FMEA DOGMA about Severity - Am I right or Wrong?



According the AIAG and Ford Manual, when evaluated the product effect in the DFMEA and PFMEA about a particular fail, the two product effect the should be logically the same.
In the DFMEA we have to reach a particular requirement, and we have to evaluate the related failure mode and their effect.
In PFMEA we are going to reach a particular requirement with an operation a with a tool, so the analysis of effects should be extended also to the process the process effect. And the severity related to this fail is the higher between the Product and Process.
An Example: The noise of a powertrain or steering component can have a medium impact on the System/End User but can cause scraps and downtime on te line. So in this case the overall severity ranking related to this fail is given by the process fail.

I discussed many time with some colleagues of mine, she said:" in the Process FMEA the severity is given only by th DFMEA and they must be the same. This severity is untouchable"
I reply "
But according the Manual only the two product effect are the same not the severity, because in the PFMEA we have to evaluate also the effect on the process"

I see that this rule DFMEA SEVERITY=PFMEA SEVERITY is so frequent.

According your experience, who is right? The colleagues of mine or myself.

Thanks all in advance & Happy New Year!
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Moved On
Carmine: You didn't mention if you produced a process flow between performing the DFMEA and the PFMEA. It's usual to lay out the manufacturing process, from which the PFMEA is derived - transport of the product may lead to some damage for example. So, in general terms you are correct, but if you don't explain to your colleague the use of the sequence of "Process Flow - PFMEA - Control Plan", you may still end up arguing.


<snip> I see that this rule DFMEA SVERITY=PFMEA SEVERITY is so frequent. <snip>

For the purposes of the PFMEA the rule is Severity = max(DFMEA_Severity, PFMEA_Severity).
An example: an oversized dimension on the DFMEA may result in a condition where an "Audible Noise can be noticed by most customers (> 75%), but the item is operable and does not conform to specification." Therefore, the DFMEA_Severity is equal to a 4.
In order to produce the dimensional feature a person may be injured with warning. Therefore the PFMEA_Severity is a 9.
For the purposes of the PFMEA the severity is = max(4,9) = 9.
This does not change the effect, DFMEA_Severity, of the feature.

What should happen: The PFMEA team should undertake measures to reduce the process severity. If they cannot reduce the possibility, then they should work with the design team to change the design in order reduce the potential of production injuries.
While this sound like what you are saying, "the DFMEA oversized should reflect the severity of the PFMEA," it does not. The oversized dimension still has a DFMEA_Severity of a 4,
BUT the DFMEA should reflect a NEW requirement which recognizes the potential for an injury during production which carries a DFMEA_Severity of a 9. Any design change to support the production team in their severity reduction activity would be documented within this requirement.

Hope this helps.


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