PFMEA Severity - What is Process FMEA Severity estimation based on?

Jim Wynne

Super Moderator
#61
Re: Severity estimation in a PFMEA is a bit confusing

Jim, this is going to be my last attempt to synchronize with you on this thread. Again, I agree with your premise, but again, you did not answer my question -

"What is the purpose of a PFMEA, automotive style particularly, if not to evaluate the failure mode and the risks involved?"
I have not said at any point that potential failure modes should not be evaluated, thus your question is not to the point. What I have said is that job shops should not use the AIAG book method of characterizing or identifying potential failure modes.

If applying a RPN number to a permaturely rusting part is not a failure mode that a painter must evaluate on a PFMEA, then we are in a parallel universe...
I have also already said, in so many words, that if I meet the specifications consistently and the thing corrodes in end use, it's ultimately the designer's problem, not mine.

Here are a few things that might result in premature corrosion of a painted part:

  • Inadequate film build (not enough paint)
  • Excessive porosity of the paint layer
  • Adhesion failure
Each of these potential eventualities should be addressed by the specifications--if not directly, then by the specification of testing for corrosion resistance and paint adhesion. Now, if I look at each of those bad things, I can associate each one of them with process failures of one kind or another. For example, film build might be inadequate due to incorrect dwell/cycle times, or the presence of Faraday cages or other part geometry issues. Adhesion failure may be due to poor surface preparation, among other things.

The things I would characterize as process failure modes are those things that can cause undesirable results where "undesirable results" equals failure to successfully complete the customer's specified testing, because that's the criterion I've been given by the customer.

"Poor surface preparation" is a potential process failure mode. Given that as a failure mode, and inability to pass the required testing as an effect, I can look to and prevent the causes of poor surface preparation, make a conforming part, and never consider what might happen to the part after it leaves my building.

My goal is to meet the specifications.
 

Stijloor

Staff member
Super Moderator
#62
Re: Severity estimation in a PFMEA is a bit confusing

<snip>What I have said is that job shops should not use the AIAG book method of characterizing or identifying potential failure modes.
Jim,

Right or wrong, the AIAG FMEA manual has become the de facto guideline for FMEA activities. A lot of emphasis is placed on the effects of failure modes as noticed/experienced by the Customer. Not speaking for Helmut, but I believe that this is one of the points he is trying to make.

Stijloor.
 

Jim Wynne

Super Moderator
#63
Re: Severity estimation in a PFMEA is a bit confusing

Jim,

Right or wrong, the AIAG FMEA manual has become the de facto guideline for FMEA activities. A lot of emphasis is placed on the effects of failure modes as noticed/experienced by the Customer. Not speaking for Helmut, but I believe that this is one of the points he is trying to make.

Stijloor.
I understand that. If constrained by shortsighted customers, you have no choice but to indulge their shortsightedness. Nonetheless, I know that some customers appreciate a conscientious demonstration of risk analysis, having seen too many "by the book" PFMEAs that are largely impotent and demonstrate that the supplier views them as a paperwork exercise.
 
S

speck

#64
Re: Severity estimation in a PFMEA is a bit confusing

Jim, I agree with your premise, but I don't think you are answering my question. A painter MUST evaluate the consequences of underpainting a part. And, those consequences only occur later to the end user. The failure mode is premature rusting. Isn't that the very purpose of a PFMEA? The spec indicates the paint mill thickness, the PFMEA considers the risk of failures. Why do you have a problem with that? The purvey of a designer is to specify the paint, the rest is process management.

Leaving the AIGA guidelines and train of thought for a moment, you as the painter and the painting FMEA risk team have decided that the required mil thickness for a particular coating should be .00X" thick. This has shown that undercarriage rust preventative measures are adequate for government DNR service vehicles that you manufacture just like it, only a little larger. You just analyzed the risk and performed all the necessary risk assessments. OK. What your customer's marketing team failed to tell you, (and probably their own design team) is that this particular line of products will not be used in Omaha, NE like the other ones, they will be shipped to Florida and will be used strictly on the beaches where the saltwater and corrosion will destroy the undercarriage parts in 6 months because the mil thickness was a fraction of the needed thickness needed for adequate protection.

If the design responsible parties do their job with DFMEA's they will tell you as a painter the specification and you as the processor should evaluate every process failure that will create a mil thickness not meeting that spec in any way shape or form. I believe this is the difference between process and design FMEA’s. Again if there is no difference and we have to call meetings with the end user (sometimes 6 tiers or more up the food chain) to determine the end use is on a beach and not in Nebraska, why don’t we call them PDFMEA’s? As a painter you cannot possibly pretend to understand all the end use situations. I would never buy a vehicle that was "designed" by a painter.

Of course a specification written by the automotive end users will always make every attempt to cover their own !%#@'s. I can hear and see GM or Chrysler now "Of course these vehicles are to be used in a saltwater environment didn't you follow the AIGA guidelines and consider these vehicles can be used as landrovers on Mars"

TO GM - "Sir , you do what you do best and design the thing, and I'll do what I do best and paint it. Let me know when you want a copy of my process FMEA's so you can analyze and consider all risks during your DFMEA process resulting from my painting process's. I can be held accountable for not meeting your specification but not because the product was used in saltwater. For saltwater use applications I have a completely different process for that right here as specifically requested by FORD. We have been manufacturing their maritime products for 8 years and they are completely happy as they have performed thorough DFMEA's and realized the need for a mil thickness 4 times your specification. My PFMEA clearly shows that this is suitable for use in freshwater environment. It's a shame your purchasing department did not forward that to your design team for consideration."

Am I just completely wrong in my thinking? :confused:
 

Helmut Jilling

Auditor / Consultant
#65
Re: Severity estimation in a PFMEA is a bit confusing

...you as the painter and the painting FMEA risk team have decided that the required mil thickness for a particular coating should be .00X" thick. This has shown that undercarriage rust preventative measures are adequate for government DNR service vehicles that you manufacture just like it, only a little larger. You just analyzed the risk and performed all the necessary risk assessments....

...If the design responsible parties do their job with DFMEA's they will tell you as a painter the specification and you as the processor should evaluate every process failure that will create a mil thickness not meeting that spec in any way shape or form. I believe this is the difference between process and design FMEA’s....

...Am I just completely wrong in my thinking? :confused:
Speck, I think your first excerpt is incorrect, and your second excerpt rightly explains the answer to your question in the first excerpt.

The painter would rarely be defining the paint spec or thickness spec. As your second statement indicates, that should be done by the design responsible parties. The product risks would be considered on their DFMEA.

The painter would take those specs, and evaluate the failure modes and risks and impact to the product if his painting process does not hold the spec. In other words, what happens if he under- or over-applies the paint? What would the failure consequences be? Those would be evaluated on the PFMEA.
 

Jim Wynne

Super Moderator
#66
Re: Severity estimation in a PFMEA is a bit confusing

Speck, I think your first excerpt is incorrect, and your second excerpt rightly explains the answer to your question in the first excerpt.

The painter would rarely be defining the paint spec or thickness spec. As your second statement indicates, that should be done by the design responsible parties. The product risks would be considered on their DFMEA.

The painter would take those specs, and evaluate the failure modes and risks and impact to the product if his painting process does not hold the spec. In other words, what happens if he under- or over-applies the paint? What would the failure consequences be? Those would be evaluated on the PFMEA.
OK, first you say the product risks would be considered on the DFMEA, then you say the painter would evaluate "...risks and impact to the product..." Why would the painter worry about the product (as opposed to the specifications) if the designer built product risk mitigation into the design?

If I'm the painter, my primary concern is not meeting the specifications. Of course I know that if I don't meet the specifications, something bad might happen. The customer might measure paint thickness and find it lacking, or the parts might corrode in the field (which might be the result of not meeting the specifications, and might not). On the other hand, if thickness exceeds the specification, at best I'm wasting paint.
 

Helmut Jilling

Auditor / Consultant
#67
Re: Severity estimation in a PFMEA is a bit confusing

...If I'm the painter, my primary concern is not meeting the specifications. Of course I know that if I don't meet the specifications, something bad might happen. The customer might measure paint thickness and find it lacking, or the parts might corrode in the field (which might be the result of not meeting the specifications, and might not). On the other hand, if thickness exceeds the specification, at best I'm wasting paint.
Jim, huh? ...that is the purpose of a PFMEA! To evaluate the effects of a process failure upon the product..., and the risks that it would impose upon the customer.
 
P

praveenraaaj

#70
Re: Severity estimation in a PFMEA is a bit confusing

Dear All,

I would like to discuss this topic again for better understanding and clarity.

We have been asked to indicate the effects of failure mode addressing the following:

Inhouse Effect:

Customer Effect:

Enduser Effect:

Can anyone give a better clarity in addressing the effects ?

My understanding is , if a failure is detected, on the inhouse effect we should indicate whether to sort or rework or scrap. Should we also consider the detection here?

If certain defects are not noted by customer can we indicate no effect or what should we indicate?

Need all your help!

Kind Regards,
R Praveen
 

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