Your Reliability Engineering Professional Development Site
A listing in reverse chronological order of articles by:
Your customers are your best testers for your next product. They will explore the features. Expose the product to use conditions in unconscious ways. And, they will let you what they consider failures without needing the specification document.
During the development process, you and team may work to understand what customer may want or expect for the new product. You may even conduct focus groups or review past product field failures and call center records. [Read more…]
Mechanical systems wear out and fail eventually. The ability of a structure to support a load, move through the specified range of motion, or spin degrades with use and time. Even our joints eventually wear out.
Accelerated life testing (ALT) has plenty of literature concerning the failure mechanisms unique to electronic components and materials. This is partially due to the limited number of unique electronic components compared to the often custom mechanical designs. ALT also has value as it provides information about a system’s reliability performance in the future.
Let’s explore an example of mechanical reliability testing (an ALT) in order to outline a basic approach to ALT design and analysis. [Read more…]
Suppliers often include reliability information along with performance specifications.
We look for reliability statements as one part of the selection process to ascertain if the component is likely to have sufficient reliability.
When the vendor’s data is clearly stated and meaningful, that information saves us from potentially having to conduct our own reliability evaluations. [Read more…]
If you buy more than one of an item used in your product, you will have to deal with variability. In general, the variability from part to part is minimal and expected. Occasionally, the variability is large and causes reliability problems. [Read more…]
It was late Friday afternoon and the phone rang. Which is rarely a good thing.
There seems to a significant spike in field failures due to one component. The initial failure analysis work reveals the issue started with a batch of parts received about two months ago and the flaw continues to appear in subsequent batches. [Read more…]
The communication between suppliers or vendors and their customers is often using a mix of specifications and requirements.
Customers set requirements and suppliers offer specifications. When they match, or when a supplier component specifications meet the customer’s requirements, we have the potential for a transaction. [Read more…]
“Keeping the end in mind”, “working toward a common objective” and “providing a vision” are all convention management wisdom based on setting goals.
Seeing a reliability goal is one of the first tasks when creating a reliability plan.
“How good (reliable) does it have to be?”
That is answered with a reliability goal statement.
There is a lot of uncertainty concerning a reliability goal. [Read more…]
My introduction to reliability engineering was my boss asking me to sort out how long a new product will last in use.
The expectation was it would last for 20 years or more buried in Italian mountain concrete bridges.
My first thought was about living in the Dolomites for 20 years monitoring the performance of the product.
That was quickly dashed as my boss explained he wanted an answer in about 6 months.
Now this was a problem. How do you cheat time to learn about the expected lifetime of a something? Thus started my career in reliability engineering.
Life testing for reliability engineering helps us answer the question how long till failure occurs. Specifically, we find the chance of failure over some duration. [Read more…]
If nothing was uncertain we would not need statistics.
Since nearly everything varies in some fashion, we need a way to describe and work with that variability.
We already know this and we know about statistics as being the right set of tools. Yet we hesitate, avoid, and refuse to pick up the appropriate tool. [Read more…]
In the poem by Oliver Wendall Holmes, The One Hoss Shay, a deacon is confounded by the various parts of his carriage the fail.
And, he decides to do something about it.
But the Deacon swore (as Deacons do,
With an “I dew vum,” or an “I tell yeou,”)
He would build one shay to beat the taown
‘n’ the keounty ‘n’ all the kentry raoun’;
It should be so built that it couldn’ break daown:
“Fer,” said the Deacon, “t’s mighty plain
Thut the weakes’ place mus’ stan’ the strain;
‘n’ the way t’ fix it, uz I maintain, Is only jest T’ make that place uz strong uz the rest.”
Translating from old English, it basically means he wanted to craft a carriage using the best materials and techniques. Later, he built a very sound carriage where every part is just as strong as all the other parts. [Read more…]
Is it possible for an individual to ‘do’ DFR? Is design for reliability something, like a specific technique, that is DFR?
What is DFR and how would you recognize it if it was occurring? Like meditation, nearly anyone can strike a pose that appears similar to someone in deep meditation, yet can you tell by observation if they really are mediating? Probably not. The same is true for an organization or person that declares they are doing DFR. Maybe they are or maybe not.
Environmental testing is the evaluation of a product or system in one or more stress conditions. Environmental as in that which surrounds and affects a product. Consider temperature. Is the product going to experience outdoor temperatures as found in Fargo, North Dakota or Belmopan, Belize?
The weather is one way to describe external stresses, yet it is so much more. Environmental testing may include fungus, insect, and animal exposure. The document MIL-STD-810G lists and describes testing methods for a wide range of environmental conditions. [Read more…]
Stop testing when the testing provides no value.
If no one is going to review the results or use the information to make a decision, those are good signs that the testing provides no value. Of course, this may be difficult to recognize.
Some time ago while working with a product development team, one of the tasks assigned was to create an ongoing reliability test plan. This was just prior to the final milestone before starting production. During development, we learned quite a bit about the product design, supply chain, and manufacturing process. Each of which included a few salient risks to reliable performance.
In the Monte Carlo method, one uses the idea that not all parts have the same dimensions, yet a normal distribution describing the variation of the part dimensions is not assumed.
Although the normal distribution does commonly apply, if the process includes sorting or regular adjustments or if the distribution is either clipped or skewed then the normal distribution may not be the best way to summarize the data.
As with any tolerance setting, getting it right is key for the proper functioning of a product. Monte Carlo method allows you to consider and use the appropriate models for the variations that will exist across your components. [Read more…]
The root sum squared (RSS) method is a statistical tolerance analysis method. In many cases, the actual individual part dimensions fall near the center of the tolerance range with very few parts with actual dimensions near the tolerance limits.
This, of course, assumes the part dimensions are tightly grouped and within the tolerance range.
Setting tolerances well, using the best available data about the part(s) variation, allows creating designs that function well given the expected part variation. This is better for reliable performance. Also, the same method can be applied when the loads and stresses are normally distributed.
Check that assumption with you data first, of course. [Read more…]