Reducing both Detection and Occurance in a Design FMEA WITHOUT a Design Change

[MSAFAI]

Hi everybody,

The following question has kept me awake to this hour (it is now about 4 o'clock AM where I live):

In the DFMEA example given in the QS9000 FMEA manual, in more than one occasion you come across a reduction of both D and O WITHOUT any design changes. It seems as if reducing D will reduce O. Whereas, the manual states "the only way to bring a reduction in the occurence number is to change the design".

Can anyone explain this apparant contradiction between the manual's text and the manual's example?

Thanks in advance
MSAFAI

 

[Al Dyer]

MSAFAI:


How did you deduce that there was no design change?

ASD...

 

[Al Dyer]

Originally posted by MSAFAI:
Dear Al,

Please have a look at the DFMEA example given in the QS9000 FMEA manual. I quote from the manual two cases, column 'Actions Taken':

" Test results (test no 1481) show specified thickness is adequate ... "

or another case:

" evaluation showed adequate access"

Regards,
MSAFAI

I'm looking at the same page you are. This is a design FMEA. Wouldn't a change under actions taken be a design change?

ASD...

 

[MSAFAI]

Originally posted by Al Dyer:
MSAFAI:


How did you deduce that there was no design change?

ASD...

Dear Al,

Please have a look at the DFMEA example given in the QS9000 FMEA manual. I quote from the manual two cases, column 'Actions Taken':

" Test results (test no 1481) show specified thickness is adequate ... "

or another case:

" evaluation showed adequate access"

Regards,
MSAFAI

 

[MSAFAI]

Dear Al,

Do you mean there has been a 'design change' or there has not?

The sentences I quoted from the FMEA manual seem to sugges there has been no design change. Do you agree?

Regards,
MSAFAI

 

[Al Dyer]

MSAFAI:

Under the actions taken (page 12 AIAG FMEA) I look at the statement that says "based on test, 3 additional vent holes provided in affected areas."

I would consider that a change in design.

I work mainly with process FMEA's but the thought process is the same.

ASD...

 

[MSAFAI]

Originally posted by Al Dyer:
MSAFAI:

Under the actions taken (page 12 AIAG FMEA) I look at the statement that says "based on test, 3 additional vent holes provided in affected areas."

I would consider that a change in design.

I work mainly with process FMEA's but the thought process is the same.

ASD...

Dear Al,

That ia a design change, you are right. But how about other cases in the same page where there is no desing change?

Regards,
MSAFAI

P.S. I think we have to give up. Since, there are no comments from other forum members.


Regards

 

[Marc]

I was looking through this old thread and wondering. Do any of you folks have any comments on this? My 'schooling' was a design change had to be made but I can't remember the arguement and logic as to why.

 

[Howard Atkins]

From the manual

Occurrence is the likelihood that a specific Cause/Mechanism (listed in the previous column) will occur during the design life. The likelihood of
Occurrence ranking number has a relative meaning rather than an absolute
value. Preventing or controlling the Causes/Mechanisms of the Failure Mode
through a design change or design process change (e.g. design checklist,
design review, design guide) is the only way a reduction in the Occurrence
ranking can be effected.

But

" Test results (test no 1481) show specified thickness is adequate ... "

The Cause/Mechanism is that insufficent wax thickness specified.This was a query as to the robustness of the design. An extra control was added, to test the specification. The specification was judged as adequate therefore the occurence was reduced.
This showed that the design did not need to be changed but it gave confidence that the problem would occur much less.

Is this thinking correct?