© 2004 Cayman Business
Systems
Rev:
Pre-G3 - Rendered Thursday,
February 12, 2004
Slide 46
Elsmar.com --- The
Cove!
8-Disciplines Problem Solving
Facts About Causes of Variation
+Special Causes of Variation
+Accounts
for 5-15% of quality problems.
+Is due
to a factor that has "slipped" into the process causing unstable or unpredictable variation.
+Are
unpredictable variations that are abnormal
to the process including human error,
equipment failure, defective/changed
raw materials, acid spills, power
failures, etc.; failure to remove
them can result is corrosion, scale, metal
fatigue, lower equipment efficiency, increased
maintenance costs, unsafe working
conditions, wasted chemicals, increased
down-time (plant shut-down...), etc.
+Removal of all special causes of variation yields a
process that is in statistical control.
+Correctable by local personnel.
+Common Causes of Variation
+Account for 85-95% of quality problems
+Are due
to the many small sources of variation
"engineered" into the process of the "system”.
+Are
naturally caused and are always present
in the process because they are linked
to the system's base ability to perform;
it is the predictable and stable inherent
variability resulting from the process
operating as it was designed.
+Standard
deviation, s, is used as a measure
of the inherent process variability;
it helps describe the well-known
normal distribution curve.
+Correctable only by management; typically
requires the repair/replacement of a
system's component, or the system itself.