Total Quality Management - CII Institute of Logistics

Total Quality Management
Your goal should be to demonstrate that your job is operating in a stable manner. When
the assignable causes have all been corrected, the variation in your products is due only
to chance causes.
When your operation is stable, then - and only then - can you know with confidence
what your quality level is. When your operation is stable, your productivity and quality
are the best they can be with your process.
Statistical methods of quality control give you a way to picture and control quality
through the use of these "tools of quality".
1. The histogram or frequency distribution
2. The control chart
THE HISTOGRAM OR FREQUENCY DISTRIBUTION
In many families it is a custom to have a picture taken each year. Just as a family
picture is a snapshot of a group of people, the histogram is a "snapshot" of a group of
parts from a manufacturing operation. It shows how a process is operating at a given
time.
A histogram is simple to construct. It is nothing more than a frequency distribution put
into block form. Let's just say we want a picture of the diameters of 100 bushings being
machined on a lathe.
By the end of our check, the frequency distribution might be as it is shown in Figure
4.6. Putting this distribution into graphic form produces the histogram shown in Figure
4.7. Like the family picture, each histogram has a story to tell.
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