Building Lean Systems Mixed Model Scheduling

2 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed-Model Scheduling and Small Batch Production  In 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

3 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed-Model Scheduling and Small Batch Production  Produce 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 time Changeover or setup times must be small Small batching in the presence of setup times

4 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

5 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 batches uneven workload uneven demand for upstream processes, pull impossible production is not synchronized with demand.  Mixed-model production: smooth work-load, smooth demand for upstream processes Allows production to match customer demand. MMS Example

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

7 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed Model Sequence For Volpens Seq. #Model Desc. 1Blue Pen 2Red Pen 3Blue Pen 4 5 Yellow Pen 6 7 Yellow Shell 8 Red Pen 9 10 Yellow Pen 11 Blue Shell Seq. #Model Desc Red Shell Blue Pen Red Pen Blue Pen Red Pen Red Shell Blue Pen Red Pen Yellow Pen Blue Shell Yellow Shell Blue Pen Red Pen Blue Pen Yellow Pen Red Shell Red Pen Blue Shell Blue Pen Yellow Shell Blue Pen Red Shell Blue Pen Yellow Pen

8 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Process 1 60 units Process 2 60 units Process 3 60 units Process 4 60 units One Piece Flow  Reduce lead time by reducing WIP  Move products between workstations  Average lead time = WIP/Throughput  What is the average lead time for the system above, if throughput is 100/week?  2.4 weeks

9 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling One Piece Flow What 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 situation  One-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.)

10 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Batch Process For Volpens, Ltd. Production Scheduler Raw Materials Finished Goods Inspect Test, Pack & Ship WIP Cap Assy Pen Assy Peel& Stick Label Press Material Flow Information Flow

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

12 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Manpower requirements for Volpens Ltd.  Pessimistic times for the current activities Cap Assembly:25 seconds Pen Assembly:17 seconds for pens, 5 seconds for shells Label Making:28 seconds Peel & Stick:16 seconds Test,Pack,Ship:15 seconds

13 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.

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

15 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling ActivityPens ( %) Shells ( %) Ave.Time/Unit Cap Assembly Pen Assembly Label Making Peel & Stick Test,Pack,Ship _____________ Total Labor Content per Unit: Takt Time per Unit: Minimum Manpower Required = Minimum Manpower Required for Volpens, Ltd.

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

17 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Mixed Model Sequence For Volpens Seq. #Model Desc. 1Blue Pen 2Red Pen 3Blue Pen 4 5 Yellow Pen 6 7 Yellow Shell 8 Red Pen 9 10 Yellow Pen 11 Blue Shell Seq. #Model Desc Red Shell Blue Pen Red Pen Blue Pen Red Pen Red Shell Blue Pen Red Pen Yellow Pen Blue Shell Yellow Shell Blue Pen Red Pen Blue Pen Yellow Pen Red Shell Red Pen Blue Shell Blue Pen Yellow Shell Blue Pen Red Shell Blue Pen Yellow Pen

18 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 PCB Red Pen & Case PCR YellowPen&Case PCY Totals

19 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Units Workload on Operators Mixed Model Scheduling: Lean Loading For Caps

20 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Units Mixed Model Scheduling: Purchase Orders For Caps

21 Ardavan Asef-Vaziri 6/4/2009Lean Thinking: 4- Mixed Model Scheduling Part 8:00 8:15 8:30 8:45 9:00 9:15 9:30 9:45 10:00 Implementing Mixed-Model Scheduling: The Load-Leveling (Heijunka) Box