Page 562 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Chapter 20 Rapid-Prototyping Processes and Operations

The simplest forms of such systems use complex software and three-dimen-
sional graphics routines to allow viewers to change the view of the parts on a com-
puter screen. More complicated versions will use virtual-reality headgear and gloves
with appropriate sensors to let the user observe a computer-generated prototype of
the desired part in a completely virtual environment.
Virtual prototyping has the advantage of affording an instantaneous rendering
of parts for evaluation, but the more advanced systems are costly. Because familiar-
ity with software interfaces is a prerequisite to their application, these systems have
very steep learning curves. Furthermore, many manufacturing and design practition-
ers prefer a physical prototype to evaluate, rather than a video-screen rendering.
They often perceive virtual-reality prototypes to be inferior to mechanical
prototypes, even though designers debug as many or more errors in the virtual
environment.
There have been some important examples of complicated products produced
without any physical prototype whatsoever (paperless design). Perhaps the best
known example is the Boeing 777 aircraft, for which mechanical fits and interfer-
ences were evaluated on a CAD system and difficulties were corrected before the
first production model was manufactured (see Section 38.5).

20.5 Direct Manufacturing and Rapid Tooling

While extremely beneficial as a demonstration and visualization tool, rapid-proto-
typing processes also have been used as a manufacturing step in production. There
are two basic methodologies used:

I. Direct production of engineering metal, ceramic, and polymer components or
parts by rapid prototyping.
2. Production of tooling or patterns by rapid prototyping for use in various
manufacturing operations.
Not only are the polymer parts that can be obtained from various rapid-
prototyping operations useful for design evaluation and troubleshooting, but occa-
sionally these processes can be used to manufacture parts directly-referred to as
direct manufacturing. Thus, the component is generated directly to a near-net shape
from a computer file containing part geometry. The main limitations to the wide-
spread use of rapid prototyping for direct manufacturing, or rapid manufacturing,
are as follows:

° Raw-material costs are high, and the time required to produce each part is too
long to be viable for large production runs. However, there are many applica-
tions in which production runs are small enough to justify direct manufactur-
ing through rapid-prototyping technologies.
° The long-term and consistent performance of rapidly manufactured parts (com-
pared with the more traditional methods of manufacturing them) may be suspect,
especially with respect to fatigue, wear, and life cycle.
Much progress is being made to address these concerns to make rapid manufactur-
ing a more competitive and viable option in manufacturing. The future of these
processes remains challenging and promising, especially in view of the fact that
rapid manufacturing is now being regarded as a method of producing a product on
demand. Customers will be able to order a particular part, which will be produced
within a relatively short waiting time.