O
Orlando Guillory
How do you do a gage R&R when the sample is destroyed or modified during the test? I have several tests such as a rupture test that we want to define the errors but cannot repeat the test with the same samples. Suggestions?
B
Batman
Up until two days ago, I would have said no way. However, I just finished reviewing the PPAPall.xls file - found in the PDF Zone elsewhere in this site. On one of the pages, near the 'regular R&R' page, it has a fill in the blanks form with calculations. While I am NOT any type of math wiz, I do have some objection to this philosophically. However, I believe it is blessed by Delphi, so have at it.
D
Don Winton
The spreadsheet Batman mentioned appears to be statistically sound. Destructive testing could also be R&R'd as attribute data, but the attribute portion of the same spreadsheet appears to be somewhat 'lacking.'
Regards,
Don
Regards,
Don
D
Don Winton
Yea, I guess I should expound upon my last post. Sorry about that.
Using logic, if the portion of the spreadsheet for attribute R&R is somewhat ‘lacking’ (IMHO), then an argument could be made that other portions of the same spreadsheet may be lacking as well, thus you must be able to justify the use of the calculations to your assessors (assuming the question is even asked) and yourself. My particular problem with the attribute page of PPAPall.xls was that is did not consider marginal samples. The samples either had to all pass or all fail for the gage test to be considered acceptable (100% same results per sample. Plueeeeeeze. Does differentiate ring a bell?). BUT, I did not design nor have input to its design. Therefore, an argument could be made that the authors had a legitimate reason for the calculations, but I cannot explain these reasons to my assessors, nor myself.
If Delphi accepts the destructive portion (or any portion, for that matter) and the calculations of PPAPall.xls, that should satisfy most assessors. But, I would not be willing to gamble my registration on it. I would want to be able to explain how if the subject came up. How I came to the conclusion that the R&R was acceptable, etc. and PPAPall.xls offers no derivations on the calculations involved. Perhaps they may be available from the source, perhaps not. Do not get me wrong, I am neither accepting nor rejecting PPAPall.xls nor its authors. They obviously put a lot of good work into it. And, I applaud Marc for providing it to the public. These are just my thoughts on this matter.
Having reviewed the destructive portion of PPAPall.xls, these are my particular issues, other than those outlined above. Under the assumption that the test was tolerance based, you could use that if you wished. Under the assumption that the test was attribute based, you may not be able to. Therefore, I humbly propose an alternative. Use process capability.
Process capability tests are available for both variable data and attribute data. Process capability does not require use of the same sample. AND process capability is something that should be acceptable as a measure of R&R, designed correctly. You perform capability on the gage, not the process. However, if the assessors do not want to accept process capability numbers, translate process capability numbers into R&R numbers. I have the method laying around here somewhere, if anyone is interested.
In short, my answer to Batman’s question is yes, assuming you are willing to work outside the normal paradigm.
Regards,
Don
Using logic, if the portion of the spreadsheet for attribute R&R is somewhat ‘lacking’ (IMHO), then an argument could be made that other portions of the same spreadsheet may be lacking as well, thus you must be able to justify the use of the calculations to your assessors (assuming the question is even asked) and yourself. My particular problem with the attribute page of PPAPall.xls was that is did not consider marginal samples. The samples either had to all pass or all fail for the gage test to be considered acceptable (100% same results per sample. Plueeeeeeze. Does differentiate ring a bell?). BUT, I did not design nor have input to its design. Therefore, an argument could be made that the authors had a legitimate reason for the calculations, but I cannot explain these reasons to my assessors, nor myself.
If Delphi accepts the destructive portion (or any portion, for that matter) and the calculations of PPAPall.xls, that should satisfy most assessors. But, I would not be willing to gamble my registration on it. I would want to be able to explain how if the subject came up. How I came to the conclusion that the R&R was acceptable, etc. and PPAPall.xls offers no derivations on the calculations involved. Perhaps they may be available from the source, perhaps not. Do not get me wrong, I am neither accepting nor rejecting PPAPall.xls nor its authors. They obviously put a lot of good work into it. And, I applaud Marc for providing it to the public. These are just my thoughts on this matter.
Having reviewed the destructive portion of PPAPall.xls, these are my particular issues, other than those outlined above. Under the assumption that the test was tolerance based, you could use that if you wished. Under the assumption that the test was attribute based, you may not be able to. Therefore, I humbly propose an alternative. Use process capability.
Process capability tests are available for both variable data and attribute data. Process capability does not require use of the same sample. AND process capability is something that should be acceptable as a measure of R&R, designed correctly. You perform capability on the gage, not the process. However, if the assessors do not want to accept process capability numbers, translate process capability numbers into R&R numbers. I have the method laying around here somewhere, if anyone is interested.
In short, my answer to Batman’s question is yes, assuming you are willing to work outside the normal paradigm.
Regards,
Don
B
Batman
Sorry for the delay, been having trouble logging into the site.
So Don, to answer Orlando's question, CAN you legitimately perform a Gage R&R in destructive testing? Even though there is a form in that PPAPall spreadsheet? As you pointed out, the calculations are 'lacking,' so could one get in trouble using it? Trouble with auditors, trouble using the data to make decisions?
So Don, to answer Orlando's question, CAN you legitimately perform a Gage R&R in destructive testing? Even though there is a form in that PPAPall spreadsheet? As you pointed out, the calculations are 'lacking,' so could one get in trouble using it? Trouble with auditors, trouble using the data to make decisions?
D
Don Winton
Will send by e-mail this weekend. Format is Word 6.0.
Enjoy and critical analysis welcome.
Regards,
Don
Enjoy and critical analysis welcome.
Regards,
Don
O
Orlando Guillory
Thanks for all the input. I would like to see the method to translate process capability into R&R.
I have been using control charts and cpk for the approvals of destructive methods at this time. The charts must be in control and cpk greater than 1.3 to accept the gage and part. This makes the assumption a bad gage R&R will not allow a cpk of 1.3 or greater. Of course if the part varies widely you are condemning the gage as well.
I cannot download the PPAPall.xls file mentioned. Is their a trick? By the way I cannot get to the listing through the Cayman system. For some reason I have to go straigt to it via a bookmark to "index of /pdf_files".
I have been using control charts and cpk for the approvals of destructive methods at this time. The charts must be in control and cpk greater than 1.3 to accept the gage and part. This makes the assumption a bad gage R&R will not allow a cpk of 1.3 or greater. Of course if the part varies widely you are condemning the gage as well.
I cannot download the PPAPall.xls file mentioned. Is their a trick? By the way I cannot get to the listing through the Cayman system. For some reason I have to go straigt to it via a bookmark to "index of /pdf_files".
O
Orlando Guillory
I was able to download and open the zip file. Thanks.