This article originally appeared in the June 1999 issue of Quality Digest under the title "How to Get More Out of Your FMEAs"
How to Get More Out of Your FMEA, Part I
by Richard Harpster, President of Harpco Systems
Organizations have used the failure mode and effects analysis process for years. Recently, however, QS-9000's mandate that suppliers utilize FMEAs during new product design and development has shed new light on this useful tool. In addition to the automotive industry, many other industries, including aerospace and electronics, now use FMEAs.
Unfortunately, despite the countless training classes and numerous books written on its use, many organizations have failed to fully realize the benefits of the FMEA process. Informal surveys with more than 100 companies reveal that the majority of people using FMEAs do not perceive them as powerful tools but as something that must be done to meet a quality audit or customer requirement. One of the major reasons for this perception is that most FMEAs are performed and used incorrectly.
FMEAs can and should be a key element in any organization's advanced quality planning process. Organizations that properly use FMEAs have saved hundreds of thousands of dollars and report higher levels of customer satisfaction.
Understanding the differences between those who use and do not use FMEAs correctly can help your organization become one of those who experience the immense benefits that FMEAs can bring.
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What are FMEAs?
Although several derivatives of FMEAs have been developed, there are two basic types: design and process.
Organizations utilize design FMEAs to verify that a product has been properly designed to meet all of the customer's requirements and that it can be manufactured at a target rate, cost and yield.
Design FMEAs capture the relationship between customer requirements, how a product can fail to meet the requirements, the effects of the failures, problems with the design that cause the failures and how the design will be validated to prove it will not fail. Rating columns exist for the effects of failure, probability of failure and the effectiveness of the design validation. These ratings are multiplied together to achieve a risk priority number(RPN) for each product failure and cause combination. Rating numbers typically range from one to five or one to ten for each of the columns, with higher numbers designating unacceptable conditions.
Organizations utilize process FMEA's to assess the adequacy of a process in producing the product whose design the design FMEA has validated. Process FMEAs also identify the process and product controls that must be implemented to ensure that the product can be produced within specifications.
Process FMEAs capture the relationship between each process step, the unacceptable process outputs that can be created at each step, the effects of the unacceptable process outputs, causes of the unacceptable outputs and how the unacceptable outputs will either be prevented or detected in the event they occur. Rating columns exist for the effects or severity of the unacceptable process outputs, probability of outputs occurring and the effectiveness of the prevention and detection methods. As with the design FMEA, these ratings are multiplied together to achieve an RPN for each unacceptable output and cause combination.
In the early days of FMEA use, RPN numbers above a certain level were used to trigger recommended actions to address the problem. As people became more proficient at using the FMEA, they realized that the RPN values were improperly prioritizing the issues to be worked on. Minor issues with low severity numbers and high occurrences were being given the same level of importance as safety related issues that had high severity numbers but low occurrence numbers. As an answer to this problem, a class column was added to the Design and Process FMEA to identify the lines of the FMEA that represented the greatest risk to the company and thus required immediate attention. (For a better understanding of the Class Column and its use, please read the article "The Problem With Using RPN To Prioritize FMEA Issues and How the Class Column Solves It" that will be appearing on the Harpco System's website in February.
In Part II of this paper the five stages of FMEA implementation are illustrated:How to Get More Out of Your FMEA-Part II