The Illusion of Control


The Problem

In industry the quality of the product and the profit of the manufacturing company are two important factors. In a manufacturing operation it is important to continually monitor the quality of the product being produced. If a manufacturing variable is out of control, the resulting product could be of poor quality and therefore not usable. A loss in profit to the manufacturing organization, as well as dissatisfied customers, may result. Many companies use process control charts to monitor the product that is being produced.

Background Information

At first glance, a control chart resembles a time series graph. It is used to monitor certain characteristics of a process, such as thickness of sheets of aluminum, size of holes bored in machine parts, and percentage of on-time delivery, over time. Control charts can be used as the process is running to make corrections as necessary, or after the process has been completed to correct mistakes before running again. It is understood that any process will experience natural variability through uncontrollable sources. The control chart is designed to detect more severe variability due to cause which indicates that a correctable problem has arisen.

Control charts use two indicators to determine whether the process is in control: a measure of center (usually the mean) and a measure of spread (either the standard deviation or the range).

Materials Included

  • Basic information about control charts and how to create them.
  • Complete example showing how to use and interpret control charts.
  • Two additional examples which can be assigned and used in class:
    • Don’t Drink the Water
    • Dribble Building Blocks