Special Characteristics in DFMEA (Design FMEA) - Carry over to PFMEA?

Hi !
Need some help in the area of Special Characteristics (S.C.) in D-FMEA.
Shall all SC's be moved over to the P-FMEA ? if so why ?
Any tips on how to identify your own S.C.'s ?
What do you do when the customer does not give you any SC's and you still have legal requirements on the product? just use your own symbol of SC or ?

Regards
Labbe

Hello Labbe,
My recommendation is yes.
Why, because the building of these SC characteristics occurs in your manufacturing process and I wanted to keep them in control.
And yes, I will keep my own SC, maybe with a different symbol in order to not confuse my customers.
Legal matters require special attention.
I hope these recommendations help you

I agree with Vicman. Our interpretation of the requirement is that all SC's (and CC's, and Safety) characteristics MUST be included in the PFMEA and the Control Plan, if they are controlled to any extent by our processes, including those which we subcontract.

If there are no SC's on the customer supplied document, then there is no requirement to have them. However, based on your own product and process knowledge, it should be easy enough to determine what characteristics ARE critical, identify them accordingly, and include them.

Don't forget, add the legend to the PFMEA, so that the auditor (and there's bound to be one SOME day) understands that means SC (grin)

Thanks for your input both Vicman and Ron. That confirms my thoughts on the subject.

Any ideas and thoughts on how to establish SC's on a product ?
Our idea is to us 0-km and fieldfailure as one input and brainstorming with engineering, production and Quality to identify our own SC's.

Or use the DFMEA as a method to identify them? by marking functions with failuremodes which has a severity at 6-7 and where re-design is not possible so additional process control and special attentions is required. SC subsecuently marked in D-, P-FMEA, Controlplan, in operator instructions and drawings.
I'm not sure if this works since you should move over these types of failuremodes anyway to the P-FMEA so it might result in a huge number of SC's which I dont want.

Regards Labbe

Are you (or your company) responsible for the DFMEA as well?

If not, I would suggest limiting yourself to extracting the higher SEV numbers (9 and 10) and assigning them as SC's, IF AND ONLY IF they are things which can be controlled by your processes, and those of your subsuppliers.

There is no 'minimum' number of SC/CC characteristics that you have to have (try and convince some design engineers of that!), so if you have one or two, that will suffice.

As an example, take a door hinge. A very basic and simple part (at least the ones that we make are), but one which has to stand up to a lot of abuse over the years. When's the last time you heard of someone having to replace one???

For an SC, I would recommend raw material and heat treat. If both of these are correct, then the finished part will (presuming the design is correct) more than meet the performance expectations.

As another example, a seat belt buckle. As well as the above SC, I would (possibly) add as a CC the radius of the web slot opening, as this could cause premature and total failure of the assembly, resulting in death or injury to the occupant.

The list can go on and on, ad infinitum. This is where your skills, knowledge of the part, and knowledge of the process play a vital role.

If you would like to share more specific details, please PM me here (my regular email isn't working for some reason) and we can discuss it further.

Yes we are as Tier 1.
Our OEM customers requires us to do a D-FMEA. The products we develop and manufacture are electronics devices which can include all up to 20 mechanical parts and hundreds of electronic components. Typical parts are injection moulded plastics and sheet metal. Electronic componets all from small SMD resistors, cpu's, Pcb's, LCD displays etc. We don not manufacture the mechanical parts our selfs we manufacture circuitboards and makes the final assembly of the product.

We are strugling not just with SC's but the DFMEA as well due to the large number of parts and functions the product has, it not just limited to mech and electronic parts it has software to ! But we has left that out.

The reason for me asking about SC's is that I'm about to release a update on our instructions and guidelines due to a remark on a TS audit.

Thanks to your input things are clearer.
Labbe

As the design-responsible agency, your job is now easier (and much more difficult at the same time).

Your design team needs to determine what is and is not a critical or significant characteristic. Evaluation and determination should follow some fairly simple guidelines.

EXAMPLE (These are not official guidelines, these are my own PERSONAL guidelines which I have used in the past, and which have been accepted as satisfactory by customers and auditors)

Which failure(s) will cause, WITHOUT WARNING, injury or death to vehicle occupants? (I am presuming that you are supplying automotive). Those would be CC's, with a SEV of 10.

Which failure(s) will cause, WITH WARNING, injury or death to occupants, or will cause the assembly to fail to properly function (i.e. unable to release seat belt buckle, unable to unlock doors, etc), resulting in potential of injury or death to occupants. These would be CC's, with a SEV of 9.

SC's would involve failure to function of the assembly which would NOT result in injury or death (i.e. ignition fails to spark, lights don't turn on) but which DO result in a total failure of the system. This would be a SEV 10

Failures which involve a MAJOR inconvenience to the occupant (seat motor does not function consistently, cannot fine-adjust seat position) would be a SEV 9.

Remember, the FMEA manual only SUGGESTS the scoring system to use, it is not mandatory. You can develop your own company, process, or part-specific scoring system, based on your knowledge of your systems. As long as it is consistent, and your customer accepts it, then it's fine.

Remember that a DFMEA is an FMEA on the failure modes of the DESIGN (product functions) while a PFMEA addresses the failure modes of the manufacturing PROCESS(es). Apples and oranges. Not every design SC will necessarily carry over.

Marc is correct....I usually don't work with DFMEA, hence the oversight in clarification.

Thanks for your input. We have TS aduit tomorrow, so we will see how it goes.