Lean Manufacturing and Six Sigma Definitions

Glossary terms, history, people and definitions about Lean and Six Sigma

FMEA

Definition

Acronym for Failure Modes and Effects Analysis. FMEA is a risk assessment tool, that evaluates the risk with 3 different categories: severity, occurrence and detection. These are used to calculate a risk score, which is used to prioritize which risks are the most urgent.

The two most popular types of FMEAs are Process (PFMEA) and Design (DFMEA).

Rating Tables

Each category has a scoring matrix with a 1-10 scale.

  • Severity of 1 denotes low risk to the end customer, and a score of 10 denotes high risk to the customer.
  • Occurrence of 1 denotes low probability of the risk happening, and a 10 denotes a very high probability of the risk happening.
  • Detection of 1 denotes a process that WILL likely catch a failure, and a 10 means the process will likely NOT catch a failure.

Here are some sample scoring tables for your reference

After scoring of each category is complete for each risk, the three scores are multiplied together (Severity x Occurrence x Detection) to determine the Risk Priority Number (RPN). The RPNs are sorted from largest to smallest, and actions are taken on the top risks in order to reduce the overall risk.

Typically, the severity cannot be reduced, so the team should evaluate ways to reduce occurrence or increase detection. After actions are completed, the RPNs are recalculated and new risks are determined.

Download a FREE FMEA Excel Template which includes a sample scoring table >>>

There is a newer approach called the Multipoint FMEA, which is an upgrade from the traditional single-point FMEA typically seen in mechanical parts. With more complex products today (using software and electrical parts), the presence of more complex failures and causes has increased. Multipoint FMEAs are conditions where a failure mode occurs under these conditions:

  • Cause A occurs by itself OR Cause B occurs by itself (either can happen)
  • Cause A and Cause B occurs (must both happen at same time)

There may be situations where more than two causes are needed (Cause A, B and C must all occur), but the idea is that more than one cause that can impact the failure mode.

Action Priority

Recent additions to the RPN include an Action Priority level, which puts more emphasis on Severity in determining which risks to mitigate. Once you determine your Severity, Occurrence and Detection scores, you can look it up in the table and determine whether it is a Low, Medium or High risk.

Download the free Action Priority Lookup Table

Courses

Want to get a broad Six Sigma training online that is affordable? Check out OpEx Learning’s Six Sigma Green Belt course, which includes a section on FMEA, along with Project Charters, Statistics, Minitab or SigmaXL software, Hypothesis Tests, DOE, SPC, Control Plans, Capability Analysis, Gage R&R, and much more! Note: This is an affiliate link.

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Books

 

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Additional Resources