Informational How to develop a Control Plan from a PFMEA (Process FMEA)

Apex Hao

Starting to get Involved
Thanks for the reply Tagin ;)

For point #1, the manufacturing process has been well designed (e.g. poka yoke) that the likelihood of misassembly and/or error is low. So essentially the test station is a detective control to mitigate failure from design -- as far as I know PFMEA should only include controls to mitigate failure from process, so I am not sure if this is something to be included inside PFMEA.

On the 2% reject, I might say it is a mixture of design/fabrication tolerance. E.g. imagine 5 parts to be fitted together, but due to respective tolerances in dimension, at worst case scenario the gap could be too big and cause excessive leakage along the path, thereby reducing the flowrate. It is quite costly to control all these tolerances to a tighter spec as compared to implementing the test station, so several parts of "the right spec" which are "assembled correctly", could still be failing the total flowrate requirement due to the said tolerance.

Jim Wynne

My queries are:
1. This total flowrate is a significant characteristic in DFMEA which is linked directly to CP without going through PFMEA. Is this ok? I have seen multiple responses saying that PFMEA and CP should always be linked.
Insofar as linkage is concerned, risks identified in the DFMEA should be addressed to the extent possible in the PFMEA. This doesn't mean that everything in the DFMEA must appear in the PFMEA. In like manner, the PFMEA process is intended to identify controls needed in production, and not everything that appears in the PFMEA will necessarily be in the control plan.
2. Is it logical to lower DFMEA RPN score since there is a detection in production? It doesn't seem right to mix DFMEA and PFMEA (or CP in this example), but it does not feel right either to keep a high RPN in DFMEA whereby the risk can be mitigated before reaching customer.
The purpose of the DFMEA is to identify and mitigate, where possible, defects in the design. You've done that. The DFMEA RPN in this instance, in its final form, should be left alone.


Starting to get Involved
Here they are. Just in case you are trying to get into a few more details, here's the key to all the abbreviations. Abbreviations are your friend on these documents. They should be concise guidelines to your control. Do not write level 3 test procedures here!
PM = Procedures Manual (our "Quality Manual")​
PR = Product Realization​
BOM = Bill of Materials​
WI = Work Instruction (a.k.a. Level 3 procedure)​
SAR = Supplier Action Request​
PCB = Printed Circuit Board​
SMT = Surface Mount Technology​
KCC = Key Control Characteristic = § (the generic symbol for KCC)​

Please note that you absolutely must cover the KCCs in your PFMEA and Control Plan and they should be marked with § (or your customer's required symbol). Furthermore, if you have lower level procedures that specify how to measure they should be marked there and anyplace you record them §.

Note the connection between the # column on the PFMEA (e.g. 01-01) with the Part/Process Number column (e.g. 1) on the Control Plan. The only characteristics on the Control Plan that I have broken out specifically are the KCC's. They are all listed as one item on the PFMEA (07-01) so they are listed on the the Control Plan in Part/Process Number 7 but all have the same characteristic number 1. If you really want to get technical, these should be listed on the PFMEA as 07-01, 07-02 and 07-03 then listed on the Control Plan as Part/Process Number 7 and characteristics 1, 2, 3. That level of detail is probably overkill. Make sure that you are matching the Process/Function Requirements Number to the Part/Process Number and you should have enough for most folks to connect everything together.
Hi, thank you for the methodology, what I understood is that the only visible link between PFMEA and control plan is the number and the proces name. please could it be a case where the a caracteristic is more broken down in the PFMEA than in the control plan ? for example in the of masking process of a some areas of a part in order for them to not get painted, in the FMEA. we can state that the failures are : 1) masking an area that should be painted, 2) completly not masking and area, 3) lost of masking during the next processes, and failure in masking tool. in the control plan, we can re-assemble 1, 2, qnd 3 in 1 caracteristic which is Presence and correct location of masking as product caracteristic, and Failure of masking tool as process caracteristic. is it correct ? thanks
Top Bottom