The importance of DFMEA in product development is cannot be underestimated. It is an analysis that is good for both product robustness and overall safety. However, this design tool is not adopted by all product developers. The main reason is that this tool is maybe time consuming and needs a highly experienced design engineer to do so.
DFMEA Definition
DFMEA stands for design failure mode and effects analysis. From the meaning itself, it is a tool which is aimed for product design or development. There is also another form of FMEA but focusing in the production process side. This is called process failure mode and effects analysis (PFMEA). This must not be mixed to DFMEA.
In DFMEA, all the possible design failure modes and its effects are tabulated. There is then a rating that assesses the severity, occurrence and detection. The product of these three items is called RPN or the risk priority number or simply the SOD. A higher SOD or RPN means that the failure mode and its effect have higher risks. With this number, the design engineer will have idea already on which section in the design to be addressed.
Elements of DFMEA
DFMEA has three main elements. These are severity, occurrence and detection. The product of these is called risk priority number (RPN) or simply SOD. A more sophisticated DFMEA has required additional preventive measures to high RPN numbers and do re-rating once the added preventive measures are in place. The level of RPN wherein it does require additional preventive measures will vary from engineer to engineer or company to company standards. In most cases, a higher severity alone will require an additional preventive measure and re-rating as well. The level of severity is still prerogative of the engineer.
Severity
The severity is describing how bad the failure and its effect are. Some engineers used numbers 1 to 10 for severity, wherein the 10 is the most severe level. From these levels, levels 9 and 10 could be the numbers that require additional preventive measures.
Occurrence
The occurrence is simply the probability of the failure to occur. This could be a historical data. This could be a number from 1 to 10 also. The higher the number means the probability of the failure to occur is high.
Detection
Detection is the ability of the existing control mechanism in place to detect the failures. This could also be a number from 1 to 10. The higher the number means that the existing control is very poor in detecting the failures.
RPN or SOD
This is the product of the severity, occurrence and detection. The higher the number, the risk is significant. There must be a set level wherein an additional preventive measures to be placed.
Importance of DFMEA in Product Development
Since DFMEA focus in the analysis of failures and its effect, it is then natural for it to highlight the weakest section of the design. By knowing this, the engineer will do the preventive measures that will ensure product robustness and safety.
During the design stage, design engineers select the best components. The term best means a component with very good quality, from a reputable maker and compliance to all certifications related to both functions and safety. However, this is an ideal scenario. Component is not ideal after all. It will fail. If it will fail, what will happen to the product functions, what happens to the overall safety, etc.? Engineers will not gamble and simply make a robust product.
How DFMEA Differs from Other Design Tools?
Aside from DFMEA, there are other engineering tools and analysis used by engineers to come up a reliable and safety products. There the so called worst case analysis (WCA) and reliability prediction analysis (RPA). In WCA, all the parts are selected to be the best part through calculations which considering the extreme. On the other hand, RPA is predicting the product life in the field with the typical operating conditions. This is something that cannot be determined by WCA.
On the contrary to WCA, DFMEA is considering all components to fail regardless if it is selected based on the extreme conditions of WCA since there is no ideal or perfect component. This will complement the WCA. DFMEA is not also looking into how the product performs in the field based on RPA. Any components are treated to fail anytime. Thus the design engineer is obliged to put a counter measure in the product to minimize the risks.