Worked example: PFMEA and control plan for a machined bracket

Abstract method is easy to nod along to and hard to apply. So let's walk one small, concrete part all the way through — process flow, PFMEA, Action Priority and the matching control plan — using a machined and welded suspension bracket. It's deliberately small; a real analysis would have more rows, but the shape is exactly this.

The process flow

The bracket is made in five steps:

1. Saw bar stock to length
2. Mill the mating faces
3. Drill & ream the Ø12 mounting bore (special characteristic — drives assembly alignment)
4. MIG weld the gusset (special characteristic — load-bearing, safety)
5. Powder coat

Two steps carry special characteristics: the bore position (significant — fit/function) and the weld penetration (critical — safety). Those are the rows we expect to drive the risk.

The PFMEA rows

For each step we name the failure mode, its effect and cause, then rate Severity, Occurrence and Detection and read the Action Priority:

Reading the risk

Notice what Action Priority does here. The weld is High even though it's expected to occur rarely (O2) — because Severity 9 (a safety effect) dominates. Under the old RPN it would have scored 9 × 2 × 4 = 72 and might have sat below a nuisance item; under AP it's correctly at the top of the list. The bore is also High (S8 with modest detection). The powder-coat row is Medium — frequent enough and hard enough to detect to deserve attention, but not safety-critical. The saw and mill rows are Low: real, but the team can address them at its discretion.

So the optimisation effort goes to two places: reduce occurrence on the weld (better fixturing, welder qualification, parameter monitoring) and improve detection/prevention on the bore (in-process gauging, a reamer-wear schedule).

The matching control plan

Every High and Medium row needs a controlling line in the control plan. For our two special characteristics:

The special-characteristic thread

This is the test of a coherent package: both special characteristics appear in the PFMEA (as the high-risk rows) and in the control plan (as controlled lines with reaction plans). If the weld were in the PFMEA but missing from the control plan, you'd have identified a safety risk with no production control for it — the classic orphan, and an instant audit finding. (See Special characteristics explained.)

In SolidLaunchpad this whole example is one connected model: the five steps are shared by the PFMEA and the control plan, the Action Priority is computed live, and the two special characteristics are single objects the method check watches across both documents. You can draft the first version of all of it from a paragraph describing the bracket — then refine the rows that matter.