Lean Thinking

Building Lean SystemsMixed Model Scheduling

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed-Model Scheduling and Small Batch ProductionIn a perfect world, when the customer pulls a product from the final station, a signal is generated on each upstream resource to produce exactly what is pulled. In the real world, changeover time, material availability, or operator availability motivates large batch production.Large-lot production exacerbates Bowlwhip effect. WIP between stations goes up, flow time goes up

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed-Model Scheduling and Small Batch ProductionProduce every product as quickly as possible, at the same rate at which customer demands are made. In a lean system, products flow smoothly through the enterprise with no delays Mixed-model scheduling (heijunka)Evenly distributing the production of different products over a period of timeChangeover or setup times must be smallSmall batching in the presence of setup times

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Demand per hour A(3), B(2), and C(1).10 min/part assembly time. 10 hrs/day, 5d/w.Batch size is one week of demand; A(150), B(100), C(50). Instead of receiving products every hour, the customer will receive them once a week. The average inventory is 75 As, 50 Bs, and 25 Cs.If production per hour was A(3), B(2), C(1), the finished goods inventory would be negligible because production would exactly match hourly demand. MMS Example

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling AAABBC is a good hourly schedule, it could be more finely sequenced as follows: ABACAB.Production in large batchesuneven workloaduneven demand for upstream processes, pull impossibleproduction is not synchronized with demand.Mixed-model production:smooth work-load,smooth demand for upstream processesAllows production to match customer demand.

MMS Example

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed Model Sequence for VolpensSmallest possible sequence length = 1/0.09 = 11.11Choose a 11 unit sequence; adjust every two cycles.Note: A mixed model sequence is used to intentionally vary work content and component requirements.

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed Model Sequence For VolpensSeq. #Model Desc.1Blue Pen2Red Pen3Blue Pen45Yellow Pen67Yellow Shell8Red Pen910Yellow Pen11Blue Shell121314151617Seq. #Model Desc.181920212223242526272829303132Red Shell3334Blue PenBlue PenRed PenBlue PenRed PenRed ShellBlue PenRed PenYellow PenBlue ShellYellow ShellBlue PenRed PenBlue PenYellow PenRed ShellRed PenBlue ShellBlue PenYellow ShellBlue PenRed ShellBlue PenBlue PenYellow Pen

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling One Piece Flow

Reduce lead time by reducing WIPMove products between workstationsAverage lead time = WIP/ThroughputWhat is the average lead time for the system above, if throughput is 100/week?2.4 weeks

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling

8

One Piece FlowWhat is the average lead time for this system?

Process 1

1 unit

Process 2

1 unit

Process 3

1 unit

Process 4

1 unit

One piece could mean a pallet, a box etc. Is not practical in every situationOne-piece flow may require relocation of the people/equipment. A process layout (grouping operations by function) must be replaced by a product layout (arranging operations in the order of flow.)

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Batch Process For Volpens, Ltd.

ProductionSchedulerRawMaterials

FinishedGoods

InspectTest, Pack& ShipWIPWIPCap AssyPen AssyPeel&StickLabelPress

Material FlowInformation Flow

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Takt Time for Volpens, Ltd.Monthly Demand =No. of days per month = 16Daily Demand =Avail. Time/Day =Takt Time =68

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Manpower requirements for Volpens Ltd.Pessimistic times for the current activitiesCap Assembly:25 secondsPen Assembly:17 seconds for pens, 5 seconds for shellsLabel Making:28 secondsPeel & Stick:16 secondsTest,Pack,Ship:15 seconds

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Note that activities 3, 4, 5 are not performed for shells. Also, activity 2 is minimal for shells. The only activity done, for all items, is cap assembly.The time for activity 3 includes an allowance for changing coils; excluding this allowance, a pessimistic time will be 23 seconds. Use this number for your calculations.Manpower requirements for Volpens Ltd.

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Minimum Manpower Required for Volpens, Ltd.Monthly Demand for Pens = 48Monthly Demand for Shells = 20Total Monthly Demand = 68Percentage Demand for Pens =Percentage Demand for Shells =

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling ActivityPens ( %) Shells ( %) Ave.Time/UnitCap AssemblyPen AssemblyLabel MakingPeel & StickTest,Pack,Ship _____________Total Labor Content per Unit:Takt Time per Unit:Minimum Manpower Required =Minimum Manpower Required for Volpens, Ltd.

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed Model Sequence for Volpens

Smallest possible sequence length = 1/0.09 = 11.11Choose a 11 unit sequence; adjust every two cycles.Note: A mixed model sequence is used to intentionally vary work content and component requirements.

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed Model Sequence For VolpensSeq. #Model Desc.1Blue Pen2Red Pen3Blue Pen45Yellow Pen67Yellow Shell8Red Pen910Yellow Pen11Blue Shell121314151617Seq. #Model Desc.181920212223242526272829303132Red Shell3334Blue PenBlue PenRed PenBlue PenRed PenRed ShellBlue PenRed PenYellow PenBlue ShellYellow ShellBlue PenRed PenBlue PenYellow PenRed ShellRed PenBlue ShellBlue PenYellow ShellBlue PenRed ShellBlue PenBlue PenYellow Pen

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed Model Assembly Schedule for Volpens Family: Pens Week 3 Week 4 Week 5 Week 6

Blue Pen & Case PCB1 7 5 7 5

Red Pen & Case PCR2 4 3 4 3

Yellow Pen&Case PCY3 2 3 2 3

Totals 13 11 13 11

Family: ShellsWeek 3Week 4Week 5Week 6

Blue Shell SB1 1 2 1 2

Red Shell SR2 2 2 2 2

Yellow Shell SY3 1 2 1 2

Totals 4 6 4 6

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling

Units

Workloadon Operators

Mixed Model Scheduling: Lean Loading For Caps

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling

Units

Units

Units

Mixed Model Scheduling: Purchase Orders For Caps

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling

Part8:008:158:308:459:009:159:309:4510:00

Implementing Mixed-Model Scheduling: The Load-Leveling (Heijunka) Box

#Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Sheet1BRO PNE PHA SIN Patients / Day 15242536Fraction of total0.150.240.250.36

Time (mininutes)BRO PNE PHA SIN AggregateCheck-In 3030303030Evaluation 2015101213.42Testing4540151525.5Assessment1515101011.95Work Content 110100656780.87

Sheet2ModelMonthly demandRatio to Total# in the sequence3 TimesBlue Pen240.35294117654.0012Red Pen140.20588235292.337Yellow Pen100.14705882351.675Blue Shell60.08823529411.003Red Shell80.11764705881.334Yellow Shell60.08823529411.003680.088235294111.333333333334TotalMin

Sheet3

ModelMonthly demand%age demand# in the sequence

Blue Pen2435%4

Red Pen1420%2

Yellow Pen1015%2

Blue Shell69%1

Red Shell812%1

Yellow Shell69%1

Work CenterPartWeek 2Week 3Week 4Week 5

Cap AssemblyCAB18787

CAR26565

CAY33535

P. DescriptionPart #Week 2Week 3Week 4Week 5

Blue CapCB18787

P. DescriptionPart #Week 2Week 3Week 4Week 5

Red CapCR26565

P. DescriptionPart #Week 2Week 3Week 4Week 5

Yellow CapCY33535