The PFMEA comes before the control plan, so the plan’s rows come from the risks. Walk each step of the process flow and rate severity, occurrence and detection, then look the three up together in an Action Priority table. Here five rows give one High, three Medium and one Low. New ratings count only once the controls are in place and working.
Week 2. The team stands at the process flow with a pen. The job is to walk it one step at a time and ask four things: how can this step fail, what is the effect, what causes it, and what stops it today.
The PFMEA comes before the control plan, not after. The plan's rows come from the PFMEA's risks. Write the plan first and the PFMEA turns into paperwork that copies it, and the risks the plan missed stay missed.
Rate with Action Priority
Each failure gets three ratings: severity of the effect, occurrence of the cause, and detection by the current controls. You do not multiply them. You look the three up together in an Action Priority table, and it returns High, Medium or Low. High means act, or write down why the current controls are enough. Medium means act or justify. Low means you may.
Here are the five rows for LC-5927, with severity (S), occurrence (O) and detection (D):
- Dry resin: resin loaded wet. Effect: a brittle snap hook that can break at the customer's assembly. Cause: dryer time not tracked. S6, O8, D7. Occurrence is high because dryer time is not tracked. Detection is poor because only a visual check after molding would catch it. Lookup: High.
- Mold: short shot at the snap hook. Effect: the cover will not latch. Cause: process window not proven on a new tool. S6, O6, D5. A visual check once an hour. Lookup: Medium.
- Mold: snap hook height out of tolerance. Effect: the cover is loose or hard to latch. Cause: tool wear and press drift. S6, O4, D8. The dimension is checked once a shift. Lookup: Medium.
- Pack: parts scuffed in the tote. Effect: an appearance complaint. Cause: parts rub in an open tote. S4, O6, D8. Lookup: Medium.
- Trim: gate cut too deep. Effect: a weakened hook near the gate. Cause: the trim fixture wears and the cut gets deeper. S6, O3, D5. Lookup: Low.
One High, three Medium and one Low. The team acts on the High and the Mediums. For the Low it writes one line saying why no action is needed and moves on.
Plan the fix, then re-rate
The planned controls change the ratings. A dryer log and a moisture check at the start of each lot take row 1 to O3, D4, which looks up Low. A proven process window with a boundary sample and a check every 30 minutes takes row 2 to O3, D3, Low. Checking the hook on a fixture every 30 minutes takes row 3 to O3, D3, Low. Divider totes take row 4 to O3, D4, Low.
Those new ratings count only once the controls are in place and working. Until then, the original ratings stand. Some customers still ask for RPN. Use whatever your customer requires.
Read more: how to write a PFMEA and a PFMEA example.
The mistake to avoid
Rating detection by hope. If the only control is "the operator will see it," that is a detection rating of 7 or worse, however good the operator is. Rate what the control can actually catch.
- Open one PFMEA and check it was written before its control plan.
- Pick its highest rated row and find the control on the floor.
- Look for any Low row with no written reason.
Open the printable Monday Board
Related on ShopFloorOps
The part, the tool, the program and every number in this book (latch cover LC-5927) are a made-up example. The tool sidebars show ShopFloorOps tools, which I make and sell. Every chapter teaches the step itself, so you can use your own forms. New to a term? See the quality glossary.