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CRE Preparation Notes

Prep notes for ASQ Certified Reliability Engineer exam ISSN 2165-8633


The idea of the CRE Preparation Notes series is to provide you short practical tutorials on all the elements that make up the ASQ CRE body of knowledge. The articles provide introductionary material, basics, how-to’s, examples, and practical use guidance for the full range of reliability engineering concepts, terms, tools, and practices.


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You will find the most recent tutorials in reverse chronological order below. Below each article is the section and specific clause of the CRE Body of Knowledge that tutorial addresses. Click on those tags to find other articles on the same topic. To the right on the sidebar, there is a listing of the 7 major categories in the body of knowledge - it's a quick way to find groups of articles on each specific area. You can also use the search function to locate articles, podcasts, or tutorials on specific topics.

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When is DOE Useful?

When is DOE Useful?

On page 6 of Statistics for Experimenters, Box, and Hunter suggest a scientist could conduct an investigation without statistics.

Whereas, a statistician could not do so without scientific knowledge.

The text’s discussion quickly expands on the benefits to a scientist when they do employ statistical thinking and tools.

Design of Experiments, DOE, is a set of statistical tools that allow an investigator to efficiently examine multiple factors and their associated influence on results.

DOE allows us to be better investigators. [Read more…]

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Plotting Repairable System Failure Data

Plotting Repairable System Failure Data

A good plot reveals the data’s story.

Repairable system data is what is called by statisticians a renewal process.

The repair activity may restore the system to as good as new. Sometimes, the repair pretty much leaves the system in a state similar to just before the repair.

What happens most often, though, is the chance of system failure changes after each repair activity.

A simple plot can help us see what is happening. [Read more…]

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Warranty Management Overview

Warranty Management Overview

Warranty is a part of doing business. Warranty management is not just the terms listed on the box.

Understanding the entire warranty process, along with your options, permits you to manage your warranty, rather than the other way around.

This is a short overview.

Pieces of a warranty program occur well before the first product ships and may affect the company bottom line for years after you ship your last product.

Brand promise, marketing, finance, customer service are not common areas for a reliability engineer.

Yet, the impact of product failures tends to dominant warranty expenses.

Therefore understanding the many elements around warranty management is essential for any reliability engineer. [Read more…]

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Warranty Prediction

Warranty Prediction

The offered warranty is an internal part of many purchase decisions, plus many business models.

While obligatory to offer a warranty, especially for consumer products, the specific terms, duration, and eventual total cost of honoring warranty claims may vary dramatically.

One key to managing the overall warranty expense is to estimate the potential future warranty claims, followed by accurately tracking actual expenses during the warranty period. [Read more…]

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Analyzing a Taguchi L4 Array Experiment

Analyzing a Taguchi L4 Array Experiment

We’ve collected data and it’s time for the analysis.

As you may recall, in the last article on Planning a Taguchi L4 Array Experiment, we drafted a set of four prototypes. The specific arrangement of factors and levels will now allow us to analyze each factor separately.

The intent is to find the optimal level or setting for each factor, plus which is the most important factor. [Read more…]

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Planning a Taguchi L4 Array Experiment

One of the simplest ways to learn design of experiments, DOE, is to just give it a try.

The Taguchi  DOE approach uses orthogonal arrays. This subset of the possible approaches to DOE simplifies the process to create and analyze experiments.

Let’s plan a simple experiment using the Taguchi DOE approach. [Read more…]

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Introduction to Physics of Failure Models

Introduction to Physics of Failure Models

When we understand how something fails, we can create a mathematical model of the effect of stress or load on the time to failure behavior.

The model may take different forms, yet it is the ability to related the conditions surrounding the use of a device to its eventual demise that is essential. The specifics include a molecular level of detail in some cases.

Physics of Failure models focus on the particular relationships between stresses and materials. [Read more…]

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The Basics of Derating Electronic Components

The Basics of Derating Electronic Components

As with strength-strength analysis, derating is a means to design robust systems.

Derating is an intentional process applied to every component of a product to reduce the opportunity of a component witnessing more stress than it is capable of withstanding.

The additional robustness also reduces the amount of damage the stress may impart, thus prolonging the life of the component. [Read more…]

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Environmental and Use Factors

Environmental and Use Factors

The definition of reliability includes four elements.

One of them is the intended environment where the device or system will experience a range of stresses.

The knowledge of where and how an item will operate enables:

  • The proper design to meet customer expectations
  • The essential durability during transportation, storage, and use
  • The complete accounting of applied stresses and their variations
  • The effective application of stress mitigation or reduction techniques
  • The efficient installation and monitoring of stress tracking

[Read more…]

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Additional Reliability Specification for Your Supplier

Additional Reliability Specification for Your Supplier

Beyond the part reliability specification, you may also add conditions or requests to your reliability specification for your supplier.

The communication with your supplier should include sufficient information that they fully understand your reliability performance expectations. When buying or contracting with a supplier, you are the customer.

Be clear about your reliability requirements including constraints and conditions.  [Read more…]

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Establishing Part Specific Reliability Specifications

Establishing Part Specific Reliability Specifications

Unless you are working with raw materials directly, you rely on your suppliers to provide reliable parts.

Do you suppliers know your reliability objectives for the parts they supply?

If you didn’t tell them, they probably do not know. If you did tell them, did you make it the reliability specification clear and understandable?

As with any specification, clear communication is essential. Guessing or assuming both parties know and have the same reliability goals is, well, not a good practice. The ability of a supplier to build and deliver the parts that meet all your specification has to include a clear and understandable reliability specification.

There is a range of common reliability specifications in use, some are better than others. Let’s start with a brief review of reliability specification types.

Then briefly outline how you establish the reliability specifications for each supplied component. [Read more…]

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Take Action to Deal with Part Obsolescence

Take Action to Deal with Part Obsolescence

Even products with relatively quick design cycles and short stays in the market deal with part obsolescence.

Long design periods along with long durations in service or in production simply increases the chance that one or more parts will become obsolete.

Designing systems with part obsolescence in mind helps. Working with suppliers to select parts with many sources, with long-term plans to produce, and with long term commitments, all may help. Even then, companies change priorities, go out of business, or simply discontinue the part you need. [Read more…]

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Identifying Parts Obsolescence Early

Identifying Parts Obsolescence Early

One aspect of creating a new product or system is the sourcing of parts, components, and materials.

Gone are the days of your organization providing every element of the final product. Henry Ford’s supply chain for early Ford automobiles includes their own forests, rubber plantations, and iron ore mines. [Gelderman, 1981]

We increasingly rely on the supply chain to create the necessary parts for the design’s functionality. Then to continue to supply those same parts for decades, in some cases. [Read more…]