Page 178 - Design for Six Sigma for Service (Six SIGMA Operational Methods)

150 Chapter Seven

After it is believed that all functions of the assembly have been defined, take
each part or segment of the system and define the function of each. There
will be some duplication, but this will be screened out later.

After all functions have been defined, screen the list to eliminate duplicate
functions and redefine functions for clarity of understanding. Now, screen
the list again to define the basic function. The basic function is the function
upon which all other system functions depend. If the basic function is not
needed, none of the other functions will be needed.

In many cases, a number of functions beyond the system scope will be
defined. These are called high-order functions and are those functions that
cause the basic function to be performed. A detailed discussion of the scope
and high- and low-order functions is beyond the intent of this orientation
and are mentioned here only to note that it is not necessary to struggle over
this step as the scope will become clear during the construction of a FAST
diagram. The team may even reconsider the original scope and redefine the
scope because of the new understanding of the overall project.
By application of the function definition principles cited here the end result
will be clearly understandable, be measurable for use in cost-function
analysis and function evaluation, and lead to outstanding opportunities in
the creative phase.

7.2.3 Function Analysis and Evaluation

After the functions have been determined, identify the basic function or
functions, as well as all the supporting functions. It is time to create a
functional analysis system technique (FAST) diagram. The functional
analysis system technique was developed by Charles Bethway in 1964, and
first presented and published as a paper at the Society of American Value
Engineers Conference in 1965. FAST contributed significantly to the most
important activity in the value-engineering project, the function analysis
and evaluation.

A FAST diagram is a logic chart that organizes the functions of a project and
arranges them in a cause-and-effect relationship. Construction of a FAST
diagram is necessary to ensure that the functions have been properly defined
and that nothing has been overlooked. Although it follows a simple concept,
the process of creating a FAST diagram is often difficult and frustrating, and
it forces people to think out their project in a detailed and precise manner.
Construction of a FAST diagram creates a focal point for the entire project,