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 24 Comments

Root Sum Squared Tolerance Analysis Method

The root sum squared (RSS) method is a statistical tolerance analysis method.

In many cases, the actual individual part dimensions occur near the center of the tolerance range with very few parts with actual dimensions near the tolerance limits. This, of course, assumes the parts are mostly centered and within the tolerance range.

RSS assumes the normal distribution describes the variation of dimensions. The bell-shaped curve is symmetrical and fully described with two parameters, the mean, μ, and the standard deviation, σ. [Read more…]

by Fred Schenkelberg Leave a Comment

Minimize Supply Chain Failure Causes

What happens when a product you produce fails? You customer may call and return the product. They may expect you to provide a replacement or refund.
Does it matter if the failure was due to a capacitor or motor that you didn’t design, just purchased?

No.

Does it matter if a supplier’s supplier made an error that directly lead to the failure?

No.

You customer experienced a failure and since the purchase was from you, you are expected to make it right.

[Read more…]

by Fred Schenkelberg 2 Comments

18 Tips for Taking Standardized Exams

Guest Post By Dan Burrows

To help you with taking standardized exams such as ASQ Certification exams, here are some tips that I learned a long time ago that have helped me. There may be cultural differences between the USA and other countries that would invalidate some of these. If anything that I included goes against what the specific examination authority recommends for test taking rules or strategy, go with their recommendations.

There may be cultural differences between the USA and other countries that would invalidate some of these. If anything that I included goes against what the specific examination authority recommends for test taking rules or strategy, go with their recommendations. [Read more…]

by Fred Schenkelberg 2 Comments

2014 in Review

The WordPress.com stats helper monkeys prepared a 2014 annual report for this blog. Thanks to everyone for making this blog and program a success.

Here’s an excerpt:

The concert hall at the Sydney Opera House holds 2,700 people. This blog was viewed about 26,000 times in 2014. If it were a concert at Sydney Opera House, it would take about 10 sold-out performances for that many people to see it.

Click here to see the complete report.

by Fred Schenkelberg Leave a Comment

2 Design Approaches to Creating a Reliable Product

There are two basic philosophies when creating a reliability plan for a new product or system.

One is to experiment with prototypes as quickly and often as possible, the build, test, fix, approach. Or, you can research and model detailed aspects of the materials and structures to characterize the strength of a product or system, the analytical approach.

Both methods have obvious applications and not so obvious limitations. [Read more…]

by Fred Schenkelberg 2 Comments

Safety Factor

Products that fail may create an unsafe situation.

For catastrophic failure mechanisms, the design team may consider establishing a safety factor or margin of safety policy. This provides the design team guidance as they size structures, select components, and evaluate performance and reliability.

A safety factor or margin are measures of the separation of the stress and strength for a specific failure mechanism. If something has a 2x safety factor it implies the element is twice as strong as the expected stress. [Read more…]

by Fred Schenkelberg 2 Comments

Why do Tolerance Analysis

The short answer is, everything varies.

The longer answer involves the agreement between what is possible and what is desired.

If we could design a product and it could be replicated exactly, including every element of the product, we would not need tolerances. Any part would work with any assembly. We would simply specify the dimensions required. [Read more…]

by Fred Schenkelberg 2 Comments

Worst Case Tolerance Analysis

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.

The worst case method simply adds the dimensions using the extreme values for those dimensions. Thus if a part is specified at 25mm +/- 0.1mm than use either 25.1mm or 24.9mm, whichever leads to the most unfavorable situation. [Read more…]

by Fred Schenkelberg 1 Comment

Purpose of Tolerances

The short answer is, everything varies.

The longer answer involves the agreement between what is possible and what is desired.

Instead, variation happens.

Widths, lengths, weights, roughness, hardness, and any measure you deem worth specifying will vary from one part to the next. Manufacturing processes impart some amount of variation between each item produced. In many cases, the variation is acceptable for the intended function. In some cases, the vacation is unacceptably large and leads to failures. When the design does not account for the variation holes will not align, components will not fit, or performance will be poor.

[Read more…]

by Fred Schenkelberg Leave a Comment

Consider Variation for Reliable Designs

The better reliability performing systems start the design process with controlling variability.

Variability of materials and processes involved thought the product lifecycle. Reliability performance occurs as a result of the decisions made throughout the design process.

When focused on understanding and minimizing variability, the design becomes robust and reliable.

[Read more…]

by Fred Schenkelberg 1 Comment

Select the Right Accelerated Life Test Approach

There are many reasons to use accelerated testing and just as many ways to conduct the testing.

Matching and balancing cost, risk, and results takes some skill.

Let’s talk about the key elements to consider so you select the best approach for your test.
ᐅ Play Episode

by Fred Schenkelberg Leave a Comment

CRE in Application

Guest post by Daniel C. Conrad

In the past, a reliability engineer developed their skills over years of practice under a mentor.

Today, a reliability engineer is a jack of all trades and needs to be a master of them as well. Reliability has developed into its own science and is a discipline in its own right which crosses many fields of engineering, statistics, and physics. One way to show you have the broad understanding needed to succeed in the diverse field of reliability is the Certified Reliability Engineering (CRE) from the American Society of Quality (ASQ). [Read more…]

by Fred Schenkelberg Leave a Comment

Steps to Improve Supplier Reliability

Situation

It’s Friday afternoon and the phone rings. It is another customer complaining about your product not working. This is the fifth call this afternoon. Something is wrong and you’re responsible for making it right.

The natural failure analysis process starts across your team. Gather information, determine the scope of the issue, work to understand the root causes, and implement an appropriate solution. This may involve stopping production, halting shipments, or even a product recall.

Initially, you just have more irate customer calls than a typical Friday afternoon. [Read more…]

by Fred Schenkelberg Leave a Comment

Elements of a Reliability Manual

One method to define an organization’s approach to reliability is to create a reliability manual. Many organizations already have a quality manual as required for ISO 9000 or similar certification. Reliability may be a section of the larger quality manual or simply integrated into the same document. [Read more…]

by Fred Schenkelberg Leave a Comment

How to Prepare for the CRE Exam

The ASQ CRE exam is difficult. The individual elements of the body of knowledge are not in themselves difficult, it is just such a broad range of topics that mastering all the subjects is a challenge.

The CRE Body of Knowledge includes elements of leadership & management, testing & failure analysis, and basic & advanced & reliability statistics. Reliability engineers work across the spectrum of consumer product design to plant maintenance.

Depending on your experience you may have a wealth of experience with availability modeling and repairable system data analysis, and have little experience with design for reliability practices. [Read more…]