FEMA provides a formal mechanism for resolving potential problems in a product，system, or manufacturing process. It is a structured approach to identifying the ways in which products, systems, or processes can fail to meet customers’ requirements by:
1. Estimating the risk of specific causes of the failures
2. Evaluating the control plan for preventing the failures from occurring
3. Prioritizing the actions taken to improve the product or process
FMEAs can be performed by teams focused on solving problems in systems, designs, or manufacturing processes. The teams should also perform process mapping of the product, process, or system to be analyzed. The types of FMEAs that can be performed are:
1. System FMEA: Performed in order to analyze systems and their subfunctions in the early concept and design stages. It should be started after systems functions are completed but before detailed design is initiated.
2. Product Design FMEA: Performed on products before they are released to manufacturing. It should be started after product functionality is defined and completed prior to release to manufacturing.
3. Manufacturing FMEA: Performed to analyze manufacturing, assembly, and transaction processes started when preliminary drawings are released. This activity should be ongoing, completed only when the product is obsolete.
The FMEA methodology begins with identifying each element, assembly, or part of the process, and listing the potential failure modes, potential causes, and effects of each failure. A risk priority number (RPN) is calculated for each failure mode. It is an index used to measure the rank importance of the items listed in the FMEA chart. These conditions include the probability that the failure takes place (occurrence), the damage resulting from the failure
(severity), and the probability of detecting the failure in-house (detection). High RPN items should be targeted for improvement first. The FMEA analysis suggests a recommended action to eliminate the failure condition by assigning a responsible person or department to resolve the failure by redesigning the system, design, or process and recalculating the RPN.
In summary, the FMEA process is comprised of the following steps:
1. FMEA preparation
Select FMEA process team and complete a process map. Identify all process steps.
List process outputs to satisfy internal and external customers.
• List process inputs for each process step and rank them.
• Develop a relationship matrix, relating product to process steps.
2. FMEA process
• List ways process inputs can vary and identify failure modes.
• List other causes and sources of variability.
• Assign severity, occurrence, and detection rating for each cause.
• Calculate risk priority number (RPN) for each failure.
3. FMEA improvements
• Determine recommended actions with time needed to reduce RPN.
• Forecast risk reduction and take appropriate action to reduce failure risk.
• Recalculate RPN and put controls in place to ensure that failure is completely eliminated from the system or process.