Question About Rolled Throughput Yield

Marlin60

Starting to get Involved
#1
I posted this on one of the other forums, but re-posting here in hopes of getting a reply:

Question:

My company builds large, commercial HVAC units. The process map is:

Assembly Station 1
Assembly Station 2
Assembly Station 3
Assembly Station 4
Assembly Station 5
Assembly Station 6
Assembly Station 7
Assembly Station 8
Assembly Station 9
Assembly Station 10
Functional Testing (100% of completed units)
Close


My Quality Technician conducts an AQL sample (12%) in the Assembly Stations. He also conducts end-of-line audits (12%) on completed units.

We currently report the audit results and test results as three separate first-pass yield numbers. What I would like to do is also combine them into a single Rolled Throughput Yield. My question is whether it would be reasonable to do so since some data is sampled and some is 100%?

Thanks in advance.
 
Elsmar Forum Sponsor

John Predmore

Trusted Information Resource
#2
"all models are wrong. Some are useful" - George Box, famous statistician

Rolled Throughput Yield is a mathematical model of your process yield. I suppose you can combine any yield numbers you choose as long as you choose numbers which are representative of reality. When you state (for example) the inspection yield of functional testing station is 97%, no educated person interprets that test station is 97% every single day of the year. Some days the station will pass 100% and some days 95% or even fewer. The 97% yield is an average figure, or a best guess. Therefore if your total yield figure combines data from sampling and data from actual counts, that is your best practical estimate of reality that you have. If you want full transparency, include a footnote with your results table to reveal the sources, assumptions or tradeoffs used in the calculation.

You did not indicate whether the 10 assembly stations are sequential (every assembly must pass through all 10 stations) or parallel (10 identical stations making the same part). I will assume sequential.

You seem to want to focus only on inspection yield. When I worked with automatic assembly stations, I always calculated total yield instead of inspection yield. Total yield is net of process fallout from misfed parts, misformed parts which do not fit the nest, machine faults, and all other causes of yield loss in a station. You may want to tally analogous causes of lost productive takt time in your manual assembly stations. If one station does not complete a machine cycle for one of these reasons, there may not be a inspectable part generated to inspect, which diminishes station throughput but may not be reflected in the denominator of inspection yield. In summary, your process model is an approximation of reality. IMO you have to decide what to include or exclude from the model.
 
Last edited:

Marlin60

Starting to get Involved
#3
John,

Thank you for the reply. The 10 stations are a progressive manufacturing process, similar to automotive assembly and all units pass through the 10 stations before going to our test cells. Unfortunately our data collection is not mature enough for net yield i.e. reworks, time lost, etc during assembly. Those things happen, but we don't record it.

My interest in using Rolled Throughput Yield is because it would allow us to merge the data collected by Production in Test and the data collected by my team (in-line and end-of-line audits) into a single metric. There's a benefit there from a report-out perspective.
 
Last edited by a moderator:

Semoi

Involved In Discussions
#4
Hi:
if you have a significant amount of rework a combined yield does not make sense unless you adjust the calculation to account for the rework. However, if (a) the rework rate is negligible, and (b) the failure rates are independent you do not run into a mathematical problem. The sampling rate is irrelevant as long as the current yield estimates are representative of the actual yields.
Hope this helps.
 

Marlin60

Starting to get Involved
#5
Semoi,

Thanks for the reply. Unfortunately I do not have tracking on reworks on the line, which are likely significant. I do have tracking for reworks from Final Test and our end-of-line audit.
 

Semoi

Involved In Discussions
#6
Hi Marlin60,
you said that before and I understood that. However, before (!) you calculate the total yield you should clarify whether or not the calculation makes sense. Personally, I would ask the operators or shift leaders how often reworks are done. A rough estimate could be enough to start with. Then you could perform several calculations, where you change this estimate and thus obtain a range in which the total yield probably lies. In addition, your calculation could trigger the demand to document the reworks for the different processes and thus enable you to optimise your processes. In the end this is what matters, if your rework rate is not negligible.
 
Thread starter Similar threads Forum Replies Date
F Technical question - U-BOLT microscopic cracks on the tooth of the rolled thread Manufacturing and Related Processes 14
D What do you think of Chat GPTs answer to this Risk Acceptability question? ISO 14971 - Medical Device Risk Management 4
M ISO 13485 Supplier Question ISO 13485:2016 - Medical Device Quality Management Systems 13
A Question regarding new VDA_AIAG fmea approach for process FMEA FMEA and Control Plans 0
Ed Panek FDA Submission Question US Medical Device Regulations 2
M Cleanroom Question Manufacturing and Related Processes 10
T Aircraft GAPP Software Testing Compliance Question AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
sonflowerinwales Quick question M3 screw plug gauge AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 0
B FDA regulations medical device prescription fulfillment DME question US Medical Device Regulations 0
M An interesting question about import company Other Medical Device Regulations World-Wide 5
Sam.F Question about training Training - Internal, External, Online and Distance Learning 20
B Labeling question about different manufacturers on a single label Manufacturing and Related Processes 4
J Question regarding classification of custom made device EU Medical Device Regulations 5
Sam.F Question about granite surface plates out of spec AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 9
Ed Panek MDR question - Meaning of Stability CE Marking (Conformité Européene) / CB Scheme 6
B GD&T Question, True Position Confusion Inspection, Prints (Drawings), Testing, Sampling and Related Topics 2
D Initial Importer question Other US Medical Device Regulations 1
Ed Panek Calibration question Manufacturing and Related Processes 4
M Class Exempt Medical Device Recall Question US Food and Drug Administration (FDA) 3
sonflowerinwales Metric or Imperial; that is the question... After Work and Weekend Discussion Topics 6
M Can someone help me with this CMM programming question? Manufacturing and Related Processes 2
A A strange question about predicate device selected in 510(k) submission Medical Device and FDA Regulations and Standards News 8
S Question regarding AQL - ISO 3951 Inspection, Prints (Drawings), Testing, Sampling and Related Topics 0
D Document Control Question involving DocuSign US Food and Drug Administration (FDA) 6
JoeRandom11 Question about Customer Supplied Equipment AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2
M ISO 13485: 2016 Lot numbering question ISO 13485:2016 - Medical Device Quality Management Systems 4
S Nadcap - Heat Treatment Proof of Verification question for Digital results AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 5
JoeRandom11 Question of Calibration Cycles AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 8
D Software Validation Question ISO 13485:2016 - Medical Device Quality Management Systems 10
B 8.5.1.1 Control Plan - question audit NC IATF 16949 - Automotive Quality Systems Standard 5
C Document Identification Question ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 8
D Question regarding PCR workstation Fume Hood upon first use ISO 13485:2016 - Medical Device Quality Management Systems 0
Moncia ISO 9001 calibration question please ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 7
Quality Specialist Quick question on the sequence of ISO 17025 external audits ISO 17025 related Discussions 14
D ISO 13485--Question regarding performing calibrations in house. ISO 13485:2016 - Medical Device Quality Management Systems 13
S Document numbering question? ISO 13485:2016 - Medical Device Quality Management Systems 7
J Has the facility been inspected? question in Certificate to Foreign Government application Other US Medical Device Regulations 0
M ESTAR 510(k) submission question Medical Device and FDA Regulations and Standards News 0
J Question on clause 5.2.2 IEC 62304 - Medical Device Software Life Cycle Processes 2
Ed Panek ISO 15223 Question EU Medical Device Regulations 2
R Question: Cg/Cgk formula Capability, Accuracy and Stability - Processes, Machines, etc. 2
J Quick question on responsible person's experience requirements UK Medical Device Regulations 3
J PFMEA/control plan question- PLEASE HELP ! IATF 16949 - Automotive Quality Systems Standard 8
3 Scope question ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
L Question regarding "Customer Property" AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 11
T Noob question regarding sample size Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
K 510(k) Manufacturer question (private label and manufacture under another persons 510(k)) US Food and Drug Administration (FDA) 1
M Quick Gage R&R Question Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 9
S Question: Best alternatives to audits for ensuring compliance Quality Tools, Improvement and Analysis 5
Ed Panek Question from 13485 Auditor ISO 13485:2016 - Medical Device Quality Management Systems 2

Similar threads

Top Bottom