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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.

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Variable Selection for Control Charting

Variable Selection for Control Charting

Every process should operate stably. Every process may have many measurements available to monitor either various aspects to the final product or the assembly equipment. There may be hundreds of possible items to measure and monitor.

We do not have the resources nor time to apply control chart principles to each possible measurement. Control charts do not directly add value and they have a cost to maintain and interpret. While it may be tempting to add a dozen or so control charts, as the cost increases the value quickly decreases.

[Read more…]

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Understanding Customer Reliability Expectations

Understanding Customer Reliability Expectations

Once asked a customer what they wanted concerning product reliability.

She fully understood that some units will fail, that it’s matter of chance. She seemed understanding of the difficulty creating every product such that none would fail.

Then she confided that all that is fine, as long as the product she buys does not fail. [Read more…]

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Special and Common Causes of Process Variation

Special and Common Causes of Process Variation

As stated before, variation happens.

The root cause of the variation for a stable process includes material, environmental, equipment, and so on, changes that occur during the process. No saw cuts the same length of material twice – look close enough there is some difference. [Read more…]

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How to Select Tasks for a Reliability Plan

How to Select Tasks for a Reliability Plan

There are a lot of reliability tools.

From FMEA to FTA, from ALT to HALT, from derating to sneak circuit analysis. We also have a lot of acronyms. We cannot afford to do all the tasks, so which do we select and why?

Each activity has some reason for existing. Each has some question that it helps answer. HALT helps to find what will fail. ALT helps to determine when failures may occur.

Knowing what each tool is capable of doing is a start. Knowing what you need to know is essential.

[Read more…]

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Pre-Control Charts

Pre-Control Charts

An easy method to monitor and control a process average. It is an alternative to the Shewhart control chart.

Pre-control charts work well with stable and slow process drifts or changes. These charts provide a means to monitor a process and act as a guide for process centering.

They are easier to setup, implement, and interpret the Shewhart charts. [Read more…]

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The Meaning of a Failure

The Meaning of a Failure

Every failure provides information. It provides time to failure, stress strength relationship, process stability and design margin types of information. In every case. Even failures directly related to human error.

A hardware intermittent failure observed by a firmware engineer should not be dismissed. Rather recorded, explored and examined.

A single intermittent failure, or glitch, may indicate nothing other than just a totally random glitch, or a design error that degrades over time causing 50% of units to fail in first three months.

[Read more…]

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Process Capability

Process Capability

The connection between the specifications or drawings or design requirements and the manufacturing process is the capability of the process to consistently create items within spec.

A ratio of the specification over the spread of measured items provides a means to describe the process capability.

The ratios rely on the standard deviation or spread of the produced items. The index is meaningful only if the process is stable. Thus beyond making sure the measurements have minimal measurement error, check the stability using the appropriate control chart.

In this article we are assuming the measurements are normally distributed, yet knowing that is not always the case, you can calculate capability indices using the actual distribution.

The indices will have similar interpretations yet take care when applying these concepts using other than normal distribution data.

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3 Supply Chain Caused Failures

3 Supply Chain Caused Failures

Some days are better than others. We sometimes run into failure when working to create a new product. With a little investigation we suspect the components are not working as expected.
We’ll call the vendor and ask for an explanation. If this is normal production and variability of performance, our product will suffer an higher than expected failure rate. The vendor will assure us with:

  1. It must have been damaged during assembly or use by us.
  2. It was a very rare manufacturing mistake and won’t happen again.
  3. We haven’t seen this before and you’re the first to report such an issue.
  4. We know about this issue and it’s been resolved in our process.
  5. Must have been an ESD (electrostatic discharge) event.

Not helpful. [Read more…]

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9 Reliability Growth Patterns for Two Test Phases

9 Reliability Growth Patterns for Two Test Phases

The basic idea of reliability growth is the information learned during testing allows the team to make improvements.

The improvements then reveal themselves in the next round of testing. There are improvements during each test phase as the immediate fixes occur.

Plus some improvements may have longer lead times and be implemented in time for the next round of testing. [Read more…]

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The Want of Modern Customer Service

The Want of Modern Customer Service

Reliability and  Customer Service

As reliability professionals know, products fail. They fail for a wide range of reasons and over a broad span of time. We know it happens.

This doesn’t help when it impacts us directly though. When we purchase a product or service, it should just work. We know the odds, we know better, yet the sting of failure remains.

Customer Service provides a range of services, one of which is helping customers receive the benefit of their purchase. We call customer service to report a failure and expect their help making it right. [Read more…]

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Duane Plot of Cumulative Failures Over Time

Duane Plot of Cumulative Failures Over Time

Let’s take a graphical view of reliability improvement that occurs during product development or improvement projects.

If we are making improvements the system reliability should increase. We can use the build, test, fix approach to measure improvements, find failures, design improvements, and repeat. [Read more…]

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Root Sum Squared Tolerance Analysis Method

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…]

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Minimize Supply Chain Failure Causes

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…]