PFMEA Injection Molding Example

Injection molding is one of the most failure-mode-rich processes in manufacturing. A single 30-second cycle compounds material chemistry, thermal control, mechanical wear and operator decisions. The PFMEA below covers a typical engineering thermoplastic part — a structural housing in PA66 with a Class-A cosmetic surface — produced on a hydraulic press with a hot-runner mold.

The scope is the full converting process: from material drying through ejection, degating and final inspection. Tool design and material specification are upstream and belong in the DFMEA; this PFMEA assumes the design and the tool are frozen.

1. Material drying (desiccant dryer, −40 °C dewpoint, 4 h residence)
2. Material conveying to press hopper with grade verification
3. Barrel heating across 5 zones, melt temperature 285 °C
4. Mold close and clamp (180 t clamping force)
5. Injection — 1st-stage velocity control with cavity pressure transfer
6. Hold / pack — 2nd-stage pressure to gate freeze
7. Cooling — closed-loop mold temperature 80 °C
8. Mold open and part ejection
9. Robot pick, degating, vision check
10. Final inspection and packaging

• Short shot — incomplete cavity fill, almost always tied to non-return valve wear or low injection velocity.
• Sink marks and voids — insufficient holding pressure or premature gate freeze.
• Flash — clamp force insufficient relative to projected area, or mold parting line wear.
• Weld lines — design-driven, but melt temperature and injection velocity can mask or aggravate them.
• Warpage — uneven cooling across cavities; the most common cause of dimensional rejection.
• Burn marks / degradation — trapped air or excessive residence time at temperature; often appears after a stoppage.
• Brittle parts in service — usually hydrolysis of PA66 or PET from insufficient drying. This is the highest-severity failure because it appears in the customer's hand, not on the line.
• Contamination — regrind, foreign material, or residual purge compound; a quality-system failure as much as a process failure.

Ten representative rows. S = Severity, O = Occurrence, D = Detection, AP = Action Priority.

Controls split into prevention (stop the cause occurring) and detection (catch the effect before it reaches the customer). The AIAG-VDA 2019 model consolidates both into the "Current Controls" column but the engineering distinction still matters.

• Prevention: dryer dewpoint logging, barcode resin verification, mold-temperature closed loop, screw PM, lubrication schedule, operator certification.
• Detection: cavity pressure sensors, in-mold thermocouples, SPC on hold pressure peak, vision system on robot pick, first-piece CMM per cavity, AQL sampling at outgoing inspection.

• Move material moisture verification from spot check to in-line moisture probe at the dryer outlet (drops Detection from 4 to 2 for the drying row).
• Install per-cavity cavity-pressure sensors and reject on profile deviation (closes the warpage and short-shot gap).
• Replace manual degating with servo-driven cutter; eliminates operator-technique variance on gate vestige.
• Move sampling on critical dimensions from AQL 2.5 to tightened inspection (II-A switching rule) for the first 30 days after any tool change.

The High-AP rows cluster around two themes: latent field failures (drying, wrong resin, weak weld structure) and process-induced cosmetic / dimensional rejection (cooling, sticking, gating). Note that row 5 (sink marks) sits at AP Medium even though it is visible — Severity is 5 because it is a cosmetic rejection, not a functional failure. The AIAG-VDA AP table weights Severity first, which is why Severity 5 with Occurrence 4 cannot promote to High no matter what Detection is. Teams that still rank by RPN typically over-prioritize this row; see RPN vs Action Priority.

• Listing a single "molding" step instead of decomposing the cycle. Every row collapses to S/O/D averages that mean nothing.
• Scoring Detection on the assumption the operator always notices. Manual visual on a cycle < 30 s is realistically D ≥ 5.
• Forgetting material drying entirely. It is the highest-severity row in most PFMEAs and is often missing.
• Treating the hot-runner controller as part of the tool design and not the process. Heater band failure is a process risk.
• Skipping the regrind path. If regrind is used, it gets its own rows.

Customer auditors and IATF 16949 auditors specifically check three things on injection-molding PFMEAs: (1) drying / moisture is a row of its own with realistic Severity, (2) mold-temperature control is treated as a process variable not a setup parameter, and (3) the PFMEA, Control Plan and Process Flow Diagram are aligned — same step numbering, same characteristics, same controls. Misalignment between these three documents is the most common non-conformance written in plastics audits. Use the FMEA audit checklist before submission.

• FMEA Example — base PFMEA walkthrough.
• What is FMEA? — methodology primer.
• AIAG-VDA 7-Step Process — the methodology this example follows.
• Action Priority Guide — how H/M/L is derived from S, O, D.
• Severity Rating Guide, Occurrence Guide, Detection Guide.
• Common Mistakes and Audit Checklist.
• FMEA → Control Plan for the downstream handoff.
• Process FMEA Software — build this PFMEA in Qhubio with deterministic AP.