Problem with "failure mode? interpretation in PFMEA (Process FMEA)

Peters

Quite Involved in Discussions
Problem with "failure mode” interpretation in PFMEA (Process FMEA)

I have a problem with "failure mode” interpretation in PFMEA.
For me “failure mode” is a problem with the product after operation. For my friend “failure mode” is a problem with the operation.
For example:
In material cutting operation blunt/damaged tool irregularly cuts material.
1.For me:
-Cause: blunt/damaged tool in machine
-Failure mode: irregularly cut material (product out of specification)
-Effect: scrap, customer complaint, customer line stop
2.For my friend:
-Cause: incorrect tool change period, lack of tool check during setup
-Failure mode: blunt/damaged tool in machine
-Effect: irregularly cut material (product out of specification)

My questions:
A.Which way is better?
B.Which way is correct?
C.Is it possible - both ways are correct?
 

Jim Wynne

Leader
Admin
Re: Problem with "failure mode” interpretation in PFMEA

I have a problem with "failure mode” interpretation in PFMEA.
For me “failure mode” is a problem with the product after operation. For my friend “failure mode” is a problem with the operation.
For example:
In material cutting operation blunt/damaged tool irregularly cuts material.
1.For me:
-Cause: blunt/damaged tool in machine
-Failure mode: irregularly cut material (product out of specification)
-Effect: scrap, customer complaint, customer line stop
2.For my friend:
-Cause: incorrect tool change period, lack of tool check during setup
-Failure mode: blunt/damaged tool in machine
-Effect: irregularly cut material (product out of specification)

My questions:
A.Which way is better?
B.Which way is correct?
C.Is it possible - both ways are correct?

The way it's described in the AIAG manual is that the mode is a product failure--it's the nonconforming condition found in the product. This has never made sense to me, seeing as how it's supposed to be a process failure mode exercise. I've always found that you're more likely to identify potential causes of failures if you concentrate on potential failures of the process, which involves prevention of defects. Unfortunately, there are some OEM robots who will expect you to cleave to the method shown in the manual, but that's not always the case. The important thing, in the end, is that you do your best to anticipate potential failures and prevent them from happening.
 
D

David DeLong

Re: Problem with "failure mode” interpretation in PFMEA

We will have lots of opinion on this one.

Failure mode is "a description of the nonconformance at that specific operation" per AIAG Process FMEA third edition.

In other words, failure mode is a product nonconformance or out-of-specification condition.
 

Jim Wynne

Leader
Admin
Re: Problem with "failure mode” interpretation in PFMEA

We will have lots of opinion on this one.

Failure mode is "a description of the nonconformance at that specific operation" per AIAG Process FMEA third edition.

In other words, failure mode is a product nonconformance or out-of-specification condition.

But a "nonconformance at that specific operation" can be a nonconformance in the process, no? As I said earlier, the examples in the manual characterize potential failure modes as part defects, but unless you're forced to go by the letter of any of the AIAG manuals it's best to insert common sense when it's called for.
 

julsbear

Involved In Discussions
Re: Problem with "failure mode” interpretation in PFMEA

I believe that they can both be right.
Although under the usual intepretation of the PFMEA, the product defect is considered.
The second intepretation in the OP exhibits a 5 why approach and shows good thinking regardless of the usual intepretation. You could say that this is truly the PFMEA whereas the usual intrretation is Product Failures Due to Process Failure Modes and Effects (PFDPFME).
Unfortunately, the first int. fits the mold better.
The secont int. might better fit in a Sytem FMEA, that is either the inspection at setup or predictive maintenace on bits.

Hopefully, CA or PA would be the same for both (although the second int. may lead to predictive maint. solution sooner).
 
D

David DeLong

Re: Problem with "failure mode” interpretation in PFMEA

But a "nonconformance at that specific operation" can be a nonconformance in the process, no? As I said earlier, the examples in the manual characterize potential failure modes as part defects, but unless you're forced to go by the letter of any of the AIAG manuals it's best to insert common sense when it's called for.

Jim:

We have been down this road in the past and here is where I am coming from. I have not been forced to think like this by the AIAG standard but simply believe in this method.

Let's look at a Design FMEA first. The end product is the design and the group reviews the design initially for weakness rather than the probable failure modes of each design weakness. Once a weakness in the design has been revealed, the group would rate the weakness for severity. Now we look at the probable causes of the design weakness if the severity ranking was considered high.

On a Process FMEA, the group reviews the end product after the process for probable specification or quality (attribute) nonconformances. We would then rate them for severity and then review probable causes for the nonconformances if the severity ranking was high the same as one would in a Design FMEA.

That is how I have presented this in the past and it does seem to work. I just delivered this seminar to an aircraft part supplier (not covered by AIAG) and I presented it in the same manner.
 

Jim Wynne

Leader
Admin
Re: Problem with "failure mode” interpretation in PFMEA

Jim:

We have been down this road in the past and here is where I am coming from. I have not been forced to think like this by the AIAG standard but simply believe in this method.

Let's look at a Design FMEA first. The end product is the design and the group reviews the design initially for weakness rather than the probable failure modes of each design weakness. Once a weakness in the design has been revealed, the group would rate the weakness for severity. Now we look at the probable causes of the design weakness if the severity ranking was considered high.

On a Process FMEA, the group reviews the end product after the process for probable specification or quality (attribute) nonconformances. We would then rate them for severity and then review probable causes for the nonconformances if the severity ranking was high the same as one would in a Design FMEA.

That is how I have presented this in the past and it does seem to work. I just delivered this seminar to an aircraft part supplier (not covered by AIAG) and I presented it in the same manner.

I think that either strategy is acceptable so long as the idea is defect prevention. My thinking is that we should characterize product defects as the effects of process failures, which seems to capture the reason for the PFMEA process more directly. At any rate, we've given the OP and others some things to think about, which is a good thing. :agree:
 
D

dullpig

Re: Problem with "failure mode” interpretation in PFMEA

:agree:
I have a problem with "failure mode” interpretation in PFMEA.
For me “failure mode” is a problem with the product after operation. For my friend “failure mode” is a problem with the operation.
For example:
In material cutting operation blunt/damaged tool irregularly cuts material.
1.For me:
-Cause: blunt/damaged tool in machine
-Failure mode: irregularly cut material (product out of specification)
-Effect: scrap, customer complaint, customer line stop
2.For my friend:
-Cause: incorrect tool change period, lack of tool check during setup
-Failure mode: blunt/damaged tool in machine
-Effect: irregularly cut material (product out of specification)

My questions:
A.Which way is better?
B.Which way is correct?
C.Is it possible - both ways are correct?

I think failure mode has to be defined as process function and requirements

please see artcle FMEA from AIAG
Potential failure mode is defined as the manner in which the
process could potentially fail to meet the process requirements
and/or design intent as described in the process function/
requirements column. It is a description of the nonconformance
at that specific operation. It can be a cause associated with a
potential failure mode in a subsequent (downstream) operation
or an effect associated with a potential failure in a previous
(upstream) operation. However, in preparing the FMEA, assume
that the incoming part(s)/material(s) are correct. Exceptions can
be made by the FMEA team where historical data indicate
deficiencies in incoming part quality.
List each potential failure mode for the particular operation in
terms of a component, subsystem, system, or process
characteristic. Assume that the failure could occur but may not
necessarily occur. The process engineer/team should be able to
pose and answer the following questions:
• How can the process/part fail to meet requirements?
• Regardless of engineering specifications, what would a
customer (end user, subsequent operations, or service)
consider objectionable?
Start by comparing similar processes and reviewing customer
(end user and subsequent operation) claims relating to similar
components. In addition, a knowledge of the design intent is
necessary. Typical failure modes could be but are not limited to:
Bent Burred Hole off-location
Cracked Hole too shallow Hole missing
Handling damage Dirty Hole too deep
Surface too rough Deformed Surface too smooth
Open circuited Short circuited Mis-labeled
NOTE: Potential failure modes should be described in
"physical" or technical terms, not as a symptom
noticeable by the customer.


I think you are correct
 

Peters

Quite Involved in Discussions
Re: Problem with "failure mode” interpretation in PFMEA (Process FMEA)

:agree:
Jim Wynne, David DeLong, julsbear, dullpig thank you for your opinions. I have also response from my friends (auditors and automotive specialists) . 2/3 of them say – failure mode is defective product after operation (and I agree with them). 1/3 of them say – failure mode is weakness/mistake in process (with defective product as an effect). I think – these are two parallel ways (possibilities) of good PFMEA preparation. PFMEA should be logical, useful and acceptable for the customer – it’s main requirement.
 
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