Robot Mechanisms and Mechanical Devices Illustrated - Profe Saul

Introduction
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form of stacked segments is removed to reveal the finished 3D model.
The models made by the LOM have woodlike finishes that can be sanded
or polished before being sealed and painted.
Using inexpensive, solid-sheet materials makes the 3D LOM models
more resistant to deformity and less expensive to produce than models
made by other processes, its developers say. These models can be used
directly as patterns for investment and sand casting, and as forms for silicone
molds. The objects made by LOM can be larger than those made
by most other RP processes—up to 30 × 20 × 20 in. (75 × 50 × 50 cm).
The LOM process is limited by the ability of the laser to cut through
the generally thicker lamination materials and the additional work that
must be done to seal and finish the model’s inner and outer surfaces.
Moreover, the laser cutting process burns the paper, forming smoke that
must be removed from the equipment and room where the LOM process
is performed.
Helysys Corporation, Torrance, California, manufactures the LOM-
2030H LOM equipment. Alternatives to paper including sheet plastic
and ceramic and metal-powder-coated tapes have been developed.
Other companies offering equipment for building prototypes from
paper laminations are the Schroff Development Corporation, Mission,
Kansas, and CAM-LEM, Inc. Schroff manufactures the JP System 5 to
permit desktop rapid prototyping.
Fused Deposition Modeling (FDM)
The Fused Deposition Modeling (FDM) process, diagrammed in Figure 5,
forms prototypes from melted thermoplastic filament. This filament,
with a diameter of 0.070 in. (1.78 mm), is fed into a temperaturecontrolled
FDM extrusion head where it is heated to a semi-liquid state.
It is then extruded and deposited in ultrathin, precise layers on a fixtureless
platform under X-Y computer control. Successive laminations ranging
in thickness from 0.002 to 0.030 in. (0.05 to 0.76 mm) with wall
thicknesses of 0.010 to 0.125 in. (0.25 to 3.1 mm) adhere to each by thermal
fusion to form the 3D model.
Structures needed to support overhanging or fragile structures in FDM
modeling must be designed into the CAD data file and fabricated as part
of the model. These supports can easily be removed in a later secondary
operation.
All components of FDM systems are contained within temperaturecontrolled
enclosures. Four different kinds of inert, nontoxic filament
materials are being used in FDM: ABS polymer (acrylonitrile butadiene
styrene), high-impact-strength ABS (ABSi), investment casting wax, and