Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Introduction
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the anticipated time and cost savings RP will offer over conventional
model-making practice. New and improved RP methods are being introduced
regularly, so the RP field is in a state of change, expanding the
range of designer choices.
Three-dimensional models can be made accurately enough by RP
methods to evaluate the design process and eliminate interference fits or
dimensioning errors before production tooling is ordered. If design flaws
or omissions are discovered, changes can be made in the source CAD
program and a replacement model can be produced quickly to verify that
the corrections or improvements have been made. Finished models are
useful in evaluations of the form, fit, and function of the product design
and for organizing the necessary tooling, manufacturing, or even casting
processes.
Most of the RP technologies are additive; that is, the model is made
automatically by building up contoured laminations sequentially from
materials such as photopolymers, extruded or beaded plastic, and even
paper until they reach the desired height. These processes can be used to
form internal cavities, overhangs, and complex convoluted geometries as
well as simple planar or curved shapes. By contrast, a subtractive RP
process involves milling the model from a block of soft material, typically
plastic or aluminum, on a computer-controlled milling machine
with commands from a CAD-derived program.
In the additive RP processes, photopolymer systems are based on successively
depositing thin layers of a liquid resin, which are then solidified
by exposure to a specific wavelengths of light. Thermoplastic systems
are based on procedures for successively melting and fusing solid
filaments or beads of wax or plastic in layers, which harden in the air to
form the finished object. Some systems form layers by applying adhesives
or binders to materials such as paper, plastic powder, or coated
ceramic beads to bond them.
The first commercial RP process introduced was stereolithography in
1987, followed by a succession of others. Most of the commercial RP
processes are now available in Europe and Japan as well as the United
States. They have become multinational businesses through branch
offices, affiliates, and franchises.
Each of the RP processes focuses on specific market segments, taking
into account their requirements for model size, durability, fabrication
speed, and finish in the light of anticipated economic benefits and cost.
Some processes are not effective in making large models, and each
process results in a model with a different finish. This introduces an economic
tradeoff of higher price for smoother surfaces versus additional
cost and labor of manual or machine finishing by sanding or polishing.