| The
term Rapid
Prototyping (RP)
refers to a class of technologies that can automatically
construct physical models from Computer-Aided Design
(CAD) data. These "three dimensional printers"
allow designers to quickly create tangible prototypes
of their designs, rather than just two-dimensional pictures.
Such models have numerous uses. They make excellent
visual aids for communicating ideas with co-workers
or customers. In addition, prototypes can be used for
design testing. For example, an aerospace engineer might
mount a model airfoil in a wind tunnel to measure lift
and drag forces. Designers have always utilized prototypes;
RP allows them to be made faster and less expensively.
In
addition to prototypes, RP techniques can also be used
to make tooling (referred to as rapid tooling) and even
production-quality parts (rapid manufacturing). For
small production runs and complicated objects, rapid
prototyping is often the best manufacturing process
available. Of course, "rapid" is a relative
term. Most prototypes require from three to seventy-two
hours to build, depending on the size and complexity
of the object. This may seem slow, but it is much faster
than the weeks or months required to make a prototype
by traditional means such as machining. These dramatic
time savings allow manufacturers to bring products to
market faster and more cheaply. In 1994, Pratt &
Whitney achieved "an order of magnitude [cost]
reduction [and] . . . time savings of 70 to 90 percent"
by incorporating rapid prototyping into their investment
casting process. 5
At
least six different rapid prototyping techniques are
commercially available, each with unique strengths.
Because RP technologies are being increasingly used
in non-prototyping applications, the techniques are
often collectively referred to as solid free-form fabrication,
computer automated manufacturing, or layered manufacturing.
The latter term is particularly descriptive of the manufacturing
process used by all commercial techniques. A software
package "slices" the CAD model into a number
of thin (~0.1 mm) layers, which are then built up one
atop another. Rapid prototyping is an "additive"
process, combining layers of paper, wax, or plastic
to create a solid object. In contrast, most machining
processes (milling, drilling, grinding, etc.) are "subtractive"
processes that remove material from a solid block. RP’s
additive nature allows it to create objects with complicated
internal features that cannot be manufactured by other
means.
Of
course, rapid prototyping is not perfect. Part volume
is generally limited to 0.125 cubic meters or less,
depending on the RP machine. Metal prototypes are difficult
to make, though this should change in the near future.
For metal parts, large production runs, or simple objects,
conventional manufacturing techniques are usually more
economical. These limitations aside, rapid prototyping
is a remarkable technology that is revolutionizing the
manufacturing process.
Notes
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