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Failure Mode Identification in PFMEA according to AIAG FMEA Rev.4

Z

Zbigniew Huber

#1
Hi,

I?d like to ask you how to properly approach to identification of potential failure modes in PFMEA according to AIAG FMEA Rev.4.

Let?s consider brazing process of two pipes in air conditioning unit in a vehicle.

Approach 1:

Process step: 50. Brazing
Function: Braze pipes in induction device
Requirements: Solder alloy uniformly bonds both components with no cracks, pinholes or holes.
Failure mode: Holes in solder alloy
Effects: End user->Coolant leak, air conditioner non operable (6), Manufacturing->Scrap (7)
Severity: 7
Cause: Brazing time too short, incorrect setup program selected


Approach 2:

Process step: 50. Brazing
Function: Braze pipes in induction device
Requirements: Proper brazing time
Failure mode: Brazing time too short
Effects: Product effect: Holes in solder alloy, End user->Coolant leak, air conditioner non operable (6), Manufacturing->Scrap (7)
Severity: 7
Cause: Incorrect setup program selected

In my opinion the AIAG FMEA Rev.4 says Approach 1 is preferred due to following:

AIAG FMEA Rev.4 page 71:
The PFMEA development continues by identifying the requirement(s) for each process/function. Requirements are the outputs of each operation/step and relate to the requirements for the product. The Requirements provide a description of what should be achieved at each operation/step. The Requirements provide the team with a basis to identify potential failure modes.

AIAG FMEA Rev.4 page 112 (about linkage between PFMEA and Control Plan):
?Product Characteristics? portion of the Control Plan may be derived from the ?Requirements? portion of the ?Process Function/Requirements? column and the ?Process Characteristics? portion may be derived from the ?Potential Cause(s) of Failure Mode? column.

For me the requirements in the PFMEA are ?expected results? from the given operation (what we want to achieve when we complete the operation) and in the above example the product characteristic should be in the requirement for value added operations and process characteristic (brazing time) is related to the potential cause.

I understand that both approaches give similar results and someone could say that both are good, but I need to clarify this for a discussion with my colleagues and how to follow the AIAG FMEA manual.

Best Regards,
Zbigniew
 
#4
I cansee what you mean - in relation to page 71 in the manual.
But how is that related to page 81 with an example of requirements in the manual?
A bit ambigous - or is it just me?

Jan
 
G

Grimaskr

#5
I'm no expert, but these questions usually circle around "analysis depth".

You could take a "too high" analysis depth and say that a requirement of the brazing process is that the AC works or that the sealant doesn't leak. However, most people will agree that those failure modes are a little removed from where your focus needs to be during the brazing step itself.

You could also take a "too microscopic" analysis depth and say that a requirement of the brazing process is that brazing time is correct, brazing temperature is correct, brazing solder is correct, brazing solder is not expired, brazing equipment is functioning correctly... et cetera.

When you drill in too close, you can find yourself mired in many requirements and your FMEA becomes a bit of a nightmare.

So I agree with Approach 1, the requirement of the brazing process is a quality brazed joint. Failure mode is a "non-quality" brazed joint (holes/cracks), and the causes can be things like too little braze time.
 
Z

Zbigniew Huber

#6
I cansee what you mean - in relation to page 71 in the manual.
But how is that related to page 81 with an example of requirements in the manual?
A bit ambigous - or is it just me?

Jan
Maybe it is a bit ambiguous, that's why I ask

IMO, page 81 and page 71 have a same meaning.

The requirements in the example shown in page 81 are typical product related requirements (design intent / spec / drawing). Examples from p.81 are in black, my comments are in blue.

Four screws - it is design intent / drawing spec.
Specified screws - it is design intent / drawing spec.
Assembly sequence: - most likely it is also a design req. specified in engineering drawing
Screws fully seated: - it is design intent / drawing spec.
Screws torqued to dynamic torque specification - it is design intent / drawing spec.


Additionally please consider the following:

The failure mode when occurred is "experienced" by customers - it is called "effects". Customers in PFMEA are: next operation, next line, next factory, OEM, product end-user, law regulator.

So next operation (the closest customer) may only experience the "faulty outcome" (hole in solder joint) from the upstream operation. The customer can not experience incorrect process parameter of the upstream operation (i.e. too short brazing time), because the upstream process parameter no longer exists at customer location.
Only results of the upstream operation exist in downstream processes (customers) so the "faulty results" of the upstream operation are failure modes.

That is my understanding so far..

BR,
Zbigniew
 
Last edited by a moderator:
#7
I think you are right in how to interpret the requirements on page 81.
Thank you! That clarified a lot for me.

Regarding the effects, I am not sure if they will differ using one or the other approach.

Jan
 
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