How do you calculate a wall-thickness risk score?

Multiply severity by 0.40, occurrence by 0.35, and detection by 0.25, then sum them. With severity 6, occurrence 4, and detection 3, the score is 4.55 on the rating scale.

How is this different from a standard RPN?

A classic RPN multiplies severity, occurrence, and detection, which lets one high number dominate and creates gaps in the scale. This weighted-sum approach is smoother and lets you emphasize severity, weighted highest here at 0.40.

What is a good wall-thickness risk score?

Lower is better. There is no universal threshold, so rank all your failure modes and attack the highest scorers first; the example's 4.55 is mid-range and warrants a look but not a line-stop.

Why weight severity the highest?

A wall-thickness defect that causes a tank to leak or a part to fail under load matters more than one that is merely cosmetic, even if rare. Weighting severity at 0.40 keeps dangerous failure modes near the top of the list.

How do I lower the occurrence score for thin walls?

Attack the root cause of uneven wall build, meaning powder bridging, uneven charge, or oven hot spots. Improving corner venting, charge accuracy, and oven air uniformity drives the occurrence rating down.

How do I improve the detection score?

Add reliable checks such as sectioning first articles, ultrasonic wall gauging, or weigh-checks against target charge. Better inspection lowers the detection rating because defects are less likely to escape.

Rotational Molding calculator

Wall Thickness Estimate Calculator

This wall thickness risk estimate is a weighted FMEA-style score that ranks how much a wall-thickness defect on a rotomolded part threatens quality. Quality engineers and process teams use it to prioritize which thin-wall, thick-wall, or non-uniform-wall failure modes to attack first, since rotomolding builds walls indirectly and thickness varies with powder flow, corner bridging, and oven uniformity. It combines how bad a defect is (severity), how often it happens (occurrence), and how likely it is to slip through (detection) into a single comparable number. That lets a team spend containment and process-improvement effort where the payback is highest.

What this calculator does

This wall thickness risk estimate is a weighted FMEA-style score that ranks how much a wall-thickness defect on a rotomolded part threatens quality.
Use it when wall thickness estimate in rotational molding needs a defensible ranking against other rotational molding risks for the next review.
It computes a weighted wall-thickness risk score by combining severity, occurrence, and detection ratings with fixed weights of 0.40, 0.35, and 0.25.

Formula used

Wall Thickness Estimate risk score = severity × 0.40 + occurrence × 0.35 + detection × 0.25

Inputs explained

Defect severity rating:
Defect occurrence likelihood rating:
Detection difficulty rating:

How to use the result

Use it during PFMEA reviews or process troubleshooting to rank rotomolded wall-thickness failure modes for corrective action.
Scores are only as honest as the ratings behind them; inconsistent or optimistic scoring across a team makes the ranking unreliable, and the weights are fixed rather than tuned to your plant.

Current U.S. benchmarks

The producer price index for plastic resins and materials stands at 319.371 (BLS, May 2026), up 19.5% from a year earlier. Quotes priced off last quarter's material cost miss this move.
The U.S. has 9,635 plastics product manufacturing establishments employing about 677,302 workers (Census County Business Patterns, 2023).

Common questions

How do you calculate a wall-thickness risk score? Multiply severity by 0.40, occurrence by 0.35, and detection by 0.25, then sum them. With severity 6, occurrence 4, and detection 3, the score is 4.55 on the rating scale.
How is this different from a standard RPN? A classic RPN multiplies severity, occurrence, and detection, which lets one high number dominate and creates gaps in the scale. This weighted-sum approach is smoother and lets you emphasize severity, weighted highest here at 0.40.
What is a good wall-thickness risk score? Lower is better. There is no universal threshold, so rank all your failure modes and attack the highest scorers first; the example's 4.55 is mid-range and warrants a look but not a line-stop.
Why weight severity the highest? A wall-thickness defect that causes a tank to leak or a part to fail under load matters more than one that is merely cosmetic, even if rare. Weighting severity at 0.40 keeps dangerous failure modes near the top of the list.
How do I lower the occurrence score for thin walls? Attack the root cause of uneven wall build, meaning powder bridging, uneven charge, or oven hot spots. Improving corner venting, charge accuracy, and oven air uniformity drives the occurrence rating down.

Last reviewed 2026-05-12.