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Drum –Buffer-Rope

Drum –Buffer-Rope. Skorkovský. Based on : R. Holt, Ph.D., PE. Traditional Approach: Divide and Conquer. Division of Labor breaks down linkages complex systems into manageable chunks. Which is harder to manage? Left or Right?. Left. Right. Too Much Overtime. Chronic Complainer.

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Drum –Buffer-Rope

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  1. Drum –Buffer-Rope Skorkovský Based on : R. Holt, Ph.D., PE

  2. Traditional Approach:Divide and Conquer • Division of Labor breaks down linkages complex systems into manageable chunks. • Which is harder to manage? Left or Right? Left Right

  3. Too Much Overtime Chronic Complainer Excellent Efficiency--Near 100% We Measure Operational Efficiency • Work flows from left to right through processes with capacity shown. MarketRequest11 Process A B C D E FG RM Capability Parts 7 9 5 8 6per Day

  4. Both found ways to look busy and appear to have a capacity of 5 parts/day. Reward Based on Efficiency • Work flows from left to right. Process A B C D E FG RM Capability P/D 7 9 5 8 6

  5. In reality... • Processes A and B won’t produce more than Process C for long. Process A B C D E FG RM Potential P/D 7 9 5 8 6 Reality 5 5 5 5 5

  6. Then Variability Sets In • Processing times are just AVERAGE Estimates Process A B C D E FG RM Reality 5±2 5±2 5±2 5±2 5±2 7+9+5+8+6=35, 7=35/5=7 (average)

  7. 0.25 Two at a time: 0.25 Over all: 3% Chance of 5 per day!!! What’s an Average? 50% • Half the time there are 5 or more per day at each process--Half the time less Process A B C D E FG RM Reality 5±2 5±2 5±2 5±2 5±2 Probability 0.5 0.5 0.5 0.5 0.5

  8. Previous Solution: Inventory • Put a day of inventory at each process! WIP 5 5 5 5 5 Total 25 Process A B C D E FG RM Variable 5±2 5±2 5±2 5±2 5±2 Process WIP=throughput in bottleneck

  9. Process A B C D E WIP 3 0 10 8 4 Total 25 FG RM System Variability Takes Over--Chaos Inventory (WIP) quickly shifts position. Inventory manager/expediter tries to smooth it out. Distribution problems result. Costs go up. Variable 5±2 5±2 5±2 5±2 5±2 Process 25=3+10+4+8

  10. System Variability Takes Over--Chaos An Average of 5 means sometimes 3 and some times 7 Process A B C D E WIP 3 0 10 8 4 Total 25 FG RM Variable 5±2 5±2 5±2 5±2 5±2 Process Shifting work-in-process creates large queues at somelocations. This makes work wait longer to be processed.

  11. System Variability Takes Over--Chaos Process A B C D E WIP 3 0 10 8 4 Total 25 FG RM Variable 5±2 5±2 5±2 5±2 5±2 Process Shifting work-in-process creates large queues at somelocations. This makes work wait longer to be processed.Other workstations can be starved for work. The work theycould be doing is delayed because it is not there(B). They can’t take advantage of their extra capability. So...

  12. System Variability Takes Over--Chaos Process A B C D E ->X 30 WIP 3 5 10 8 4 Total 25 30=25+5 FG RM Variable 5±2 5±2 5±2 5±2 5±2 Process So… Management Helps! Management puts in more work (Inventory) to give everyone something to do! Result: It takes longer and longer from time of release until final shipping. More and more delay!!!!!!!!!!!

  13. Attempts to Control WIP • Use Kanban Cards-JIT WIP 5 5 5 5 5 Total 25 Process A B C D E FG RM Variable 5±2 5±2 5±2 5±2 5±2 Process Just-In-Time uses Kanban Cards to limit the queues building in the system. No more than 5 parts are allowed at any station. Looks good, but is it?

  14. Can’t exceed 5 AfterKanban Before Kanban Average = 3,5 = (3*5+5*0,5)/5 5+/-2Average = 5 Effects of Inventory Limits on Production • What does a Kanban card of 5 Mean? WIP 5 5 5 5 5 Total 25 Process A B C D E FG RM Variable 5±2 5±2 5±2 5±2 5±2 Process 7 2 5,5 3

  15. Produce a lot Increase work-in- process Costs & delivery in control Decrease work-in-process Operation’s Dilemma Assumption: We can’t both increase WIP and decrease WIP at the same time. Manage production effectively Injection: Put a large inventory where its needed and low everywhere else!

  16. TOC Steps to Continuous Improvement Step 1. Identify the system’s constraint. Step 2. Exploitthe system’s constraint. Step 3. Subordinate everything else to the above decision. Step 4. Elevate the system’s constraint. Step 5. If a constraint is broken (that is, relieved or improved), go back to Step 1. But don’t allow inertia to become a constraint.

  17. 12 12 7 Step 1. Identify the Constraint (The Drum) Step 2. Exploit the Constraint (Buffer the Drum) Step 3. Subordinate Everything Else (Rope) Step 4. Elevate the Constraint ($?) Step 5. If the Constraint Moves, Start Over Five Steps Applied to Flow Operations WIP Total A B C D E RM FG 7 9 5 (5,5) 8 6 Five Focusing Steps

  18. FG Understanding Buffers WIP Total 12parts/5parts per day=2.5 Days A B C D E RM 7 9 5 8 6 • The “Buffer” is Time! • In general, the buffer is the total time from work release until the work arrives at the constraint. • Contents of the buffer ebb and flow within the buffer • If different items spend different time at the constraint, then number of items in the buffer changes • but Time in the buffer remains constant.

  19. Raw Material Buffer Finished Goods Buffer There is variability in the Constraint. To protect our delivery to our customer we need a finished goods buffer. There is variability in our suppliers.We need to protect ourselves from unreliable delivery. We need more than one Buffer A B C D E FG RM 7 9 5 8 6

  20. Buffer Time is Constant-Predictable Raw Material Buffer Finished Goods Buffer A B C D E FG RM Raw Material Buffer 2 Days 7 9 5 8 6 Constraint Buffer2.5 Days Finished Goods Buffer1 Day Processing Lead Time is Constant

  21. FG Buffer Management Constraint Buffer WIP Total 12/5=2.5 Days A B C D E RM 7 9 5 8 6 WO21 WO17 WO13 • The Constraint is scheduled very carefully • Buffer Managed by location • Individual activities in the buffer are not scheduled WO12 WO16 WO20 WO19 WO15 WO11 WO18 WO14 WO10 2.5 Days 0 Time until Scheduled at Constraint

  22. RM FG Constraint schedule is in jeopardy! (Red Zone Hole) Watch WO14 (Yellow) WO19 OK (Green) Problem Identification A B C D E RM 7 9 5 8 6 WO19DelayedParts WO21 WO17 WO13 WO20 WO12 WO16 WO19 WO11 WO15 WO14 WO18 WO10 2.5 Days 0 Time until Scheduled at Constraint

  23. Additional Buffers • Constraint Buffer (as we discussed) • Protects the Constraint from running out of work • Finished Goods Buffer • Protects customer delivery from Constraint variation • Raw Material Buffer • Protects the Release of material from suppliers • Assembly Buffer • Facilitates speedy flow of products

  24. Ropes Constraint Finished goods Assembly Raw Material Additional Buffers Buffer Types:ConstraintFGRMAssembly WIP A B C D E RM FG 7 9 5 8 6 F G H RM 8 7 6

  25. Manufacturing is an integrating discipline TOCThinking ProcessesPhysical Systems Behavior OperationsOptimization SimulationDecisionsReliabilitySupply Chain PeopleOrganizationsPerformance MeasurementAssignmentsQuality FinanceCapital Projects UncertaintyInvestmentMeasures StrategyCorporate DepartmentalSubordinationFocus ProjectsFull Theory SchedulingManageQualityDesign for Experiments

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