Production and Operations Management Systems Chapter 4 Capacity

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Production and Operations Management Systems Chapter 4: Capacity Management and Aggregate Production Planning Sushil

Production and Operations Management Systems Chapter 4: Capacity Management and Aggregate Production Planning Sushil K. Gupta Martin K. Starr 2014 1

After reading this chapter, you should be able to: Ø Define and measure capacity

After reading this chapter, you should be able to: Ø Define and measure capacity Ø Make clear what aggregation does and why that is important. Ø Explain the function of aggregate planning (AP). Ø Discuss the systems nature of AP in terms of classes of resources and product-mix families. Ø Explain standard units of work. Ø Relate the importance of forecasting to AP. 2

After reading this chapter, you should be able to (continued): Ø Compare constant (or

After reading this chapter, you should be able to (continued): Ø Compare constant (or level) production with a chasing policy—where supply chases demand. Ø Detail the cost structure for aggregate planning. Ø Develop aggregate plans using overtime and subcontracting. Ø Distinguish between planning for manufacturing and service industries. 3

Definitions of Capacity n Definition of Available Capacity: The amount of resource time that

Definitions of Capacity n Definition of Available Capacity: The amount of resource time that is available to deliver product. This translates into the maximum number of units of goods or services that can be delivered in a given period of time. These units can be used for inventory or for shipment to customers. n Example: There are 3 machines. These 3 provide 120 hours of available capacity per week. It takes 2 hours to make a unit. So available capacity translates into 60 units. Less efficient machines take longer, so fewer units can be made. In that case, actual capacity is less than available capacity. 4

Classic Formula for Capacity Utilized* C=Tx. Ex. U q q C = actual capacity

Classic Formula for Capacity Utilized* C=Tx. Ex. U q q C = actual capacity used (std. hours*) T = available capacity (max cap. ) E = efficiency (percent) U = utilization (percent) *all times are in standard hours 5

Capacity Stated in Standard Hours n n n Time is measured in standard hours

Capacity Stated in Standard Hours n n n Time is measured in standard hours to provide a basis for aggregating different jobs on different machines. Pick the fastest production systems (machines, people, etc. ) as the basis for the production time standard. E = 1 for best-in-class efficiency (best machine-best job) Less-than-best efficiency is < 1 Jobs, machines, materials, workers, and methods interact resulting in different E values. 6

Example using the Equation for Capacity Utilized n n n n T = 120

Example using the Equation for Capacity Utilized n n n n T = 120 standard hours - std. hrs. E = 90% of standard time (E = 0. 9) U = 92. 6% (machine breakdown, U = 0. 9259) C = T x E x U = 100 std. hrs. R = 100/120 = 0. 833 (ratio actual/available) D = demand = 120 std. hrs. (D - C) = 20 std. hrs. (unfilled orders to be carried over to next week) 7

Theoretical vs. Actual capacity Actual Capacity is the Greatest Output rate achievable with the

Theoretical vs. Actual capacity Actual Capacity is the Greatest Output rate achievable with the Real process. It is less than theoretical capacity because of breakdowns, under-utilized facilities etc. Some examples that reduce theoretical capacity include: o The storm limits power that can be delivered. o Water main break decreases flow to the fire department. o Supplier of tubes for Tom’s of Maine has a strike, and it is now necessary to find a new source. 8

Aggregate Production Planning n An aggregate production plan provides the production rate and the

Aggregate Production Planning n An aggregate production plan provides the production rate and the number of workers required in each period (generally a month). n These are medium term plans that span over a period of 6 to 18 months. n The plans are made at the aggregate demand level which includes demand for all products. n The definition of aggregate is a collection, conglomeration, assemblage. 9

Types of Production Plans The following three plans will be presented: Ø Level Plan:

Types of Production Plans The following three plans will be presented: Ø Level Plan: The number of units produced in each month is constant at a chosen level. Ø Chase Plan: The number of units produced in a given month is equal to the exact demand in that month. Ø Mixed or Hybrid Plan: The number of units produced is constant at a given level for a few months and then changes. The level may change several times. 10

Example 1: Data The fluctuating demand for 12 periods (months) is given in the

Example 1: Data The fluctuating demand for 12 periods (months) is given in the second row in the table below. The total demand is 5, 520 units and the average demand is 460 units per month. Problem: Develop a production plan. A production plan gives the number of units to be produced in each month. Period 1 Demand 210 2 3 4 5 6 7 8 9 10 11 12 Total Average 440 600 300 480 610 560 800 200 400 380 540 5520 460 11

Example 1: Level Plan In this plan the production quantity is constant at the

Example 1: Level Plan In this plan the production quantity is constant at the average demand level, 460 (= 5, 520/12) units per month. Demand Data Month Expected Demand Production Plan Cumulative Inventory Demand Production 1 210 460 250 2 440 460 650 920 270 3 600 460 1250 1380 130 4 300 460 1550 1840 290 5 480 460 2030 2300 270 6 610 460 2640 2760 120 7 560 460 3200 3220 20 8 800 460 4000 3680 -320 9 200 460 4200 4140 -60 10 400 4600 0 11 380 460 4980 5060 80 12 540 460 5520 0 Total 5520 Average 460 The plan results in inventory in some months and shortages in other months. See table on right hand side (RHS). The inventory level in any month is the difference between cumulative production and cumulative demand in that month. Level Production Plan Note: Inventory = Cumulative Production - Cumulative Demand 12

Example 1: Graph for Level Plan The solid line shows cumulative demand; cumulative production

Example 1: Graph for Level Plan The solid line shows cumulative demand; cumulative production is depicted by the dotted line. In some periods the dotted line is above the solid line (indicating inventory). In other periods the dotted line is below the solid line (indicating shortages). This plan is not suitable for service industries because services cannot be inventoried. 13

Example 1: Chase Plan In the Chase plan, production is equal to the demand

Example 1: Chase Plan In the Chase plan, production is equal to the demand in every period. There are no inventories and no shortages in this plan. See table on RHS. Demand Data Chase Production Plan Month Expected Demand Cumulative Production Demand Plan Cumulative Production Inventory 1 210 210 0 2 440 650 0 3 600 1250 0 4 300 1550 0 5 480 2030 0 6 610 2640 0 7 560 3200 0 8 800 4000 0 9 200 4200 0 10 400 4600 0 11 380 4980 0 12 540 5520 0 Total 5520 Note: Inventory = Cumulative Production - Cumulative Demand 14

Example 1: Graph for Chase Plan The cumulative production and cumulative demand graphs overlap

Example 1: Graph for Chase Plan The cumulative production and cumulative demand graphs overlap as shown in figure on RHS. No inventories and no shortages occur. 15

Example 1: Hybrid (Mixed) Plan Produce 440 units (average demand of the first six

Example 1: Hybrid (Mixed) Plan Produce 440 units (average demand of the first six months) per month for months 1 thru 6. Change the production level to 680 units per month for the next two months (average demand of months 7 and 8). Produce 380 units (average demand of last four months) per month for the last four months. Demand Data Mixed Production Plan Month Expected Demand Cumulative Production Demand Plan Cumulative Production Inventory 1 210 440 230 2 440 650 440 880 230 3 600 1250 440 1320 70 4 300 1550 440 1760 210 5 480 2030 440 2200 170 6 610 2640 440 2640 0 7 560 3200 680 3320 120 8 800 4000 680 4000 0 9 200 4200 380 4380 10 400 4600 380 4760 11 380 4980 380 5140 160 12 540 5520 380 5520 0 Total 5520 Note: Inventory = Cumulative Production - Cumulative Demand 16

Example 1: Graph for Hybrid Plan The proposed plan is depicted graphically in figure

Example 1: Graph for Hybrid Plan The proposed plan is depicted graphically in figure on RHS. There could be inventories and/or shortages in this plan. Inventories occur but no shortages exist in this plan. Hybrid plans are based on judgment; and different hybrid plans will give different inventory/shortage levels. 17

Regular Time Production Capacity, Overtime and Subcontracting q Feasibility of the three plans depends

Regular Time Production Capacity, Overtime and Subcontracting q Feasibility of the three plans depends on the productive capacity of the plant. q Capacity constraints exist; these plans are developed within those constraints. q Assume: single shift regular time production capacity is 480 units per month. q This is sufficient for the level plan in which production is 460 units per month. q There will be idle capacity of 20 (480 – 460) units per month. q If planned production exceeds the regular time production capacity in any month then production using overtime and/or subcontracting may be needed. This is discussed in the next slide for the hybrid plan. 18

Regular Time Production Capacity, Overtime and Subcontracting (continued) In the hybrid plan, 440 units

Regular Time Production Capacity, Overtime and Subcontracting (continued) In the hybrid plan, 440 units are produced every month during regular time for the first six months. Therefore, there will be idle capacity of 40 (480 -440) units in each of the first six month. Similarly, during the last 4 months the idle capacity will be 100 (480 -380) units per month since the production level is 380 units per month. In months 7 and 8, the production level is 680 units per month of which 480 units can be produced during regular time. The additional 200 units have to be obtained by working overtime and/or through subcontracting. 19

Regular Time Production Capacity, Overtime and Subcontracting (continued) There always limits on overtime production

Regular Time Production Capacity, Overtime and Subcontracting (continued) There always limits on overtime production and amount of subcontracting. Suppose overtime is limited to 20% of regular time production meaning 96 (20% of 480) units can be produced using overtime per month. Therefore, 480 units can be produced during regular time and 96 units can be produced using overtime in months 7 and 8. The remaining 104 (680 – 480 – 96) units will be obtained through subcontracting. The maximum number of units that can be subcontracted depends on the availability of appropriate suppliers. 20

Best Plan? n n Which plan is the best? There are cost implications for

Best Plan? n n Which plan is the best? There are cost implications for each plan. The plan that minimizes the total cost is the best cost plan. * What are the costs? *Other factors may need to be considered such as the effect on morale caused by workforce disruption 21

Costs in APP n n n n Cost of carrying (holding) inventories. Cost of

Costs in APP n n n n Cost of carrying (holding) inventories. Cost of shortages or back orders. Regular time production cost. Overtime production cost. Cost of subcontracting or outsourcing. Cost of idle facilities and workers. Cost of changing production levels – up or down. This is usually accomplished by hiring or firing workers. Material Cost 22

Example 2: Aggregate Manufacturer’s Production Planning q q The table below gives the expected

Example 2: Aggregate Manufacturer’s Production Planning q q The table below gives the expected demand (row 2) and number of working days per month (row 3) for a 12 -month planning horizon. The total number of working days in the year is 251. The total yearly demand is 5, 856 product units (henceforth called units) with an average of 488 units per month. The demand varies from a high of 650 units in August to a low of 350 units in October. The demand per day for each month and the average demand for the 12 -month planning period (23. 33) are also included in the following table. Month Expected Demand (Units) Working Days Demand per Day (Units) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Average 400 440 600 396 480 610 560 650 450 380 540 5856 22 20 22 21 20 22 19 22 22 21 20 20 18. 18 22. 00 27. 27 18. 86 24. 00 27. 73 29. 47 29. 55 20. 45 16. 67 19. 00 27. 00 251 488 23. 33 *Note: This example employs fractional numbers for production per day. Therefore, rounding errors can be expected to occur 23

Example 2: Cost and Capacity Data Assumptions o Production time/unit is 4 hours. o

Example 2: Cost and Capacity Data Assumptions o Production time/unit is 4 hours. o 8 hours per day for each worker. Cost Data Assumptions o The number of workers remains constant for entire month. o The plant currently produces 21 units per day. o Beginning inventory = 0. No defective items are produced. o *Increase and decrease in production levels are normally achieved by hiring and firing workers 24

Calculating Production Levels Production level per day in any month = Production in that

Calculating Production Levels Production level per day in any month = Production in that month/working days in that month Suppose in a given month, say March, we expect to produce 600 units and the number of working days is 22. Then to produce 600 units in 22 days, Production level per day = 600/22 = 27. The fractional result can be interpreted in various ways. It can be rounded up with extra production being treated as inventory. Alternatively, it can be rounded down and extra units are completed using overtime. We deal with a production level of 27. 27 units as production of 27 units on that given day; then, production continues to work on the unfinished product on the next day. 25

Calculating Number of Workers = (Units x Production Time per Unit)/Hours Worked Suppose each

Calculating Number of Workers = (Units x Production Time per Unit)/Hours Worked Suppose each employee works for 8 hours per day and required production time is 4 hours per unit. To achieve a production level of 27. 27 in March, the required number of workers is: (27. 27 x 4)/8 = 13. 64. A work force of 13. 64 is considered as 13 full time workers and 0. 64 part time workers. 26

Example 2: Level Plan Sample calculations for this plan are shown in the next

Example 2: Level Plan Sample calculations for this plan are shown in the next two slides. Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Average Expected Demand (Units) 400 440 600 396 480 610 560 650 450 380 540 5856 488 Working Days 22 20 22 21 20 22 19 22 22 21 20 20 251 23. 33 23. 33 Total Production (Units) 513 467 513 490 467 513 443 513 490 467 5856 Inventory Addition/ Shortages (Units) 113 27 -87 94 -13 -97 -117 -137 63 140 87 -73 Ending Inventory/ Shortages (Units) 113 140 53 147 134 37 -80 -216 -153 -13 73 0 Ending Inventory (Units) 113 140 53 147 134 37 0 0 73 0 697 Ending Shortages (Units) 0 0 0 80 216 153 13 0 0 462 Inventory Cost ($) 2825 3500 1325 3675 3350 925 0 0 1825 0 17425 Shortage Cost ($) 0 0 0 8000 21600 15300 1300 0 0 46200 Change in Production Level (Units) 2. 33 0 0 0 Change in Production Level - Up (Units) 2. 33 0 0 0 2 Change in Production Level - Down (Units) 0. 00 0 0 0 Cost of Changing Production Level Up ($) 466. 14 0 0 0 466 Cost of Changing Production Level Down ($) 0. 00 0 0 0 Production per Day (Units) 27

Sample Calculations for Level Plan Production/Day = 23. 33 units. o o o Production

Sample Calculations for Level Plan Production/Day = 23. 33 units. o o o Production in any given month = Number of days in that month x 23. 33. The production numbers are rounded to the nearest integer. For example, in January 513 is the number of units produced where (23. 33 x 22 = 513. 26), However, the demand in January is only 400 units. Therefore, 113 (513 - 400) units go into inventory. In February, 467 (23. 33 x 20) units are produced whereas the expected demand is for 440 units. Therefore, 27 units (467 – 440) are added to inventory and the inventory level at the end of February is 140. In March, the production is 513 (23. 33 x 22) which is 87 units less than the demand (600 units). Therefore 87 units are withdrawn from inventory to meet the demand for March. The inventory level at the end of March becomes 53. In this way, the calculations continue. 28

Sample Calculations for Level Plan (continued) Shortages occur in any month if (production +

Sample Calculations for Level Plan (continued) Shortages occur in any month if (production + inventory) is less than demand. The inventory and shortage costs in each month are calculated by multiplying the end of month inventory or shortage by the respective costs. The costs of this plan are: Category Level Plan Regular time Labor Cost Over Time Labor Cost Inventory carrying Cost Shortage Cost Increasing Production level Decreasing Production level Material Cost Total Cost $468, 480 $17, 425 $46, 200 $466 $585, 600 $1, 118, 171 Note: rounding errors can make small changes in the various totals 29

Example 2: Chase Plan Sample calculations for this plan are shown in the next

Example 2: Chase Plan Sample calculations for this plan are shown in the next slide. Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Expected Demand (units) 400 440 600 396 480 610 560 650 450 380 540 5856 Working Days 22 20 22 21 20 22 19 22 22 21 20 20 251 18. 18 22. 00 27. 27 18. 86 24. 00 27. 73 29. 47 29. 55 20. 45 16. 67 19. 00 27. 00 440 600 396 480 610 560 650 450 380 540 5856 Production per Day (units) Total Production (units) Inventory Addition/ Shortages (units) There are no inventories or shortages in this plan. Change in Production Level (Units) -2. 82 3. 82 5. 27 -8. 42 5. 14 3. 73 1. 75 0. 07 -9. 09 -3. 79 2. 33 8. 00 Change in Production Level - Up (Units) 0. 00 3. 82 5. 27 0. 00 5. 14 3. 73 1. 75 0. 07 0. 00 2. 33 8. 00 30. 11 Change in Production Level - Down (Units) 2. 82 0. 00 8. 42 0. 00 9. 09 3. 79 0. 00 24. 11 Number of Workers 9. 09 11. 00 13. 64 9. 43 12. 00 13. 86 14. 74 14. 77 10. 23 8. 33 9. 50 13. 50 30

Sample Calculations for Chase Plan In this plan there are no inventories or shortages.

Sample Calculations for Chase Plan In this plan there are no inventories or shortages. However, the production level has to be adjusted in each month. For example, In January the production level is 18. 18 units per day. Therefore, the production level is reduced by 2. 82 (21 -18. 18) units. In February the production level increases to 22 and the level has to be adjusted upward by 3. 82 (level in February – level in January = 2218. 18) units. The costs of this plan are: Category Chase Plan Regular time Labor Cost $468, 480 Over Time Labor Cost Inventory carrying Cost Shortage Cost Increasing Production level $6, 023 Decreasing Production $7, 234 level Material Cost $585, 600 Total Cost $1, 067, 336 Note: rounding errors can make small changes in the various totals 31

Example 2: Hybrid (Mixed) Plan Month Expected Demand (Units) Working Days Jan Feb Mar

Example 2: Hybrid (Mixed) Plan Month Expected Demand (Units) Working Days Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total 400 440 600 396 480 610 560 650 450 380 540 5856 22 20 22 21 20 22 Average Demand per Day (Jan to Jun) Production per Day Sample calculations for this plan are shown in the next slide. 19 22 22 Average Demand per Day (Jul to Sep) 21 20 20 Average Demand per Day (Oct to Dec) 251 23. 04 26. 35 20. 82 507 461 507 484 461 507 501 580 437 416 5856 107 21 -93 88 -19 -103 -59 -70 130 87 36 -124 107 128 35 122 103 0 -59 -130 0 87 124 0 107 128 35 122 103 0 0 87 124 0 706 0 0 0 59 130 0 0 189 Inventory Cost ($) 2675 3200 875 3050 2575 0 0 2175 3100 0 $17, 650 Shortage Cost ($) 0 0 0 5900 13000 0 0 $18, 900 Change in Production Level (Units) 2. 04 0 0 0 3 0 0 -6 0 0 Change in Production Level - Up (Units) 2. 04 0. 00 3. 31 0. 00 5. 35 Change in Production Level - Down (Units) 0. 00 0. 00 5. 53 407. 87 0. 00 661. 97 0. 00 $1, 070 0. 00 0. 00 1658. 86 0. 00 $1, 659 11. 52 13. 17 10. 41 Total Production (Units) Inventory Addition/ Shortages (Units) Ending Inventory (Units) Ending Shortages (Units) Cost of Chaning Production Level Up ($) Cost of Changing Production Level Down ($) Number of Workers 32

Sample Calculations for Mixed (Hybrid) Plan The production level is constant at 23. 04

Sample Calculations for Mixed (Hybrid) Plan The production level is constant at 23. 04 units per day for the first six month which is the average demand for the first six months, January to June. Then it changes to 26. 35 which is the average demand for the next three months. Finally the production level changes to 20. 82 which is the average demand for the last three months. The costs of this plan are: Category Regular time Labor Cost $468, 480 Over Time Labor Cost Inventory carrying Cost $17, 650 Shortage Cost $18, 900 Increasing Production level $1, 070 Decreasing Production level $1, 659 Material Cost Total Cost This plan entails inventories, shortages, and changing production levels up and down. Hybrid Plan $585, 600 $1, 093, 359 Note: rounding errors can make small changes in the various totals The calculations are done in the same way as for the level and chase plans. 33

Example 2: Level Production with Overtime Month Jan Feb Mar Apr May Jun Jul

Example 2: Level Production with Overtime Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Expected Demand (Units) 400 440 600 396 480 610 560 650 450 380 540 5856 Working Days 22 20 22 21 20 22 19 22 22 21 20 20 251 16. 67 16. 67 367 333 367 350 333 367 317 367 350 333 4184 33 107 233 46 147 243 283 83 0 47 207 1672 400 440 600 396 480 610 560 650 450 380 540 5856 Ending Inventory/ Shortages (Units) 0 0 0 Ending Inventory (units) 0 0 0 0 Ending Shortages (Units) 0 0 0 0 Inventory Cost ($) 0 0 0 0 Shortage Cost ($) 0 0 0 0 -4. 33 0 0 0 0 0 0 4 0 0 0 4. 33 0 0 0 0 1299 0 0 0 1299 8. 34 8. 34 Production per Day (Units) Regular Time Production (Units) Overtime Production (Units) Total production (Units) Change in Production Level - Up (Units) Change in Production Level - Down (Units) Cost of Changing Production Level Up ($) Cost of Changing Production Level Down ($) Number of Workers Sample calculations for this plan are shown in the next slide. 34

Sample calculations for Level Production with Overtime Level production is set at 16. 67

Sample calculations for Level Production with Overtime Level production is set at 16. 67 units per day which is equal to the minimum of the production per day in 12 months. The minimum production per day (16. 67) is for October. The difference between the demand production in any month is the number of units to be produced during over time. The costs of this plan are: Category Regular time Labor Cost $334, 720 Overtime Labor Cost $200, 640 Inventory carrying Cost Shortage Cost Increasing Production level Decreasing Production level Material Cost For example, the production in January is 367 (16. 67 x 22) units. Therefore, overtime production will be 33 (400 -367). Level Plan with Over Time Total Cost $1, 299 $585, 600 $1, 122, 259 Note: rounding errors can make small changes in the various totals In this plan 4, 184 units are produced during regular time and 1, 672 units are produced during overtime for a total of 5, 856 units. 35

Cost Comparison Level Plan Chase Plan Hybrid Plan Level Plan with Overtime $468, 480

Cost Comparison Level Plan Chase Plan Hybrid Plan Level Plan with Overtime $468, 480 $334, 734 $200, 636 Inventory carrying Cost $17, 425 $17, 650 Shortage Cost $46, 200 $18, 900 Increasing Production level $466 $6, 023 $1, 070 Decreasing Production level $7, 234 $1, 659 $1, 299 $585, 600 $1, 118, 171 $1, 067, 336 $1, 093, 359 $1, 122, 269 Regular time Labor Cost Overtime Labor Cost Material Cost Total Cost 36

Selection of a Production Plan Table on RHS gives the cost comparison of the

Selection of a Production Plan Table on RHS gives the cost comparison of the four production plans discussed above. The Chase Plan is the least expensive plan and is a top candidate for being selected. However, other non-financial considerations must also be taken into account when choosing the final plan. Regular time Labor Cost Overtime Labor Cost Inventory carrying Cost Shortage Cost Increasing Production level Decreasing Production level Material Cost Total Cost Level Plan Chase Plan Hybrid Plan Level Plan with Overtime $468, 480 $334, 720 $200, 640 $17, 425 $17, 650 $46, 200 $18, 900 $466 $6, 023 $1, 070 $7, 234 $1, 659 $1, 299 $585, 600 $1, 118, 171 $1, 067, 336 $1, 093, 359 $1, 122, 259 37

Beginning Conditions Beginning conditions specify the existing inventory level and the existing production level

Beginning Conditions Beginning conditions specify the existing inventory level and the existing production level per day when planning starts. The same beginning conditions must be used in each plan for comparing the costs. The beginning inventory is used to reduce the production requirements of the first period while solving the problem. For example, if the beginning inventory for Example 2 discussed earlier was 100 units, then the demand in the first month will be reduced to 300 (400 -100) because the 100 units in stock can be used to meet the demand of the first month. We assumed a beginning inventory of zero in Example 2. 38

Beginning Conditions (continued) The existing production level affects the cost of changing the production

Beginning Conditions (continued) The existing production level affects the cost of changing the production level (up or down) in the first month. In Example 2, we assumed the existing production level per day to be 21 units. Therefore, the production level was: v Increased by 2. 33 (23. 33 – 21) in the level plan. v Decreased by 2. 82 (21 – 18. 18) in the chase plan, v Increased by 2. 04 (23. 04 – 21) in the hybrid plan and v Decreased by 4. 33 (21 – 16. 67) in the level plan with overtime. 39

Aggregate Production Planning in a Service Industry In a service industry the service or

Aggregate Production Planning in a Service Industry In a service industry the service or “product” cannot be stored. A blood-testing laboratory provides a good illustration of a service system with testing capacity that cannot be fully used when there is not enough demand. Technicians’ time cannot be stored when technicians are idle. On the other hand, when demand is greater than the technical capacity to supply tests, the tests must be postponed or subcontracted or done on overtime. The big difference with the manufacturer’s example is the inability to create a useful inventory when capacity to test is greater than demand for testing. 40

Aggregate Planning in a Blood Testing Lab q Blood tests are the product of

Aggregate Planning in a Blood Testing Lab q Blood tests are the product of the blood testing lab. q Because all tests are individual and unique, they can only be made on demand. q Demand for tests of different kinds are aggregated—some take longer than others and use different kinds of materials and equipment. q The aggregation is based on averaging across the normal mix of blood test procedures. Demand, in this example, is stated in units (occasionally as test kit units). q For sake of comparison, this service case and the prior manufacturing case use the same set of numbers for demand levels, production capacity, and applicable costs applied to different strategies for matching supply and demand. The difference to note is that the manufacturer can store units in inventory to meet later demand but the blood-testing laboratory cannot. 41

Data for Blood Testing Lab o o o Table below provides the number of

Data for Blood Testing Lab o o o Table below provides the number of working days for each month over a 12 -month planning horizon. The total yearly demand is 5, 856 blood tests with an average of 488 testing units per month. The demand varies from a high of 650 test kit units in August to a low of 350 units in October. The total number of working days in the year is 251. The demand per day for each month and the average demand for the 12 -month planning period are also included in this table. 42

Costs for Blood Testing Lab The back order cost (arises because the lab is

Costs for Blood Testing Lab The back order cost (arises because the lab is not able to provide the blood test on time in the given month). $100 Idle time costs (occurs when there is too much capacity for testing. $25 This is higher than regular time labor cost due to idle apparatus). Cost of increasing production level per unit* $200 Cost of decreasing production level per unit* $300 Regular time labor cost per hour $20 Overtime labor cost per hour--not used $30 Subcontracting (outsourcing) cost per unit--not used $650 Material cost per unit $100 *Increase and decrease in production levels are normally achieved by hiring and dismissal. Changes are costly because blood-testing involves responsibility for proficiency. 43

Level Plan for Blood Testing Lab Month Jan Feb Mar Apr May Jun Jul

Level Plan for Blood Testing Lab Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Expected Demand 400 440 600 396 480 610 560 650 450 380 540 5856 Working Days 22 20 22 21 20 22 19 22 22 21 20 20 251 23. 33 23. 33 Total Production 513 467 513 490 467 513 443 513 490 467 5, 856 Idle Time (+) or Back Orders (-) * 113 27 -87 94 -13 -97 -117 -137 63 140 87 -73 Idle Time (+) or Net Back Orders ** 113 27 -87 7 -13 -110 -227 -364 -301 -161 -74 -147 Idle Time 113 27 0 0 0 0 0 147 0 0 87 0 13 110 227 364 301 161 74 147 1484 2, 825 675 0 175 0 0 0 0 3, 675 Back Order Cost 0 0 8700 0 1300 11, 000 22, 700 36, 400 30, 100 16, 100 7, 400 14, 700 148, 400 Change in Production Level 2 0 0 0 Change in Production Level – UP 2 0 0 0 2 Change in Production Level – Down 0 0 0 0 Cost of Changing Production Level UP 466 0 0 0 0 0 0 0 Production per Day Back Orders Idle Time Cost of Changing Production Level Down 44

Level Plan: Total Costs The total cost of this plan is $1, 206, 621.

Level Plan: Total Costs The total cost of this plan is $1, 206, 621. Various cost components are given in the table on RHS. This plan is 7. 5% worse than the worst of all of the prior plans. The total backorder costs are too large. Total Idle Time Cost $3675 Total Back Order Cost $148, 400 Regular Time Labor Cost $468, 480 Material Cost $585, 600 Changing Production Level $466 That suggests two things. Total Cost $1, 206, 621 First, increase the number of technicians and let the idle cost go up; second, opt for a chasing strategy. It might do better. 45

Thank you 46

Thank you 46