Process Flow Diagram -> PFMEA -> Control Plan Linkage

Mortalis

Involved In Discussions
#1
Good day everyone,

I am updating our Process Flow, PFMEA and Control Plans. I have a few questions regarding their content. The documents that are currently in our system are, IMO, too generic yet they contain unnecessary steps.

Process Flow:
We have been using the Process Flow format presented in the download from the AIAG. Currently we have steps such as, transport material to storage rack, transport material to <next process>. We have not experienced any issues during the transport of material to storage or to a process step. Its not like these steps move the material further than 10 feet during the process.
Are steps such as these necessary to list on the Process Flow?
Why is there a "movement" column in the AIAG Process Flow format?

PFMEA:
Our PFMEA lists every process step that is in the Process Flow (see Process Flow questions for clarity).
Is it necessary to list every Process Flow step in the PFMEA even if there is no history of issues at certain process steps (again, see the Process Flow questions for clarity)?

Control Plan:
Our Control Plan lists every step contained in the Process Flow and PFMEA. My understanding is that only items that can affect the outcome of the process to the customer be that internal or external need to be on the Control Plan.
Is it necessary to list every Process Flow and PFMEA step in the Control Plan?

TIA

Kevin
 
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#2
Process Flow: movement is not required in my opinion. I have seen many flows without it. On other hand, it could be helpful, for example with outsourced processes. There are risks that must be analyzed.

PFMEA: yes, every process step must be in the PFMEA. Every control must be listed in the PFMEA. That is the proper way to justify low occurrence and good detection. If there is not a history of issues, then list all the controls that prevent and detect issues.

Control Plan: The TS standard only states that special characteristics must be on the control plan (7.5.1.1) and it states "list the controls" (and does not state all the controls). The control plan does not have to have all the process steps.

The goal is to identify all the controls in the PFMEA and reduce the size of the control plan. Drive down occurrence and improve detection / prevention.
 

Mortalis

Involved In Discussions
#3
@Kayes
Thank you for the reply.
You missed the point I was trying to get an answer to and that was does the PFMEA need to reflect all the steps in the Process Flow not the Process. I understand all the Process steps need to be represented but I guess my question stems from the fact that our Process Flow has, IMHO, "unnecessary" detail.
 
A

adamsjm

#5
You may wish to study the Characteristic Matrix. It is basically the Phase 3 QFD matrix. Requirements (print, engineering specs., shipping requirements, etc.) are listed on the vertical side of the matrix. The process flow is listed horizontally across the matrix (basically your VSM). When a requirement intersects with a process you place a 9, 3, or a 1 at the intersection depending if there is a very strong, strong, or weak relationship.
Examine the matrix. If you have a requirement without a process to develop it, you have missed something. If you have a process with no requirement, then why are you performing (or going to perform) the non-value added process? [Are you doing "stuff" because you like doing it?]

You have now balanced you requirements with your processes.

Now, add the requirements need to perform the processes. Determine the failure modes of all of the requirements. This will lead to additional value added processes. Rank the Severity of the failure modes and, wa-la, you have completed you PFD and the first columns of your PFMEA.

With some work you can complete the PFMEA and Control Plan. This may mean a lot of work. That is why a company desires to use standardized work / processes which can be reused.

Also read as much as possible. Material motion is extremely important to efficiency and quality. NEVER move finished product counter to workflow. Unfinished parts will appear in finished goods containers. Always move material to be scraped or reworked counter to workflow. If a piece looses containment it will be caught by the process again. If the material to be scraped or reworked is not moved counter to the work flow, it is possible to have non-conforming material reach conforming material containers.
"U-cells" (or better yet "horse-shoe" cells) are a more efficient manufacturing layout than an "assembly Line"

This is one reason why process movement is to be analyzed in the PFMEA. There are many more (depending upon what business you are in.)
 
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Mortalis

Involved In Discussions
#6
According to the Process Failure Mode and Effects Analysis book 4th edition, "In preparing the FMEA, assume that the incoming part(s)/material(s) are correct. Exceptions can be made by the FMEA team where historical data indicate deficiencies in incoming part quality"

Incoming inspection "steps" should not be included in the PFMEA?

We also have a step that creates a "set-up" piece that is used for making adjustments to the process to bring it into nominal.
Again, using the idea that incoming parts are correct I feel this is an uncessary step. The step is used to tweak the process. Realistically, nothing could go wrong with this step as it almost always creates a bad part which is used to determine modifications to the line.
 
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Jim Wynne

Staff member
Admin
#7
According to the Process Failure Mode and Effects Analysis book 4th edition, "In preparing the FMEA, assume that the incoming part(s)/material(s) are correct. Exceptions can be made by the FMEA team where historical data indicate deficiencies in incoming part quality"

Incoming inspection "steps" should not be included in the PFMEA?
In the production process, it should be assumed that material entering an operation is conforming. An exception would be a discrete inspection operation, where the state of incoming material is, by definition, unknown. There are varying opinions as to whether inspections (again, as discrete operation) should be included in the PFMEA. I say they should be, as they are a point of potential failure.
 

Mortalis

Involved In Discussions
#8
That would be a potential failure of the part not the process. How could you ever know that the state of the incoming part is known without an inspection step of some kind? :cool:
PFMEA is supposed to evaluate the process with the contention that the "gosinto" goes into, otherwise you cannot evaluate the process without a gosinto to come out the other end. :notme:.
 

Jim Wynne

Staff member
Admin
#9
That would be a potential failure of the part not the process. How could you ever know that the state of the incoming part is known without an inspection step of some kind? :cool:
PFMEA is supposed to evaluate the process with the contention that the "gosinto" goes into, otherwise you cannot evaluate the process without a gosinto to come out the other end. :notme:.​
The whole PFMEA is a theoretical construct, not a documentary. The idea behind assuming that material entering a process is conforming is that you should be concentrating on potential failure modes of each operation independently of what happened upstream. You have (or should have) already considered upstream operations in the PFMEA before you get to the one in question.

If you feel that inspection is necessary between operations, that's fine. You still shouldn't assume, using your logic, that just because WIP has been inspected that it must be in conformance. You treat the inspection operation separately on the PFMEA/
 

toniriazor

Involved In Discussions
#10
Good Afternoon,

Can someone please give clear explanation why before DFMEA it is required to have a Preliminary Process Flow Diagram as per APQP phase 1 and later on during Process Design and Development APQP phase 3 we should have process flow as well ? I never received process flow diagram in APQP phase 1 in my short practice so far.

thank you.
 
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