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Reactive and Proactive FMS Reliability


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A short story and discussion on reliability programs that are reactive or proactive. The culture and approach make a difference.

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Reactive and Proactive FMS Reliability

  1. 1. f msreliabilit Reactive and Proactive Do you let events happen to you, or do events f ollow your designs and expectations? Are you a spectator or actor? Do you wonder about your products f uture or do you control your products f uture? Are you reactive or proactive? Every reliability and maintenance program is a system. Every program has inputs, such as product testing results and f ield returns. Every reliability program has outputs, such as product design and production. In the most basic terms, a reliability program includes product specif ications f or f unctionality including expected durability. The program includes some f orm of design, verif ication, production and f ield perf ormance. Given this basic lif ecycle description it is possible f or two types of approaches to executing the product lif ecycle. Every design will fail Let’s consider the notion that every product will eventually f ail. Even the most robust product on Earth will f ail when the Sun expires. Well bef ore the collapse of the solar system most products made today will have completely f ailed. The f ailures will range f rom deterioration of materials, to stress conditions (i.e. lightning strike), or simply to misuse. Some will simply wear out, others will become obsolete and lose compatibility with other systems; others will simply not provide suf f icient value anymore. Another important notion is that upon product design, there are a f inite number of f aults in the design. A button has a limited number of actuation cycles bef ore accumulated stress cracks the switch dome. A material has a degradation mechanism (corrosion, polymer chain scission) that slowly deteriorates the material’s strength. A’bug’ in the sof tware can disable the equipment temporarily. Further, there are possible def ects designed into the product that do not account f or production variation, user demand or environment variations, or do not anticipate user expectations. In every case, sooner or later, the design f law will lead to f ailure. Nonetheless, given only a f inite number of f ailures, it is possible to f ind and remove most design errors. Reactive Approach One way to approach product reliability, and the most common method, is to wait f or product f ailures and then respond with analysis, adjustments and ref inements in an attempt to improve product reliability. The naive wait f or the f ailure reports f rom customers bef ore taking action. The team’s logic, if even considered is the f ollowing: We are good designers The customer will use the product in unf oreseen environments and applications If there are customer f ailures we will consider improvements
  2. 2. For some products, with limited release and ample time to redesign the product, this may be perf ectly f easible. A simple improvement the design team could consider is an estimate of the customer’s use prof ile and environmental conditions. Armed with this inf ormation, the team then evaluates the impact of the conditions on the product’s reliability though standardized testing. Setting testing conditions at or slightly above expected operating environments permits direct evaluation of the design to meet expected conditions. The f aults f ound would be similar to the f ailure expected to occur in the customer’s hands, and there may be time f or a redesign bef ore the product is shipped to customers. Carrying out this logic may lead to a broad spectrum of testing that is both expensive and time consuming. Part of the logic of product testing includes the thought, “If we test in enough ways over the f ull range of use and environmental conditions, we should f ind and correct every design f ault.” There is of ten a heavy reliance on industry standards and common test methods f or every product. Further improvements to product reliability can ref ine this reactive method, and include using simulations, risk analysis, and early evaluation and testing of subsystems and components. The overall approach is of ten limited by knowledge of actual use conditions, lack of test samples, and lack of time. Proactive Approach Moving to a proactive approach can permit the reduction of product testing and the increase of product reliability. While this may seem similar to the above approach, it involves a f ocus on f ailure mechanisms instead of test methods. Products f ail because they do not have suf f icient strength to withstand a single application of high stress (drop, static discharge, etc.) or they accumulate damage (wear, corrosion, drif t, etc.) with use or over time. Thinking though how a product could f ail by considering the materials, design, assembly process, and the same f or vendor supplied elements, the product team determines a list of possible f ailure mechanisms. In this approach not all the f ailure mechanisms will be f ully understood or characterized. The risk in this case is the decision to launch the product while not understanding the possibility or potential magnitude of product f ailure. The amount of risk itself is unknown. Theref ore, the proactive team proceeds to characterize the design or material under the expected use conditions. The intent is to reduce the uncertainty of the risk. A second result of the proactive approach risk assessment is the rank ordering of f ailure mechanisms by expected rate of occurrence. One way to accomplish this ranking is to evaluate the stress versus strength relationships. The items with the largest overlap of the two distributions (stress and strength) indicate they have the highest potential f or f ailure. The solutions may include increasing strength, or reducing the variance of the strength. A third result of the risk assessment is similar to the stress and strength evaluation and includes the impacts of time or usage on the change in the stress and strength distributions. Either curve may experience changes to the mean or variance over time. This may be due to degradation, wear, or increased expectation of durability by customers. The proactive approach takes more thinking and understanding of how testing stresses create f ailures, plus characterization of product designs, materials, and processes, and their related f ailure mechanisms. Summary In summary, a reactive approach creates a design, and then waits f or f ield returns or standard product testing f ailures to prompt product improvements. The proactive approach anticipates f ailure mechanisms, experimentally or via simulation, characterizes the response of the design and materials to expected stresses, and then designs.
  3. 3. There are other aspects that identif y a reactive versus proactive reliability program. For example, if the only time management discusses product reliability is when a major customer complains about product f ailures, that is a reactive approach. If the management team regularly inquires and discusses the risk a particular design presents to reliability perf ormance– that is a proactive approach. How does your team approach product reliability? Are the results as expected or are there regular surprises?