Simply stated, FMECA is a disciplined method of product or process analysis that is conducted to identify potential failures that could affect the customer's expectations of product quality or process performance. It is by no means a new technique; it started to come into prominence in the early 1950s in the aerospace industries as flight control systems became more complex.
Although the technique is inherently simple, its application has been misunderstood and consequently many organisations have failed to gain the enormous benefit that can result if it is applied properly. For most products, it is possible to assess at the end of the product life cycle the most common failure modes. By this stage, however, it is too late to take action as the product is now out of service. If we were able to obtain such data during the concept and design phases of a product's life cycle we could do much to prevent future failures occurring. FMECA provides us with the opportunity of acquiring such knowledge; it is one of the simplest yet most powerful predictive tools available to us.
When questioned, many groups express poor experiences of using this technique. Examples of frequently held opinions include it takes too long; it is boring; it is done too late and nothing is done with the results. Some organisations apply the technique because its customer requires it to do so; often such organisations will delegate the job to some hapless engineer who conducts the analysis in miserable isolation from those who understand the product or process being studied. The aim of the course notes supporting this section is to offer a counter view to the poor experiences and provide some guidelines upon which a successful analysis may be conducted.
While it is true that the conduct of FMECA requires an investment of time, the analysis can be used to resolve many issues that are often studied separately. Its key application is to:
- Identify failures that have undesirable or significant effects; to determine the failure modes that may seriously affect the expected or required quality.
- However, because we are attempting to understand how a product or process may fail to achieve the requirements placed upon it and which to categorise the failure causes for their severity, the analysis will enable us to
- Identify safety hazard and liability problem areas, or non-compliance with regulations.
- If we are able to understand the areas of technical risk associated with a product or process, then provided we have that understanding early enough in the life cycle we will be able to
- Focus development testing on areas of greatest need.
Instead of using the "scatter gun" approach to testing which occurs when we do not have sufficient understanding of how a product or process may fail. Many organisations apply standard tests to successive generations of product. This is a strategy that is doomed to failure unless every generation of product has to meet identical requirements and operate in an identical environment. If this is the case, it begs the question why we should wish to continue testing the product.
The application of built-in test and diagnostic routines is becoming ever more common. If the diagnostic part of the system is treated as a "bolt on" it can often cause more problems than the system it is supposed to diagnose. If we use FMECA to gain an appreciation of how the system can fail it follows that the analysis will assist
- The design of Built-in-Test and failure indications.
- Preparation of diagnostic flowcharts or faultfinding tables.
- Maintenance planning.
- The application of FMECA to processes will help us to
- Identify key areas in which to control the process and, where appropriate, place inspection and manufacturing controls.
- Provide a systematic and rigorous study of the process and its environment that will almost always improve our understanding of how the process might fail.
- Support the need for a standby or alternative process or improvements to current processes.
- Identify deficiencies in operator and supervisor training and practices.