For our use of the Weibull distribution, we typically use the shape and scale parameters, β and η, respectively. For a three parameter Weibull, we add the location parameter, δ. [Read more…]
Calculate Weibull Mean and Variance
Articles
Find all articles across all article series listed in reverse chronological order.
Finding Value in FMEA
Failure modes and effect analysis (FMEA) is a tool that works to prevent process and product problems before they occur.
I like to define FMEA’s as an organized brainstorm. The process examines a product or process and asks what could go wrong. Then the team systematically determines and rank orders for each failure mode:
– the severity of the problem when it occurs
– the probability of the problem occurring
– the ability to detect the problem before it occurs
Good design engineers think about how the design could fail and improve the design. FMEA provides a structured team approach to further improve the design.
Top 10 CRE Exam Preparation Tips
My best CRE exam preparation tips
Over the past few years, we have been helping people from around the world prepare for and pass the ASQ CRE exam. Over this time, and from personal experience, I’ve learned a few things about what makes a difference.
Here are ten tips to help you prepare. [Read more…]
Consider Reliability Prediction Value
One of the primary questions we answer as reliability engineers is:
How long will it last?
Reliability prediction is the forecast or prognostication attempting to quantify either the time till failure, or expected future failure rate or warranty claims, or required spare parts.
We need to know as we make decisions today about the design or purchase.
Recipe for CRE Exam Preparation
In a recent discussion in the Linkedin group ASQ Reliability Division, John Pagendarm replied with his recipe for CRE exam preparation. With John’s permission, I’m posting here.
When Are We Out of Control
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…]
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.
