Your Reliability Engineering Professional Development Site
A continuous distribution is useful in many statistical applications such as process capability, control charts, and confidence intervals about point estimates. On occasion time to failure, data may exhibit behavior that a normal distribution models well. [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…]
Learn more and register for the CRE Prep course here. (registration is closed at this time)
The course is 16 two hour sessions – a mix of lecture, discussion and Q&A that focused on what you need to know to pass the ASQ CRE exam. Sure, beyond the course you will need to study. This involved practicing sample exam questions, using your references and calculator, and practicing finding answers quickly.
We discuss ways to study along with any issues or ideas you have as you prepare for the exam.
*Note: These online classes will be Archived and you will be able to access them later even if you cannot make it to the Live class session! This means you may watch them again in case you forget something, miss a class, or can’t make it one day. Saturdays may be scheduled with the instructor for extra sessions or make-up classes if needed.
Mondays, July 13 – August 17, 2015 (3:00PM-5:00PM PDT)
Last Session for questions, September 21 and 28, 2015 (3:00PM-5:00PM PDT)
This class ends prior to the semi-annual ASQ Section testing, where everyone may sign-up through their local Section to take their test. Be sure to check out the ASQ website to get the early-bird rate before the end of this course!
Looking forward to seeing you in the course. And, of course, at any time, feel free to ask questions here, or in the CRE Preparation LinkedIn group.
Learn more and register for the CRE Prep course here.
Similar to the Weibull distribution yet with slightly heavier tails. While not as easy to interpret if the data shows early life or wear out features, the lognormal distribution often fits time to repair data accurately.
Transform the data by taking the natural log of each data point. The resulting values tend to be normally distributed if the original data fits a lognormal distribution.
You can use base 10 or base 2 or any base and the results will still tend to be normally distributed. It is common to use natural log, ln(). [Read more…]
Worst-case tolerance analysis is the starting point when creating a tolerance specification.
It is a conservative approach as it only considers the maximum or minimum values of part variation—whichever leads to the worst situation. Setting tolerances such that the system will function given the expected variation of manufactured components improves that ability of the system to perform reliably.
In the worst-case method, you simply add the dimensions using the extreme values for those dimensions. Thus, if a part is specified at 25 ± 0.1 mm, then use either 25.1 or 24.9 mm, whichever leads to the most unfavorable situation.
The actual range of variation should be the measured values from a stable process. It may be based on vendor claims for process variation, industry standards, or engineering judgment. [Read more…]
We work on projects to improve reliability.
There may not be the field data immediately available. Let’s explore how you can improve the overall program while delivering on your project.
Specifically, what’s with cost and procurement?
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A discreet distribution useful when counting events within a time period.
It models rates, such as the number of gophers in your garden, paint scratches on your car, or the number of shopping carts that arrive in the 5 minutes before you in line. Essentially it’s the count of something over a time period or defined area. [Read more…]
The exponential distribution is a model for items with a constant failure rate (which very rarely occurs).
If the chance of failure is the same each hour (or cycle, etc.), including the first hour, 100th hour, and 1 millionth hour or use, then the exponential distribution is suitable.
Many practitioners assume the failure rate either is constant or changes so little as to be essential constant in order to make reliability calculations simpler. [Read more…]
And, being encouraged to write a paper or two on drone reliability. Now that Amazon has a delivery drone patent, and industrial applications continue to announced daily, there is a need for serious reliability in these devices.
The early adopters and explorers in any nascent industry generally discover the many design faults including reliability issues. That is common.
As the drone industry develops, improving product reliability becomes a business necessity. For industrial application it is essential. [Read more…]
It is not enough to simply state your organization has a proactive stance concerning reliability. It more than running a few tests or thinking about reliability before the product ships or the equipment is installed.
It is a way of doing business.
A point estimate of the mean of a population is determined by calculating the mean of a sample drawn from the population. The calculation of the mean is the sum of all sample values divided by the number of values. [Read more…]
Asking the right question is important.
During a review meeting (informal or formal) asking a few reliability questions may reveal weaknesses, strengths, or uncertainty. The design team has many priorities and reliability is often difficult to estimate, yet knowing what is and isn’t known provides a clear picture of risks for decision makers.
If you are a decision maker and need to ascertain the reliability risks of the current design, then asking a couple of questions may provide just the insights you need. It also conveys that reliability is on your mind and that you want to have answers that are meaningful and well thought out.
The basic measures of central tendency are mean, median, and mode.
Given a collection of data, a common question is about where the data resides. Knowing the center or mid-point or average is a starting point as we consider the data. [Read more…]
Selecting a supplier for components or subsystems involves many aspects including the desired reliability performance.
Once selected the ability of the supplier to provide items that meet or exceed the reliability requirements relies on their understanding of the requirements and operational conditions related to the specific item within the system. It also relies on the supplier’s knowledge of their own design and manufacturing processes as it related to the reliability performance. [Read more…]
It is rare that a third party generated FMEA/FMECA has any value. The development or manufacturing teams and supporting staff should comprise the bulk of the study’s team. Team size for a specific study would include 4 to 10 individuals.
The FMEA/FMECA should provide clear action items that may include:
Conduct research or experiments to understand and quantify uncertainty. This may include exploring how an item responds to specific stress, errors or inputs. Or include experiments to estimate the occurrence rating for a specific potential cause of a failure mode. [Read more…]
