FMEA

FMEA (failure mode and effects analysis) is a preventive risk management method. A cross-functional team systematically works through the functions of a product or the steps of a process, identifies the potential failure modes of each, their effects and causes, rates the risk and proposes actions before a defect ever reaches the customer.

The most common types are design FMEA (DFMEA), focused on the product design, and process FMEA (PFMEA) for the manufacturing and assembly process. When a criticality analysis is added, the method is called FMECA. FMEA is a standard part of development in the automotive industry and is widely used in aerospace, medical devices and mechanical engineering.

Risk is rated with three indicators on a scale of 1 to 10, where a higher number means a worse situation: severity of the effect (S), occurrence of the cause (O) and detection (D), meaning the ability to detect the failure or its cause before the design is released to production or the part reaches the customer. Traditionally the three are multiplied into the risk priority number, RPN = S × O × D (1 to 1000). The 2019 AIAG & VDA FMEA Handbook replaces the RPN with action priority (AP: high, medium, low), which gives more weight to severity, and introduces a seven-step approach running from planning through structure, function and failure analysis to optimization and documentation of results.

The output is an FMEA worksheet with actions, owners and due dates. It is a living document that is updated after design or process changes and feeds into the test plan (in automotive often called the DVP&R) and the control plan.

DFMEA delivers the most value once the concept has been chosen but the design is not yet frozen, typically before functional prototypes are built. Actions such as changing a material, adding a mistake-proofing (poka-yoke) feature against incorrect assembly or adding a test are still cheap at that point. PFMEA is prepared before the start of series production and revisited whenever the process changes.

It pays off for products whose failure threatens safety or causes costly warranty claims or downtime, for new technologies and for automotive projects, where customers usually require it.

An FMEA filled out by one person at the end of a project just to satisfy a customer requirement achieves nothing. It needs a team (design, manufacturing, quality, service) and has to happen early enough for the results to change the design. Another common mistake is mixing up the terms: the failure mode is how a function fails, the effect is the impact on the user or the downstream process, and the cause is what triggers the failure.

The RPN alone can mislead. High severity combined with low occurrence gives a low number even though the risk needs to be addressed. Always deal with the highest-severity items, and aim actions primarily at eliminating the cause, not just at improving inspection. Agree on the rating scales with the team in advance; otherwise the results are not comparable.