Content By Donald J. Wheeler

Donald J. Wheeler’s picture

By: Donald J. Wheeler

The average and range chart handles most situations where the data can be logically organized into homogeneous subgroups. However, this chart breaks down when faced with a hierarchical data structure containing two or more levels of routine variation. For these situations I developed the three-way chart in 1982.

Donald J. Wheeler’s picture

By: Donald J. Wheeler

Good measurements are like apple pie and motherhood. Who could ever be against having good measurements? Since we all want good measurements, it sounds reasonable when people are told to check out the quality of their measurement system before putting their data on a process behavior chart. Fortunately, this is simply one more bit of advice that is completely unnecessary.

Donald J. Wheeler’s picture

By: Donald J. Wheeler

What can be done when a test is destructive? How do we characterize measurement error? How can we determine if a test method is adequate for a given product or application? How can we check for bias?

Donald J. Wheeler’s picture

By: Donald J. Wheeler

Who can be against apple pie, motherhood, or good measurements? This is why everyone stands up and salutes when we are told to maintain our measurement systems in good calibration. But what is good calibration? By what method will we achieve it? And how will we know when we have it?

Donald J. Wheeler’s picture

By: Donald J. Wheeler

Opinion

There was an election in Xanadu recently. One of the issues that was repeatedly brought up was the possibility of election fraud. So out west in the town of Hawtch-Hawtch, the people got some “Hawtch-Hawtch bee watchers” to go out and watch the polls.

Donald J. Wheeler’s picture

By: Donald J. Wheeler

Now we come to the sixth way to use a process behavior chart. Here we are going to look at how one group of workers used their average and range chart to improve their process. Their part had only one critical dimension, and this dimension had a standard deviation of only 15 microns. What kind of high-tech product might this be? Read on.

Donald J. Wheeler’s picture

By: Donald J. Wheeler

While we may tweak things in production, we rarely get permission to conduct formal experiments with an operating production line. Production’s job is to make product, whereas experiments are what they do in R&D. So how can we learn about an existing production process without rocking the boat? This is where input and outcome charts have a role to play.

Donald J. Wheeler’s picture

By: Donald J. Wheeler

The question “Is this batch like the others?” is asked all over the world on a daily basis. It turns out that the process behavior chart provides a very effective answer for questions about the homogeneity of the product stream.

In World War II, Gen. Leslie Simon used the process behavior chart to define “grand lots” of material. Material in the same grand lot should all be treated alike, but material belonging to different grand lots might need to be treated differently.

Donald J. Wheeler’s picture

By: Donald J. Wheeler

Donald J. Wheeler’s picture

By: Donald J. Wheeler

The simple process behavior chart may be used in several ways. Many articles and some textbooks describe process behavior charts as tools for process monitoring. In Norway the words used for SPC translate as “statistical process steering.” In this column we will look at the pros and cons of using a process behavior chart as a process monitor to steer a process.