Failure Modes And Effects Analysis

Failure Modes and Effects Analysis (FMEA) is a systematic element by element assessment to highlight the effects of a product or process failure to meet all the requirements of a customer specification, including safety.

This is indicated by high points scores for those elements of a product or process requiring priority treatment to reduce the likelihood of failure to conform to a reliability standard. It can apply to office processes as well as manufacturing processes within a natural group, once a process flow chart is drawn.

Factors assessed in an FMEA:

• Potential Failure Mode - How could the product, component or process element fail to meet each aspect of the specification?
• Potential Causes of Failure - What would make the product or process fail in the way suggested by the potential failure mode?
• Current Controls - What is done at present to reduce the chance of this failure occurring?
• Occurrence, Severity and Detection - These are assessed on a scale of 1 to 10 as illustrated below:

RPN is the Risk Priority Number. This is the severity, occurrence and detection ratings multiplied together. This number should be used as a guide to determine the most serious problems, with high numbers requiring the most urgent action.

In the case of products and manufacturing processes, the FMEA score can:

Ø Emphasise areas requiring better design for manufacture
Ø Establish measure of performance
Ø Highlight a priority order for focusing limited resource
Ø Highlight the need for SPC, 100% inspection, no inspection, etc
Ø Highlight elements for full Taguchi treatment
Ø Prioritise suppliers listing as targets for supplier development

Example of a Process FMEA

A company offers the service of fitting coat hooks. These are attached by two screws.

A part of the potential failure mode analysis could look like:

From this we can identify a problem, that of fitting the hook using the wrong screws.

To overcome this we could supply each hook packaged with screws and the result has been added to the above FMEA.

FMEA can be used to improve quality and highlight potential failures for engineers’ attention.

FMEA can be used for any situation where failure modes can be identified, for example, Stock Control Systems of manufacturing processes as well as product design.

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