Rolled Throughput Yield (RTY)

Report
Dave Dortman
920-207-1648
[email protected]
Rolled Throughput Yield
(RTY)
Six Sigma Black Belt Presentation
What do we need to know about RTY?
Define
Measure
Analyze
Improve
Control
• What is RTY and why is it important?
• The “Hidden Factory”
• How to calculate RTY
• How to estimate RTY using e-dpu
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What is Rolled Throughput Yield?
Define
Measure
Analyze
Improve
Control
• Rolled Throughput Yield (RTY)
is the product of the observed
yields from each step in a
process. It is the probability of
a unit passing through all steps
of a process and incurring no
defects.
• RTY shows the effect of
variation on both rework and
scrap.
• Rework is known as the
“Hidden Factory.”
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The Hidden Factory
Define
Measure
Analyze
Classic Yield is Y 
S
N
N
Rework
“The Hidden
Factory”
4
AKA
Improve

“Classic Yield”
Control
Number Shipped

Started  Scrapped
Number Started
Operation
Started
Inspection
S
Rework
Scrap
Classic Yield does
not account for
rework
Rolled Throughput Yield (RTY) Calculations
Define
N
Measure
Operation
Analyze
Improve
Control
Inspection
Operation
Rework
Rework
FPY includes
no defects
Scrap
Rolled Throughput Yield, RTY:
RTY  FPY 1  FPY

 FPY

   FPY N
FPY  first pass yield (defect
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N  number
Inspection
of process
free)
steps
Scrap
Rework accounts
for differences
between Classic
Yield and RTY
S
Rolled Throughput Yield (RTY)
Define
Measure
Analyze
Improve
Control
RTY = FPY1 x FPY2 x FPY3
Parts
Receiving
RTY = 0.955 x 0.970 x 0.944 = 0.875
Receiving Inspection:
First Pass Yield #1 = 0.955
Machining Operations:
First Pass Yield #2 = 0.970
Finishing Operations:
First Pass Yield #3 = 0.944
Dollars lost to
rework and scrap
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For every 1,000 parts
received, only 875
reach this point
without rework
Why is RTY important?
Define
Measure
Analyze
Improve
Control
• Measures the percent of product that goes through the
process without being scraped or reworked.
• Reworks within an operation have no value and comprise
what is termed “The Hidden Factory!”
• Is the yield calculated below a RTY?
Yield = Amount of Material Exiting Process
Amount of Material Entering Process
• No! It is an overall yield of scrapped product, it ignores
rework.
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Defective Units versus Defects per Unit
Define
Measure
Analyze
Improve
Control
• If you can count the number of defective units after
each process step, then you can calculate RTY as
RTY = FPY1 x FPY2 x FPYN
N = number of process steps
• If you can only count the number of defects after each
step, then you must estimate the Frist Pass Yield using
the Poisson approximation
FPY = e-dpu
where dpu is the average defect per process step
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Rationale for e-dpu
Define
Measure
Analyze
Improve
Control
Mr. Poisson
Based on the Poisson distribution
Y = e–dpu
“e” is a constant 2.718281828…
The natural log (ln) of this constant is 1.
If the number of defects per unit is known, RTY can be
calculated.
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e-dpu provides a good approximation!
Define
Measure
Analyze
Y = e–dpu
Y = Yield
e = 2.718281828…
dpu = defect per unit
In Microsoft Excel,
the EXP function
returns e raised to
the nth power, where
e = 2.71828183.
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Improve
Control
RTY = FPY1 x FPY2 x FPY3
RTY = 0.955 x 0.970 x 0.944 = 87.45%
Yield
0.955
0.97
0.944
Total DPU
DPU
0.045
0.03
0.0565
0.131
RTY
87.72%
Braun is Batting .500 !!!
Define
Measure
Analyze
Improve
Control
• If Braun is batting .500 what does that mean?
• What would a RTY of 50% indicate?
• Answer: 50% of product made it through the process
without being scrapped or reworked.
• If RTY = 50%, how much product would be scrapped
versus reworked?
• Answer: We don’t know just from the single RTY number.
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Dave Dortman
920-207-1648
[email protected]
Questions ???
Variation, Rework, and Scrap
Define
Measure
Analyze
Improve
Control
The goal of Six Sigma is
to eliminate rework and
scrap by eliminating
variation!
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