Page 194 - Six Sigma Demystified

174 Six SigMa DemystifieD

parameters. These changes may result in reallocation of personnel to adjust for
peak demand at certain times of the day or control of the variation in key
parameters, such as room temperature, to control the size of a key dimension.
The natural response of process personnel may be to gradually or even
abruptly return to past practices. This may occur the first time the process
experiences a shift in behavior, when personnel return from vacation and fall
into old habits, or when you’re just not looking.
There are several practices that are useful for standardizing on the new pro-
cess methods:

• Process control is used to monitor process variation. The most effective
methods often minimize process variation by precision control of the
input parameters.
• Control plans are used to define the methods of control and to ensure that
all potential sources of variation are addressed.
• Work instructions, flowcharts, and process maps are used to document
process procedures and responsibilities.
• Training is essential for process personnel to understand their new respon-
sibilities. The communication of these methods, procedures, and respon-
sibilities should be integrated into a training program for process personnel.

Process Control

How do we prevent the process from deviating from its improved state, includ-
ing returning to past performance levels? There are two main strategies for
achieving process control, stemming from the work done in the failure modes
and effects analysis (FMEA):

• Prevent or greatly reduce the occurrence of errors.
• Detect the occurrence of the error and correct its effect before the cus-
tomer experiences the undesirable effect.

Of course, if the cost to implement were the same, prevention always would
be preferred to detection owing to
1. The increased costs of remedying the error

2. The delay experienced by the customer as the error is remedied
3. The uncertainty in detecting all errors even when all product output is
sampled