production scheduling

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Production SchedulingProduction SchedulingProduction SchedulingProduction Scheduling

B2 [----------]B2 [----------] E5 [--------------E5 [-------------- P9 [---]P9 [---] D1 [--------D1 [-------- X8 ----]X8 ----] C6 [-C6 [-

3 3 44 55 66 77 88

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Minimizing Total Production TimeMinimizing Total Production TimeMinimizing Total Production TimeMinimizing Total Production Time

Sequencing n Jobs through Two Work CentersSequencing n Jobs through Two Work Centers When several jobs must be sequenced through two When several jobs must be sequenced through two

work centers, we may want to select a sequence work centers, we may want to select a sequence that must hold for both work centersthat must hold for both work centers

Johnson’s rule can be used to find the sequence Johnson’s rule can be used to find the sequence that minimizes the total production time through that minimizes the total production time through both work centersboth work centers

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Johnson’s RuleJohnson’s RuleJohnson’s RuleJohnson’s Rule

1. Select the shortest processing time in either work 1. Select the shortest processing time in either work centercenter

2. If the shortest time is at the first work center, put the 2. If the shortest time is at the first work center, put the job in the first unassigned slot in the schedule. If the job in the first unassigned slot in the schedule. If the shortest time is at the second work center, put the job shortest time is at the second work center, put the job in the last unassigned slot in the schedule. in the last unassigned slot in the schedule.

3. Eliminate the job assigned in step 2.3. Eliminate the job assigned in step 2.

4. Repeat steps 1-3, filling the schedule from the front 4. Repeat steps 1-3, filling the schedule from the front and back, until all jobs have been assigned a slot.and back, until all jobs have been assigned a slot.

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Example: Minimizing Total Production TimeExample: Minimizing Total Production TimeExample: Minimizing Total Production TimeExample: Minimizing Total Production Time

It is early Saturday morning and The Finest It is early Saturday morning and The Finest Detail has five automobiles waiting for detailing Detail has five automobiles waiting for detailing service. Each vehicle goes through a thorough service. Each vehicle goes through a thorough exterior wash/wax process and then an interior exterior wash/wax process and then an interior vacuum/shampoo/polish process. vacuum/shampoo/polish process.

The entire detailing crew must stay until the The entire detailing crew must stay until the last vehicle is completed. If the five vehicles are last vehicle is completed. If the five vehicles are sequenced so that the total processing time is sequenced so that the total processing time is minimized, when can the crew go home. They will minimized, when can the crew go home. They will start the first vehicle at 7:30 a.m.start the first vehicle at 7:30 a.m.

Time estimates are shown on the next slide.Time estimates are shown on the next slide.

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ExteriorExterior InteriorInteriorJobJob Time (hrs.)Time (hrs.) Time (hrs.)Time (hrs.)

CadillacCadillac 2.02.0 2.52.5BentleyBentley 2.12.1 2.42.4LexusLexus 1.91.9 2.22.2

PorschePorsche 1.81.8 1.61.6InfinitiInfiniti 1.51.5 1.41.4

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Johnson’s RuleJohnson’s Rule

Least Least WorkWork ScheduleScheduleTimeTime Job Job CenterCenter Slot Slot

1.4 1.4 InfinitiInfiniti InteriorInterior 5 5thth

1.61.6 PorschePorsche InteriorInterior 4 4thth

1.91.9 Lexus Lexus ExteriorExterior 1 1stst

2.02.0 CadillacCadillac ExteriorExterior 2 2ndnd

2.12.1 BentleyBentley ExteriorExterior 3 3rdrd

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ExteriorExterior

InteriorInterior

0 1.9 3.9 6.0 7.8 9.3 12.00 1.9 3.9 6.0 7.8 9.3 12.0

0 1.9 4.1 6.6 9.0 10.6 12.00 1.9 4.1 6.6 9.0 10.6 12.0

LL CC BB

LL

PP II

Idle CC BB PP II

Idle

It will take from 7:30 a.m. until 7:30 p.m. (not It will take from 7:30 a.m. until 7:30 p.m. (not allowing for breaks) to complete the five vehicles.allowing for breaks) to complete the five vehicles.

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SchedulingScheduling

Product-FocusedProduct-Focused

ManufacturingManufacturing

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Product-Focused SchedulingProduct-Focused SchedulingProduct-Focused SchedulingProduct-Focused Scheduling

Two general types of product-focused production:Two general types of product-focused production: BatchBatch - large batches of several standardized - large batches of several standardized

products producedproducts produced ContinuousContinuous - few products produced - few products produced

continuously.... minimal changeoverscontinuously.... minimal changeovers

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Scheduling DecisionsScheduling DecisionsScheduling DecisionsScheduling Decisions

If products are produced in batches on the same If products are produced in batches on the same production lines:production lines: How large should production lot size be for each How large should production lot size be for each

product?product? When should machine changeovers be scheduled?When should machine changeovers be scheduled?

If products are produced to a delivery schedule:If products are produced to a delivery schedule: At any point in time, how many products should At any point in time, how many products should

have passed each operation if time deliveries are to have passed each operation if time deliveries are to be on schedule?be on schedule?

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Batch SchedulingBatch SchedulingBatch SchedulingBatch Scheduling

EOQ for Production Lot SizeEOQ for Production Lot Size How many units of a single product should be How many units of a single product should be

included in each production lot to minimize annual included in each production lot to minimize annual inventory carrying cost and annual machine inventory carrying cost and annual machine changeover cost?changeover cost?

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Example: Example: EOQ for Production LotsEOQ for Production LotsExample: Example: EOQ for Production LotsEOQ for Production Lots

CPC, Inc. produces four standard electronic CPC, Inc. produces four standard electronic assemblies on a produce-to-stock basis. The annual assemblies on a produce-to-stock basis. The annual demand, setup cost, carrying cost, demand rate, and demand, setup cost, carrying cost, demand rate, and production rate for each assembly are shown on the production rate for each assembly are shown on the next slide.next slide.a) What is the economic production lot size for each a) What is the economic production lot size for each

assembly?assembly?b) What percentage of the production lot of power b) What percentage of the production lot of power units is being used during its production run?units is being used during its production run?c) For the power unit, how much time will pass c) For the power unit, how much time will pass between production setups?between production setups?

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AnnualAnnual SetupSetup CarryCarry DemandDemand Prod.Prod.DemandDemand CostCost CostCost RateRate RateRate

Power UnitPower Unit 5,000 5,000 $1,200$1,200 $6$6 2020 200200

ConverterConverter 10,00010,000 600 600 4 4 4040 300300

EqualizerEqualizer 12,00012,000 1,500 1,500 1010 4848 100100

TransformerTransformer 6,000 6,000 400 400 2 2 2424 50 50

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Economic Production Lot SizesEconomic Production Lot Sizes

EOQ = (2DS/C[p/(p-d)]EOQ = (2DS/C[p/(p-d)]

1EOQ = (2(5,000)(1,200)/6[200/(200-20)] 1, 490.71EOQ = (2(5,000)(1,200)/6[200/(200-20)] 1, 490.7

2EOQ = (2(10,000)(600)/4[300/(300-40)] 1,860.52EOQ = (2(10,000)(600)/4[300/(300-40)] 1,860.5

3EOQ = (2(12,000)(1,500)/10[100/(100-48)] 2,631.23EOQ = (2(12,000)(1,500)/10[100/(100-48)] 2,631.2

4EOQ = (2(6,000)(400)/2[50/(50-24)] 2,148.34EOQ = (2(6,000)(400)/2[50/(50-24)] 2,148.3

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% of Power Units Used During Production% of Power Units Used During Production

d/p = 20/200 = .10 or 10%d/p = 20/200 = .10 or 10%

Time Between Setups for Power UnitsTime Between Setups for Power Units

EOQ/d = 1,490.7/20 = 74.535 daysEOQ/d = 1,490.7/20 = 74.535 days

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Limitations of EOQ Production Lot SizeLimitations of EOQ Production Lot Size Uses annual “ballpark” estimates of demand and Uses annual “ballpark” estimates of demand and

production rates, not the most current estimatesproduction rates, not the most current estimates Not a comprehensive scheduling technique – only Not a comprehensive scheduling technique – only

considers a single product at a timeconsiders a single product at a time Multiple products usually share the same scarce Multiple products usually share the same scarce

production capacityproduction capacity

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Run-Out MethodRun-Out Method Attempts to use the total production capacity Attempts to use the total production capacity

available to produce just enough of each product available to produce just enough of each product so that if all production stops, inventory of each so that if all production stops, inventory of each product runs out at the same timeproduct runs out at the same time

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Example: Run-Out MethodExample: Run-Out MethodExample: Run-Out MethodExample: Run-Out Method

QuadCycle, Inc. assembles, in batches, four QuadCycle, Inc. assembles, in batches, four bicycle models on the same assembly line. The bicycle models on the same assembly line. The production manager must develop an assembly production manager must develop an assembly schedule for March.schedule for March.

There are 1,000 hours available per month for There are 1,000 hours available per month for bicycle assembly work. Using the run-out method bicycle assembly work. Using the run-out method and the pertinent data shown on the next slide, and the pertinent data shown on the next slide, develop an assembly schedule for March.develop an assembly schedule for March.

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AssemblyAssembly MarchMarch AprilAprilInventoryInventory TimeTime Forec.Forec. Forec.Forec.On-HandOn-Hand RequiredRequired DemandDemand

DemandDemandBicycleBicycle (Units)(Units) (Hr/Unit)(Hr/Unit) (Units)(Units) (Units)(Units)

RazerRazer 100100 .3.3 400400 400400SplicerSplicer 600600 .2.2 900900 900900TrackerTracker 500500 .6.6 1,5001,500 1,5001,500HiLanderHiLander 200200 .1.1 500500 500500

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Convert inventory and forecast into assembly hoursConvert inventory and forecast into assembly hours

Assemb.Assemb. MarchMarch MarchMarchInvent.Invent. TimeTime Forec.Forec. Invent.Invent. Forec.Forec.

On-HandOn-Hand Req’d.Req’d. Dem.Dem. On-HandOn-Hand Dem.Dem.BicycleBicycle (Units)(Units) (Hr/Unit)(Hr/Unit) (Units)(Units) (Hours)(Hours) (Hours)(Hours)

RazerRazer 100100 .3.3 400400 3030 120120SplicerSplicer 600600 .2.2 900900 120120 180180TrackerTracker 500500 .6.6 1,5001,500 300300 900900HiLanderHiLander 200200 .1.1 500500 2020 5050

TotalTotal 470470 1,2501,250

(1)(1) (2) (2) (3) (3) (4) (4) (5) (5)

(1) x (2)(1) x (2) (2) x (4)(2) x (4)

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Compute aggregate run-out time in monthsCompute aggregate run-out time in months

Aggregate Run-out Time =Aggregate Run-out Time =

== [(Total Inventory On-Hand in Hours)[(Total Inventory On-Hand in Hours)

+ (Total Assembly Hours Available per + (Total Assembly Hours Available per Month)Month)

(March’s Forecasted Demand in Hours)](March’s Forecasted Demand in Hours)]

/ (April’s Forecasted Demand in Hours)/ (April’s Forecasted Demand in Hours)

= (470 + 1,000 = (470 + 1,000 1,250)/1,250 = .176 months 1,250)/1,250 = .176 months

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Develop March’s Production ScheduleDevelop March’s Production Schedule

March’sMarch’s March’sMarch’sDesiredDesired DesiredDesired AssemblyAssemblyEndingEnding End.Inv.End.Inv. RequiredRequired TimeTime

InventoryInventory & Forec.& Forec. ProductionProduction AllocatedAllocatedBicycleBicycle (Units)(Units) (Units)(Units) (Units)(Units) (Hours)(Hours)

RazerRazer 7070 470470 370370 111.0111.0SplicerSplicer 158158 1,0581,058 458458 91.691.6TrackerTracker 264264 1,7641,764 1,2641,264 758.4758.4HiLanderHiLander 8888 588588 388388 38.838.8

999.8999.8

(6)(6) (7) (7) (8) (8) (9) (9)

(3) x .176(3) x .176 (3) + (6)(3) + (6) (7) (7) (1) (1) (8) x (2)(8) x (2)

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Computerized SchedulingComputerized SchedulingComputerized SchedulingComputerized Scheduling

Develops detailed schedules for each work center Develops detailed schedules for each work center indicating starting and ending timesindicating starting and ending times

Develops departmental schedulesDevelops departmental schedules Generates modified schedules as orders moveGenerates modified schedules as orders move Many packages available.... select one most Many packages available.... select one most

appropriate for your businessappropriate for your business

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Wrap-Up: World-Class PracticeWrap-Up: World-Class PracticeWrap-Up: World-Class PracticeWrap-Up: World-Class Practice

In process-focused factories:In process-focused factories: MRP II refined.... promises are met, shop loading MRP II refined.... promises are met, shop loading

is near optimal, costs are low, quality is highis near optimal, costs are low, quality is high In product-focused factories:In product-focused factories:

EOQ for standard parts containers, this sets S, lot EOQ for standard parts containers, this sets S, lot sizes are lower, inventories slashed, customer sizes are lower, inventories slashed, customer service improvedservice improved

Scheduling is integral part of a computer information Scheduling is integral part of a computer information systemsystem

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End of Chapter 16End of Chapter 16End of Chapter 16End of Chapter 16

production scheduling

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