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Dave Dortman920-207-1648
Rolled Throughput Yield (RTY)Six Sigma Black Belt Presentation
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Define Measure Analyze Improve Control
What do we need to know about RTY?
• 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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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.”
What is Rolled Throughput Yield?
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Define Measure Analyze Improve Control
The Hidden Factory AKA “Classic Yield”
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StartedScrappedStartedNumber
StartedNumber Shipped
NS Y is Yield Classic
Rework
Scrap
Operation InspectionN S
Rework “The Hidden
Factory”Classic Yield does not account for
rework
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Define Measure Analyze Improve Control
Rolled Throughput Yield (RTY) Calculations
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Inspection
Rolled Throughput Yield, RTY:
Rework
N S
steps process ofnumber N free)(defect yieldpassfirst FPY
FPY FPY FPY FPY RTY N1
Scrap
Operation Inspection
Rework
Scrap
Operation
FPY includes no defects
Rework accounts for differences
between Classic Yield and RTY
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Define Measure Analyze Improve Control
Rolled Throughput Yield (RTY)
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Receiving Inspection:First Pass Yield #1 = 0.955
Machining Operations: First Pass Yield #2 = 0.970
Finishing Operations:First Pass Yield #3 = 0.944
RTY = FPY1 x FPY2 x FPY3
RTY = 0.955 x 0.970 x 0.944 = 0.875PartsReceiving
For every 1,000 parts received, only 875
reach this point without rework
Dollars lost to rework and scrap
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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 ProcessAmount of Material Entering Process
• No! It is an overall yield of scrapped product, it ignores rework.
Why is RTY important?
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Define Measure Analyze Improve Control
Defective Units versus Defects per Unit
• If you can count the number of defective units after each process step, then you can calculate RTY as
RTY = FPY1 x FPY2 x FPYNN = 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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Define Measure Analyze Improve Control
Rationale for e-dpu
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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Mr. Poisson
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Define Measure Analyze Improve Control
e-dpu provides a good approximation!
Yield DPU0.955 0.0450.97 0.030.944 0.0565
Total DPU 0.131RTY87.72%
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RTY = FPY1 x FPY2 x FPY3
RTY = 0.955 x 0.970 x 0.944 = 87.45%Y = e–dpu
Y = Yielde = 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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Define Measure Analyze Improve Control
Braun is Batting .500 !!!
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• 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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Define Measure Analyze Improve Control
Variation, Rework, and Scrap
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The goal of Six Sigma is to eliminate rework and
scrap by eliminating variation!