For a stable process, nothing much happens. If the stable process is producing acceptable products, we should expect to continue to produce acceptable products.
Unless something changes. [Read more…]
When Are We Out of Control
Articles
Find all articles across all article series listed in reverse chronological order.
2013 in Review
Thanks to you all for a great year. The idea of the blog is to assist those preparing for the CRE exam or wanting to learn about reliability engineering. It seems to have found the audience.
The WordPress.com stats helper monkeys prepared a 2013 annual report for this blog.
Here’s an excerpt:
The concert hall at the Sydney Opera House holds 2,700 people. This blog was viewed about 21,000 times in 2013. If it were a concert at Sydney Opera House, it would take about 8 sold-out performances for that many people to see it.
8 Steps to Creating an X-bar and s Control Chart
Once you decide to monitor a process and after you determine using an $- \bar{X} -$ & s chart is appropriate, you have to construct the charts.
The $- \bar{X} -$ & R charts use the range as an approximation of the variation in the population. When feasible use the standard deviation, s, rather than the range, R for the improved efficiency in detecting meaningful changes in process variation. [Read more…]
5 Ways to Be in Service of Others
Over the past week or two (originally published in December 2013), I’ve received requests and comments that have given me pause. Why is it that I have time to answer questions and share information? Why do I spend the time to do so in the first place?
I have found that responding to questions or requests for assistance is rewarding.
Today I received a request for help in a job search. Last week it was an employer looking for a perfect candidate. I’ve received questions about graduate school in the US from a Chinese undergraduate. A question on accelerated life testing approaches. Another on maintenance practices and data analysis.
For each, I try to provide an answer or direct to find an answer.
8 steps to Creating an X-bar and R Control Chart
Once you decide to monitor a process and after you determine using an $- \bar{X} -$ & R chart is appropriate, you have to construct the charts.
This is not difficult and by following the 8 steps below you will have a robust way to monitor the stability of your process. [Read more…]
3 Investments in Reliability
When a product or asset works as it’s expected for as long or longer than expected, we often consider it reliable.
Consumers around the world look for reliable products and services. Some will pay a premium with the desire to obtain failure free value from the purchase. When designing a product or service we often want to create the most reliable item within the constraints of time, resources, and cost. Designers and engineers may add margin or safety factors into calculations and decisions to avoid failures.
Many of us have heard that fixing a design is orders of magnitude less expensive early the product lifecycle. Product recalled or major failures can damage profits and brand image.
Here are three ways you can invest in improving product reliability. [Read more…]
Intro to Fault Tree Analysis
The NASA Fault Tree Handbook with Aerospace Applications
This is a break from the usual format of this site. I’m highly recommending that as your review materials and prepare for the CRE exam or prepare to conduct an FTA, you read this NASA document as an intro to fault tree analysis.
For a review, I suggest the first chapter or two. If working in the aerospace industry, you should print and use a copy.
The following is an extended excerpt from the first section of the document. [Read more…]
Building Reliability Leadership
Some believe leaders are born and become natural leaders. Others believe leadership can be taught and anyone can become a leader. I believe leadership is situational and when intentional can be very powerful.
I learned leadership theory and enjoyed plenty of practice attending the US Military Academy. I certainly practiced leadership during my tour in the Army.
And, I’m not an expert on leadership.
Variables Control Chart Background
What are Variables Control Charts?
From NIST Engineering Statistics Handbook, section 6.3.2, with edits and additions.
During the 1920’s, Dr. Walter A. Shewhart proposed a general model for control charts as follows: [Read more…]
Just Plot The Data
One of the first things taught in a data analysis class, or in first-grade math, is the plot. A graphical representation of the data. Bar charts, pie charts, histograms, box plots, and the x-y scatter plot. These and others simply help us to understand the nature of the data.
The ‘nature’? The data is only a record of an observation. Counts, colors, numbers, or something similar. The ‘nature’ is, to me, the behavior, maybe pattern, or story the data may reveal.
Selecting Control Charts
Consider a handy flow chart and set of descriptions that will assist you in selecting the appropriate control chart, or at least understand the differences. [Read more…]
It Should Just Work
The forums, chats, tweets (#bluelightofdeath), blogs, and mainstream media (CNN & Vancouver Sun) are looking closely at the launch of Sony’s Playstation. There are reports of dead on arrival and ‘blue light of death’ failures. One business blog discusses the need to understand and match customer expectations as a way to avoid bad press.
I find the expectation is pretty simple.
It should be simple
A brand new device, in this case, an expensive new game console, the entire experience of the purchase, transport, unpacking, hookup and first turn on should be a joy. The anticipation for those picking up the device on the first day comes crashing down to despair when the device fails to work. Products are expected to provide value, and you expect the device in front of you to work as expected. It’s simple.
I once explained to my son that not all units from production will work (he was in junior high school). He said he understood and that it is fine if the game console he buys just works. Ship the ones that don’t work to someone else. [Read more…]
Statistical Process Control Overview
Basic introduction to key concepts of SPC
Statistical process control (SPC) is not a control chart alone.
SPC is a set of tools and a thought process to identify, measure, monitor and improve important elements of product development and production. I’ve seen very good and very bad implementations of SPC. [Read more…]
Early Reliability Problems in the News
Working down product launch reliability problems
Boeing representatives explained the Dreamliner would need an additional 6 months of work to bring the aircraft’s reliability on par with the existing 777 model.
They made the announcement at the start of the Dubai air show. Not a good start to a week of showing off the features of the aircraft. How does a companay respond to early reliability problems in the news?
Generally, even the most general reliability goal of a new product is to be as good or better than the last model. Sure, the Dreamliner has many new features, materials, and upgrades. Yet, it did as much or more design evaluation and testing as any model previously. [Read more…]
Norris-Landzberg Solder Joint Fatigue
Before Norris-Landzberg’s study there was the work of Coffin and Mason.
Coffin-Manson
One way to approach accelerated life testing is to use a model for the expected dominant failure mechanism. One such model is for solder joint low-cycle fatigue originally published by Coffin (1954) and Manson (1953), independently.
Norris-Landzberg
Norris and Landzberg proposed the plastic strain range is proportional to the thermal range of the cyclic loading (ΔT). They also modified the equation to account for effects of thermal cycling frequency (f) and the maximum temperature( T). They and other than empirically fit the parameters for the equation. [Read more…]
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