FMEA has an important role for engineering design, manufacturing companies and it becomes a key tool for improving safety. Aim of FMEA setting up links between causes and effects of defects, as well as finding the best decisions concerning application of proper action. This article explains the history of FMEA and how to analyse risks and define effects using this method.

Failure mode and efect analysis (FMEA) is a risk analysis tool widely used in the manufacturing industry. Three risk parameters – severity (s), occurrence (o) and detection (d) – is defined for every risk. By multiplying the ranking for the three factors (severity × occurrence × detection), a risk priority number (RPN) will be determined for each potential failure mode and effect. RPN is used to rank the need for corrective actions to eliminate or reduce the potential failure modes. FMEA is one of the most effective tools used to prevent potential failures in the entire production sector, especially in the automotive industry.

WHAT IS FMEA ?

FMEA (Failure Mode and Effect Analysis) is a systematic method of identifying and preventing product and process problems before they occur. FMEAs are focused on preventing defects, enhancing safety, and increasing customer satisfaction. Ideally, FMEAs are conducted in the product design or process development stages, although conducting an FMEA on existing products and processes can also yield substantial benefits.[1] Different from other reliability analysis techniques, the goal of FMEA is to list all potential failure modes, analyze the causes of each failure and their effects on the system, and then remove or reduce the critical failure modes by implementing corrective actions before they occur. Since its advent, the FMEA has been commonly used and shown a great success in various industries, such as the automotive, healthcare, marine, nuclear, and electronic industries. [2]

The History of FMEA

In the mid-1960s, the first formal FMEAs were conducted in the aerospace industry in the United States and were specifically focused on safety issues. Before long, FMEAs became a key tool for improving safety, especially in the chemical process industries. The goal with safety FMEAs was, and remains today, to prevent safety accidents and incidents from occurring. While engineers have always analyzed processes and products for potential failures, the FMEA process standardizes the approach and establishes a common language that can be used both within and between companies. It can also be used by nontechnical as well as technical employees of all levels. The automotive industry adapted the FMEA technique for use as a quality improvement tool.[1]

What is the purpose of FMEA?

Preventing process and product problems before they occur is the purpose of Failure Mode and Effect Analysis (FMEA). Used in both the design and manufacturing processes, they substantially reduce costs by identifying product and process improvements early in the develop process when changes are relatively easy and inexpensive to make. The result is a more robust process because the need for after-the-fact corrective action and late change crises are reduced or eliminated.[1]

The FMEA Process

The objective of an FMEA is to look for all of the ways a process or product can fail. A product failure occurs when the product does not function as it should or when it malfunctions in some way. Even the simplest products have many opportunities for failure. For example, a drip coffeemaker—a relatively simple household appliance—could have several things fail that would render the coffeemaker inoperable. Here are some possible ways the coffeemaker can fail:

-The heating element does not heat water to sufficient temperature to brew coffee.

-The pump does not pump water into the filter basket.

-The coffeemaker does not turn on automatically by the clock.

-The clock stops working or runs too fast or too slow.

-Calcium deposits from impure water clog up the brewing process.

-There is either not enough or too much coffee used.

-There is a short in the electrical cord.

Failures are not limited to problems with the product. Because failures also can occur when the user makes a mistake, those types of failures should also be included in the FMEA. Anything that can be done to ensure the product Works correctly, regardless of how the user operates it, will move the product closer to 100 percent total customer satisfaction. Ways in which a product or process can fail are called failure modes. Each failure mode has a potential effect, and some effects are more likely to occur than others. In addition, each potential effect has a relative risk associated with it. The FMEA process is a way to identify the failures, effects, and risks within a process or product, and then eliminate or reduce them.

Evaluating the Risk of Failure

The relative risk of a failure and its effects is determined by three factors:

Severity—The consequence of the failure should it occur.

Occurrence—The probability or frequency of the failure occurring.

Detection—The probability of the failure being detected before the impact of the effect is realized.

Assessing the Risk Priority Number

Using the data and knowledge of the process or product, each potential failure mode and effect is rated in each of these three factors on a scale ranging from 1 to 10, low to high.

By multiplying the ranking for the three factors (severity × occurrence × detection), a risk priority number (RPN) will be determined for each potential failure mode and effect. The risk priority number (which will range from 1 to 1,000 for each failure mode) is used to rank the need for corrective actions to eliminate or reduce the potential failure modes. Those failure modes with the highest RPNs should be attended to first, although special attention should be given when the severity ranking is high (9 or 10) regardless of the RPN. Once corrective action has been taken, a new RPN for the failure is determined by reevaluating the severity, occurrence, and detection rankings. This new RPN is called the “resulting RPN.” Improvement and corrective action must continue until the resulting RPN is at an acceptable level for all potential failure modes. Risk factor with a high RPN will need to be thoroughly investigated. In general, these three items are estimated by experts in accordance with a scale based on commonly agreed evaluation criteria [3]

The FMEA procedure is summarized as follows [4]

(1) Define the scale table of Severity, Occurrence, and Detection.

(2) Study intent, purpose, goal, and objective of a product/process; generally, it is identified by interaction among components/process flow diagrams followed by a task analysis.

(3) Identify potential failures of product/process; this includes problems, concerns, and opportunity of improvement.

(4) Identify consequence of failures to other components/next processes, operation, customers and government regulations.

(5) Identify potential root causes of potential failures.

(6) First level method/procedure to detect/prevent failures of product/process.

(7) Severity rating: rank the seriousness of the effect of the potential failures.

(8) Occurrence rating: estimation of the frequency for a potential cause of failures.

(9) Detection rating: likelihood of the process control  to detect a specific root cause of a failure.

(10) RPN calculation: product of the three inputs rating; severity, occurrence, detection.

(11) Correction. It may need to go back to Step (2) if necessary.

Figure 1 contains an example of an FMEA template with the columns that need to be filled.

Conclusion

To improve product quality and prevent the potential failure, companies have started implementing FMEA method. This paper identified the Fmea, evaluation of fmea and assessing the risk priority number.

References

[1] Mikulak, R. J., McDermott, R., & Beauregard, M. (2017). The basics of FMEA. CRC Press.

[2] Liu, H. C., Wang, L. E., Li, Z., & Hu, Y. P. (2018). Improving risk evaluation in FMEA with cloud model and hierarchical TOPSIS method. IEEE Transactions on Fuzzy Systems, 27(1), 84-95.

[3] Stamatis, D. H. (2003). Failure mode and effect analysis: FMEA from theory to execution. Quality Press.

[4] Tay, K. M., & Lim, C. P. (2006). Fuzzy FMEA with a guided rules reduction system for prioritization of failures. International Journal of Quality & Reliability Management.

[5] Franceschini, F., & Galetto, M. (2001). A new approach for evaluation of risk priorities of failure modes in FMEA. International Journal of Production Research, 39(13), 2991-3002.