posbul1a
Drum –Buffer-Rope

•Based on : R. Holt, Ph.D., PE

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We Measure Operational  Efficiency
* Work flows from left to right through processes with capacity shown.
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•Process A B C D E
•RM
•FG
•Capability (Throughput Rate)
•Parts/Day 7 9 5 8 6
•Excellent Efficiency--Near 100%
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•Chronic Complainer
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•Too Much Overtime
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•Market
Request
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•RM = raw material
•FG = finished goods

Reward Based on Efficiency
* Work flows from left to right.
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•Process A B C D E
•Capability(Throughput Rate)
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•Parts/Day 7 9 5 8 6
•Both found ways to look busy and
appear to have a capacity of 5 parts/day.
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•RM
•FG
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In reality...
•Process A B C D E
•Potential
•P/D 7 9 5 8 6
•Reality 5 5 5 5 5
* Processes A and B won’t produce more than Process C for long.
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•RM
•FG
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•P/D=parts/day

Then Variability Sets In
* Processing times are just AVERAGE Estimates
•Process A B C D E
•Reality        5±2       5±2        5±2         5±2        5±2
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•RM
•FG
 7
 9
• 5
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What’s an Average?  50%
•Process A B C D E
•Reality        5±2       5±2        5±2         5±2        5±2
•Probability 0.5 0.5 0.5 0.5 0.5
* Half the time there are 5 or more per day at each process--Half the time less
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•Two at a time:      0.25
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•0.25
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•Over all: 0,5*0,5*0,5*0,5*0,5=0,03125=3% Chance of 5 per day !!!
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•RM
•FG
 7
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• 5
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Previous Solution: Inventory
•WIP       5       5      5      5     5         Total 25
•Process A B C D E
•Variable 5±2       5±2        5±2         5±2        5±2
•Process
* Put a day of inventory (WIP) at each process!
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•RM
•FG
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System Variability Takes Over--Chaos
•Variable      5±2       5±2        5±2         5±2        5±2
•Process
•WIP       3              0       10               8       4     Total 25
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•RM
•FG
•Process      A B C D E
•Inventory (WIP) quickly shifts position.
•Inventory manager tries to smooth it out.
•Distribution problems result. Costs go up !!!
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System Variability Takes Over--Chaos
•WIP       3              0       10               8       4     Total 25
•Variable      5±2       5±2        5±2         5±2        5±2
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•Process
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•Shifting work-in-process creates large queues at some
locations.  This makes work wait longer to be processed.
•(based on Little´s law)
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•RM
•FG
•An Average of 5 means sometimes 3 and some times 7
•Process      A B C D E
 7
 9
• 5
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System Variability Takes Over--Chaos
•WIP       3             0       10           8       4     Total 25
•Variable     5±2       5±2        5±2         5±2        5±2
•Process
•Shifting work-in-process creates large queues at some
locations.  This makes work wait longer to be processed.
•Other workstations are starving for work (B)  The work they
could do is delayed because they have no input material. They
•can’t take advantage of their extra capability.  So....... ?
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•RM
•FG
 7
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•Process      A B C D E

System Variability Takes Over--Chaos
•WIP       3             5       10            8       4     Total 25
•Variable     5±2       5±2        5±2         5±2        5±2
•Process
•So…  Management Helps!  Management puts in more work
•(Inventory) (rate of input RM) to give everyone something to do (Cost world)!
•Result:  It takes longer and longer from time of release
•until final shipping.  More and more delay!!!!!!!!!!!
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•RM
•FG
•Process      A B C D E
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•->X 30
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TOC Steps to
Continuous Improvement
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Step 1.  Identify the system’s constraint.
Step 2. Exploit the 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.

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

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•FG
Understanding Buffers
•   A B C D E
• 7 9 5 8 6
•RM
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•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 alters (see below)
•If different items spend different time at the constraint, then number of items in the buffer
changes
•but  Time in the buffer remains constant.
•WIP                        Total 12parts/5parts per day=2.5 Days
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We need more than one Buffer
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•FG
•   A B C D E
• 7 9 5 8 6
•RM
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•There is variability in the Constraint.
To protect our delivery to our customer we
need a finished goods buffer.
•Finished Goods
Buffer
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•There is variability in our suppliers.
We need to protect ourselves from unreliable
delivery.
•Raw Material
Buffer
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Buffer Time is Constant-Predictable
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•FG
•   A B C D E
• 7 9 5 8 6
•RM
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•Finished Goods
Buffer
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•Constraint
Buffer
2.5 Days
•Raw Material
Buffer
•Finished Goods
Buffer
1 Day
•Processing Lead Time is Constant
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•Raw Material
•Buffer
•2 Days=10/5
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•12

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

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