3 OverviewProduction Scheduling Problems are Resource Allocation Problems when outputs are fixed and when outputs and inputs occur at different periods in time. The simplest problems consider only two time periods.Production Scheduling Problems with Dynamic Inventory help managers find an efficient low-cost production schedule for one or more products over several time periods (weeks or months).Workforce Assignment Problems are Resource Allocation Problems when labor is a resource with a flexible allocation; some labor can be assigned to more than one work center.Make or Buy Problems are Linear Programming Profit Maximization problems when outputs are fixed and when inputs can be either made or bought. Make or Buy Problems help minimize cost.Product Mix Problems are Resource Allocation Problems when outputs have different physical characteristics. Product Mix Problems thus determine production levels that meet demand requirements.Blending Problems with Weight Constraints help production managers blend resources to produce goods of a specific weight at minimum cost.
4 OverviewTool SummaryDo not make integer restrictions, and maybe the variables at an optimum will be integers.First Example: Pi = (integer) number of producers in month i.Use compound variables:First Example: Pi = number of producers in month iUse dynamic or recursive constraints:First Example: Define the constraint that the number of apprentices in a month must not exceed the number of recruits in the previous month: A2 - R1 < 0; A3 - R2 < 0Constrain one variable to be a proportional to another variable:First Example: Define the constraint that each trainer can train two recruits: 2T1 - R1 > 0; 2T2 - R2 > 0Use inventory variables:Second Example: P2 + I1–I2 = 150 (production-net inventory = demand)
6 Production Scheduling OverviewProduction Scheduling Problems are Resource Allocation Problems when outputs are fixed and when outputs and inputs occur at different periods in time. Production Scheduling Problems thus help managers find an efficient low-cost production schedule for one or more products over several periods in the future (weeks or months). The manager determines the production levels that meet demand requirements, given limitations on production capacity, labor capacity, and storage space, while minimizing total production and storage costs. The simplest problems consider only two time periods.
7 The cost of storing a wheel from one month to the next is $2. Production SchedulingQuestion: Chip Foose is the owner of Chip Foose Custom Cars. Chip has just received orders for 1,000 standard wheels and 1,250 deluxe wheels next month and for 800 standard and 1,500 deluxe the following month. All orders must be filled.The cost of making standard wheels is $10 and deluxe wheels is $16. Overtime rates are 50% higher. There are 1,000 hours of regular time and 500 hours of overtime available each month. It takes .5 hour to make a standard wheel and .6 hour to make a deluxe wheel.The cost of storing a wheel from one month to the next is $2.Minimize total production and inventory costs for standard and deluxe wheels.
8 SI = number of standard wheels held in Production SchedulingDefine the production variables: Determine the regular-time and overtime production quantities in each month for standard and deluxe wheels.Month Month 2Wheel Reg. Time Overtime Reg. Time OvertimeStandard SR SO SR SO2Deluxe DR DO DR DO2Define the inventory variables: Determine the inventory quantities for standard and deluxe wheels.SI = number of standard wheels held ininventory from month 1 to month 2DI = number of deluxe wheels held in
9 Min (production cost per wheel) x (number of wheels produced) Production SchedulingDefine the objective function: Minimize total production and inventory costs for standard and deluxe wheels.Min (production cost per wheel)x (number of wheels produced)+ (inventory cost per wheel)x (number of wheels in inventory)Min 10SR1 + 15SO1 + 10SR2 + 15SO2+ 16DR1 + 24DO1 + 16DR2 + 24DO2+ 2SI + 2DI
10 (1) SR1 + SO1 = 1,000 + SI or SR1 + SO1 - SI = 1,000 Deluxe: Production SchedulingDefine the production month 1 constraint on (units required) + (units stored).Standard:(1) SR1 + SO1 = 1,000 + SI or SR1 + SO1 - SI = 1,000Deluxe:(2) DR1 + DO1 = 1,250 + DI or DR1 + DO1 - DI = 1,250
11 (3) SR2 + SO2 = 800 - SI or SR2 + SO2 + SI = 800 Deluxe: Production SchedulingDefine the production month 2 constraint on (units required) + (units stored).Standard:(3) SR2 + SO2 = SI or SR2 + SO2 + SI = 800Deluxe:(4) DR2 + DO2 = 1,500 - DI or DR2 + DO2 + DI = 1,500
12 Production Scheduling Define the constraint Reg. Hrs. Used Month 1 < Reg. Hrs. Avail. Month 1:(5) .5SR1 + .6DR1 < 1000Define the constraint OT Hrs. Used Month 1 < OT Hrs. Avail. Month 1:(6) .5SO1 + .6DO1 < 500Define the constraint Reg. Hrs. Used Month 2 < Reg. Hrs. Avail. Month 2:(7) .5SR2 + .6DR2 < 1000Define the constraint OT Hrs. Used Month 2 < OT Hrs. Avail. Month 2:(8) .5SO2 + .6DO2 < 500
13 Interpretation: Total cost $67,500, no storage, production schedule: Production SchedulingInterpretation: Total cost $67,500, no storage, productionschedule:Month Month 2Reg. Time Overtime Reg. Time OvertimeStandardDeluxe
15 Production Scheduling with Dynamic Inventory OverviewProduction Scheduling Problems with Dynamic Inventory help managers find an efficient low-cost production schedule for one or more products over several time periods (weeks or months). A production scheduling problem is resource-allocation problem for each of several periods in the future. Complex problems consider more than two time periods, so there are many periods of inventory.
16 Production Scheduling with Dynamic Inventory Question: Wilson Sporting Goods produces baseballs. Wilson must decide how many baseballs to produce each month. It has decided to use a 6-month planning horizon.The forecasted demands for the next 6 months are 10,000; 15,000; 30,000; 35,000; 25,000; and 10,000.Wilson wants to meet these demands on time, knowing that it currently has 5,000 baseballs in inventory and that it can use a given month’s production to help meet the demand for that month.During each month there is enough production capacity to produce up to 30,000 baseballs, and there is enough storage capacity to store up to 10,000 baseballs at the end of the month, after demand has occurred.
17 Production Scheduling with Dynamic Inventory The forecasted production costs per baseball for the next 6 months are $12.50, $12.55, $12.70, $12.80, $12.85, and $12.95.The holding cost per baseball held in inventory at the end of the month is figured at 5% of the production cost for that month: $0.625, $0.6275, $0.635, $0.64, $0.6425, and $The selling price for baseballs is not considered relevant to the production decision because Wilson will satisfy all customer demand exactly when it occurs – at whatever the selling price.Therefore, Wilson wants to determine the production schedule that minimizes the total production and holding costs.
18 The following constraints define inventories: Production Scheduling with Dynamic InventoryThe decision variables are the production quantities for the 6 months, labeled P1 through P6. To keep quantities small, all quantities are in hundreds of baseballs.Constraints are easier to understand if we add variables I1 through I6 to be the corresponding end-of-month inventories (after meeting demand). For example, I3 is the number of baseballs left over at the end of month 3.The following constraints define inventories:P1 – I1 = (production–inventory = net demand)P2 + I1–I2 = 150 (production-net inventory = demand)P3 + I2–I3 = 300 (production-net inventory = demand)P4 + I3–I4 = 350 (production-net inventory = demand)P5 + I4–I5 = 250 (production-net inventory = demand)P6 + I5–I6 = 100 (production-net inventory = demand)
19 Finally, production and inventory storage are assumed non-negative. Production Scheduling with Dynamic InventoryThere are obvious constraints are on production and inventory storage capacities: Pj 300 and Ij 100 for each month j (j = 1, …, 6).Finally, production and inventory storage are assumed non-negative.
20 Production Scheduling with Dynamic Inventory There
23 Workforce AssignmentOverviewWorkforce Assignment Problems are Resource Allocation Problems when labor is one of the resources, and labor allocation has some flexibility; at least some labor can be assigned to more than one department or work center. Workforce Assignment Problems thus help when employees have been cross-trained on two or more jobs or, for instance, when sales personnel can be transferred between stores.
24 Type of Production Rate Wage Employee (Wings/Month) Per Month Workforce AssignmentQuestion: National Wing Company (NWC) is gearing up for the new B-48contract. NWC has agreed to supply 20 wings in April, 24 in May, and 30 in June. Wings can be freely stored from one month to the next.Currently, NWC has 100 fully-qualified workers. A fully qualified worker can either be placed in production or can train new recruits. A new recruit can be trained to be an apprentice in one month. After another month, the apprentice becomes a qualified worker. Each trainer can train two recruits. At the end of June, NWC wishes to have at least 140 fully-qualified workers. (Note: NWC must use firm-specific training. There is no outside market for fully-qualified workers.) The production rate and salary per employee type is listed below.Type of Production Rate WageEmployee (Wings/Month) Per MonthProduction $3,000Trainer $3,300Apprentice $2,600Recruit $2,200How should NWC optimize?
25 Workforce AssignmentAnswer:Define the Decision VariablesPi = number of producers in month i (where i = 1, 2, 3 for April, May, June)Ti = number of trainers in month i (where i = 1, 2 for April, May)Ai = number of apprentices in month i (where i = 2, 3 for May, June)Ri = number of recruits in month i (where i = 1, 2 for April, May)Define the objective functionMinimize total wage cost for producers, trainers,apprentices, and recruits for April, May, and June:Min 3000P T R1+ 3000P T A2+2200R2+ 3000P T A3+2200R3
26 Workforce AssignmentDefine the constraint that total production in Month 1 (April)must equal or exceed contract for Month 1:.6P1 + .3T1 +.05R1 > 20Define the constraint that total production in Months 1-2 (April, May) must equal or exceed total contracts for Months 1-2:.6P1 + .3T R1 + .6P2 + .3T2 + .4A R2 > 44Define the constraint that total production in Months 1-3 (April, May, June) must equal or exceed total contracts for Months 1-3:.6P1+.3T1+.05R1+.6P2+.3T2+.4A2+.05R2+.6P3+.4A3 > 74Define the constraint that the number of producers and trainers in a month (fully qualified workers) must not exceed the initial supply of 100, plus any apprentices employed in a previous month:(4) P1 + T1 < 100P2 + T2 < 100P3 + T3 < A2
27 Workforce AssignmentDefine the constraint that the number of apprentices in a month must not exceed the number of recruits in the previous month that have not already become apprentices:A2 < R1; (8) A3 < (R1 - A2) + R2Note: Constraint (8) allows a recruit from Month 1 to be laid off in Month 2, then rehired as an apprentice in Month 3.Define the constraint that each trainer can train two recruits:2T1 - R1 > 0; (10) 2T2 - R2 > 0Define the constraint that at the end of June, there are to be at least 140 fully qualified workers:(11) A2 + A3 > 140
28 Workforce AssignmentInterpretation: Total wage cost = $1,098,000, using the following workforce assignment:April May June JulyProducersTrainersApprenticesRecruits
30 Make or BuyOverviewMake or Buy Problems are Linear Programming Profit Maximization problems when outputs are fixed and when inputs can be either made or bought. Make or Buy Problems thus help production managers to minimize cost by comparing, for some inputs, the lower cost of manufacturing those inputs (rather then buying them) to the opportunity cost of the scarce resources used in manufacture.
31 Make or BuyQuestion: The Janders Company markets business and engineering products. Janders is currently preparing to introduce two new calculators: one for the business market called the Financial Manager, and one for the engineering market called the Technician. Each calculator has three components: a base, an electronic cartridge, and a faceplate or top. The same base is used for both calculators, but the cartridges and tops are different. All components can be manufactured by the company or purchased from outside suppliers.
32 Make or BuyCompany forecasters indicate that 3000 Financial Manager calculators and 2000 Technician calculators will be demanded. However, manufacturing capacity is limited. The company has 200 hours of regular time manufacturing time and 50 hours of overtime that can be scheduled for the calculators. Overtime involves a premium at the additional cost of $9 per hour.
33 Manufacture cost (regular time) per unit Make or BuyDetermine how many units of each component to manufacture and how many to buy given the cost, purchase price and manufacturing time requirements:ComponentManufacture cost (regular time) per unitPurchase cost per unitManufacturing TimeBase$0.50$0.601.0 minutesFinancial cartridge$3.75$4.003.0 minutesTechniciancartridge$3.30$3.902.5 minutesFinancial top$0.65Technician top$0.75$0.781.5 minutes
34 Define decision variables BM = number of bases manufactured Make or BuyAnswer:Define decision variablesBM = number of bases manufacturedBP = number of bases purchasedFCM = number of Financial cartridges manufacturedFCP = number of Financial cartridges purchasedTCM = number of Technician cartridges manufacturedTCP = number of Technician cartridges purchasedFTM = number of Financial tops manufacturedFTP = number of Financial tops purchasedTTM = number of Technician tops manufacturedTTP = number of Technician tops purchasedOT = number of overtime hours
35 Manufacture cost (regular time) per unit Make or BuyDefine the objective:Min 0.5BM + 0.6BP FCM + 4FCP+ 3.3TCM + 3.9TCP + 0.6FTM FTP TTM TTP + 9OTComponentManufacture cost (regular time) per unitPurchase cost per unitManufacturing TimeBase$0.50$0.601.0 minutesFinancial cartridge$3.75$4.003.0 minutesTechniciancartridge$3.30$3.902.5 minutesFinancial top$0.65Technician top$0.75$0.781.5 minutes
36 FCM + FCP = 3000 Financial cartridges Make or BuyDemand Constraints:BM + BP = BasesFCM + FCP = 3000 Financial cartridgesTCM + TCP = 2000 Technician cartridgesFTM + FTP = 3000 Financial topsTTM + TTP = 2000 Technician topsOvertime Resource Constraint:OT < 50Manufacturing Time Constraint (right-side in minutes):BM + 3FCM + 2.5TCM + FTM + 1.5TTM < OT
37 Make or BuyThe Management Scientist can solve this 11-variable, 7-constraint linear program:BM = 5000BP = 0FCM =FCP =TCM =TCP = 0.000FTM = 0.000FTP =TTM = 0.000TTP =OT = 0.000
39 Product MixOverviewProduct Mix Problems are Resource Allocation Problems when outputs have different physical characteristics. Product Mix Problems thus help managers determine the production levels that meet demand requirements, given limitations on production capacity and labor capacity, to maximize profit or minimize cost.
40 Product MixQuestion: Floataway Tours has $420,000 that can be used to buy new rental boats for hire during the summer. The boats can be bought from two different manufacturers.Floataway Tours would like to buy at least 50 boats, and would like to buy the same number from Sleekboat as from Racer to maintain goodwill. At the same time, Floataway Tours wishes to have a total seating capacity of at least 200.Maximum ExpectedBoat Builder Cost Seating Daily ProfitSpeedhawk Sleekboat $ $ 70Silverbird Sleekboat $ $ 80Catman Racer $ $ 50Classy Racer $ $110How should Floataway Tours optimize?
41 Product MixDefine the Decision Variablesx1 = number of Speedhawks orderedx2 = number of Silverbirds orderedx3 = number of Catmans orderedx4 = number of Classys orderedDefine the Objective FunctionMaximize total expected daily profit:Max (Expected daily profit per unit)x (Number of units)Max 70x1 + 80x2 + 50x x4
42 Product MixDefine the constraint to spend no more than $420,000:(1) 6000x x x x4 < 420,000Define the constraint to buy at least 50 boats:(2) x1 + x2 + x3 + x4 > 50Define the constraint that the number of boats from Sleekboat equals the number of boats from Racer:(3) x1 + x2 = x3 + x4 or x1 + x2 - x3 - x4 = 0Define the constraint that seating capacity be at least 200:(4) 3x1 + 5x2 + 2x3 + 6x4 > 200
43 Interpretation: Expected daily profit is $5,040.00. Product MixInterpretation: Expected daily profit is$5,Buy 28 Speedhawks from Sleekboat; buy 28 Classy’s from Racer.The minimum number of boats was exceeded by 6 (surplus for constraint #2).The minimum seating capacity was exceeded by 52 (surplus for constraint #4).
45 Blending with Weight Constraints OverviewBlending Problems with Weight Constraints help production managers blend resources to produce goods of a specific weight at minimum cost.
46 Blending with Weight Constraints Question: The Maruchan Corporation receives four raw grains fromwhich it blends its Maruchan Ramen Noodle Soup. Maruchan advertises that each 8-ounce packet meets the minimum daily requirements for vitamin C, protein and iron. The following is the cost of each raw grain, the vitamin C, protein, and iron units per pound of each grain.Vitamin C Protein IronGrain Units/lb Units/lb Units/lb Cost/lbMaruchan is interested in producing the 8-ounce mixture atminimum cost while meeting the minimum daily requirements of 6units of vitamin C, 5 units of protein, and 5 units of iron.
47 Blending with Weight Constraints Answer:Define the decision variables.xj = the pounds of grain j (j = 1,2,3,4) used in 8-ounce mixtureDefine the objective. Minimize the total cost for an 8-ounce mixture:Min .75x x x x4
48 Blending with Weight Constraints Constrain the total weight of the mix to 8-ounces (.5 pounds):(1) x1 + x2 + x3 + x4 = .5Constrain the total amount of Vitamin C in the mix to be at least 6 units:(2) 9x1 + 16x2 + 8x3 + 10x4 > 6Constrain the total amount of protein in the mix to be at least 5 units:(3) 12x1 + 10x2 + 10x3 + 8x4 > 5Constrain the total amount of iron in the mix to be at least 5 units:(4) 14x2 + 15x3 + 7x4 > 5
49 Blending with Weight Constraints Interpretation: The mixturecosts Frederick’s 40.6 cents.Optimal blend:0.099 lb. of grain 10.213 lb. of grain 20.088 lb. of grain 30.099 lb. of grain 4