Your Reliability Engineering Professional Development Site
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…]
It may be possible to pass the CRE exam knowing one formula.
The math elements of the exam may take a bit of time to solve, and knowing reliability statistics well is a good plan heading into the exam. Knowing the exponential distribution reliability function is one that you should memorize. [Read more…]
Preventive Maintenance or PM is a set of inspections and tasks that help prevent equipment from failing. Keeping equipment operating improves plant capacity and throughput. Avoiding unwanted downtime helps the plant avoid unnecessary expenses and lost productivity.
Checking the oil level in your car’s engine and adding more as needed, along with regular oil changes are examples of PMs. [Read more…]
A reliable product does not fail often. Customers expect to a level of reliability performance and failures that occur too early dash their expectation.
The design and development team work to create a robust product. To meet the customer’s reliability expectations. The team may use a range of tools to detect any reliability problem prior to launch.
Yet, customers do uncover problems that surprise us. This may be a problem with how we identify and resolve risks, yet it could also be the development process didn’t look close enough to find the issues. Or, worse, we saw the issue and ignored it. [Read more…]
A specific reliability plan may include any number of specific tasks. To build an effective plan you need the knowledge of the individual tools and techniques, plus how they may fit together to create an overall plan to achieve your goals.
Of course, this starts with establishing complete reliability goals that include function, environment characterization, probability of success (reliability) and duration.
I recommend setting specific goals for setup/installation (early life), the warranty period and the expected customer use period. [Read more…]
A reliability block diagram is a graphical and mathematical model of the elements of a system permitting the calculation of system reliability given the reliability of the elements.
The model reflects the reliability performance structure including series, parallel, standby and other arrangements of system elements.
Each block in an RBD represents a component or subsystem of the system. The organization and connecting lines represent the reliability structure of the system and may or may not be representative of the system’s functional block diagram. [Read more…]
The reliable performance of a system is important. It is important to the customer, to our business and to us.
Very few argue that we should ignore the reliability characteristics of a product. We also deem cost, time to market or feature set as important also. The trouble is we can measure the latter directly every day, where the reliability performance is often difficult to measure.
A simple assumption in many experiments is to assume the variable act independently on the response.
This means when I change the temperature a little in a polymer dryer silo that time to achieve a certain dryness goes down. And, changing the humidity or airflow rate or pressure either do not change or as they change has no impact on the relationship between temperature and drying time. [Read more…]
