Failure Analysis: FMEA and FMECA
Failure analysis is an intrinsic part of assessing a design for Reliability and Maintainability. Comprehensive analysis of failure is part of the design process and is aimed at reducing these failures, and that is why systematic techniques are so useful.
Drivers for FMEA and FMECA
There are many reasons why your organisations might wish perform an FMEA or FMECA. The most common reason is to minimise your company’s exposure to liability claims by building quality in (rather than inspecting defects out) and enabling designers to understand how the product can fail so that improvements can be made to the design before production starts.
Other reasons include;
- reducing the likelihood of customer complaints;
- reducing maintenance and warranty costs;
- reducing the possibility of safety failures;
- reducing the possibility of extended life or reliability failures.
Product design is generally carried out on the basis that the product will function as intended and there is often little effort spent on assessing the way that a product can fail and the effects of those failures.
FMEA and FMECA are are widely used throughout industry to improve product quality at the design stage in order to build quality into the product rather than inspect it in afterwards.
Design FMEA and FMECA enables designers to identify product failures before they happen and provides a process for categorising these failures in order to prioritize items of risk.
These techniques can also be used later in the product life-cycle to improve an existing design. FMEA and FMECA can provide many internal benefits, including right-first-time, quality improvement and lowering overall product cost.
Increasingly, FMEA and FMECA are a mandatory requirement for many contracts. A properly-conducted analysis provides your customers with assurance that the product will meet their requirements for reliability and/or safety.
Failure Modes Analysis or FMEA
Failure Modes Effects Analysis (FMEA) and Failure Modes Effects and Criticality Analysis (FMECA) are systematic techniques used together for assessing a design and understanding the possible types and severity of failures. Though they were created by the aerospace industry they have been universally adopted as an integral part of the design process. The British Standard for FMEA and FMECA, BS 5760-5, has been superseded by BS EN 60812: 2006.
FMEA is a system for improving reliability; it assesses potential modes of failure and the effects of failure by systematically considering each possible symptom of failure for the item under consideration, and then establishing the effects that this failure will have on those items and ultimately on the whole system. FMEA is a qualitative process and can be performed on its own.
FMEA can be carried out in the concept, planning, definition and design & development phases. In the conception, planning, and definition stages the analysis is usually limited due to the absence of firm data on the design. Once the design & development stage is reached there are usually sufficient data to allow the level of detailed FMEA that is needed to produce reliable information about failure modes.
While FMEA has traditionally been used in product design, FMEA is equally applicable to the analysis of processes.
Failure Modes Effects and Criticality Analysis (FMECA)
A FMECA considers the likelihood of the failure occurring and the severity of the result should failure occur in service and the likelihood of its detection.
Unlike FMEA, FMECA can’t be carried out on its own. It has to be carried out in conjunction with FMEA. Furthermore, FMECA is quantitative and uses numerical data to make predictions of reliability, so can be used to prioritize items of risk.
The end result of an FMEA is a risk severity rating or Risk Priority Number (RPN) for the potential failures of a product or a process and this can then be used to improve the design to give greater reliability and safety.
The FMEA and FMECA Process
Failure analysis systems are based on:
- investigation and assessment of your designs, products or systems to provide independent evidence of resilience against failure;
- ensuring compliance with any contractual requirements;
- identifying any weak points in a design before manufacturing starts;
- optimising your designs by identifying where savings can be made without compromising reliability.
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