It's tempting
sometimes to put additive fabrication machines into just two buckets. One of
them has high-end, six-figure systems capable of producing precision prototypes
and even finished components in rugged materials. The other contains 3-D printers, a growing class of lower-cost systems that engineers often use for
concept and testing models. Yet 3-D printer capabilities vary so widely that
perhaps they shouldn't be lumped together.
Consider, for example, the newest line of ProJet machines from 3D Systems Corp. The company's senior director
of global marketing, Buddy Byrum, argues these machines fit into an
emerging class of "professional modelers." The surface finish, accuracy,
feature resolution and throughput of machines occupy a middle ground between
the low-cost concept modelers, some of which cost less than $20,000, and
high-end fabrication machines whose prices start at $100,000. "The difference between
professional modelers and concept modelers is like the difference between
high-def and analog television," Byrum says.
Like 3D
System's earlier InVision family, the new machines employ Multi-Jet Modeling
(MJM), one variant of several related 3-D
printing methods that use ink jet technology to deposit the layers of build and
support material.
However, a
couple of things set MJM apart from other ink jet systems. For one, its acrylate
polymer build material undergoes a phase change once it leaves the jets,
allowing it to "set" on the model even before each build layer is cured by UV
light. "The droplets freeze in place on the model," Byrum says. "And that lets
us build high-quality parts with crisp features." Byrum adds freezing of
the drops also permits relatively thick build layers without a loss of part
quality. "That gives us high throughput capacity for a given build volume," he
says.
For
another, the MJM is a single-pass design in that the ink jet head spans the
entire y-axis. So its build speed is unaffected by the number of parts packed
onto the build platform. "Build time is determined only by the how tall the
parts are," Byrum says.
MJM
technology is a two-material system that lays down both a build material and
wax-based support material. That support material is later melted away from the
model, which is important when working with delicate part features that could
be broken with more aggressive methods of removing supports, such as using a
blast of pressurized liquid. "We have a support removal method that doesn't put
any pressure on the part," Byrum says. The result is the machine's
accuracy and resolution dictate the smallest feature size rather than the
feature's ability to survive a wax removal process.
3D Systems
has rolled out three versions of its new ProJet platform, one specifically for
the dental industry and two models better suited to design engineering work.
The first of these two engineering models, the ProJet HD 3000, appeared earlier
this year. This week, the company launched a brand new model, the ProJet SD
3000.
What's the
difference between the two? Ten thousand dollars and a handful of features.
The $69,900 HD builds in two modes, a high-definition (HD) mode
offering a 328 x 328 x 606 DPI (xyz) resolution and and an ultra-high-definition (UHD) mode offering 656
x 656 x 800 DPI. The ProJet HD 3000 has a typical accuracy of 0.001 to 0.002
inch per inch of part dimension, though Byrum stresses accuracy varies
with build parameters, part geometry and size, part orientation and
post-processing methods.
The z-direction build speed for the HD mode is about 0.25 in/hr,
while the UHD mode builds at 0.1 in/hr, Byrum reports. The ProJet HD also has
the ability to stack different parts within the z-direction. "You can pack them
in any way that fits as long as the parts aren't touching," Byrum says. Build
volume in the HD mode is
11.75 x 7.3 x 8 inches while the UHD mode offers 5 x 7 x 6 inches.
The $59,900
ProJet SD, meanwhile, is basically what Byrum calls an "entry-level machine for
professional modeling." It lacks the UHD
resolution and the ability to stack parts in the z-direction. Other than those
two differences, it shares the capabilities of the ProJet HD.
Applications
for the ProJet machines include the production of complex parts, especially
ones that require form-fit-and-function testing. It also turns out models ready
for use as investment casting patterns for intricate metal components.
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