What should the FMEA Occurence Rating be based upon?

[Andrews]

Sub : Occurence rating
Should occurrence rating be based on the no. of times a failure occurs or no. of non-conforming parts i.e if a particular undersize problem had occurred twice when running a batch of 10,000 components and if on segregation we found 2000 components non-conforming then should we take the failure rate as 2/10,000 thereby assigning occurrence rating of 5 or should we take the failure rate as 2000/10000 ,thereby getting an occurrence rating of 10.Likewise an undersize problem could have occurred 10 times when running 10000 nos. but on segregation found only 100 pieces.In this case should the failure rate be taken as 10 / 10000 i.e occurrence rating of 7 or take failure rate as 100/10000 nos. i.e occurrence rating of 10.

[Atul Khandekar]

Andrews,

Is it 2 out of 10000 or 2 out of some sample size? In any case I think you should take the maximum number that you found (in this case after segregation) to decide the occurence rating. You would get an occurence rating of 10.

Occurence must always be seen in conjunction with detection. Segregation or 100% inspection would be an inefficient and expensive method of detection. If you are doing sampling or SPC, you should be able to get a close enough estimate (PPM) of non-conforming.
-Atul.

Atlu,

Occurance happans before detection, therefore detection can't be assumed when rating occurance?

The detection may be the best in the world, but it only detects what has already occurred.

To reduce an occurance rating don't we need to implement improvement on the front end as opposed to the rear end (detection?)

[db]

Andrews, I think you are mixing data (if I understand you properly). Here is the data as I see it:

10000 components
2000 nonconforming parts

2 process deviations (which lead to the 2000 n/c parts)
? possible process deviations

If you use the 10000 components, then your comparison must also be in components. If you are going to compare the number of process deviations, then you must have something to compare it with, for example the number of possible deviations. Let me explain.

Let’s say you produced 10 million parts. You had one process deviation that resulted in 100% of the parts being rejected. Would you say you had 1 deviation in 10 million parts? Probably not, it just would not make sense.

If your FMEA is looking for the number of possible deviations, then use the 2 versus what ever the number of runs.

One last thing. Normally, FMEAs are developed prior to the manufacture. The historical data can then be used to test the validity of the FMEA

[Udawantsaraf]

I would like to know details about
ISO 9000 , 90001, 9002, 9003, 90004 and 9005
Is that depends on type of industries ? If yes let me know which standards are using for which type of industies.

Narhari

[D.Scott]

Try this link for some good background on what ISO 9000 is and how it can apply to a your company:

http://www.iso.ch/

This is another good link:

http://www.qualitydigest.com/html/iso9000.html

If you are an automotive company, look at TS16949.

Hope this gives you enough information to get you started.

Dave

[Sam]

Andrews,

"Occurrence is the likelihood that a specific cause /mechanismof failure will occur".

The fact that that you had two failures during the run and 2000 after sorting only indicates that you chose the wrong occurrence number.

You chose a particular Occ. no. based on something, past history, detection process in place or a "gut feeling". This was found to be incorrect during the sorting process.
The information you gathered during sorting is not used to change the Occ. no., it should be used to improve the process.

[Andrews]

I feel the thread is going in a different direction. Maybe because I did not project my problem properly.Let me explain my problem with a hypothetical example.

Example :Let us assume that we work from 8.30 a.m to 5.00p.m (8hrs with an 1/2 hr lunch break) and that 'X' job was running from 8.30 a.m on 21.03.2002 after setting approval and we had detected a hole undersize problem during the hourly inspection (DETECTION method) that was conducted at 11.30 a.m whereas during 10.30 inspection we did not have this failure.Since we keep the items that ran between the last hourly check and the present check separately,we were able to quarantine the quantity between 10.30 inspection and 11.30 inspection.So maximum number of non-conforming products is the quantity that will run between 10.30 check and 11.30 check (say 1000 nos.).After correcting the problem we ran the machine till 2.30 p.m without a problem.But at 2.30 hourly inspection we detected the SAME problem.We quarantine the quantity between 1.30 inspection and 2.30 inspection.Let us say we again got 1000 defective pieces.We correct the problem and run this machine till 9.00 next day without this or any other problem.Totally we have got the same failure (hole undersize) twice during the production run of 10000 pieces and the total no. of defectives is 1000+1000=2000nos.
Based on this case what is the occurence rating I should give and why?