Fred Schenkelberg — Thought Leader

Author of CRE Preparation Notes, Musings", NoMTBF, multiple books & ebooks>, co-host on Speaking of Reliability>/a>, and speaker in the Accendo Reliability Webinar Series.

This author's archive lists contributions of articles and episodes.

by Fred Schenkelberg Leave a Comment

Is this FMEA good?

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…]

by Fred Schenkelberg 21 Comments

Using The Exponential Distribution Reliability Function

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…]

by Fred Schenkelberg 4 Comments

Preventive Maintenance Goals and Activities

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…]

by Fred Schenkelberg 1 Comment

Uncovering Hidden Field Failure Problems

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…]

by Fred Schenkelberg 1 Comment

5 Steps to Create a Reliability Plan

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.

Reliability 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…]

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Reliability Block Diagrams Overview and Value

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…]

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Purpose of a Reliability Program

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.

[Read more…]

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Confounded DOE

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…]

by Fred Schenkelberg 2 Comments

Life Cycle Cost Analysis and Reliability

The purchase price of a product may be the start of the cost of ownership.

Maintenance and repairs may cost many times the initial purchase price. An efficient maintenance process and low-cost spare parts may help minimize cost, yet a design that optimizes the total cost of ownership is the most effective method. [Read more…]

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Duration and Reliability Goals

Coupled with probability is the duration over which the probability applies.

For example, if we desire 99 of 100 to survive, we must state over which period of time this applies. It is proper to state the couplet of 99% reliable over 1 year.

It is not sufficient to define reliability as ‘5-year product’ as it does not contain the information related to how many are expected to survive the 5 years. Likewise, it is not sufficient to say a product has 5 – 9’s reliability (meaning the probability of failure is less than 0.00001) as it does not contain the duration.

If the product has high reliability for only a few seconds, that does not help us make judgments about the first year of life. [Read more…]

by Fred Schenkelberg 1 Comment

Nelson Funnel Experiment

Dr. Nelson created a simple experiment to illustrate the effect of meddling with a stable process. (Dr. Deming did something similar)

While the intent of making small changes to a process may be to make improvements, these perturbations generally increase the variation of the results.

To improve a process requires understanding the source of the variation and often controlled experiments to identify process improvements. [Read more…]

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Recent CRE exam date

For those that sat for the exam last Saturday – how did it go? what surprised you or confused you? Was your preparation adequate?

Cheers,

Fred

by Fred Schenkelberg 2 Comments

Probability and Reliability Goals

Roll the dice.

It is about that simple if any one product will survive to a specific time. Every product has a chance, not a guarantee. The time to failure for each product is a function of the use, stresses, assembly, latent defects or imperfections, and many other variables.

The result is generally unknown. And, we often establish a reliability goal that includes the probability of success. Keep in mind that a probability is only meaningful when defined over a specific duration.

[Read more…]

by Fred Schenkelberg 2 Comments

Individuals and Moving Range Charts

Another variation of the X-bar and R chart, in this case measuring and plotting individual readings instead of a sample average. The range value is obtained from the current reading and a fixed number of previous readings.

This type of control chart is suitable for calibration or testing situations where it is not practical to create subgroups of items for samples. [Read more…]

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Environment Element of Reliability Goal

This element of a reliability requirement answers the questions of where and under what conditions the product should operate.

It includes storage, transportation, and installation conditions too. One way to think of the environment is to consider the weather around the device. Temperature, humidity, preoccupation, etc.

[Read more…]