown in following Table. Obtain the aggregate plan in this case37Table 8.5 Optimal Aggregate Plan for Demand in example 8.1PeriodHtLt WtOtItSt CtPt012345600000000150000080656565656565000000010002583216795001175000000126768300000000258325832583258325832583Ht: No. Hired; Lt: No. Laid off; Wt: Workforce size;Ot: Overtime; It: Inventory;