100-Metodos-de-Qualidade-Total

ANALYTICAL METHODS 117
Method 48
System design
Purpose
To apply special scientific and engineering knowledge to produce a basic
functional prototype model, having surveyed the relevant technology,
manufacturing environment and customer need.
When to use
To design quality into the process by carrying out research and development
experiments in order to find the best operating conditions for the
satisfaction of the customer.
How to use
Reject the notion that to be outside specification is bad, but to be within
specification, even by only a whisker, is satisfactory. Replace it by the new
idea of process capability in connection with the criteria Cp and Cpk. Make
people think in terms of aiming for a target value and work to reduce the
mean square error that is the sum of the square of the bias and the
variance. It is necessary to control both of them because the process
requires zero bias and smallest possible variance.
Benefits
It helps to take the prototype model and make it happen according to
customer requirements.
Example
The process capability index Cp is
C =
p
USL-LSL _
6a
21)
6a
When USL and LSL are the upper and lower specification limits respectively.
As a (standard deviation) decreases, Cp increases. 21) is specification
width.