A PFMEA, or process failure mode and effects analysis, is a structured list of the ways each manufacturing step could go wrong, what that would do to the part, and how likely it is. A control plan is the working document that says which checks the plant will run, how often and what it will do when a check fails.
The two belong together. The PFMEA finds the risks, and the control plan turns them into daily routines on the shop floor.
How a PFMEA works
The team takes each step of the process flow, such as turning, drilling, heat treatment or plating. For each step it asks what could go wrong, what the effect would be and what could cause it.
Each failure is rated for severity, occurrence and detection. Older practice multiplied the three into a risk priority number. The joint AIAG and VDA FMEA handbook, published in 2019, replaced that with an action priority rating, which puts more weight on severity.
High-priority items need actions. These might be a poka-yoke fixture, an in-process gauge or a change of tool. The PFMEA is then updated to show the new rating.
What a control plan contains
- The process step and the machine or fixture used.
- Each product and process characteristic to be controlled, such as a diameter or a furnace temperature.
- Special characteristics marked for safety or fit, usually flagged with a symbol.
- The specification and tolerance for each one.
- The measuring method and gauge.
- The sample size and frequency, such as five parts every hour.
- The control method, such as an SPC chart or a go/no-go check.
- The reaction plan if a result falls outside the limit, including what happens to suspect parts.
Why you should ask for them
A supplier that can show you a real PFMEA and control plan has thought about how your part could go wrong. One that cannot is likely to rely on final inspection alone, which catches problems late.
These documents are part of every full PPAP file, as explained in PPAP submission levels. They are also required under IATF 16949.
How to check they are real
Many plants keep tidy documents that nobody follows. Take the control plan to the machine. Check that the gauge listed is there, calibrated and in use. Check that the frequency matches the records. Ask the operator what they do when a part is out of limit.
Then check the PFMEA against real problems. If your part has had a defect before, it should appear in the PFMEA with an action against it.
Next step
We review control plans and PFMEAs at the plant and check them against what happens on the line. Book a free sourcing review to see how this fits your parts.