The third mitigation, which is for the failure of the ball skipping, is a design change to tighten tolerances. The second mitigation, changing the ball material to a different material with which there is a know history, changes the probability of occurrence score. The first mitigation, adding testing, impacts the detection score of the failure of the ball not rolling. In the pen example that has been used in previous lessons, there are three failure modes requiring mitigation. This is one of the reasons that it is important to do Design FMEAs prior to design freeze on a product. This is the easiest element to change at the beginning of a project, but it becomes very expensive and adds delays if it is attempted at the end of the project. In particular, it normally means more rigorous testing that occurs earlier in the development process. Mitigating detection requires a change to the design and development process used to create the new product. Reverting to the old technology defeats the purpose of introducing new technology. However, if your new product’s goal is to use new technology, you will normally have a high score in this area. A frustration that can occur with this type of mitigation is that a lower score can be obtained by using old, proven technology. Often reverting to the known design concept will also allow you to use actual data rather than relying on familiarity and knowledge of the design concept or application. This knowledge of the design, will reduce the probability that an undesirable failure mode is introduced. The easiest way to mitigate probability of occurrence is to revert to a design concept that is well known and understood by the organization. These changes may also make the design more expensive. Also, change the design so that it is more reliable, such as adding redundancy. Change the design to eliminate harms and hazards to customers or users. However, if severity is high, it will also be the most impactful. Therefore, it is one of the most difficult approaches. Mitigating severity will require a design change. However, the overall business risk is low. If the failure cause occurs, the effect will occur. If the mitigation action is a redesign, it may eliminate the failure mode, but will likely introduce new failure modes that must now be analysed and scored.įailure modes with an RPN below the threshold can still occur – the risk is not eliminated. After the mitigation action has been completed, the failure mode should be re-scored. Normally, the mitigation action is focused on reducing the largest scores. The mitigation action will either be a change to the design or the design process. The actual threshold varies by industry and many companies establish their own threshold. When the RPN exceeds the business threshold, normally a number near 100, the failure mode should be mitigated.
If all the scores were 10 ,the RPN would be 1,000. If all the scores were 1, the RPN would be 1. The RPN is the product of the three scores. If the RPN exceeds the business threshold number, those failure modes should be mitigated by redesign or changes to the development project plan. The RPN number is normally calculated automatically by the Design FMEA spreadsheet or form. When appropriate, action is taken to mitigate the high risks. This indicates the level of technical risk due to this failure. The product of the three scores is the Risk Priority Number (RPN).
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