A product or system’s actual reliability performance is a function of the design, assembly, and use.
Decisions made during design predominately create the inherent reliability capability performance.
The selected components, manufacturing, transportation and installation all can add variability and errors to the product, often reducing the actual reliability performance.
The use conditions and maintenance add another layer of variability, again reducing reliability capability.
Understanding the customer’s environment and use profiles early within a development program permits the team to create a design and control the manufacturing processes that will minimize the impact of the assorted sources of variability.
One aspect of reliability engineering is to work with teams during the development of the design and manufacturing process to understand the consequences of the many decisions on the resulting reliability performance.
Reliability considerations across the development lifecycles
Reliability may or may have existing procedures or guidelines to support the development teams.
Your organization may have a range of tools and processes already in place which may complement the achievement of adequate reliability performance. Being able to work within the existing product development cycle, for example, allows reliability considerations and evaluations to occur at the appropriate times during the lifecycle.
- During the concept phase of product development, we should focus on setting reliability goals.
- During the detailed design phase, reliability plays a role in component selection though stress strength or derating analysis.
- During component qualification characterizing the variability of potential component parameters may provide insights on potential system failure root causes and the establishment of control plans.
- During the development of the manufacturing processes, considering the variability of interconnects, assemblies, joining, shaping, fabrication, or essentially any step in the process, allows reliability engineers to understand the relative chances of errors, out of specification components or subsystems, and ultimately the impact on reliability performance of process capability.
Integration with existing development support tools and processes
The lifecycle development process includes phase gate reviews.
Each phase outlines a set of tasks to accomplish which is then reviewed before the program moves to the next phase of the development process. Reliability whether specifically listed in the set of tasks is an important performance characteristic of the product. Thus incorporation reliability elements thought the existing lifecycle/phase gate process keeps reliability visible to the entire development team.
Development engineers desire to create a design or process that works, and works over time (is reliable).
Henry Petroski suggests that engineers design away from failure. [Design Paradigms] Given the amount of uncertainty of the product’s functional performance development engineers often use a range of different tools and techniques to evaluate options before finalizing the design or process.
Here are a few examples:
- As development engineers conduct finite element analysis to evaluate the performance of a mechanical element of the product, the reliability considerations of over-stress, stress concentrations, cyclic loading, shock or impact loading, thermal cycling, changes in material properties over time (oxidations, for example), and more allow the existing FEA study to also consider potential reliability risks and performance.
- As prototypes become available, the initial evaluations generally include function performance, then a set of evaluations to determine the performance over a range of expected stress conditions. Each failure is dissected and evaluated for possible design or process improvements.The reliability engineering tools of risk assessment, environmental testing, stress testing, and failure analysis are already in use to some degree. Add reliability engineering specialized skills and knowledge to the process enhances the development team’s ability to maximize the information gained from each round of prototypes. Detailed root causes analysis enables the team to understand and solve failures effectively.
- As the supply chain provides samples and first articles for consideration, the development team already evaluates these components for function performance. Adding the reliability consideration of aging or the impact of variability on performance, allows the team to identify and potentially mitigate reliability problems. A set of power line variability tests on a power supply, designed and manufactured by a supplier, may reveal weaknesses within the design or manufacturing of the subsystem.
- As the manufacturing processes develop, the engineers may conduct trial runs to assess throughput and resulting product quality. Incorporating the reliability considerations of the incorporation of latent defects, for example, permits the process evaluation to extend beyond initial product performance. An accelerated life test on units undergoing a repair process provides information on the potential degradation of the process.
- Many of the existing steps the development team will employ may already contain elements of reliability engineering. Enhancing those elements, extending a few, and incorporating the impacts of variability or aging, for example, enables the entire team to make well-informed decisions including the reliability performance impacts of their decisions.
The basic idea is reliability is the result of the many decisions that occur during the development process.
Enhancing the information, insights, and abilities of the existing development tool to consider the impact on reliability performance, is one way to effectively incorporate reliability thinking throughout the organization.
The common goal of creating a reliable product along with leveraging existing practices gently brings in reliability engineering tools and techniques into routine use by the entire development team.
Reliability as Part of Every Decision (article)
How to Assess Your Reliability Program (article)
Material Selection & Reliability (article)