The idea is to get something in your hands as soon as possible. This may be a Lego mock-up or a crude electronic breadboard. It may only have one feature at the moment and not look like the finished product at all, or it may be many variations of the industrial design so that you can evaluate the look and feel aspects of a design. With each iteration you learn a little about what works and what does not work. As the process continues the mock-ups or prototypes begin to resemble the final product in appearance and functionality. The learning continues and the design evolves into a final form.

BUILD, TEST, FIX APPROACH

The build, test, fix approach for reliability planning has the benefit of allowing the exploration of failure mechanisms early in the design process. One uses risk assessment tools to focus on the areas of highest reliability risk and create prototypes that allow experimentation related to the specific risks. If a potential element of a product is not reliable but can be identified early, the designers may address it early with minimal impact on the design or schedule.

The downside of the approach is the changing nature of the design. With each evolution of the design there may be multiple changes that may improve or degrade the system’s reliability performance. Since many reliability tests take time to accomplish, the results may no longer apply or may not provide feedback fast enough to impact the design.

The reliability program must continue to address reliability risk with each change in the product. Creative reliability testing on limited prototypes must provide meaningful results quickly. By focusing on high-risk areas and testing elements of a product for specific failure mechanisms that address the latest proposed changes, the reliability program can provide guidance to create a very reliable product.

ANALYTICAL APPROACH

The other approach for product or system development is to conduct careful design analysis, virtual modeling, and evaluation of material and component failure mechanisms. This approach relies heavily on simulation tools such as SPICE modeling for electronics, finite element modeling for mechanical elements, and computational fluid dynamics for air or fluid flow. The challenge for reliability engineering is to have sufficient characterization of failure mechanisms to model the behavior within the simulations tools or with sufficient knowledge of the use environment. There are plenty of physics of failure models available for select failure mechanisms, yet not all may apply well enough in any particular situation.

For novel materials or constructions you may need to conduct detailed studies to develop an appropriate model. For many simulation tools you will need to know how material properties change or how electrical component parameters may drift. It does take more knowledge but does not demand prototypes.

Like the build, test, fix approach, the analytical approach does rely on risk assessment tools to focus the effort. When the analytical approach is used, it is assumed that you know about and have sufficient knowledge to fully model all relevant (likely to occur during expected use conditions) failure mechanisms. This is not always true.

BALANCED APPROACH

In practice, a balanced approach is best. To minimize the downsides of each approach we often use a combined approach to building a reliability program during product development. The advantage is that you can minimize expensive testing by using existing knowledge and models.

Typically, a new design builds on existing products and systems. The power supply may use the same technology as the display, while a new module for a specific new feature may be added. The motors and bearings remain the same while a new material for the housing and structure may be used.

Starting with the risk assessment, you should build the plan using the tools that reduce uncertainty. For novel designs, you should plan to expose new failure mechanisms. The intent is to provide feedback to the design team with meaningful information. Using testing or simulations are just approaches as you design for reliability.

Bio:

Fred Schenkelberg is an experienced reliability engineering and management consultant with his firm FMS Reliability. His passion is working with teams to create cost-effective reliability programs that solve problems, create durable and reliable products, increase customer satisfaction, and reduce warranty costs. If you enjoyed this articles consider subscribing to the ongoing series Musings on Reliability and Maintenance Topics.