Your Reliability Engineering Professional Development Site
Hypothesis testing of paired data may include two populations that have the equal standard deviations. The t-test for differences considered in a previous post used the standard deviation of the differences. In this test, we want to consider if one population is different in some way than the other and we use the samples from each population directly. [Read more…]
Hypothesis testing previously discussed (link to past posts) generally considered samples from two populations. Maybe the experiments explored design changes, different component vendors, or two groups of customers. Occasionally you may find data that has some relationship between the samples, or where the samples are from the same population. Paired (or matched) data involves samples that are related in some meaningful way. [Read more…]
Reliability professionals today have a challenge. Engineering and operations staff members are taught to think for themselves, to make decisions, to get things done. The entire staff is highly educated, motivated and willing to lead a team or organization to results. In order to be effective as a reliability profession, we have to engage those independent and fast moving individuals. We have to compel others to listen to and understand reliability predictions, risk assessments and models. If they listen and act on the information we provide, they then may fully consider the impact of decisions on reliability performance. [Read more…]
A product reliability program is a process. Like any process, it has inputs and outputs, generally some form of an objective, and feedback. Furthermore, the process may or may not be controlled, or even a conscious part of the organization. Reliability may just happen, good or bad. Results may or may not be known or understood.
In some organizations, the reliability program may be highly structured with required activities at each stage along the product lifecycle. In other organizations, reliability is considered as a set of tests (e.g. environmental or safety compliance). In some organizations, reliability is effectively a part of everyone’s role. [Read more…]
Statistics is the language of variation. Everything varies, and we use variance (σ2) to describe the spread of the data. For any experimental work aimed at making improvements, whether in the design, manufacturing process or field performance, there are two ways to make improvements. Move the center of the distribution, or reduce the spread of the data. [Read more…]
This is also called the “p test”
When comparing proportions that are from a population with a fixed number of independent trials and each trial has a constant probability of one or another outcome (Bernoulli experiments) then we can use a p test. p is the probability of success, and 1-p is the probability of failure. Caution: stay consistent once you define success otherwise, like me, you’ll have a bit of confusion. n is the number of trials. [Read more…]
The target, objective, mission or goal is the statement that provides a design team with focus and direction. A well-stated goal will establish the business connection to the technical decisions, related to product durability expectations. A well-stated goal provides clarity across the organization and permits a common language for discussing design, supply chain, and manufacturing decisions.
Let’s explore the definition of a ‘well-stated reliability goal.’ First, is it not simple MTBF, “as good as or better than…” or ‘a 5-year product’. These are common ‘goals’ found across many industries, yet none permit a clear technical understanding of the durability expectations for the product.
The common definition for reliability is [Read more…]
The design of a product includes the arrangement of all of the product elements. When considering the reliability of a system, the arrangement matters. Many systems are arranged serially. This means that with the failure of any one element, the system will not work. See the article on Series Systems for more details. [Read more…]
It’s always necessary to estimate the value of specific reliability activities. It is needed to justify the investment required to accomplish the task. Prototypes, diagnostics equipment, and environmental chambers are expensive. The difficulty is an inability to know what will be found, before conducting the experiment.
Not doing the test means the certainty of not finding anything. That is often not enough motivation to invest, to learn something about the reliability performance. The following scenario is just one situation, along with a few ideas to help you estimate the value of investments in reliability work. [Read more…]
Creating a product or maintaining equipment is actually about our ability to manage risk. The various risks are outlined below, and there are more to consider. This summary covers the basics related to reliability. [Read more…]
This example is based on a real situation. After a class on design for reliability, a senior manager declared that every component would be fully derated in every product (electronic test & measurement devices). Within a year the design team redesigned all new and existing products, with strict adherence to the derating guidelines provided in the class. A year after the class the product line enjoyed a 50% reduction in warranty claims. They learned about derating and a manager saw the potential value. [Read more…]
This is a two part series where I outline the basic elements of creating and supporting a reliability program. [Read more…]
Here is an example of how to determine the future value of a specific reliability task. Many of us face the challenge of how to justify spending product development resources to provide insights and information to the rest of the team. Accelerated life testing (ALT) is particularly difficult: It is time consuming, expensive, and at times statistically complex. Having a clear method to estimate the value serves your career and the organization well, as both benefit from the right investments.
A recent forum post included the notion that many engineers and managers developing products or maintaining equipment have knowledge apathy concerning reliability. “They don’t care!” was the poster’s words. Has this happened? Have we lost the ability to care about reliability?
In a course I teach on reliability engineering management I ask my students to find an advertisement using reliability as a central theme or claim. This isn’t very hard to do, and I’ve regularly been surprised at the range of uses advertising finds around the concept of reliability. ‘Reliable Movers’ claims to reliably and safely move your belongings to your new home. A reliable shotgun ammunition-loading device suggests each shell will fire reliably. And, many other advertisements use the basic concepts of consistent, repeatable, safety, and trustworthy via the term reliable or reliability. There is a common and good association with reliability. [Read more…]
This is a two part series where I outline the basic elements of creating and supporting a reliability program.