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Dave Dortman 920-207-1648 ddortman@yahoo.com 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 2 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.” 3 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 5 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 6 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. 7 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 8 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. 9 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. 10 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. 11 Dave Dortman 920-207-1648 ddortman@yahoo.com Questions ??? Variation, Rework, and Scrap Define Measure Analyze Improve Control The goal of Six Sigma is to eliminate rework and scrap by eliminating variation! 13