Poor GR&R results due to Low Part Variation

X

xavierthomas

#1
My dilemma is with Automotive customers who reject my GR&R because of low ndc of 2 and %R&R at 30%.

Our parts are high tolerance molded parts. 50 cavity shots that vary less than .002" from part to part. Customer tolerance requirements are fairly wide at +/- .010". Our parts are virtually never out of spec and always in statistical control.

We typically use 6" digital verniers with .0005" readout.

Due to the lack of part to part variation, I can't get an acceptable GR&R. Buying Verniers that would readout to 5 places isn't financially acceptable nor practical.

What other options do i have? The customer QA zealots won't budge and hold me by my PPAPs to force me to do something.

Any help is greatly appreciated.
 
Elsmar Forum Sponsor

Golfman25

Trusted Information Resource
#2
Man. I think you're stuck. We have never been able to get a "good" gage R&R with a vernier, although we have used them for 60+ years. With such a small variation of .002 I don't think your verniers are capable of picking up the variation. I would love to here some solutions.

Can you get your process guys to put some variation on the parts by changing some process parameters?
 
Last edited by a moderator:

Bev D

Heretical Statistician
Staff member
Super Moderator
#3
I sympathize with your position...can you post your data? I have had a great deal of success with an alternative approach that is more sensible in these cases...but it's easier to demonstrate than to just describe.
 
C

Coleman Donnelly

#4
NDC is important if you are looking to do process control. The method that I would recomend is to cherry pick your samples so that they span the +/-3Sigma of your process as much as possible.

The reason this is important is if you cannot break your process up into enough distinct categories:
- You won’t be able to tell the difference between the parts that you are producing
- You will be unable to identify when your process has shifted until long after the actual trend has already begun
- This is really a signal to noise issue - you can’t see the signal because of all the noise in your measurement...

I think before we go around the situation it may be good to understand it :)

What a lot of people have been known to do is provide samples that vary outside of the tolerance - this is important to do as you should demonstrate that your measurement system is consistent even if you are making bad parts - this is not always as straight forward as it seems!

I am also concerned that your R&R P/T ratio is at 30% I think this is a good place to focus your effort. Typically 30% is not considered a "good gage R&R" and things should be done to try and improve this!

Unless you are under 20% you will not be able to get 5 NDC unless you make parts that are out of spec :)

I do understand the perspective of trying to meet a customer’s requirements to move a project forward, but if these things are not important to you I think we should back up a couple of steps and have a different conversation.
 

Kales Veggie

People: The Vital Few
#5
My dilemma is with Automotive customers who reject my GR&R because of low ndc of 2 and %R&R at 30%.

Our parts are high tolerance molded parts. 50 cavity shots that vary less than .002" from part to part. Customer tolerance requirements are fairly wide at +/- .010". Our parts are virtually never out of spec and always in statistical control.

We typically use 6" digital verniers with .0005" readout.

Due to the lack of part to part variation, I can't get an acceptable GR&R. Buying Verniers that would readout to 5 places isn't financially acceptable nor practical.

What other options do i have? The customer QA zealots won't budge and hold me by my PPAPs to force me to do something.

Any help is greatly appreciated.
I agree with you. They are zealots. It almost sounds like they want you to increase part variation, so that you can pass their GRR requirements.

Can you create a wider spread in your parts by using some of rare scrap parts or start-up parts?

Also, the results of the GRR tell that you cannot do SPC on this process, because the measurement system cannot measure the process variation.
 

Miner

Forum Moderator
Staff member
Admin
#6
The ONLY time it is permissable to cherry pick parts or to deliberately select parts out os specification is when your gauge is used as an inspection device and the only metric is %Tolerance.

If your gauge is used for SPC or capability studies it is never acceptable to select anything other than random parts that represent the process. Doing so is no different than deliberately falsifying test results. See my blog on MSA, specifically the section on Part Selection.
 

Ninja

Looking for Reality
Staff member
Super Moderator
#7
The ONLY time it is permissable to cherry pick parts or to deliberately select parts out os specification is when your gauge is used as an inspection device and the only metric is %Tolerance.

If your gauge is used for SPC or capability studies it is never acceptable to select anything other than random parts that represent the process. Doing so is no different than deliberately falsifying test results. See my blog on MSA, specifically the section on Part Selection.
I love the rigid code...it makes the conclusions drawn from the data that much more compelling.
++++++++++++++++++++++

All the same, though, when the goal is customer acceptance of a measuring system,
AND the method for creating higher ndc that are not a normal part of the process is disclosed to the customer,
I would have no issue with cherry picking the parts for this study.
(No guarantee they'll accept it though)

+++++++++++++++++
If the approach was not disclosed to the customer, though, you are begging for future relationship issues.

"I'm sorry, my process doesn't vary enough to test your whole spec range." is compelling for production engineering, but is apparently hard for the Quality guys to swallow.

Short of that, micrometers or CMM may be needed.
 

Kales Veggie

People: The Vital Few
#8
The ONLY time it is permissable to cherry pick parts or to deliberately select parts out os specification is when your gauge is used as an inspection device and the only metric is %Tolerance.

If your gauge is used for SPC or capability studies it is never acceptable to select anything other than random parts that represent the process. Doing so is no different than deliberately falsifying test results. See my blog on MSA, specifically the section on Part Selection.
The OP is dealing with zealots and is looking for a practical solution. In certain cases it is better to give the customer what they want than arguing with facts until the cows come home.:sarcasm:

As I wrote: The OP cannot do SPC using the current gauge.

Just wondering how often true "random" parts are selected.
 
X

xavierthomas

#9
Thanks for the feed back to everyone.

The whole PPAP process is a bit of bureaucratic waste at times. We actually do not bother with monitoring dimensions with SPC because of the the low variation. SPC is done on process variables such as injection pressure, but the PPAP gurus at the customer demand data on part print dimensions.

We also give them GR&R on our CMM which computes well. They insist on GR&R on verniers because the floor inspectors do use them at times for quick checks when the CMM would take too long.

I like idea of cherry picking some out of spec startup parts, with full disclosure, just to prove the vernier acceptability. Or perhaps we can simply eliminate the use of verniers in the control plan and rely on the CMM results.

The losses due to their holding up PPAP approvals runs into the $10's of thousands and the pressures are huge.

Thanks again to all the true professionals.
 
Thread starter Similar threads Forum Replies Date
Y Poor Gage R&R Results - High R&R result and poor ndc value Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 5
M Poor Gage R&R results (30%RR to 80%RR) - What Next? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
S Cost of Poor Quality (CoPQ) - Scrap element of calculation includes lost margin? Misc. Quality Assurance and Business Systems Related Topics 7
qualprod Addressing poor commitment in people Misc. Quality Assurance and Business Systems Related Topics 23
qualprod Best criteria to measure Corrective Action effectiveness - Poor Maintenance ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 10
C What is your Cost of Poor Quality (COPQ)? Misc. Quality Assurance and Business Systems Related Topics 8
V For screening a design, can we live with the low/poor predicted R-Sq.? Statistical Analysis Tools, Techniques and SPC 3
M Reducing Cost of Poor Quality - Your opinion requested Quality Manager and Management Related Issues 14
M Contractors with poor Quality Records ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 9
M Customer Satisfaction Survey - Poor Response ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 11
S Difference between COQ (Cost of Quality) vs COPQ (Cost of Poor Quality)? Misc. Quality Assurance and Business Systems Related Topics 8
M Which metric is better for Cost of Poor Quality (COPQ)? Quality Tools, Improvement and Analysis 17
N Improving Poor Communication with Customers Customer Complaints 6
P Smart or Sexy (CAR) - Poor Root Cause Analysis and Poor Effectiveness Check Nonconformance and Corrective Action 8
Y FDA News bulletin: It's the FDA's fault! FDA at Fault for Poor Quality Devices US Food and Drug Administration (FDA) 6
F Poor Containment - Supplier Nonconformance Problem Solving, Root Cause Fault and Failure Analysis 7
R Development Rejection Costs in COPQ (Cost of Poor Quality) Calculations Misc. Quality Assurance and Business Systems Related Topics 6
AnaMariaVR2 Poor Writing Skills Overshadow Good Content, Credibility & Revenues Records and Data - Quality, Legal and Other Evidence 19
1 Cost of Poor Quality form or template wanted Quality Tools, Improvement and Analysis 1
S COPQ (Cost of Poor Quality) Vs PONC (Price of Non Conformance) - Explanation wanted Quality Manager and Management Related Issues 5
P Measuring Costs of Poor Quality Quality Manager and Management Related Issues 2
A Chaotic Industry, Poor Service From Almost Everyone Coffee Break and Water Cooler Discussions 12
M Cost of Poor Quality Reports IATF 16949 - Automotive Quality Systems Standard 15
E Poor Manufacturing Planning fixes Misc. Quality Assurance and Business Systems Related Topics 4
K Generic worksheet for calculating Supplier Chargeback and Cost of Poor Quality (COPQ) Supplier Quality Assurance and other Supplier Issues 2
N Personnel COPQ (Cost of Poor Quality) Quality Manager and Management Related Issues 6
P Evidence of Supplier Corrective Action - Poor Responses by Suppliers ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
Marc Poor Hungry Kitty Funny Stuff - Jokes and Humour 8
S COPQ (Cost of Poor Quality) - Can we add Premium Freight? Misc. Quality Assurance and Business Systems Related Topics 6
S COPQ - Cost of Poor Quality - COPQ course for non-financial people Misc. Quality Assurance and Business Systems Related Topics 1
N Identification of COPQ (Cost of Poor Quality) aspects Quality Tools, Improvement and Analysis 2
bobdoering Consumer Reports: Poor Man's Opera Coffee Break and Water Cooler Discussions 0
S Examples of major problems caused by Poor document control Document Control Systems, Procedures, Forms and Templates 14
T Poor Capability - Electric torque screwdriver Capability, Accuracy and Stability - Processes, Machines, etc. 2
H Cost of Poor Quality (COPQ) - All returned/defective parts (plastic) are recycled Training - Internal, External, Online and Distance Learning 7
Manix Cost of Poor Quality (COPQ) and Reputation Quality Tools, Improvement and Analysis 25
Z Consequences for Poor Performance based on a Monthly Scorecard - Actions? Supplier Quality Assurance and other Supplier Issues 15
I High COPQ (Cost Of Poor Quality) from Our Quality Department IATF 16949 - Automotive Quality Systems Standard 7
N Poor control of testing chemicals ? which ISO 13485/9001 clause does it contravene? ISO 13485:2016 - Medical Device Quality Management Systems 8
S New Auditor wants Mould tool repair bill included in Cost of Poor Quality! IATF 16949 - Automotive Quality Systems Standard 18
Z Creating and Maintaining a Top Ten Poor Quality Supplier Performer List Supplier Quality Assurance and other Supplier Issues 16
S Operator Capability - Gage R&R Poor Repeatability Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 8
M One weakness of audit non-conformance reports is the poor writing Miscellaneous Environmental Standards and EMS Related Discussions 10
S Is there any standard for "Cost of Poor Quality" (COPQ) by ISO Various Other Specifications, Standards, and related Requirements 5
J Cost of Poor Quality (COPQ) - Iceberg picture Quality Tools, Improvement and Analysis 4
D Scary stories - the REAL consequences of poor quality Misc. Quality Assurance and Business Systems Related Topics 3
B Machine failure defects due to no/poor maintenance for FMEA - Looking for examples FMEA and Control Plans 6
M Need input - Potential poor external auditor? My first ISO 14001 registration audit ISO 14001:2015 Specific Discussions 4
P Acronym COPQ (Cost of Poor Quality) and COQ (Cost of Quality) - Differences Definitions, Acronyms, Abbreviations and Interpretations Listed Alphabetically 26
L TS 16949 Clause 5.6.1.1 - Cost of "POOR" Quality vs. Cost of Quality IATF 16949 - Automotive Quality Systems Standard 4

Similar threads

Top Bottom