Process FMEA (PFMEA) Assumptions Regarding Causes Identification

[Marcelo - 2008]

Dear all,

When listing potential failure modes (PFMs) within a specific process step, we need to consider that expected outcomes of previous steps have fulfilled requirements. However, once we have identified the PFMs - limited to the boundaries of a specific process step - as well as their effects and start listing the causes, my understanding is that we may list any cause regardless of where it is originated, such that one cause may appear for multiple PFMs in different process steps. Am I correct?

Thank you!

 

[Jim Wynne]

Re: Process FMEA Assumptions Regarding Causes Identification

Dear all,

When listing potential failure modes (PFMs) within a specific process step, we need to consider that expected outcomes of previous steps have fulfilled requirements. However, once we have identified the PFMs - limited to the boundaries of a specific process step - as well as their effects and start listing the causes, my understanding is that we may list any cause regardless of where it is originated, such that one cause may appear for multiple PFMs in different process steps. Am I correct?

Thank you!

Potential causes should be restricted to the operation under consideration, with the exception of inspection operations, where the state of the incoming material is in question. If operation #1 has been properly addressed, and potential causes of defects have been tabulated, there should be no need to address the same causes in operation #2. The effects of the potential failure modes addressed in operation #1 should include adverse effects on operation #2, or any other operation in any other process, that's a "customer" of operation #1.

 

[David DeLong]

Re: Process FMEA Assumptions Regarding Causes Identification

Potential causes should be restricted to the operation under consideration, with the exception of inspection operations, where the state of the incoming material is in question. If operation #1 has been properly addressed, and potential causes of defects have been tabulated, there should be no need to address the same causes in operation #2. The effects of the potential failure modes addressed in operation #1 should include adverse effects on operation #2, or any other operation in any other process, that's a "customer" of operation #1.

I agree with Jim on restricting the potential causes to the current process operation (per AIAG guidelines) although Jim and I do differ on whether process FMEAs are applied to inspection but that is another subject.

 

[Marcelo - 2008]

Re: Process FMEA Assumptions Regarding Causes Identification

Wouldn't there be an exception when previous operations have been left out of the FMEA? Then, in such case, causes coming from left-out operations could be considered? Even because otherwise they wouldn't appear anywhere else. One example: a process FMEA applied to a chemical mfg process. Let's say the team decides to cover from production planning to product release. Consider we are listing causes of PFMs at the production planning step and that the lack of standardized formulas (that should be made available by the left-out product development step, for instance) is one of the causes. Shouldn't such cause be listed then?

 

[Jim Wynne]

Re: Process FMEA Assumptions Regarding Causes Identification

Wouldn't there be an exception when previous operations have been left out of the FMEA? Then, in such case, causes coming from left-out operations could be considered? Even because otherwise they wouldn't appear anywhere else. One example: a process FMEA applied to a chemical mfg process. Let's say the team decides to cover from production planning to product release. Consider we are listing causes of PFMs at the production planning step and that the lack of standardized formulas (that should be made available by the left-out product development step, for instance) is one of the causes. Shouldn't such cause be listed then?

No. The previous PFMEA(s) should be updated to include the new information. If there is no upper-level PFMEA, you've just described why there should be one. If you know about the issue (lack of standardized formulas) downstream, why didn't they know about it in the beginning and account for it?

 

[Marcelo - 2008]

Re: Process FMEA Assumptions Regarding Causes Identification

Dear Jim, as I don't have a downstream PFMEA - covering the product development step -, would you recommend I add such step prior to the production planning one (first in the example mentioned)?

 

[Jim Wynne]

Re: Process FMEA Assumptions Regarding Causes Identification

Dear Jim, as I don't have a downstream PFMEA - covering the product development step -, would you recommend I add such step prior to the production planning one (first in the example mentioned)?

It's an upstream step that's causing the worry, no? In other words, a process that proceeds (or should proceed) the one for which you're doing the PFMEA? You've identified a potential source of variation that can't be controlled within the process, which means that your own PFMEA is at least partially premature. These things need to work from the top down, not the other way around. This means that you need to take care of those issues, and if that means a higher-level PFMEA, then that's what should be done.