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Production Scheduling

3. 4. 5. 6. 7. 8. B2 [----------]. E5 [--------------. P9 [---]. D1 [--------. X8 ----]. C6 [-. Production Scheduling. Minimizing Total Production Time. Sequencing n Jobs through Two Work Centers

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Production Scheduling

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  1. 3 4 5 6 7 8 B2 [----------] E5 [-------------- P9 [---] D1 [-------- X8 ----] C6 [- Production Scheduling

  2. Minimizing Total Production Time • Sequencing n Jobs through Two Work Centers • When several jobs must be sequenced through two work centers, we may want to select a sequence that must hold for both work centers • Johnson’s rule can be used to find the sequence that minimizes the total production time through both work centers

  3. Johnson’s Rule 1. Select the shortest processing time in either work center 2. If the shortest time is at the first work center, put the job in the first unassigned slot in the schedule. If the shortest time is at the second work center, put the job in the last unassigned slot in the schedule. 3. Eliminate the job assigned in step 2. 4. Repeat steps 1-3, filling the schedule from the front and back, until all jobs have been assigned a slot.

  4. Example: Minimizing Total Production Time It is early Saturday morning and The Finest Detail has five automobiles waiting for detailing service. Each vehicle goes through a thorough exterior wash/wax process and then an interior vacuum/shampoo/polish process. The entire detailing crew must stay until the last vehicle is completed. If the five vehicles are sequenced so that the total processing time is minimized, when can the crew go home. They will start the first vehicle at 7:30 a.m. Time estimates are shown on the next slide.

  5. Example: Minimizing Total Production Time Exterior Interior Job Time (hrs.) Time (hrs.) Cadillac 2.0 2.5 Bentley 2.1 2.4 Lexus 1.9 2.2 Porsche 1.8 1.6 Infiniti 1.5 1.4

  6. Example: Minimizing Total Production Time • Johnson’s Rule Least Work Schedule Time Job Center Slot 1.4 Infiniti Interior 5th 1.6 Porsche Interior 4th 1.9 Lexus Exterior 1st 2.0 Cadillac Exterior 2nd 2.1 Bentley Exterior 3rd

  7. Example: Minimizing Total Production Time 0 1.9 3.9 6.0 7.8 9.3 12.0 L C B P I Idle Exterior Interior Idle L C B P I 0 1.9 4.1 6.6 9.0 10.6 12.0 It will take from 7:30 a.m. until 7:30 p.m. (not allowing for breaks) to complete the five vehicles.

  8. Scheduling Product-Focused Manufacturing

  9. Product-Focused Scheduling • Two general types of product-focused production: • Batch - large batches of several standardized products produced • Continuous - few products produced continuously.... minimal changeovers

  10. Scheduling Decisions • If products are produced in batches on the same production lines: • How large should production lot size be for each product? • When should machine changeovers be scheduled? • If products are produced to a delivery schedule: • At any point in time, how many products should have passed each operation if time deliveries are to be on schedule?

  11. Batch Scheduling EOQ for Production Lot Size • How many units of a single product should be included in each production lot to minimize annual inventory carrying cost and annual machine changeover cost?

  12. Example: EOQ for Production Lots CPC, Inc. produces four standard electronic assemblies on a produce-to-stock basis. The annual demand, setup cost, carrying cost, demand rate, and production rate for each assembly are shown on the next slide. a) What is the economic production lot size for each assembly? b) What percentage of the production lot of power units is being used during its production run? c) For the power unit, how much time will pass between production setups?

  13. Example: EOQ for Production Lots Annual Setup Carry Demand Prod. Demand Cost Cost Rate Rate Power Unit 5,000 $1,200 $6 20 200 Converter 10,000 600 4 40 300 Equalizer 12,000 1,500 10 48 100 Transformer 6,000 400 2 24 50

  14. Example: EOQ for Production Lots • Economic Production Lot Sizes

  15. Example: EOQ for Production Lots • % of Power Units Used During Production d/p = 20/200 = .10 or 10% • Time Between Setups for Power Units EOQ/d = 1,490.7/20 = 74.535 days

  16. Batch Scheduling • Limitations of EOQ Production Lot Size • Uses annual “ballpark” estimates of demand and production rates, not the most current estimates • Not a comprehensive scheduling technique – only considers a single product at a time • Multiple products usually share the same scarce production capacity

  17. Batch Scheduling • Run-Out Method • Attempts to use the total production capacity available to produce just enough of each product so that if all production stops, inventory of each product runs out at the same time

  18. Example: Run-Out Method QuadCycle, Inc. assembles, in batches, four bicycle models on the same assembly line. The production manager must develop an assembly schedule for March. There are 1,000 hours available per month for bicycle assembly work. Using the run-out method and the pertinent data shown on the next slide, develop an assembly schedule for March.

  19. Example: Run-Out Method Assembly March April Inventory Time Forec. Forec. On-Hand Required Demand Demand Bicycle (Units) (Hr/Unit) (Units) (Units) Razer 100 .3 400 400 Splicer 600 .2 900 900 Tracker 500 .6 1,500 1,500 HiLander 200 .1 500 500

  20. Example: Run-Out Method • Convert inventory and forecast into assembly hours Assemb. March March Invent. Time Forec. Invent. Forec. On-Hand Req’d. Dem. On-Hand Dem. Bicycle (Units) (Hr/Unit) (Units) (Hours) (Hours) Razer 100 .3 400 30 120 Splicer 600 .2 900 120 180 Tracker 500 .6 1,500 300 900 HiLander 200 .1 500 20 50 Total 470 1,250 (1) (2) (3) (4) (5) (1) x (2) (2) x (4)

  21. Example: Run-Out Method • Compute aggregate run-out time in months Aggregate Run-out Time = = [(Total Inventory On-Hand in Hours) + (Total Assembly Hours Available per Month) - (March’s Forecasted Demand in Hours)] / (April’s Forecasted Demand in Hours) = (470 + 1,000 - 1,250)/1,250 = .176 months

  22. Example: Run-Out Method • Develop March’s Production Schedule March’s March’s Desired Desired Assembly Ending End.Inv. Required Time Inventory & Forec. Production Allocated Bicycle (Units) (Units) (Units) (Hours) Razer 70 470 370 111.0 Splicer 158 1,058 458 91.6 Tracker 264 1,764 1,264 758.4 HiLander 88 588 388 38.8 999.8 (6) (7) (8) (9) (7) - (1) (3) x .176 (3) + (6) (8) x (2)

  23. Computerized Scheduling • Develops detailed schedules for each work center indicating starting and ending times • Develops departmental schedules • Generates modified schedules as orders move • Many packages available.... select one most appropriate for your business

  24. Wrap-Up: World-Class Practice • In process-focused factories: • MRP II refined.... promises are met, shop loading is near optimal, costs are low, quality is high • In product-focused factories: • EOQ for standard parts containers, this sets S, lot sizes are lower, inventories slashed, customer service improved • Scheduling is integral part of a computer information system

  25. End of Chapter 16

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