
80 Control for Aluminum Production
Characterized by a pattern of variation that changes
resulting in an unpredictable pattern over time
Special (assignable) and common causes
of variation are present
is process does not
exhibit statistical control
Evidence of Special
Cause
Evidence of Special
Cause
On a control chart, it might look something like this
A process will be regarded as being “in control” when,
through the use of past experience, we can predict, at
least within limitts, how the process will behave in the
future.
It is important that our processes are “In control”.
However, a proc