Don't Forget 3 Metrics If You Want to Avoid Unreliable Product Designs

To ensure the design of a reliable product, it is imperative that reliability metrics are used early in the design process and continue to be used regularly throughout the product lifecycle.

February 16, 2016

3 Min Read
Don't Forget 3 Metrics If You Want to Avoid Unreliable Product Designs

An unreliable product can destroy the brand and hard-earned reputation of a company. Not only do faulty products drive up financial expenses due to higher warranty and product recall rates, they also increase the chances of potentially damaging lawsuits. To counteract this risk, reliability metrics should be incorporated early, often, and throughout the entire product development lifecycle in order to regularly measure overall product readiness.

The following reliability metrics can effectively be used in all phases of product development in order to continuously track ongoing product reliability growth.

Incorporating effective reliability metrics regularly throughout all design phases ensures a more reliable product at launch.
(Source: Digitalart at

Reliability Modeling

Early in the design cycle, a mathematical reliability model of the proposed design should be created either manually or by using a reliability software package. The goal at this stage is to break up the overall system design into appropriately sized subsystem blocks and then allocate reliability values to each of these blocks.

For existing subsystems that are being reused, reliability values are assigned based upon their historical performance. For new or modified subsystems, reliability values are determined based upon known component data reliability calculations, estimated performance of similar equipment, or best engineering judgment.

During regular development intervals, the entire reliability model is rolled up to show how overall reliability is tracking over time and how quickly the design is maturing.

Risk Priority Numbers (RPNs)

Risk Priority Numbers, or RPNs, generated from the severity, occurrence, and detection values in failure mode effects analyses, can also be incorporated from the beginning of the project to track reliability growth of the design. To use this method, sum up all RPNs (above a certain threshold level) and use this result as the overall RPN metric of the design. As the development team improves the overall reliability of the product, the overall RPN value should correspondingly decrease.

Percentage of Design Reuse

While design innovation is always important, adapting, leveraging, and reusing existing and proven design segments are great ways to improve the reliability of a subsystem.


Previously used design segments already have withstood the test of time in the field and allow the team to have greater confidence that they will perform as predicted. This reliability metric is generated by calculating the percentage of the product that is based on reused design segments, where a higher percentage of design segment reuse predicts a higher overall product reliability.

Number of Change Orders

Once a product is in the final stages of maturity or is released, the rate at which engineering change orders occur can track reliability growth. To use this metric, plot the total number of change orders over time on a rolling, ongoing basis. As the design becomes more reliable and stable, the total number of change orders should correspondingly decrease and trend downward.

Reliability Metrics Help Produce Winning Products

To ensure the launch of a reliable product, it is imperative that reliability metrics are used early in the design process and continue to be used regularly throughout the entire product lifecycle. Incorporating effective reliability metrics throughout all design phases will ensure a more reliable product launch and help your organization win in today's highly competitive business arena.

Greg Jung has more than 25 years of experience designing medical equipment and electro-mechanical products for a wide variety of industries. He also served in various project management roles and has led global, cross-functional development teams for a wide variety of programs. During this time, he developed several award-winning and patented product designs. Greg holds bachelor and master of science degrees in mechanical engineering from the Georgia Institute of Technology.

Sign up for the Design News Daily newsletter.

You May Also Like