运营管理基础 4E-戴维斯英文IMChap015.docx

CHAPTER 15 AGGREGATE PLANNINGChapter OverviewAggregate planning is the first step in a process that takes the long-range strategic plan and converts it to the operational level. The aggregate plan is maintained primarily for determining the amount of materials and labor requirements for the next 12 months. Specifically, this chapter provides an overview of aggregate planning.Major Points of ChapterThe aggregate plan is used to set product rates by broad groups for the intermediate term, generally 6 to 18 months.1. The process of aggregate planning can be very formal or it can be informal. Many small companies use informal methods of aggregate production planning.2. There are three basic production-planning strategies-chase, stable workforce, and level strategy.3. The relevant costs are basic production costs, labor costs, costs associated with changes in the production rate, inventory holding costs, and backlogging costs.4. Many companies use trial-and-error charting and graphical methods for aggregate planning. However, more sophisticated approaches include linear programming, Linear Decision Rule, and various heuristic methods.5. Yield management is used for aggregate planning in services. It attempts to integrate demand and supply management simultaneously. Specifically, it tries to sell all available capacity, but not turn away a full paying customer.Review and Discussion QuestionsWhat are the basic controllable variables of a production planning problem? What are the four major costs?Basic controllable variables: production rate, work force levels, labor costs, and inventories.Major costs: production costs (fixed and variable), production rate change costs, inventory holding costs, and backlog costs.1. Distinguish between pure and mixed strategies in production planning.Pure strategies use only one variable to absorb demand fluctuations. Mixed strategies involve two or more pure strategies.180Level StrategyLevel StrategyLa Buena Compania de EspanaJanFebMarAprMayJunTotalForecasted Demand1,7401,7402,4603,2402,2201,86013,260On-Hand Inventory300AveNet Demand1,4401,7402,4603,2402,2201,86012,960 2,160Aggregate Plan:Production2,1602,1602,1602,1602,1602,16012,960Number of Workers363636363636Number Hired1100000Number Fired000000Ending Inventory720420(300)(1,080)(60)300Cumulative Inventory7201,140840(240)(300)0Incremental Costs:Hiring Costs2,200000002,200Firing Costs0000000Inventory Costs1,4402,2801,6800005,400Stockout Costs0002,4003,00005,400Totals:3,6402,2801,6802,4003,000013,000Total Incremental Costs of Level Strategy = 13,000 Based upon cost, the level strategy should be used.Chapter 15La Buena Compania de EspanaLevel Strategy with OvertimeJanFebMarAprMayJunTotalForecasted Demand1,7401,7402,4603,2402,2201,86013,260On-Hand Inventory300360420000AveNet Demand1,4401,3802,0403,2402,2201,86012,180 2,030Aggregate Plan:Production1,8001,8001,8001,8001,8001,80010,800Number of Workers303030303030Number Hired500000Number Fired000000Overtime production002401,44042060Ending Inventory3604200000Cumulative Inventory7201,1401,1401,1401,1401,140Overtime Hours:006003,6001,050150Incremental Costs:Hiring Costs1,000000001,000Firing Costs0000000Inventory Costs1,4402,2802,2802,2802,2802,28012,840Stockout Costs0000000Overtime Premium002,40014,4004,20060021,600Totals:2,4402,2804,68016,6806,4802,88035,440Total Incremental Costs of Overtime Strategy = 35,440The level strategy is still the best.2. An alternate plan would be to go with a level work force of 36 people and then work overtime to eliminate any stockouts. One problem with working overtime, especially during the peak month is that workers will become very tired. This can cause a decrease in productivity and poor workmanship.190Compare the best plans in the C&A Company and the Tucson Parks and Recreation Department. What do they have in common?The plans have little in common. The C&A plans used a constant low work force and subcontracting. The Tucson Parks plan, on the other hand, used a constant high work force and no subcontracting.3. How does forecast accuracy relate, in general, to the practical application of the aggregate planning models discussed in the chapter?A highly accurate forecast encourages the use of deterministic techniques such as linear programming which in turn permits the development of near optimal plans. Clearly, though, any reduction in uncertainty enhances the likely accuracy of any production planning method.4. In which way does the time horizon chosen for an aggregate plan determine whether it is the best plan for the firm?Many factors affect the selection of an appropriate time horizon. Perhaps, the most important is what the firm intends to plan during that time period. An aggregate plan implies a period of up to 18 months wherein the firm takes its forecast and plans production using inventory, work force size, overtime and under time, subcontracting, and backlogging orders to achieve a reasonable schedule at reasonable costs. A very stable firm in a very stable environment with a very stable demand really doesn't need to go out very far with its aggregate plan. However, when there is variation, especially when this variation is considerable, then a longer aggregate plan will show the need to find subcontractors, new workforce availability, etc. Planning for these can start early.5. Under what conditions is the concept of yield management most appropriate for service operations?To gain the maximum from yield management, a service should have the ability to segment its markets, high-fixed and low variable costs, product perishability, and the ability to presell capacity.ProblemsProblemType of ProblemDifficultyCheck Figure in Appendix DAggregate planning1YesModerateYes2YesModerate3YesModerate4YesModerateYes5YesModerate6YesModerate7YesModerateChapter 15ForecastBeginning Production Production Production Overtime ActualEnding inventoryWorkers Workers hired laid offinventoryrequiredhours requiredhours availablehoursproductionFall1000()500950019000144007200-2300Winter8000-23001030020600144006200103000Spring70000700014000144007200200Summer120002001200023600144001200020020*20BackOvertimeHiringLay offInventoryStraightTotalForecastBeginning Production Production Production Overtime ActualEnding inventoryWorkers Workers hired laid offinventoryrequiredhours requiredhours availablehoursproductionFall1000()500950019000144007200-2300Winter8000-23001030020600144006200103000Spring70000700014000144007200200Summer120002001200023600144001200020020*20BackOvertimeHiringLay offInventoryStraightTotal1.order$23,000FallWinter Spring SummerTotal$49,600$2,000$4,000$1,000time$72,000$72,000$72,000$1,000 $118,000$95,000$121,600$73,000$125,000$414,600* Workers hired = (23,600-14400)/(8*60) = 19.17 workers2.ForecastBeginningInventoryProduction Production Production Overtime ActualEnding Workers Workersrequiredhours requiredhours availablehoursproductioninventory hiredlaid offFebruary80000080000200001600080000025*March64000064000160002000064000025April10000001000002500016000500084000-16000May40000-16000560001400016000640008000BackOvertimeHiringLay offInventoryStraightTotalordertimeFebruary$1250$200000$201,250March$1750$160000$161,750April$32000$75000$160000$267,000May$80000$160000$240,000Total$870,000*(20,000-16,000)/(8*20)= 25 workers1823.ForecastBeginnin g InventoryProduction Production Production Overtime ActualEnding Workers Workersrequiredhours requiredhours availablehoursproductioninventory hiredlaid offSpring2000010001900038000280001000()190000Summer10000010000200002800010000020Fall15000015000300002000015000025WinterSpring Summer Fall Winter Total18000Back order$240000Overtime $15000018000Hiring$250036000Lay off$400030000InventoryStraight time $280000 $200000 $300000 $30000015000Total$430000$204000$302500$324000$1260500-30004. Number of workers = (40500-500)/( 12)( 1 )(8)20 = 20.83 or 21 workersJanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecemberAverageForecast250030004000350035003000300040004000400030003000Beginning50012501500200017501750150015002000200020001500inventoryProduction3250325045003250350027503000450040004000250030003458.3requirements Ending inventory125015002000175017501500150020002000200015001500TotalCostForecast25003000400035003500300030004000400040003000300040500Beginning50013601720108094080011601520880240-400-40inventoryProduction33603360336033603360336033603360336033603360336040320S403,200.00plan Ending13601720108094080011601520880240-400-40320inventorySafety stock125015002000175017501500150020002000200015001500Excess11022020350$1,750.00inventoryBack order40040440$8,800.00Total$413,750.00Next, try increasing or decreasing the number of workers by one, and recalculate the total cost. A better solution may be found.Chapter 15Number of workers = (Year's production - beginning inventory)(labor hrs/unit)/(working days per year) = (6700-200)10/(22)(11)+7) = 32.6 or 33 workersMonthly production (except July) = 22(8)33/10 = 580 units/monthJanuary February March April May June July August Septem- October November December Total berForecast6008009006004003002002003007008009006700Beginning2001800001804604448241104984764inventoryProduction5805805805805805801845805805805805806564requirementsEnding180-40-320-201804604448241104984764444inventoryCostsTotalLost Sales80064004007600Inventory900900230022204120552049203820222026920Total9008006400400900230022204120552049203820222034520Since there appears to be excessive inventory costs, another plan should be attempted with 32 workers for comparison purposes.1845. a-c.(1)Qtr.(2)Demand(3)Prod. Hours Req.(2)x2(4)Prod. Days per Qtr.(5)Prod Hrs. per Qrt. per Worker(4)x8(6)No. of Empls(7)Total Prod.Hrs. Avail, per Qtr.(5) x (6)Straight- Time Cost(4) x (6)(9)No. of Units Short(10)Short Cost(11)No. of OT Units Req.(12)No. of OT Days Req.(11)/4Now9,90019,800635044020,160$133,5600000110,00020,000564484017,920$118,720000029,80019,600604804019,200$127,200000039,40018,800614884019,520$129,3200000410,20020,400635043919,656$130,2210000Total 1-4$505,461(13)Overtime Cost(12) x $80(14)No. of Unit Sub.(15)Sub. Cost(16)No. of Empls. Hired(17)HiringCost(16) x $1200(18)No. of Empls. Fired(19)FiringCost(18) x $1000(20)Begin.Inv.(21)End. Inv.(22)Ave. Inv.(20)+(21)/2(23)Inv. Cost(22)x$1500000001,2001,3801,290$19,35000000001,380340860$12,9000000000340140240$ 3,6000000000140500320$ 4,8000000011,000500128314$ 4,7100001,000$26,010Total cost is $532,471.Chapter 157.Level StrategyMonthHours($30/hr.)Cumulative cost(1.5%/mo.November1604,8004,80072December1604,8009,600144January1604,80014,400216February1604,80019,200288March1604,80024,000360April1604,80028,800432CostCarrying CostTotal Incremental Cost=$1,512Chase StrategyTotal HoursRequired950HrsAV orker/Month160Number of Workers5.9375Or 6 workersHiring Cost (5 + handyman) Firing Cost (5 + handyman from last season)Total Incremental Cost600450$1,050Chase Strategy With OvertimeTotal HoursRequired950HrsAV orker/Month240Number of Workers3.958333Hiring Cost (3 + handyman)Firing Cost (3 + handyman from last season)Overtime Costs (80 hours/worker * $10/hr.)Total Incremental CostOr 4 workers4003003,200 $3,900The best option appears to be the chase strategy, with an incremental cost of $1,050.186Case: XYZ Brokeraae Firm1.Dept. A (cashiering)Dept. B. (order processing)Work ProcessWork ProcessPhysical materials and information Information onlyTechnologySimple (now)ComplexSkills RequiredRelatively lowRelatively highLevel capacityWorkforce Planning Chase capacityThe key determinant of the planning strategy in this case is the nature of the work itself. Department A requires low skills from its workforce due to the simple tasks they are called upon to perform. Department B has more complex work, and hence needs a more skilled staff to perform it. Do these differences eliminate certain strategy choices for either manager? Yes, it could be very difficult for manager B to follow a chase strategy and still maintain quality and output requirements.2. A's strategy is described because it keeps head count down and, presumably, labor costs low. B's strategy is desirable because it assures enough adequately trained (and no doubt better motivated) workers. Additional considerati