Articles

Find all articles across all article series listed in reverse chronological order.

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.

[Read more…]

by Fred Schenkelberg 1 Comment

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:

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

Not helpful. [Read more…]

by Fred Schenkelberg Leave a Comment

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…]

by Fred Schenkelberg Leave a Comment

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…]

by Fred Schenkelberg Leave a Comment

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…]

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…]