Page 214 - The Handbook for Quality Management a Complete Guide to Operational Excellence

200 P r o c e s s C o n t r o l Q u a n t i f y i n g P r o c e s s Va r i a t i o n 201

However, because a company has only a limited resource base and
can’t solve all problems simultaneous ly, it must set priorities for its
efforts. The tools for this include Pareto analysis and fishbone
diagrams.
2. Define the process. It is all too easy to slip into the trap of solving the
wrong problem. Once the candidate area has been selected in step
1, define the scope of the study. A process is a unique combination
of machines, tools, meth ods, and personnel engaged in adding
value by providing a product or service. Each element of the
process should be identified at this stage. This is not a trivial
exercise. The input of many people may be required. There are
likely to be a number of conflicting opinions about what the
process actually involves.
3. Procure resources for the study. Process capability studies disrupt
normal operations and require signif icant expenditures of both
material and human resources. Since it is a project of major
importance, it should be managed as such. All of the usual project
management techniques should be brought to bear. This includes
planning, scheduling, and management status reporting.
4. Evaluate the measurement system. Using the techniques described
in Chap. 14 evaluate the measure ment system’s ability to do the
job. Again, be prepared to spend the time necessary to get a valid
means of measuring the process before going ahead.
5. Prepare a control plan. The purpose of the control plan is twofold:
(1) isolate and control as many important variables as possible,
and (2) provide a mechanism for tracking variables that cannot
be completely controlled. The object of the capability analysis is
to determine what the process can do if it is operated the way it
is designed to be operated. This means that such obvious sources
of potential variation as operators and vendors will be controlled
while the study is conducted. In other words, a single well-
trained operator will be used and the material will be from a
single vendor.
There are usually some variables that are important, but that
are not controllable. One example is the ambient environment,
such as tem perature, barometric pressure, or humidity. Certain
process variables may degrade as part of the normal operation;
for example, tools wear and chemicals are used. These variables
should still be tracked using log sheets and similar tools. See
Chap. 7 for information on designing data collection systems.

6. Select a method for the analysis. The SPC method will depend on
the decisions made up to this point. If the performance measure
is an attribute, one of the attribute charts will be used. Variables

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