5.30 - Failure Modes & Effects Analysis (FMEA)

A Failure Modes and Effects Analysis (FMEA) is a systematic clement 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 point scores on those elements of a product or process requiring priority examination to reduce the likelihood of failure to conform to a reliability standard. It can also apply to office processes as well as manufacturing processes in a natural group.

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:-

Rating	Occurrence	Severity	Detection
1	Almost Never	Hardly Noticeable	Absolutely obvious
↓	↓	↓	↓
	Occasionally	Dissatisfaction	Visible but could go unnoticed
	↓	↓	↓
10	Often	Serious effects	Undetectable

The Occurrence, Severity and Detection scores are multiplied together to get a Risk Priority Number (RPN). This number is then used as 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:-

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

Example of a product FMEA

A company offers the services of fitting coat hooks which are attached by two screws. The potential failure mode analysis could look like:-

Potential Failure Mode	Potential Effects of Failure	Potential Causes of Failure	Existing Conditions
			Current Controls				Occurrence	Severity	Detection	RPN
Hook comes of wall	Coats fall on Floor	Screws to small	Advise fitter of screws to use				5	7	7	245
		1 screw omitted	Customer checks work done				2	7	3	42

 

Recommended Actions and Status		Resulting Conditions					Responsible Area / Engineer
		Revised Controls	Occurrence	Severity	Detection	RPN
Supply the hook in package with correct screws		None	1	7	7	49	J Smith - Packing Dept

From this we can identify a problem - that of fitting the hooks using the wrong screws. To overcome this each hook is packaged with the correct screws. The new condition evaluation has been added to the FMEA table.

The FMEA can be used to improve quality and highlight potential failures for the engineer’s 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.

IT Support for FMEA

There are two types of IT support for conducting FMEA’s:-

Integrated in QFD packages or Integrated in design or PLM tools