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An Effective Method for Finding Potential Process and Assembly Problems
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Process Failure Mode and Effects Analysis (FMEA) is a technique normally used to evaluate manufacturing and assembly processes at the system, subsystem or component levels. It is commonly used in the automotive business along with industries that center heavily on making products, particularly when human safety factors are involved. This kind of FMEA focuses primarily on possible failure modes of the process that are due to manufacturing or assembly process deficiencies. Specific attention is given to any process step that may result in a safety hazard for either the device operator involved in the manufacturing or assembly of a product or the end-user of the item.
SAE J1739 presents recommendations regarding how to perform a process FMEA. It offers assessment criteria regularly used in the automotive industry for ranking the severity (S) of failure effects, along with the likelihood of occurrence (O) plus the effectiveness of process controls to stop or detect (D) the cause or failure mode before the failure reaches the customer. The Risk Priority Number (RPN) is usually a measure utilized to assess risk and help find critical failure modes. It is calculated by multiplying the Severity, Occurrence, and Detection values, RPN = S x O x D. While it is true that larger RPN values usually indicate more critical failure modes, this may not be always the case. Whatever the RPN value, always pay special attention to any failure mode which includes an effect resulting in a severity of 9 or 10.
A simple process FMEA example found in SAE J1739 examines each step active in the process of applying wax to the inside of a car door. Each process step is considered and graded based on the risk that it presents. In this particular example, the third step demands an operator to utilize a spray wand to manually apply the wax. In the evaluation, this task is presumed to be the greatest risk area, since if it is not done correctly, then there may be too light or too heavy a coat of wax applied to the inside of the car door. This high-risk step could be the focus of our process FMEA analysis. The FMEA team would then look at ways that this process step could be improved upon.
In addition to the automotive industry, process FMEA is becoming more commonly employed in the medical and health care industry, and it is now being employed in a good many service industries. Typically here, the idea is to identify and prioritize processes which are high risk and then conduct a process FMEA on them. For each process the group would identify possible failure modes where the failure modes would represent various ways that a process or sub-process step could fail to provide the anticipated result.
In medical care, this might be an analysis of the process steps in place to assure patient safety. For example, maybe the analysis team would look at the process involved prior to surgery, or some of the process steps involved in post operation recovery procedures to determine if improvements could be made.
When failure modes have been determined for the high-risk processes, then this team would identify possible effects for each failure mode. For the most critical effects a close analysis would be completed to discover the root cause, and then recommendations would be made to redesign the process to either eliminate the failure mode or lessen the risk, if it did indeed occur.
This information is meant to merely introduce you to the concept of process FMEA. For in depth process FMEA examples along with a more in-depth discussion on this topic, please make use of many of the resources on our website.
Rich Herman has been involved in reliability engineering for over 25 years and a lot of that time has been spent working with FMEA. To learn more about process FMEA visit his website: FMEA and FMECA
Article submitted Saturday, September 17, 2011 & read 25 times.
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