Page 587 - Design for Six Sigma a Roadmap for Product Development

544 Chapter Fifteen

y=Measured
value

M=Standard
value

d. Analysis. The ideal measurement system should be able to give exactly
the same value of the characteristic as the true value; for example, an
ideal scale should show one gram (1 g) if the item weighs truly 1 g.
When we use the ideal function shown above to benchmark a measure-
ment system, for example, using several different standard weights to
benchmark a scale, the standard weight is again a “control.” The robust-
ness of ideal function is the indication of the robustness for
(1) Different levels of transformation
(2) Controllability
4. Injection-molding process
a. Main function. Making parts to the mold shape
b. Main transformation. Material transformation
c. Ideal function

y=Part
Dimension

M=Mold Dimension

d. Analysis. Injection molding transforms polymer granules into shaped
parts, so the main transformation is obviously a material transfor-
mation. The mold is a “control” for the shape. The linear relationship
in the ideal function shown above means that when the mold changes,
say, into a larger mold, then the magnitude of material transforma-
tion also changes. This linear relationship also indicates controllabil-
ity. Therefore, the robustness of the ideal function is an indication of
the robustness for
(1) Different levels of transformation
(2) Controllability
All of these examples have shown the following common features of
ideal functions: