Page 89 - Design for Six Sigma a Roadmap for Product Development

64 Chapter Three

mean the ability to accelerate from a speed of 0 to 100 km/h within 10 s,
and this is a functional requirement. Clearly, a product may have
many functional requirements. Specifically, functional requirements
(FRs) are a minimum set of independent requirements that completely
characterize the functional needs of the design solution in the func-
tional domain.
The physical domain is also called the design parameter domain,
and design parameters (DPs) are the elements of the design solution
in the physical domain that are chosen to satisfy the specified FRs.
Design parameters cover the specific physical design that can be
used to deliver all required functions. For example, if a functional
requirement for a car is to accelerate from 0 to 100 km/h in 10 s, the
design parameter for that would include necessary power train
design specifications, including engine design, transmission design,
and so on.
The process domain deals with process variables. Process domain
refers to the relevant manufacturing process specifications that can
build production facility to produce the designed product. Process vari-
ables (PVs) are the elements in the process domain that characterize
the process which satisfies the specified DPs. Figure 3.4 illustrates the
four domains in the design process.
Another important feature in design work is the hierarchical design
deployment. See Fig. 3.5. For many products, the design has to follow a
hierarchical system structure within each domain. If we take automo-
bile design, as an example, in the design parameter domain the car is
a system; it consists of several subsystems, such as body, interior,
power train, chassis, and so on. Each subsystem can be further decom-
posed into the next level of details. The design is not done until all the
finest specifications on part dimension, material, tolerance, etc., are
finished.

Y=f(x)
CAs FRs DPs PVs
• • • •
• • • •
• • • •

Y= f(x)
Physical mapping Process mapping
Customer Functional Physical Process
domain domain domain domain
Figure 3.4 Four domains in the design process.