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. We Measure Operational Efficiency
Work flows from left to right through processes with capacity shown.
Market Request 11
Process A B C D E RM FG
Capability
Parts per Day
Excellent Efficiency--Near 100%
Chronic Complainer
Too Much Overtime

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

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

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

7. 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 RM FG
Reality ± ± ± ± ±2
Probability
0.25
Two at a time:
Over all: 3% Chance of 5 per day !!!

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

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

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

11. System Variability Takes Over--Chaos
Process A B C D E
WIP Total 25 RM FG
Variable ± ± ± ± ±2
Process
Shifting work-in-process creates large queues at some locations. This makes work wait longer to be processed. Other workstations can be starved for work. The work they could 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 Total 25
30=25+5 RM FG
Variable ± ± ± ± ±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 Total 25
Process A B C D E RM FG
Variable 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. Effects of Inventory Limits on Production
What does a Kanban card of 5 Mean?
WIP Total 25
Process A B C D E RM FG
Variable 5± ± ± ± ±2
Process
5+/-2 Average = 5
Before
Kanban 7
Average = 3,5 = (3*5+5*0,5)/5
Can’t exceed 5
After Kanban 2
5,5 3

15. Operation’s Dilemma Increase work-in- process Produce a lot
Assumption:
We can’t both increase WIP and decrease WIP at the same time.
Manage production
effectively
Costs & delivery in control
Decrease work-in-process
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. 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.

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

18. Understanding Buffers
WIP Total 12parts/5parts per day=2.5 Days
A B C D E FG RM
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. We need more than one Buffer
There is variability in our suppliers. We need to protect ourselves from unreliable delivery.
Raw Material Buffer
There is variability in the Constraint. To protect our delivery to our customer we need a finished goods buffer.
Finished Goods Buffer
A B C D E RM FG

20. Buffer Time is Constant-Predictable
Raw Material Buffer
Finished Goods Buffer
A B C D E RM FG
Raw Material
Buffer
2 Days
Constraint Buffer 2.5 Days
Finished Goods Buffer 1 Day
Processing Lead Time is Constant

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

22. Problem IdentificationRM
Watch WO14 (Yellow)
A B C D E
Constraint schedule is in jeopardy! (Red Zone Hole)
WO19 OK (Green) FG RM
WO19 Delayed Parts
WO21
WO17
WO13
WO20
WO16
WO12
WO19
WO15
WO11
WO18
WO14
WO10
2.5 Days
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. Additional Buffers Ropes Buffer Types: Constraint FG RM Assembly WIP
Finished goods
A B C D E
Raw Material RM FG
F G H
Assembly RM
8 7 6

25. Manufacturing is an integrating discipline
TOC Thinking
Processes Physical Systems
Behavior
Operations Optimization
Simulation Decisions Reliability Supply Chain
People Organizations Performance
Measurement Assignments Quality
Finance Capital Projects
Uncertainty Investment Measures
Projects Full Theory
Scheduling Manage Quality Design for Experiments
Strategy Corporate
Departmental Subordination Focus