Product prototyping (as discussed in F.1.15 ) is an
essential part of the product design cycle. It is a technique for design
functionality and aesthetic quality assessment. Through use of a prototype, a
designer can get feedback on design information and initial part acceptance for
further use in the manufacturing process. Prototyping is used to check design
features and identify complexity issues and is helpful in tradeoff studies.
The use of prototyping begins in the preliminary design
phase and can continue throughout the early stages of the detailed design.
Prototyping can also be performed in production to test whether a new process
can be used to produce a product that meets the customer's quality requirements.
The ability to quickly transform a design into a three-dimensional solid model
or prototype can significantly streamline the design and product development
process, while substantially reducing costs.
Rapid prototyping may also be used early in the product
development cycle, before tooling has been developed, to provide visualization
and verification feedback. This allows the designers to evaluate and refine a
design prior to manufacturing, as well as to accelerate the production of
prototype molds and tooling.
Traditional prototyping is time-consuming and costly. For
this reason, rapid prototyping has emerged as a breakthrough process in the
product design cycle. While conventional prototyping may take weeks or even
months, rapid prototyping turnaround time for a typical part is usually no more
than a few days. If the CAD models of the part exist beforehand, turnaround time
can be less than 24 hours for smaller parts.
The two most widely used rapid prototyping processes are
StereoLithography (SLA) and Selective Laser Sintering (SLS). SLA uses a
photopolymer process to create complex, three-dimensional models by successively
"laser-curing" cross-sections of liquid resin, using data from virtually any
surface or solid modeling CAD system. The liquid photopolymer hardens in the
specific areas where there is interaction with the ultraviolet (UV) laser beam,
and the model is built layer-by-layer, without tooling, programming, or
SLS is a similar process that makes use of a laser to
elevate the temperature of a heat-fusible powder to near its melting point to
fuse the particles in solid form. Like SLA, SLS is a three-dimensional process
that vertically builds the part layer-by-layer. With either method, the
transition from CAD data to physical part can take place in a matter of
Specific attributes of SLA and SLS include:
- Surface finish: The surface finish of SLA is superior to that of SLS due to the
formation of voids between particles during the SLS process.
- Small feature definition: Both SLA and SLS are capable of producing features in the range of
0.010 inches. The accuracy of the parts will be dependent on part geometry and
- Material selection: While SLA is only applicable to polymeric resins, SLS can
be used on a range of materials including nylon, polycarbonate, resins, and
wax. Research is currently ongoing to apply the SLS process to metals.
While SLS shows promise for future development, SLA is
the more popular rapid prototyping technique in use today. The main components
of a SLA system include: a vat containing liquid photopolymer, galvanometer
controlled mirrors which direct a UV laser onto the surface of the liquid, and,
just below the surface of the liquid, a vertical elevator tray. At the onset of
the SLA process, the first layer of the part model is generated in software, and
this information is used to control the mirrors to direct the laser onto the
surface of the liquid resin. Where the laser strikes, the liquid turns to a
solid almost instantaneously. When one layer has finished, the elevator lowers
to submerge the newly solid top surface with liquid resin for the next layer.
The next layer is generated in software, and, again, the mirrors direct the
laser onto the surface of the resin. This process is repeated until the model
has been built, at which time it will be fully submerged in liquid resin. The
elevator is raised, and the model removed for post-curing and clean-up.
Rapid prototyping is used widely to accelerate the
product development process. Design engineers across all manufacturing
industries have used rapid prototyping to improve product quality. Form, fit,
and function tests can be performed earlier in the design cycle, thereby
reducing costly engineering changes required after production has begun.
Jacobs, P. F. (1996). StereoLithography and Other RP&M Technologies: From Rapid Prototyping to Rapid Tooling. Society of Manufacturing Engineers.
Kai, C. C., & Fai, L. K. (1997). Rapid Prototyping: Principles and Applications in Manufacturing. New York: Wiley & Sons.
Kochan, D. (1993). Solid Freeform Manufacturing: Advanced Rapid Prototyping. New York: Elsevier Science.
Wood, L. (1992). Rapid Automated Prototyping: An Introduction. New York: Industrial Press.