Rapid prototyping
The process
uses a numerical data set representing the 3D geometry such as a stereolithography
file (.stl) to grow the part layer by layer. Each RP equipment supplier
has proprietary software to slice the geometry into layers for use in
the equipment. Various RP processes use different manufacturing approaches
with different materials.
RP machines
are used by manufacturers, designers, and researchers around the world
for low-volume production, prototyping, and mold mastering. They are
also used by scientists and surgeons for solid imaging, and by a few
modern artists for innovative computerized sculpture.
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Solid Model in CAD
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Surfaces tessellated
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Exported .stl file
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Sliced .stl
file
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Build file
with supports
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Model building
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Finished physical
model
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What capability
does LBNL have?
Currently,
DesignWorks has two rapid prototyping machines. The Fused Deposition
Modeler (FDM®) is a patented rapid prototyping process by Stratasysä Inc. The process extrudes a thermoplastic material and deposits it layer
by layer to form solid three-dimensional parts.
The 3D
systemsä Stereolithography machine (SL or SLA) uses a process that builds
an object one layer at a time by curing photosensitive resin with a
laser-generated beam of ultraviolet radiation. Originally applied to
the technology of 3D Systems, the term "stereolithography"
has broadened to include all technologies that process prototypes parts
in this manner.
What kind of
parts can the SLA and FDM make?
These machines
generate 3-dimensional, solid objects you can hold in your hands, submit
to
Developers
can increase the quality of their products by realizing, in the same
amount of time, a larger number of variations on the objects envisioned
by creative people working in CAD.
Fabrication
time for the layering process is mostly dependent on overall part volume
and only slightly dependent on the level of part complexity. Comparatively,
traditional machining is highly dependent on the complexity of the surface
shapes and less dependent on overall part volume. For example, a 4-foot
diameter circular plate would be much faster to fabricate using traditional
fabrication techniques, but a replica of a mouse (computer or real)
would be much faster to build using rapid prototyping. Indeed, rapid
prototyping has been used to fabricate parts and replicate organic items
that are impossible to build in any other fashion.
Although build
volumes are generally smaller for RP machines, techniques such as scaling
and building larger parts in smaller pieces may be used to compensate.
How long does
it typically take to build a part?
The SLA and
FDM machines use different processes to produce parts. The time it takes
to go from CAD to physical object is a bit longer for SLA due mainly
to post processing of the object after it is built. However, the SLA
part can produce smaller features with higher accuracy than the FDM.
The actual
time to build parts ranges from hours to days based on the volume of
the object. Parts can be combined in single build sessions to produce
assemblies or accommodate different customers’ parts at the same
time. The FDM machine can also build “assembled” assemblies
in a single build session.
I have a solid
model on my computer; how do I get a part built?
The 3D CAD
file is typically exported as an “.stl” file. The solid model
surfaces are converted to a series of triangles. The conversion from
CAD representation to triangles is called tessellation, which mathematically
divides surfaces into planar facets or triangles. Pro/ENGINEERä, SolidDesignerä, SolidWorksä, and almost all other CAD programs have the ability to export this
file type. There are settings that can be applied to the file prior
to export that improve the quality of the final RP part. The preferred
method is a Pro/ENGINEER “.prt” file. Contact Steve
Dellinges in DesignWorks at extension x2539 to send the part over
for a quote or if you have any questions about preparing CAD parts for
rapid prototyping. We can consult with the customer as to which machine
will be the best choice for the particular job.
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What are the
accuracies of RP parts?
Because “Free
Form Fabrication” utilizes a layered process, there is no single
answer to this question. Depending on the type of machine and materials
utilized, “Z” layers are made as low as 0.001” while
the X and Y components are dictated by the laser spot size, droplet
size, extrusion nozzle, photo mask, etc. For the FDM and SLA, see the feature list below
for accuracy information. Generally, RP machines make parts from ± 0.001” to 0.005”. Additionally, RP parts can be further
machined after fabrication to higher specifications. There are processes
being developed that can produce parts a small as 10mm.
What materials
can RP parts be made of?
For the FDM
and SLA, see the feature list below. Other RP technologies can make
objects out of Metal, Ceramic, Paper, and Wax.
Features of
the FDM (information from Stratasys):
Investment Casting Wax
Elastomer
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Tensile Strength
(psi) 5,000 |
Unnotched
Impact (ft*lb./in) --- |
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Flexural
Strength (psi) 9,500 |
Elongation
(%): 50.0 |
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Tensile Modulus
(kpsi) 360 |
Hardness
(Shore D): R105 |
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Flexural
Modulus (kpsi) 380 |
Softening
Point (R&B): 220 |
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Notched Impact
(ft*lb/in) 2.00 |
Specific
Gravity (g/cc): 1.05 |
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Build Envelope
(in.): 10 X 10 X 10
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Achievable
Accuracy: ± 0.005”
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Colors: Black, White, Blue, Red, Green, and
Yellow.
Features of
the SLA250 (information from 3D Systems):
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Material: A
variety of Epoxy Resin and Acrylate Ester Blends
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Material properties
(SLA 250/30) Liquid Photopolymer SL-5170
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Tensile Strength
(psi) 8,600 – 8,800 |
Unnotched
Impact (ft*lb./in) --- |
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Flexural
Strength (psi) 15,500
– 15,700 |
Elongation
(%): 8.0 |
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Tensile Modulus
(kpsi) 542 - 603 |
Hardness
(Shore D): 85 |
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Flexural
Modulus (kpsi) 423 - 436 |
Glass transition,
Tg 65-90°C (184°F) |
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Notched Impact
(ft*lb/in) 0.5 – 0.7 |
Specific
Gravity (g/cc): 1.22 |
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Build Envelope
(in.): 10 X 10 X 10
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Color: natural
Note: A new material called Stereocolâ H-C 9100R is a specially formulated SL material for building 3-dimensional
models with selectively colored areas for information visualization.
