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Chapter 19: B. Statistical Process Control 247
decreased cost. This is due to the need for less rework, thus less scrap, fewer raw
materials used, fewer man-hours, and fewer machine hours wasted. All of this
ultimately means increased productivity, better competitive position, and hence
higher sales and higher market share. On the other hand, losses due to poor quality
are enormous. Poor quality not only affects sales and competitive position, but
also carries with it high hidden costs, which usually are not calculated and therefore
are not known with precision. These costs include unusable product, product
sold at a discounted price, and so on. In most companies the accounting departments
provide only minimum information to quantify the actual losses incurred
due to poor quality. Lack of awareness concerning the cost of poor quality can lead
company managers to fail to take appropriate actions to improve quality.
WHAT IS A PROCESS?
A process may be defined as a series of actions or operations performed in producing
manufactured or nonmanufactured products. A process may also be defined as
a combination of workforce, equipment, raw material, methods, and environment
that work together to produce output. The flowchart in Figure 19.1 is an example
showing where each component of a process fits.
Note that statistical process control is very useful in any process, whether in
the manufacturing, service, or retail industries. There are several tools that are
very valuable in achieving process stability. The set of all these tools, including
control charts, constitute an integral part of SPC. These tools are:
1. Histogram
2. Stem-and-leaf diagram
3. Scatter diagram
4. Pareto chart
5. Check sheet
6. Cause-and-effect diagram (also known as fishbone or Ishikawa diagram)
7. Defect concentration diagram
8. Run chart (also known as line graph or time series graph)
9. Control charts
The first four of these tools we have already discussed in Chapter 18. We are now
going to discuss the rest.
Part IV.B
CHECK SHEET
In order to improve the quality of a product, management must try to reduce the
variation of all the quality characteristics; that is, the process must be brought into
a stable condition. In any SPC procedure used to stabilize a process it becomes
essential to know precisely what type of defects are affecting the quality of the
final product. The check sheet is an important tool to achieve this goal. We discuss
this tool with the help of a real-life example.