DESIGN, ASSEMBLY AND CHARACTERIZATION OF COMPOSITE ...

2.3. Solid Freeform Fabrication
In this section, a brief overview for solid freeform fabrication (SFF) is first
provided, followed by descriptions of major relevant SFF techniques. Finally, a
comparison of process characteristics among these techniques is given. A more detailed
introduction to the Robocasting process is provided separately in the next section.
2.3.1 Overview
SFF uses an additive approach to assemble solid objects layer by layer. Although
this additive concept is not new, the use of computer aided design and automation to
assist digitized placement of materials has created a field of active research and
development since the 1990's. SFF enables much freedom for fabricating objects with
customized shape, complex structure, and compositional gradients.
The overall concept of SFF is similar for all the techniques, but specifics of
material delivery and post processing vary. The similar features include: 1) preparation
of feedstock materials, 2) generation of machine code from CAD model, 3) assembly of
3D object through layer-by-layer addition of materials, and 4) finishing the assembled
object, if necessary. There is an underlying requirement that each formed layer have
enough mechanical strength for shape retention and structure evolution.
The SFF techniques are not in competition with current methods for mass
production of inexpensive everyday consumables. Rather, SFF focuses on low throughput,
small volume, but high value added parts that are either uneconomical or impossible to
fabricate by other means. Those unusual but highly demanding needs may justify the high
unit cost and low productivity in SFF. Currently, SFF has benefited the commercial
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