Chapter 6: Failure Mode and Effect Analysis (FMEA)

OVERVIEW

This chapter has been developed to assist and instruct design, manufacturing, and assembly engineers in the development and execution of a potential Failure Mode and Effect Analysis (FMEA) for design considerations, manufacturing, assembly processes, and machinery.

An FMEA is a methodology that helps identify potential failures and recommends corrective action(s) for fixing these failures before they reach the customer. A concept (system) FMEA is conducted as early as possible to identify serious problems with the potential concept or design. A design FMEA is conducted prior to production and involves the listing of potential failure modes and causes. An FMEA identifies actions required to prevent defects and thus keeps products that may fail or not be fit from reaching the customer. Its purpose is to analyze the product's design characteristics relative to the planned manufacturing or assembly process to ensure that the resultant product meets customer needs and expectations. When potential failure modes are identified, corrective action can be initiated to eliminate them or continuously reduce their potential occurrence. The FMEA also documents the rationale for the manufacturing or assembly process involved.

Changes in customer expectations, regulatory requirements, attitudes of the courts, and the industry's needs require disciplined use of a technique to identify and prevent potential problems. That disciplined technique is the FMEA.

A process FMEA is an analytical technique that identifies potential product- related process failure modes, assesses the potential customer effects of the failures, identifies the potential manufacturing or assembly process causes, and identifies significant process variables to focus controls for prevention or detection of the failure conditions. (Also, process FMEAs can assist in developing new machine or equipment processes. The methodology is the same; however, the machine or equipment being designed would be considered the product.)

A machinery FMEA is a methodology that helps in the identification of possible failure modes and determines the cause for and effect of these failures. The focus of the machinery FMEA is to eliminate any safety issues and to resolve them according to specified procedures between customer and supplier. In addition, the purpose of this particular FMEA is to review both design and process with the intent to reduce risk.

All FMEAs utilize occurrence and detection probability in conjunction with severity criteria to develop a Risk Priority Number (RPN) for prioritization of corrective action considerations. This is a major departure in methodology from the Failure Mode and Critical Analysis (FMCA), which focuses primarily on the severity of the failure as a priority characteristic.

In its most rigorous form, an FMEA summarizes the engineer's thoughts while developing a process. This systematic approach parallels and formalizes the mental discipline that an engineer normally uses to develop processing requirements.