Design For Reliability (DfR)

During this stage, a clearer picture about what the product is supposed to do starts developing. It is important to understand how much change is introduced with this new product. A product can be an upgrade of an existing product, an existing product that is introduced to a new market or application, or a product that is not new to the market but is new to the company and could be introduced as completely new product. With more design or application changes, more reliability risks are introduced to the success of the product and company.

Using ReliaSoft XFMEA software, you can identify potential failure modes, assess the risk associated with those failure modes, prioritize issues for corrective actions and identify and carry out corrective actions to address the most serious concerns. A properly applied DFMEA takes requirements, customer usage and environment information as inputs and, through its findings, initiates and/or informs many reliability-centered activities.

It is highly important to estimate the product's reliability, even with a rough first cut estimate, early in the design phase. This can be done with estimates based on engineering judgment and expert opinion, simulation models, prior warranty and test data analysis from similar products/components using ReliaSoft Weibull++ software or with standard based prediction available in ReliaSoft Lambda Predict software. You can use common military or commercial libraries, such as MIL-217, Bellcore and Telcordia, to come up with rough MTBF estimates or to compare different design concepts when failure data is not yet available.

By this stage, prototypes should be ready for testing and more detailed analysis. This involves an iterative process where different types of tests are performed, the results are analyzed, design changes are made, and tests are repeated.

A wide array of tools is available for the reliability engineer to uncover product weaknesses, predict life and manage the reliability improvement efforts available in ReliaSoft Weibull++. With testing comes data, such as failure times and censoring times. Test results can be analyzed and its techniques to statistically estimate the reliability of the product and calculate various reliability-related metrics with a certain confidence interval. Such calculations can help in verifying whether the product meets its reliability goals, comparing designs, projecting failures and warranty returns. Additionally, using Weibull++'s Accelerated Life Testing module, you can cut down on the testing time, and by carefully elevating the stress levels applied during testing, failures may occur faster and thus failure modes are revealed more quickly.

A very important aspect of the DfR process also includes performing root cause analysis using XFRACAS software, which provides better understanding of physics of failure and can discover issues not foreseen by techniques used prior to testing (such as FMEA).

Using BlockSim's RBDs, you can model the overall reliability of the system, identify weak areas of the system, find optimum reliability allocation schemes, compare different designs and perform auxiliary analysis such as availability analysis. Fault tree analysis may be employed to identify defects and risks and the combination of events that lead to them.

During this stage, you need to make sure that the product is ready for high volume production. Statistical methods can be used to develop a test plan that will demonstrate the desired goal with the least expenditure of resources.

When reaching the manufacturing stage, the DfR efforts should focus primarily on reducing or eliminating problems introduced by the manufacturing processes. Manufacturing introduces variations in materials, processes, manufacturing sites, human operators, contamination, etc. The product's reliability should be reevaluated, and design modifications might be necessary to improve robustness. Continuous sampling of units for testing using ReliaSoft Weibull++ is highly desirable throughout manufacturing to estimate the reliability of the product and assess whether the reliability goal is still expected to be met.

Process FMEAs can be used to examine the ways the reliability and quality of a product or service can be jeopardized by the manufacturing and assembly processes. With ReliaSoft XFMEA’s Control Plans you can assure that all process outputs will be in a state of control.

The manufacturing process is also prone to deviations. Using Weibull++ to perform warranty analysis can be useful in preventing infant mortality failures, which are typically caused by manufacturing-related problems, from happening in the field. Deciding on the appropriate burn-in time can be derived from QALT and/or LDA. Also, manufacturability challenges might force some design changes that would trigger many of the DfR activities already mentioned.

Continuous monitoring and field data analysis are necessary to observe the behavior of the product in its actual use conditions and use the gained knowledge for further improvements or in future projects. In other words, you need to close the loop, review the successful activities as well as the mistakes, and ensure that the lessons learned are not lost in the process.