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

Optimizing Maintenance

One of the considerations when planning maintenance is the timing of the replacement of parts of the system. In some cases it makes sense to wait for the item to fail, sometimes, it makes sense to place it on an interval or set an amount of operating time, and yet in others, we can measure indicators that a replacement is necessary.

In order to make these decisions, we need data.

According to O’Connor and Kleyner (Practical Reliability Engineering, 5th Ed.), we need specific information for each part. The following list outlines the recommended information. [Read more…]

by Fred Schenkelberg 10 Comments

When to Conduct HALT

HALT (highly accelerated life testing) is a method to reveal product weaknesses. Design prototypes experience the step-stress application of relevant stresses until failures appear.

The intent is to find design or process related weaknesses early in the design process thus providing time to economically address the issue. Using a build-test-fix approach does improve a product’s robustness and reliability.

Being a useful tool, should you conduct HALT on every project? It seems that revealing weaknesses is certainly useful. [Read more…]

by Fred Schenkelberg 7 Comments

Expectation and Moment Generating Functions

In statistics and reliability, we use distributions to describe time to failure patterns. The four functions commonly used in reliability engineering include

The probability density function
The cumulative distribution function
The reliability function
The hazard function

We often use terms like, mean, variance, skewness, and kurtosis to describe distributions (along with shape, scale, and location). The mean is defined as the use of a moment generating function. First though let’s first back up to the concept of center of gravity (cog) from mechanics. [Read more…]

by Fred Schenkelberg 2 Comments

Benefits of Reliability Engineering

We see the terms ‘reliable’ and ‘reliability’ in daily advertising, business names and in casual conversations on a regular basis. Reliability has meaning and importance in our society. Product and brand reputations are made or broken by their product reliability performance.

[Read more…]

by Fred Schenkelberg Leave a Comment

Establishing Reliability Goals

The way we communicate goals directly impacts the achievement of the goal. Creating and succinctly stating a reliability goal necessary for the leadership it provides an organization when designing a new product. The reliability goal statement includes four elements:

function
environment
probability of success
duration.

The function definition provides one means to define failure conditions. The environment includes elements such as weather and elements related to use frequency. ᐅ Play Episode

by Fred Schenkelberg 1 Comment

Censored Data and CDF Plotting Points

Reliability testing and data collection is a messy business.

We rarely receive perfect data where all units involved have a precise time to failure record. Sometimes we do not the precise time to failure information or some of the units are still operating.

The data is censored.

There are a few common types of censoring, each of which has statistical techniques to appropriately account for the unknown elements. [Read more…]

by Fred Schenkelberg 2 Comments

How to Assess Your Reliability Program

“How do you know so much about our program?” was a question the quality manager asked after reading the assessment report. The assessment took one day with eight interviews.

The reliability that results is going to happen whether or not the team designing the product or production line deliberately use reliability engineering tools or not. The elements of a product or system will respond to the environment and either work or fail.

While working at Hewlett-Packard I had the opportunity to conduct reliability program assessment of about 50 product divisions. One hypothesis related the number of reliability tasks the team actively used would correlate to their warranty expenses.

That worked to a point. [Read more…]

by Fred Schenkelberg 2 Comments

4 Electronics Nondestructive Evaluations

It is possible to use the circuit design or the circuit itself to evaluate electronics. This ranges from checking if the system is wired correctly (the right parts are present and attached properly) to a complex evaluation including the proper functioning of firmware and attached software.

Beyond visual inspection, we need a way to evaluate the microscopic structures with today’s electronic components.

The ability to provide inputs and measure outputs provides one view and in most cases is nondestructive. [Read more…]

by Fred Schenkelberg Leave a Comment

Reliability Risk Reduction Tools

The process to create a new product has risk. There are safety, technical, schedule and financial risks
The risk of a product failing more often then deemed acceptable by the customer or the business falls in the realm of reliability engineering to address.

We can provide insight on what is expected to failure and when. Working with the entire team we can influence the design and assembly process to minimize the risk of field failures.

Below is a short list the most common risk reduction tools in our arsenal. [Read more…]

by Fred Schenkelberg 3 Comments

8 Nondestructive Evaluation Techniques

There are times when we need to evaluate a product to determine is it assembled correctly or when looking for clues concerning a failure mechanism. Simple visual inspection may be sufficient and there are times when we need more information or detail.

A great first step is the use of an appropriate nondestructive evaluation (NDE) method.

Done correctly, we keep the item unchanged and available for shipment or further inspection.

[Read more…]

by Fred Schenkelberg 5 Comments

8 Factors of Design for Maintainability

The first time I changed the oil filter of my car (first car in high school) I smashed my knuckles against a grimy block of metal. More than once. It may have been my lack of experience or improper tools. Or, it may have been a rather poor design.

Watching the Indy 500, especially the pit stops, I quickly realized there has to be something different about those cars that lets them change tires, add oil & fuel, and clean the windshield in less time than it took me to get under the hood and find the oil filter. The cars were designed differently and that is what permitted the difference in service time.

In order to increase availability and minimize the cost of maintenance, we have to deliberately design the system to accommodate the needs of maintenance. [Read more…]

by Fred Schenkelberg Leave a Comment

Big Picture of Reliability Plans

Reliability is an attribute of an item. The item, with its design, assembly, and use, has a finite probability of working over some duration.

We deliberately attempt to create items that meet our and our customer’s expectations concerning that probability and duration. We maintain and operate our equipment with an expectation of successful performance.

We and our customers are let down when a failure occurs. We do not enjoy the benefits of the item’s value. [Read more…]

by Fred Schenkelberg 2 Comments

Reliability Testing Considerations

Reliability testing to determine what will fail or when will failures occur is expensive.

Organizations invest in the development of a product and attempt through the design process to create a product that is reliable. [Read more…]

by Fred Schenkelberg Leave a Comment

Reliability is Not Just Statistics

In a common definition used by engineers reliability is a probability of success. It is the chance of an item operating as expected over some duration in a given environment. In this case, we have probability as part of the definition of reliability.

Reliability in common use definition includes trustworthiness, dependability and similar definitions. It’s more than how many times your friends help you move to a new apartment, it’s a feeling or sense we have concerning our ability to count on our friends for the help.

[Read more…]

by Fred Schenkelberg Leave a Comment