Design for Six Sigma—Failure Mode and Effects Analysis


1. Introduction

The previous post covered Quality Function Deployment as one of the methodologies for designing in quality, with the House of Quality being a tool of that methodology. Another way of designing quality into a product from its conception is to do what is called a Failure Mode and Effects Analysis, or FMEA for short.

There are two types of FMEA:

a) those related to the design, which calls for a breakdown of the components of the product, and then an analysis of the possible defects or failures that can occur with each. This is Design FMEA or DFMEA.

b) those related to the manufacturing process, which calls for a breakdown of the processes involved in manufacturing the product, and then an analysis of the possible defects or failures that can occur with each. This is Process FMEA or PFMEA.

2. How does FMEA work?

The failure mode in every component (for DFMEA) or process (for PFMEA) is analyzed to see its effect on the other components or processes and for the required function of the product.

The effects of each failure mode are considered regarding their a) probability of occurring (OCCUR), b) their severity when they do occur (SEV), and c) ability to be detected if they do occur (DETEC). Usually each of these are expressed in terms of a 0 to 10 scale, with 0 meaning the best possible outcome, and 10 the worst.

Then these three factors are multiplied as the following diagram shows to create an or Risk Priority Number or RPN.

All failure modes are then ranked according to their RPN, and this gives you an idea in which priority to tackle either the components or processes that are contributing to the overall risk involving the product.

This is a very summary treatment of the subject, but that is all that is required for the Overview section of the Six Sigma Green Belt. More detail is gone into under the Define section, which will come in a later post.

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