Your Reliability Engineering Professional Development Site
Short essays and thoughts (musings) on reliability and maintenance engineering topics.
Let me know your reaction and thought, plus any questions.
ISSN 2329-0080
There are a lot of reliability tools.
From FMEA to FTA, from ALT to HALT, from derating to sneak circuit analysis. We also have a lot of acronyms. We cannot afford to do all the tasks, so which do we select and why?
Each activity has some reason for existing. Each has some question that it helps answer. HALT helps to find what will fail. ALT helps to determine when failures may occur.
Knowing what each tool is capable of doing is a start. Knowing what you need to know is essential.
Every failure provides information. It provides time to failure, stress strength relationship, process stability and design margin types of information. In every case. Even failures directly related to human error.
A hardware intermittent failure observed by a firmware engineer should not be dismissed. Rather recorded, explored and examined.
A single intermittent failure, or glitch, may indicate nothing other than just a totally random glitch, or a design error that degrades over time causing 50% of units to fail in first three months.
Some days are better than others. We sometimes run into failure when working to create a new product. With a little investigation we suspect the components are not working as expected.
We’ll call the vendor and ask for an explanation. If this is normal production and variability of performance, our product will suffer an higher than expected failure rate. The vendor will assure us with:
Not helpful. [Read more…]
As reliability professionals know, products fail. They fail for a wide range of reasons and over a broad span of time. We know it happens.
This doesn’t help when it impacts us directly though. When we purchase a product or service, it should just work. We know the odds, we know better, yet the sting of failure remains.
Customer Service provides a range of services, one of which is helping customers receive the benefit of their purchase. We call customer service to report a failure and expect their help making it right. [Read more…]
What happens when a product you produce fails? You customer may call and return the product. They may expect you to provide a replacement or refund.
Does it matter if the failure was due to a capacitor or motor that you didn’t design, just purchased?
No.
Does it matter if a supplier’s supplier made an error that directly lead to the failure?
No.
You customer experienced a failure and since the purchase was from you, you are expected to make it right.
There are two basic philosophies when creating a reliability plan for a new product or system.
One is to experiment with prototypes as quickly and often as possible, the build, test, fix, approach. Or, you can research and model detailed aspects of the materials and structures to characterize the strength of a product or system, the analytical approach.
Both methods have obvious applications and not so obvious limitations. [Read more…]
The short answer is, everything varies.
The longer answer involves the agreement between what is possible and what is desired.
If we could design a product and it could be replicated exactly, including every element of the product, we would not need tolerances. Any part would work with any assembly. We would simply specify the dimensions required.
Instead, variation happens.
Widths, lengths, weights, roughness, hardness, and any measure you deem worth specifying will vary from one part to the next. Manufacturing processes impart some amount of variation between each item produced. In many cases, the variation is acceptable for the intended function. In some cases, the vacation is unacceptably large and leads to failures. When the design does not account for the variation holes will not align, components will not fit, or performance will be poor.
The better reliability performing systems start the design process with controlling variability.
Variability of materials and processes involved thought the product lifecycle. Reliability performance occurs as a result of the decisions made throughout the design process.
When focused on understanding and minimizing variability, the design becomes robust and reliable.
It’s Friday afternoon and the phone rings. It is another customer complaining about your product not working. This is the fifth call this afternoon. Something is wrong and you’re responsible for making it right.
The natural failure analysis process starts across your team. Gather information, determine the scope of the issue, work to understand the root causes, and implement an appropriate solution. This may involve stopping production, halting shipments, or even a product recall.
Initially, you just have more irate customer calls than a typical Friday afternoon. [Read more…]
Reliability goals provide you and your team a focus for the reliability program. They provide a measurable way to design, test, and maintain systems that meet customer expectations.
A goal of any kind in a business is relatively easy to set and publish. They are not easy to entwine into the culture of the organization so the objectives desired by achieving the goal become a meaningful focus. A product development team may have hundreds of pages of specifications and a long list of priorities and objectives. Simple listing a reliability goal, no matter how clearly stated, may not be sufficient to garner the interest of your team.
Simple listing a reliability goal, no matter how clearly stated, may not be sufficient to garner the interest of your team.
Reliability engineering is a blend of disciplines from material science to asset management. We use problem-solving, design, maintenance, and statistical tools on a regular basis, yet that is not the only thing we do.
Having met a few engineers that define their role as a reliability engineer as conducting HALT or FMEA only, strikes me as to what most believe we do, or should do, as a reliability engineer. It is true that someone may specialize by choice or chance on one tool, yet even then is that all they do?
I don’t think so.
A reliability block diagram is a graphical and statistical representation of the reliability structure of a system.
Graphical as an RBD is drawn with blocks for each element of a system and connecting lines representing the relationship between elements.
I’ve recently received a couple of notes from individuals looking at starting a career in reliability engineering. One is a student looking at a career path, another a working engineer with an interesting in reliability.
Both asked how to land a position given no reliability engineering experience.
Hum, I don’t know anyone that had reliability engineering experience before they got started working in reliability engineering. Not counting taking apart the family toaster and trying to repair it before Mom got home as a kid.
The easy answer is very often. Each time you want to know how long a product will operate. The accompanying question on how well the estimate will match actual performance makes the real answer more difficult.
We regularly and intuitively do reliability predictions all the time. When starting a car at the beginning of a trip, we estimate the ability of the vehicle to complete the journey. When we purchase a phone, we expect it to operate for at least two years (your expectations may differ).
During the design process, we may have formal or informal useful life expectations. It is not knowing if our decisions related to the design will fulfill the lifetime expectations that leads to the desire to know how well the resulting system will operate. We also may need to estimate warranty or maintenance costs, thus knowing what is likely to fail becomes important.
In general, knowing how long something will operate without failure provides the feedback we need to create a viable system that meets our business and customer reliability expectations.
In short, we do reliability predictions regularly to gauge is we are making good decisions. [Read more…]
Failure modes and effect analysis is a tool to identify potential failures and prioritize based on severity, occurrence, and detection. I like to describe FMEA as an organized brainstorm. You probably have some experience with FMEA.
In some industries, there is a high expectation or mandate to do an FMEA study. In some industries FMEA maybe just another tool to consider using during various stages of the product or asset lifecycle.
In my opinion, FMEA should be a part of your project plan when it is likely to add value.
Value in the sense that the organization will receive an adequate benefit based on the investment to conduct the FMEA study. [Read more…]