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D
Don Watt
Thanks Paul -usefil clip.
I'm still a little confused, maybe a little more detail may help the forum in trying to sort out my problems.
Do we need to include every process step (including inspection, or simply the operations that amy cause defects?)Would we class defects not found by an unstable inspection system as failure modes?
How specific do we need to be regarding potential effects of failure to the customer.
One point of view is that any defect reaching the customer could be classified as "Customer receives defective component"
I believe that this is far too general & that we should go into more detail, e.g. "Groove out of position , cannot fit to gearbox assembly" The severity rating would reflect how serious an individual problem may be, but does the FMEA need to include the detail for reference?
My view is that we should attempt to "Describe the effects of the failure in terms of what the customer might notice or experience ..... stated in terms of product or system performance.
Hope somebody can help me with this
TIA
[This message has been edited by Don Watt (edited 10 July 2000).]
I'm still a little confused, maybe a little more detail may help the forum in trying to sort out my problems.
Do we need to include every process step (including inspection, or simply the operations that amy cause defects?)Would we class defects not found by an unstable inspection system as failure modes?
How specific do we need to be regarding potential effects of failure to the customer.
One point of view is that any defect reaching the customer could be classified as "Customer receives defective component"
I believe that this is far too general & that we should go into more detail, e.g. "Groove out of position , cannot fit to gearbox assembly" The severity rating would reflect how serious an individual problem may be, but does the FMEA need to include the detail for reference?
My view is that we should attempt to "Describe the effects of the failure in terms of what the customer might notice or experience ..... stated in terms of product or system performance.
Hope somebody can help me with this
TIA
[This message has been edited by Don Watt (edited 10 July 2000).]
P
Paul Vragel
Don - let's try some specifics:
You mentioned a "groove out of position - can't fit to gearbox assembly" as one example.
Can't fit to gearbox assembly is one failure mode
Causes could be:
Groove out of position
Diameter too large
Taper incorrect
A correlation diagram can help you identify where in your process these defects can be created (what process steps affect what results). These process steps need to be looked at for occurrence.
Inspection is a detection mechanism, rather than a failure mode. An unstable inspection system means you have a diminished ability to detect problems, so a higher detection number (for RPN).
One failure mode (as above), may involve multiple process steps, each with its own occurrence and detection situation (i.e., a separate line on the FMEA).
As you correctly note you should also consider the different severity to the customer of failures.
For example, a "less severe" failure might be a cosmetic defect that has no effect on performance, but is noticed by the customer.
On the other hand, a part that fits in the gearbox, but later fails for some reason, could likely be a "more severe" failure, due to potentially dangerous results for the ultimate customer, high warranty costs for the gearbox manufacturer etc.
------------------
Paul
You mentioned a "groove out of position - can't fit to gearbox assembly" as one example.
Can't fit to gearbox assembly is one failure mode
Causes could be:
Groove out of position
Diameter too large
Taper incorrect
A correlation diagram can help you identify where in your process these defects can be created (what process steps affect what results). These process steps need to be looked at for occurrence.
Inspection is a detection mechanism, rather than a failure mode. An unstable inspection system means you have a diminished ability to detect problems, so a higher detection number (for RPN).
One failure mode (as above), may involve multiple process steps, each with its own occurrence and detection situation (i.e., a separate line on the FMEA).
As you correctly note you should also consider the different severity to the customer of failures.
For example, a "less severe" failure might be a cosmetic defect that has no effect on performance, but is noticed by the customer.
On the other hand, a part that fits in the gearbox, but later fails for some reason, could likely be a "more severe" failure, due to potentially dangerous results for the ultimate customer, high warranty costs for the gearbox manufacturer etc.
------------------
Paul
P
Paul Morrow
Don
I agree that it is often difficult to judge the level of detail when preparing FMEAs, coz as we all know its a PAIN to do it properley. I look upon it as a test of my character (sad!). Saying that it can be satisfying to know you've covered all angles (helped prompt many process improvements here).
To make it more manageable you could try breaking a process down into sub-processes and tackling each in turn, progressively working through the process.
We try to keep things as simple as possible here and brainstorm the following questions in turn:
1. What can go wrong?
2. How likely is it to go wrong?
3. Will our current controls find it if it has gone wrong?
If you follow this simple sequence you may well find that it gives weight and authority to overcoming issues such as 'unstable' inspection systems (if I've got your drift).
I find the real value of FMEAs is that it allows you and your team to understand your process. Of course customer requirements must be considered but if you focus soley on them you run the risk of missing out on opportunities for real process improvement.
As a final point I would suggest that "Customer receives defective component" is not a failure mode, its a pissed off customer.
I agree that it is often difficult to judge the level of detail when preparing FMEAs, coz as we all know its a PAIN to do it properley. I look upon it as a test of my character (sad!). Saying that it can be satisfying to know you've covered all angles (helped prompt many process improvements here).
To make it more manageable you could try breaking a process down into sub-processes and tackling each in turn, progressively working through the process.
We try to keep things as simple as possible here and brainstorm the following questions in turn:
1. What can go wrong?
2. How likely is it to go wrong?
3. Will our current controls find it if it has gone wrong?
If you follow this simple sequence you may well find that it gives weight and authority to overcoming issues such as 'unstable' inspection systems (if I've got your drift).
I find the real value of FMEAs is that it allows you and your team to understand your process. Of course customer requirements must be considered but if you focus soley on them you run the risk of missing out on opportunities for real process improvement.
As a final point I would suggest that "Customer receives defective component" is not a failure mode, its a pissed off customer.
B
Brian Dowsett
Don,
My 0.02 punts worth.
In answer to your first question about including inspection, I think you're refering to a physical process step here, as in a test station which is part of the manufacturing process. Although, as already pointed out, this will constitute a means of detection for earlier (in the process) failure modes, I think you are trying to capture things that can go wrong with the station itself. In this case I'd say yes you should include it as a process step. As you suggest, a failure mode for an inspection station might be that the gauge becomes unstable- and you would then apply severity occurence and likelyhood of detection to that scenario.
On the other point I'd definitely get as much detail recorded regarding the effect on the customer. For some reason a lot of people try to generalise these effects into bland statements like "defective material to the customer". If this is done, as you say the severity will make some differentiation but when you, or the next person in the job, goes back to the fmea, they may not understand what the thinking was at the time. Therefore if the effect to the customer is "groove out of position" then write that down on the form. I'd even go further and say "Groove out of position leading to poor fit with associated part, leading to premature wear, noise, and associated warranty claims"
Another thing I've seen a lot (soapbox time)
is Engineers trying to couch everything in technical jargon on fmeas. We'll have our meeting and discuss how this failure results in a split seal and grease running out, but can we write "seal splits and grease runs out" ?
No, someone has to try to think of a more complicated phrase like "Part subject to stress failure resulting in egress of lubrication medium"
My opinion is that on the first day a student sits in your office bored sh**less, you should be able to hand him the fmea book and the process flow charts, and in a few hours he'll have a good idea of how the process goes and what can go wrong.
Cheers Don
My 0.02 punts worth.
In answer to your first question about including inspection, I think you're refering to a physical process step here, as in a test station which is part of the manufacturing process. Although, as already pointed out, this will constitute a means of detection for earlier (in the process) failure modes, I think you are trying to capture things that can go wrong with the station itself. In this case I'd say yes you should include it as a process step. As you suggest, a failure mode for an inspection station might be that the gauge becomes unstable- and you would then apply severity occurence and likelyhood of detection to that scenario.
On the other point I'd definitely get as much detail recorded regarding the effect on the customer. For some reason a lot of people try to generalise these effects into bland statements like "defective material to the customer". If this is done, as you say the severity will make some differentiation but when you, or the next person in the job, goes back to the fmea, they may not understand what the thinking was at the time. Therefore if the effect to the customer is "groove out of position" then write that down on the form. I'd even go further and say "Groove out of position leading to poor fit with associated part, leading to premature wear, noise, and associated warranty claims"
Another thing I've seen a lot (soapbox time)
is Engineers trying to couch everything in technical jargon on fmeas. We'll have our meeting and discuss how this failure results in a split seal and grease running out, but can we write "seal splits and grease runs out" ?
No, someone has to try to think of a more complicated phrase like "Part subject to stress failure resulting in egress of lubrication medium"
My opinion is that on the first day a student sits in your office bored sh**less, you should be able to hand him the fmea book and the process flow charts, and in a few hours he'll have a good idea of how the process goes and what can go wrong.
Cheers Don
M
Mike1245
Don:
In answer to your question about what to include on the FMEA - a good first step is do as the FMEA manual suggests, start with a flow chart / risk assessment. In appendix C of the manual you'll find an example (and as with most AIAG examples it's not the best, but it should get the idea across). The primary wording on pg 51 in the manual, though, is asteriked at the bottom, *FMEA Required (high risk). The example corresponds to the FMEA form layout for the Process FMEA starting on page 25. In other words, no, you don't have to list every single potential failure mode (if you choose not to), but those that are identified as being high risk per the risk assessment MUST be included on an FMEA. It's a good tool, and gives the user a pretty good idea of where to start. The only problem is defining high risk, and that, to an engineer, is any risk at all, with the end result of every prcess step being put on the FMEA anyway.
In answer to your question about what to include on the FMEA - a good first step is do as the FMEA manual suggests, start with a flow chart / risk assessment. In appendix C of the manual you'll find an example (and as with most AIAG examples it's not the best, but it should get the idea across). The primary wording on pg 51 in the manual, though, is asteriked at the bottom, *FMEA Required (high risk). The example corresponds to the FMEA form layout for the Process FMEA starting on page 25. In other words, no, you don't have to list every single potential failure mode (if you choose not to), but those that are identified as being high risk per the risk assessment MUST be included on an FMEA. It's a good tool, and gives the user a pretty good idea of where to start. The only problem is defining high risk, and that, to an engineer, is any risk at all, with the end result of every prcess step being put on the FMEA anyway.
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