| What is it? |
| Introduced
in the 1950s by George Box, EVOP is an ongoing mode of using an operating full-scale
process, so that information on how to improve the process is generated from a simple
experimental design while production is underway. To avoid appreciable changes in the
characteristics of the product, only small changes are made in the levels of the process
variables. EVOP is designed to be run by process operators on a full-scale manufacturing
process while it continues to produce satisfactory products. |
| Why is it
important? |
| Classic
experimental design and Taguchi methods are revolutionary methodologies which help us to
establish an optimum combination of the design factors and their proper levels for the
manufacturing process. They are very powerful tools; but they cost money, time, manpower
and require special training to conduct the experiments. In most cases, they interrupt
production. Experimental design should be used in the design stage and trouble shooting to
solve specific quality problem. It cannot be a routine operation. EVOP is a tool in which
a continuous investigative routine becomes the basic mode of operation for the plant and
replaces normal static operation. |
| When to use it? |
| The
basic idea is to replace the static operation of a process by a continuous and systematic
scheme of slight perturbations in the control variables. The effect of these perturbations
is evaluated and the process is shifted in the direction of improvement. |
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| How to use it? |
There are one/two/three factor EVOP designs.
Single Factor EVOP Design:
| 1 |
If X were to be current production level,
usually this is set as the new center of specification and is determined by designed
experimentation. |
| 2 |
Choose acceptable levels, X-D and X+D (within the specification
limits) which still produces satisfactory products. |
| 3 |
Evaluate the quality of the process at all
three production levels (X, X-D and X+D)
and choose one that produces the highest quality of product. |
Two Factor EVOP Design:
| 1 |
If X is the first factor at the current
production level, Y is the second factor at the current production level - evaluate the
quality of the output at all different combinations of X & Y including the D. The combination that produces the highest quality is the new
center point and repeat EVOP for the next cycle of continuous improvement. |
Then there is the three-factor
EVOP which goes on same lines as above but with three factors.
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| Food for Thought ! |
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