Chemical Engineering January 2017 - 16

At European tradeshows last Fall,
Linde Gases (Munich, Germany;
www.linde.com) launched ADDvance
O2 precision, a first-of-its-kind measuring
and analysis unit that enables
metal additive manufacturers to analyze
and control more precisely the
level of O2 and humidity within the
printer chamber, the company says.
The new technology - developed
in response to a need identified by
aerospace company Airbus Group
Innovations - can detect O2 levels
up to 10 parts per million (ppm) within
the printer chamber and then modify
the gas atmosphere by adjusting the
level of argon or nitrogen. ADDvance
O2 allows for more accurate detection
of oxygen and humidity without
cross-sensitivity to other species in
the complex mixture of impurities.
" Handling powders can also introduce
some humidity, and this is
known to increase porosity in the final
part, " explains Pierre Foret, of Linde
Gas. " ADDvance O2 allows manufacturers
to accurately and reliably measure
oxygen in the build chamber and
lower the levels by adjusting inert gas
flow, " he notes. Currently with the
instrument, a small pipe is installed
on the printer and sucks a sample of
gases from the build chamber and
analyzes it externally for O2 and H2O
content, Pierre explains, but in the future,
the sensor should be integrated
into the print chamber.
The ADDvance O2 launch comes
on the heels of Linde's recent opening
of a dedicated industrial gases
laboratory specifically for AM in Unterschleissheim,
Germany. The focus
of the facility is to study the effects of
various atmospheric gases and gas
mixtures on the different metal powders
used in AM to optimize the various
layering processes, Linde says.
Speed and post-processing
Two significant obstacles to widespread
adoption of 3DP for manufacturing
finished parts have to do with
its speed, and the fact that 3D-printed
parts often have to undergo postproduction
finishing steps in order
to be suitable for use. If these steps
are not integrated well or are costly,
it may make the particular part uneconomical
for certain applications. A
number of approaches and technolo16
gies
are aimed at improving
speed
and streamlining the downstream
processing of 3D-printed parts.
In some laser-based 3DP technologies,
for example, unfused material
may have to be cleaned off in a
post-production process. Linde Gas
has developed a post-production
cleaning technology that claims to be
faster, more cost effective and more
environmentally friendly than existing
alternatives, such as power-washing
and sand-blasting. Tradenamed
CryoClean Snow, the method uses
small particles of dry ice (solid CO2)
for cleaning. The particles are formed
on-demand by feeding liquid CO2
into a specially designed snow chamber
to form very hard dry-ice particles.
The particles are then propelled
against the component surface using
compressed air. Uses for CryoClean
Snow in the context of 3D-printed
parts include
removal of unfused
powder from laser-fused AM parts
and removal of surface oxides from
steel, aluminum and other metals.
Printing technologies are also
evolving to reduce post-processing.
Rize Inc. (Woburn, Mass.; www.
rize3d.com) has developed a printing
technology, known as augmented
polymer deposition (APD), that the
company says achieves zero postprocessing
(such as filing or sanding)
of parts and generates no toxic
fumes. APD allows the extrusion of
Rize's proprietary engineering-grade
thermoplastic simultaneously with
the jetting of functional inks that can
change the properties of the thermoplastic.
The printer is capable of jetting
these functional inks with each
voxel (3DP version of a pixel) of material,
so parts can be stronger, and
downstream processing steps can
be eliminated, the company says.
Another factor limiting the use of
3DP technologies for finished parts
is their relatively slow speed. " Current
technologies require many
hours to days to generate parts,
which is acceptable for prototyping
applications, but not for manufacturing
of finished parts, " says Jason
Rolland, vice president of material for
Carbon (Redwood City, Calif.; www.
carbon3D.com), a company that recently
introduced a printer designed
to address both speed and finishing
issues in 3DP.
When selecting materials and
printing technologies, there are
often tradeoffs between mechanical
properties and surface finish. " Lightbased
technologies (such as stereolithography)
offer the best choice for
surface finish and resolution, but the
parts have poor mechanical properties,
especially when compared
to injection-molded thermoplastics,
explains Rolland. " Heat-based technologies
[like fused deposition modeling
and selective laser sintering]
offer better mechanical properties,
but are limited with respect to surface
finish and resolution, " he says.
Carbon recently introduced a
unique technology, known as continuous
liquid interface production
(CLIP; Figure 1) that the company
says addresses significant current
gaps. CLIP is a
photochemicalbased
process in which ultraviolet
(UV) light is projected through an oxygen-permeable
window into a reservoir
of liquid UV-curable resin. The
resin solidifies in a specific shape according
to a series of UV images projected
through the window. The built
part rises out of the reservoir as the
UV images induce resin hardening.
The company has also developed
resins with both UV- and thermal-cure
components, which allow improved
strength after triggering secondary
heat-activated reactions after printing.
Carbon's printer, known as the
M1, can make parts with high resolution,
engineering-grade mechanical
properties and surface-finish properties
like those of injection-molded
parts, the company says. CLIP is
faster than current stereolithography
technology, Rolland says, and it
does not involve layering of material,
which, when coupled with digital optics
to define part geometry, results in
a clean surface finish.
" By expanding the available formulation
space to include thermally
curable materials, we open up a
much broader range of chemistries
and mechanical properties than ever
before, " Rolland says.
n
Scott Jenkins
Editor's note: For more information on mainstream
investment in 3DP, the LR Roadmap,
next-generation 3DP, potential application areas for the
CPI and more, please view the expanded online version
of this article at www.chemengonline.com.
CHEMICAL ENGINEERING WWW.CHEMENGONLINE.COM
JANUARY 2017
http://www.linde.com http://www.rize3d.com http://www.carbon3D.com http://www.chemengonline.com http://WWW.CHEMENGONLINE.COM
Chemical Engineering January 2017

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