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Continuous Improvement Toolkit Process Yield Measures
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The Continuous Improvement Map
Multivariate Brainstorming IDEF0 Document control Check Sheets** Flowcharting Flow Process Charts** KPIs SCAMPER*** Pugh Matrix Lateral Thinking Reliability Service Blueprints Affinity Diagrams Mind Mapping* Attribute Analysis Morphological Analysis How-How Diagram*** Control Charts Waste Analysis** Time Value Map** Value Stream Mapping** Value Analysis** Suggestion Systems Histograms Activity Networks RACI Matrix Stakeholder Analysis Improvement Roadmaps DMAIC SWOT Analysis Policy Deployment Project Charter PDCA Gantt Charts MOST PERT/CPM Daily Planning Delphi Method Payoff Matrix Relations Mapping Data Mining Just in Time Automation Product Family Matrix Flow Spaghetti** Multi-vari Studies Decision Tree FMEA PDPC RAID Log* Fault Tree Analysis Paired Comparison Traffic Light Assessment TPN Analysis Risk Analysis* Run Charts Scatter Plots A3 Thinking Importance Urgency Matrix Four Field Matrix Critical-to X Portfolio Matrix Force Field Analysis Decision Balance Sheet Break-even Analysis Voting Quality Function Deployment Pick Chart Gap Analysis* Bottleneck Analysis Cost Benefit Analysis Kaizen Events Control Planning Standard Work Mistake Proofing Quick Changeover Visual Management Simulation TPM 5S Health & Safety Best Practices Pareto Analysis 5 Whys Prioritization Matrix Hypothesis SIPOC* Matrix Diagram Fishbone Diagrams Tree Diagram* Root Cause Analysis Correlation DOE ANOVA Nonparametric Chi-Square Regression Observations Kano Lean Measures Benchmarking*** Interviews Graphical Methods Data collection planner* Questionnaires Probability Distributions MSA Descriptive Statistics Cost of Quality* Sampling Focus Groups Capability Indices Process Yield Project KPIs Normal Distribution
Data Collection Understanding Performance** Implementing Solutions*** Planning & Project Management* Managing Risk Understanding Cause & Effect Designing & Analyzing Processes Group Creativity Selecting & Decision Making
Five Ws Process Redesign Pull Process Mapping OEE
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Process Yield Measures
An ideal process must produce without defects or rework
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Process Yield Measures
A defect is a failure to conform requirements (include scrap & rework) A rework is an additional work required to conform requirements
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Process Yield Measures
You should have the appropriate metrics to measure process yield
These metrics should be able to reveal even the smallest inefficiencies in a process
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Process Yield Measures
You should have the appropriate metrics to measure process yield
They should enable operations to understand their true process yield in
- rder to set realistic improvement targets
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Process Yield Measures
Many companies use two measures for process yield
Final yield First time yield (FTY) They represent the classical approach for calculating process yield
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Process Yield Measures
First Time Yield (FTY)
Obtained by dividing the good product units by the number of total units that entered the process at a given process step
Process Step (X) Inspect for Defects End Start
The reworked units are included in the calculation of FTY
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Process Yield Measures
First Time Yield (FTY) Question: Find the FTY for a process knowing that the second process steps has produced 90 good units from 100 processed units.
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Process Yield Measures
First Time Yield (FTY)
Not sensitive to product complexity and only looks at the volume of the produced units. Corrective actions are often taken on spot when mistakes are discovered, and rework are not recorded in quality logs making the process yield rate looks better than what it really is.
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Process Yield Measures
Final Yield (FY)
Another widely used yield metric that is easy to calculate
The probability that a unit will successfully pass all steps inspected at the end of the process
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Process Yield Measures
Final Yield (FY) Obtained by counting the good units that made it through until the last process step divided by the total number of units that entered the process
Last Process Step Inspect for Defects End Start
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Process Yield Measures
Final Yield (FY)
Find the final yield in the following 3-step process . . . C B A 90
Outputs
100
Inputs
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Process Yield Measures
First Time Yield and Final Yield
Not sensitive to product complexity Don’t reflect the actual defect rates and ignore the hidden factory Only look at the volume of the produced units Corrective actions are often taken on spot when mistakes are discovered Process yield rates often look better than what they really are
A
P/F 100 Inputs 100 Outputs FTY = 100%
B
P/F FTY = 100%
- FY = 100%
- No scrapped units
were generated
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Process Yield Measures
More Process Yield Measures
+ Accuracy -
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Process Yield Measures
Throughput Yield (TPY)
Sometimes rereferred to as First Pass Yield
The probability that a product or service unit will pass through a given process step defect-free
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Process Yield Measures
Throughput Yield (TPY) The number of units coming out a given process step divided by the number of units going into that process step over a specified period
Only good units with no rework or scrap are counted
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Process Yield Measures
Throughput Yield vs. First Time Yield The difference between the two metrics is due to the inclusion of reworked units
A reworked unit that passed the process step will not be considered in the calculation
A reworked unit is considered in the calculation of the FTY
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Process Yield Measures
Rolled Throughput Yield (RTY) The probability of passing all performance standards through the entire process defect-free
Inspection at the end of the process
RTY is a true reflection of the process performance
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Process Yield Measures
Rolled Throughput Yield (RTY) It is calculated by multiplying the individual throughput yield values of each process step
RTY = Throughput Yield of process step 1 * Throughput Yield of process step 2 * … * Throughput Yield of process N.
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Process Yield Measures
Rolled Throughput Yield (RTY)
Provides a better insight of the rates of defects and rework Allows companies to be much more accurate when assessing the performance of their industrial or commercial processes Quantifies the cumulative effects
- f inefficiencies found throughout
the process Substantially less than final yield Calculations are done at each process step
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Process Yield Measures
Rolled Throughput Yield (RTY) – Example
RTY = TPY(A) * TPY(B) * TPY(C) = 94% * 91% * 92% = 78.7% FY = 89% Not equal!
C
TPY= 92%
B
TPY= 91%
A
TPY= 94%
89
Outputs
100
Inputs
6 4 9 4 8 4 Defects (Rework & Scrap) 2 5 4 Scrap
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Process Yield Measures
Rolled Throughput Yield (RTY) – Example
RTY = 78.7%
This means that even if the 3 process steps are performing well, one out of every 5 units will not make it through the process without being reworked or scrapped
C
TPY= 92%
B
TPY= 91%
A
TPY= 94%
100
Inputs
89
Outputs
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Process Yield Measures
Example – Can Making Process
Printed can count 98.18% Cupper count 99.54% Formed can count 99.11% Trimmed can count 99.77% Washed can count 98.34% Palletized can count 98.89% Light inspected can count 97.88% Internally sprayed can count 98.88% Coated can count 99.26%
The probability of manufacturing a can that meets all specifications is 90.28%
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Process Yield Measures
Example - High Volume and Low Complexity
What is the RTY of a process that involve 5 steps and produces 30,000 units per hour, knowing that the throughput yield for each process step is 95%?
RTY = (0.95)5 = 77.4% Throughput Yield / hour = 0.7738 * 30,000 = 23,213 TPY / hour i.e. 6787 non-conforming units / hour (22.6%)
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Process Yield Measures
Example - Low Volume and High Complexity
What is the RTY of a process that involves 30 steps and produces 10 units per hour, knowing that the throughput yield for each process step is 95%?
RTY = (0.95)30 = 22.5% Throughput Yield / hour = 0.2146 * 10 = 2.15 TPY / hour i.e. 8 non-conforming units / hour (77.5%)
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Process Yield Measures
Further Information
A best practice is to use a process map as a guide in the process yield evaluation.
10 50 20 60 40 30
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Process Yield Measures
Further Information
TPY is sensitive to the number of critical-to-quality characteristics (CTQs) in a product (product complexity). RTY is sensitive to the number of CTQs, and the number of process steps (process complexity).
Simplification of the process needs to be considered to improve the process yield rates
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Process Yield Measures
Further Information
This provides a sense of the overall flow performance
Some process yield measures can be averaged together to measure the entire production flow
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Process Yield Measures
Further Information - Other Yield Measures
Rolled throughput yield loss is the inverse of RTY Average completion rate is the output of a process over a defined period Normalized yield is the average throughput yield result at any given step
