Chapter 16. Simplified Control Charts
What you will learn in this chapter is how to make simplified control charts that are intuitive and improve process stability. This tool is used in the Improve and Control steps of the DMAIC process. This tool is primarily for those involved in manufacturing or process work.
Control charts have a chaotic history. In the 1960s, when Japan was showing the United States what quality really meant, some people here tried to implement some quick fixes, which included control charts. Few understood control charts and control charts were never used enough to realize their full potential.
NOTE
Control Chart
A control chart is a tool for monitoring variance in a process over time. A traditional control chart is a chart with upper and lower control limits on which are plotted values of some statistical measure for a series of samples or subgroups. A traditional control chart uses both an average chart and a sigma chart.
Now with Six Sigma control charts are getting a second look and have had some impressive successes. However, in a society that is geared to make product within tolerances and with a workforce that generally thinks "sigma" is a health insurance company, control charts are a hard sell. But their potential has been proven and there is a way to implement them that people will more readily accept and use. That way is the simplified control chart.
Traditional control charts use two graphs. The simplified control chart has one graph. The rationale for this simplification is covered throughout the chapter.
In most cases, if a supplier can reduce defect excursions (incidents of higher-than-normal quality issues), the customers will be happy with the product. This does not necessarily mean that all products will be within specification. It means the customers have designed their processes to work with the normal incoming product. So, the emphasis should be on reducing defect excursions, which is the reason control charts were designed.