PFMEA for a Membrane Assembly - Automotive Application

ROOTS

Involved In Discussions
#1
Hello,

Can any one help me on the following querry?

We are an ISO/TS 16949 company manufacturing Automotive parts.

We are having different types of process and we have PFMEA for all process.

One of the process is measuring a membrane assembly and the requirement is height of the membrane assembly. The membrane assembly is assembled by spacers and washers and the height will be measured. Due to cumulative tolerance variation in the Spacers / washers, if the height is not achieved the membrane assembly will be reworked to achieve the required height by adding or removing washers. (May be 50% of the assemblies are reworked). The height will be measured 100% for all the membrane assemblies to check whether the height is within the specification. If the height is within the specification then only the assembly will be moved to next operation.

We have prepared a PFMEA stating the Failure mode as "Diaphragm assembly height not within the limit" and given the occurance rating as 1 because all the membrane assemblies are checked 100% for height and none of the assemblies will moved to next operation if the required specification is not met. Hence there is no failure in meeting the height when the assemblies are move to next operation. Whether our understanding is correct or we have to consider the rework at the individual stage and rate the occurance accordingly?

Pl help?
 
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Jim Wynne

Staff member
Admin
#2
Re: Pfmea

Hello,

Can any one help me on the following querry?

We are an ISO/TS 16949 company manufacturing Automotive parts.

We are having different types of process and we have PFMEA for all process.

One of the process is measuring a membrane assembly and the requirement is height of the membrane assembly. The membrane assembly is assembled by spacers and washers and the height will be measured. Due to cumulative tolerance variation in the Spacers / washers, if the height is not achieved the membrane assembly will be reworked to achieve the required height by adding or removing washers. (May be 50% of the assemblies are reworked). The height will be measured 100% for all the membrane assemblies to check whether the height is within the specification. If the height is within the specification then only the assembly will be moved to next operation.

We have prepared a PFMEA stating the Failure mode as "Diaphragm assembly height not within the limit" and given the occurance rating as 1 because all the membrane assemblies are checked 100% for height and none of the assemblies will moved to next operation if the required specification is not met. Hence there is no failure in meeting the height when the assemblies are move to next operation. Whether our understanding is correct or we have to consider the rework at the individual stage and rate the occurance accordingly?

Pl help?
Somewhere within your process there's a cause for the inconsistency in assembly height. If that cause has been identified and it's been decided that the best way to proceed is to measure and adjust (as needed) all assemblies, the fact that an assembly doesn't initially meet the height requirement isn't a "failure"--it's an expected result. It seems to me that your risk is in passing nonconforming assemblies after measurement and adjustment, and from what you say, that risk is negligible and worthy of a relatively low "Occurrence" number. Whether that number is 1 or something higher is a matter of how your rating system is defined.
 

ScottK

Not out of the crisis
Staff member
Super Moderator
#3
Re: Pfmea

Hello,

Can any one help me on the following querry?

We are an ISO/TS 16949 company manufacturing Automotive parts.

We are having different types of process and we have PFMEA for all process.

One of the process is measuring a membrane assembly and the requirement is height of the membrane assembly. The membrane assembly is assembled by spacers and washers and the height will be measured. Due to cumulative tolerance variation in the Spacers / washers, if the height is not achieved the membrane assembly will be reworked to achieve the required height by adding or removing washers. (May be 50% of the assemblies are reworked). The height will be measured 100% for all the membrane assemblies to check whether the height is within the specification. If the height is within the specification then only the assembly will be moved to next operation.

We have prepared a PFMEA stating the Failure mode as "Diaphragm assembly height not within the limit" and given the occurance rating as 1 because all the membrane assemblies are checked 100% for height and none of the assemblies will moved to next operation if the required specification is not met. Hence there is no failure in meeting the height when the assemblies are move to next operation. Whether our understanding is correct or we have to consider the rework at the individual stage and rate the occurance accordingly?

Pl help?
I'm coming from a medical device perspective, but here's my 2 cents:

First - inspection is represented in the Detection number, not Occurrence.
Occurrence would be the 50% rework you say in the first paragraph, which would be a pretty hight number.

Second - I would not give 100% inspection a 1 for detection unless it is fully automated (and validated) inspection. If it's 100% manual inspection I would give it 5 on my scale. Fully Automated inspection is the only way I'd give 1 for detection.

(The scale I use is based on GE Heatlhcare's RPN guide)
 
#4
Re: Pfmea

We have prepared a PFMEA stating the Failure mode as "Diaphragm assembly height not within the limit" and given the occurance rating as 1 because all the membrane assemblies are checked 100% for height and none of the assemblies will moved to next operation if the required specification is not met. Hence there is no failure in meeting the height when the assemblies are move to next operation.
Well... I agree that the rating should be low, but suppose the measuring equipment goes awry?

/Claes
 
#6
Re: Pfmea

Thanks Claes for your reply,

But the measuring equipment is maintained and calibrated with a specified frequency and there is no chance of going away...
Good. I expected as much, :agree1: but with all due respect, there is always a risk (albeit a small one) that something happens to the equipment between calibrations.

/Claes
 

ROOTS

Involved In Discussions
#7
Re: Pfmea

I'm coming from a medical device perspective, but here's my 2 cents:

First - inspection is represented in the Detection number, not Occurrence.
Occurrence would be the 50% rework you say in the first paragraph, which would be a pretty hight number.

Second - I would not give 100% inspection a 1 for detection unless it is fully automated (and validated) inspection. If it's 100% manual inspection I would give it 5 on my scale. Fully Automated inspection is the only way I'd give 1 for detection.

(The scale I use is based on GE Heatlhcare's RPN guide)

Thanks ScottK,

As you said we have given the detection rating 5 only and not 1 since this is 100% manual inspection. But i would like to know what the occurance rating has to be given? The confusion is, 50% rework done at this stage, so whether we have to give the rating as high (more than 5) or it is measured and adjusted before passing to next stage, so whether we have to give low occurance rating (i.e 1)
 
I

Ingo1966

#8
Re: PFEMA for a Membrane Assembly - Automotive Application

Hello,

as allready stated from the Gentlemen here

WHAT are the CAUSES from the Failure Mode "Diaphragm assembly height not within the limit" ?

There might be several reasons why these Operation failed.

And for these reasons (Causes of the Failure) the Team gives an assesment of how often it happens (Occurence).

Also for every single reason (causes of the Failure) the Team discusses "Clever Prevention" and Dedection for the cause or the subsequent Failure.
 

ScottK

Not out of the crisis
Staff member
Super Moderator
#9
Re: Pfmea

Thanks ScottK,

As you said we have given the detection rating 5 only and not 1 since this is 100% manual inspection. But i would like to know what the occurance rating has to be given? The confusion is, 50% rework done at this stage, so whether we have to give the rating as high (more than 5) or it is measured and adjusted before passing to next stage, so whether we have to give low occurance rating (i.e 1)
Here's how I'm visualizing the flow...

1. Assemble
2. Measure - if with in spec then pass on to next process, if not then...
3. Adjust
4. Measure
5. Pass on to next process

is that about right?
 

Chennaiite

Never-say-die
Trusted Information Resource
#10
Re: Pfmea

Somewhere within your process there's a cause for the inconsistency in assembly height. If that cause has been identified and it's been decided that the best way to proceed is to measure and adjust (as needed) all assemblies, the fact that an assembly doesn't initially meet the height requirement isn't a "failure"--it's an expected result. It seems to me that your risk is in passing nonconforming assemblies after measurement and adjustment, and from what you say, that risk is negligible and worthy of a relatively low "Occurrence" number. Whether that number is 1 or something higher is a matter of how your rating system is defined.
This makes lot of sense. It is very important how the Top Management sees the adjustment activity. If the focus is on eliminating or reducing the thing, 'Wrong height' would be the appropriate Failure mode, tolerance stack up - the cause and your occurrence rating shall correspond to 50% rework. Other way around, if adjustment is considered the most feasible option, it becomes part of the process flow and failure mode could read 'wrong height setting' of sorts.
 
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