Page 368 - Design for Six Sigma a Roadmap for Product Development

338 Chapter Nine

■ Each component or subsystem within a system may have its own
S curve. Different components or subsystems usually evolve accord-
ing to their own schedules. Likewise, different system components
reach their inherent limits at various times.
■ The components that reach their limits first are “holding back” the
overall system. Such a component becomes the weak link in the
design. An underdeveloped part is also a weak link.
■ The formulation of weak links (contradiction) reveals the compo-
nent(s) of the system that are holding back the development of the
overall system. It seems obvious that the system can be improved by
enhancing links (by eliminating the contradiction) that are con-
straining these components. A frequent mistake in system develop-
ment, however, is the improvement of some strong element other than
that which is limiting the system’s development.

The following examples underscore the importance of focusing
improvement on the weakest link in the system.

Example 9.34 Early airplanes were limited by poor aerodynamics. Yet for
many years, rather than trying to improve the aerodynamics, engineers
focused on increasing airplane engine power.
Example 9.35 A manufacturer of plastic car bumpers was producing scrap
at twice the expected rate. All problem-solving efforts were directed at
improving the manufacturing. Since the company president had been
involved in formulation of material, changes to the formula were not seri-
ously considered. Once, out of frustration, the organization purchased a
commercial formulation. The manufacturing process became stable, and
scrap production fell to one-tenth the target level.

9.9.4 Increasing the degree of dynamism
When a new technical system is developed, it is usually rigid and
inflexible and able to provide only basic functions. The rigidity will
hamper the performance of the system on different user environ-
ments. As the system develops further, the degree of dynamism will
improve.
Example 9.36. Evolution of Lenses Before 1950, the focal length of lens of
a camera was fixed. Then the zoom lens was developed, and has improved
constantly, with a focal length that can be varied at the mechanical level.
One of the patents is presented here:

U.S. Patent 4,958,179 (1990): Camera with changeable focal length.
A variable-focal-length camera uses a lens system which has at least
two different focal lengths: a relatively long focal length suitable for