Models and Prototypes:

Models and prototypes are essential to understanding the
implications of design decisions.  However, while contributing to
a better informed design process, the production of models and
prototypes is expensive and time consuming.  Experience suggests
that on average, physical prototyping can account for over half
the time required to bring a design to its final manifestation
(Leonard, 1989).  Electronic processes that promise to transform
graphic designs and simulations (virtual reality) into tangible
3-D objects represent an essential component in the process of
reconciling virtual realities with real needs and applications. 
The StereoLithographic Apparatus (SLA) can dramatically reduce
the time and costs required for model building, and can enhance
the design process by permitting the iterative testing of design
decisions with rapid prototyping.

The SLA method forms 3-D objects by successively layering thin,
cross sectional profiles of the object on top of one another. 
The plastic matrix in which the object is created is a liquid
photocurable polymer that transforms into a solid state when
exposed to an ultraviolet laser light source.  A scanner device
driven by computer generated coordinates controls the movement of
the laser in the "X-Y" coordinate plane across the surface of the
polymer bath.  The object is formed on an elevator which moves
the object through the "Z" coordinate plane in the resin bath
(Rowell, 1989).

<ffile58>   StereoLithography