Question on determining defective units - I am not recording fixture to part rejected

rmundroff

Starting to get Involved
#1
I have a process that has 100's of fixture
for a lot I use some fixtures say 10-25 fixtures
for a lot I know # good pcs from lot, number of bad pcs, (lot size) as well as fixtures used HOWEVER I am not recording fixture to part rejected.

trying to find method to track this down for old data [Yes - I know I need to fix my data collection going foreword]

but if I have a lot of 10 and 2 were bad and I weight all 10 fixtures with a .20 POTENTIAL defect
then for a second lot of 15 with 6 defective I take those fixtures and weight them with a .40 potential defective
then after lots of lots 300+ I sum all the potential defective by a fixture and divide by number times fixture used
will this give me a fair good indication of the problem and not problem fixtures
If the distribution of the final proportion all the fixtures 100 fixture & 100 proportions (average potential defective) is normally distributed

this seems to be a good method, I ran a model and it was significant
so I think this would work

thought , comments, etc.
or if there is a standard or statistical test for this method I would appreciate the name so I can look it up

Thanks in advance,
 
Elsmar Forum Sponsor

Bev D

Heretical Statistician
Staff member
Super Moderator
#2
In theory, practice is just like theory, but in practice, practice is nothing like theory.

So in theory if the fixture has nothing to do with the number of defective units, then the number of defects will be a simple percentage of the lot size. If you were to plot percent defective per lot on a SPC chart you would see where the defect rate is statistically different. This might be because a few fixtures are ‘bad’ OR it might be due to some other causal mechanism acting up. You’ll never know.

Yes you should record the fixture(s) used per part I suppose. But why don’t you just directly test the parts on different fixtures? If the failure repeats on other fixtures, it’s not the fixture. If the failure only occurs on a specific fixture and not on others then it’s the fixture. You dont’ need fancy math...
 

GRP

Involved In Discussions
#3
But why don’t you just directly test the parts on different fixtures? If the failure repeats on other fixtures, it’s not the fixture. If the failure only occurs on a specific fixture and not on others then it’s the fixture.
Following up with the theory-practice dichotomy, I bet the part wont fail on one fixture but on some of them. And then you test a different part and the profile of failure among the fixtures is different. And then you try to understand why on some but not on others, and then you start measuring...

...and attribute gauging is quick and nice, in theory. Determining if the attribute gauging is doing a proper job, that´s hard work!
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#4
Yeah - if the failure is intermittent or the defect is marginal then you get inconsistent results but the right diagnostic study can answer that question fairly easily. (This is where simple probability math can actually help) Not sure that the fixture is the measuring device, an assembly aid or an inspection holding fixture. to give better advice the OP would have to describe the defect, the role of the fixture and the measurement system itself.
 

rmundroff

Starting to get Involved
#5
Fixture is an assembly aid believed to cause the defects if worn

we have the % defects for 4 years
we are just trying to lok a select fixtures (the ones most likely to cause the defects of the 100's we have to prove that the Fixture DOES cause the defects if worn
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#6
Looking at the data won’t really help you at this point. Looking at the fixtures and the parts will. Physics and geometry are your friend. So...get up from your desk and go out on the manufacturing floor.
First does the wear on the fixtures match the defect? Does it make physical sense that the wear can could cause the defect?
Next select a few really good/new fixtures and a few oldest/most worn fixtures (3 each will do it). (If you want to geek out on math look up Tukey-Duckworth). Then make some parts using the fixtures and test/inspect for the defect. You should use different operators for each fixture, but you could use randomly selected material/components from the Same lot or batch IF your trended defect rates dont’ Line up with material/component batch/lot changes...How many parts do you need to make? Well, that depends on the defect rate...you might start with the best defect rate you’d seen in the last year. If the fixtures do cause the defect, then you probably won’t need to make too many. If you selected the fixtures correctly, then teh defect rate for the 3 ‘bad’ fixtures should be substantially worse than the defect rates for the 3 ‘good’ fixtures (which should be near or at zero if the fixture is the only causal factor). If the defect rates are similar then it’s not the fixtures...
Of course it’s possible that there is a material/component and/or operator interaction. If you don't get clear results you can post your results here...and we can help you.
 
Thread starter Similar threads Forum Replies Date
S Determining the Total Sample Size using AQL - AQL Lot Quantity question AQL - Acceptable Quality Level 8
S Study sign off question / responsibilities ISO 17025 related Discussions 0
S Qualification question - ISO 13485 Reliability Analysis - Predictions, Testing and Standards 0
M Question for Auditors - "Off the Record" Conversation? General Auditing Discussions 14
D Question regarding ECO process, specifically for Life Science products and defining form fit and function ISO 13485:2016 - Medical Device Quality Management Systems 1
R Accelerated Aging - Creating test samples - Implantable medical device Question Other Medical Device Related Standards 4
A Question on Authorized Representative in Malaysia Other Medical Device Regulations World-Wide 1
D Limited Scope for second site Question? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 5
I ISO 2233:2000 Question - Medical Device Shipping/Transportation Validation Other ISO and International Standards and European Regulations 1
Anonymous16-2 Labeling Question (Dietary Supplements/Food) Pharmaceuticals (21 CFR Part 210, 21 CFR Part 211 and related Regulations) 1
T Question for: Cg & Cgk calculation General Measurement Device and Calibration Topics 3
N ASL Question for GitHub ISO 13485:2016 - Medical Device Quality Management Systems 6
hogheavenfarm GDT Flatness measurement question Inspection, Prints (Drawings), Testing, Sampling and Related Topics 10
A Question on ISO 14001:2015 - Are annual audits required? ISO 14001:2015 Specific Discussions 8
dinaroxentool Question about FDA Classification of a Device 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 3
J Another DFAR question 252.225-7009 AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 0
F Conflict Mineral Smelter Question RoHS, REACH, ELV, IMDS and Restricted Substances 8
R NRTL - Scope Question - Off-the-Shelf Plug In IEC 60601 - Medical Electrical Equipment Safety Standards Series 0
D API 6A Certification Question Oil and Gas Industry Standards and Regulations 4
dinaroxentool Question about qualification as a medical device or accessory in Europe EU Medical Device Regulations 2
R DHR question: Traceability of components ISO 13485:2016 - Medical Device Quality Management Systems 2
C MDR - Question around software accesories EU Medical Device Regulations 2
K My question is, what/when is a nonconformity? Therefore what requires an NCR? Nonconformance and Corrective Action 9
Watchcat Authoritative References about the Research Question? Quality Tools, Improvement and Analysis 0
T Question about Quality Department employee position titles Quality Manager and Management Related Issues 10
N Question on creepage/clearance requirements for HF Active Accessories for 2nd edition 60601-1 IEC 60601 - Medical Electrical Equipment Safety Standards Series 1
I Question 1 - Nitpicking on Document Approval - can a document approval record be separate? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
J Question: How to create an IMDS RoHS, REACH, ELV, IMDS and Restricted Substances 3
K Question on whether IEC 60601-2-62 standard is applied IEC 60601 - Medical Electrical Equipment Safety Standards Series 4
B QMS question in regards to multiple medical devices/products and N/A activities Other Medical Device Related Standards 12
C NB approval - Basic question about Notified Bodies and their role EU Medical Device Regulations 10
G Question about Non-conformances during New Product Introduction Nonconformance and Corrective Action 14
F ISO 13485 8.2.3 Reporting to regulatory authorities: Question regarding a procedure for this clause. ISO 13485:2016 - Medical Device Quality Management Systems 4
O Mitutoyo Digital Caliper to PC USB question General Measurement Device and Calibration Topics 2
R Probability - Need a help to solve the below question Statistical Analysis Tools, Techniques and SPC 5
B Minitab Type 1 Gage Study on True Position Question Measurement Uncertainty (MU) 1
Q Supplier audit question cataloque VDA Standards - Germany's Automotive Standards 0
Ed Panek Inactive key supplier question - We are not actively buying from them ISO 13485:2016 - Medical Device Quality Management Systems 2
T Potential Off-Label Use question 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 5
Ed Panek Rule 11 Question - CE approvals for software as well as the medical device EU Medical Device Regulations 6
H Question about implications of performing Firmware upgrade via MDDS - Medical Device Data Systems 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 2
D Company Moving - Relabelling Question Medical Device and FDA Regulations and Standards News 0
Ronen E Tolerance intervals (?) question - Flow Rate Probability Range Statistical Analysis Tools, Techniques and SPC 6
S Conformity Assessment Route question for Class IIa medical device under MDR EU Medical Device Regulations 3
K AS9100D 8.4.1.1 external providers question - Walmart, Home Depot, our lawn care team. etc. AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 20
E Question on GD&T added to print - Positional callout for the small holes Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
J IEC 60601-1, ed 3.1 - Blue icon question IEC 60601 - Medical Electrical Equipment Safety Standards Series 4
A PFMEA English language question IATF 16949 - Automotive Quality Systems Standard 4
D GD&T Drawing Question - I have a drawing and it makes no sense to me whatsoever Inspection, Prints (Drawings), Testing, Sampling and Related Topics 7
D Yet another torque question... Assembly processes AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 2

Similar threads

Top Bottom