Manufacturing Processes 73
RAPID PROTOTYPING
Overview
Selecting a method of prototyping a three-dimensional product is depend-
ent on multiple factors, including purpose, cost, and time available to produce it. In
choosing a process, consider if it is for an appearance model, an ergonomic study,
or a mock-up of a mechanism. For many applications, a fast, inexpensive prototype
with low finish level works very well, but in some cases, a realistic representation
is critical.
3D Printing
On a vertically articulating platen, a layer of wax, ink, or glue is printed
on a thin layer of build material such as starch or plaster, which then solidifies and
hardens. The configuration of each printed layer is determined by a 3D CAD data
file. The platen indexes down and another layer of build material is laid across the
previous one, resulting in a thicker combination. This process is repeated many
times until the entire three-dimensional part is built. The print material is usually
available in different colors, and in some devices, multiple colors can be printed
in a single part. Some materials require a secondary process, such as impregnating
the part with wax, glue, or resin. Although these processes are relatively inexpensive
and fast, the finish and resolution can be low.
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A Thermo-Jet wax-based 3D printer
Courtesy of Altitude, Inc.
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74 PROCESS, MATERIALS, AND MEASUREMENTS
Computerized Numerical Control (CNC)
A process in which parts are produced using
a CNC machine tool to cut the part from metal, plastic, or composite stock. Starting
with 3D CAD data, a milling sequence is developed that performs the actual machin-
ing. This sequence may use one tool for the entire milling, or may require tool
changes to achieve finer details and surface quality. Depending on the shape of the
object to be machined, one or more fixtures may be required.
The primary advantage of CNC prototypes is that they can be produced in the exact
material planned for the final product. This process results in the creation of fully
functional prototypes that can be used for testing in the planned product environ-
ment. The primary disadvantage of CNC prototypes is that the time required and
the cost of the prototype is highly dependent on the size and geometric complexity
of the piece.
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Manufacturing Processes 75
Fused Deposit Modeling (FDM)
This
process is embodied in a small desktop
machine that may run in an ordinary
office environment. Based on a 3D CAD
data file, the machine builds up thin lay-
ers of liquid resin one after another. As
each layer hardens, the next is added.
When the build is complete, the proto-
type is removed from the build platform
and the support material is removed.
FDM systems often allow different mate-
rial and color choices. FDM prototypes
are not suited for highly finished parts
or as master patterns because of the
poor quality and resolution produced.
Laminated Object Manufacturing (LOM)
A process that involves laminating
sheets of paper or plastic that have been
laser-cut to a specific shape based on a
3D CAD data file. The sheet material in
roll form advances to the cutting plat-
form, and a laser beam cuts one layer
of the desired shape. The material
advances, and an uncut layer is heated
or pressure-laminated onto the previous
layer, where it is then laser-cut. The
process is repeated until the object
is formed. The process is inexpensive,
but the finish level is low.
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Roller
Laser Cuts
Sheet Material
LAMINATED OBJECT MANUFACTURING (LOM)
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