SRI has developed an alternative technique for making ceramic
green bodies. Named Direct Photo Shaping (DPS), it is viewed as a solid
freeform fabrication process, rather than a prototyping process. A slurry
containing about 50% by volume silicon nitride powder (supplied by
Norton) is
spread one layer at a time. The build canister acts similarly to the one
in the
DTM machines, dropping down as each layer is added.
The polymer binder is sensitive to visible light, rather than UV light,
and the entire layer is
exposed to a light pattern directed by digital micromirror devices (DMDs,
made using micromachining technology and commercialized by Texas
Instruments), rather than by scanning the layer with a laser beam. The
green
bodies are fired and sintered by conventional methods, to produce
ceramic parts with mechanical properties nearly identical to those parts
produced by conventional methods.
A paper with details was presented at the Seventh
International Conference on Rapid Prototyping, last Spring. Since the
conference, finished parts have been tested by Allison Engine and the
performance
characteristics appear to be acceptable.
The focus of the current SRI work, funded by DARPA, is silicon nitride
parts, for use as blades at operating temperatures up to 1370 C in gas
turbine engines. However, the process could be extended to virtually any
powdered material, including metals and other polymers and, with multiple
slurry feeds, functionally gradient materials and composites. Research is
still
underway, but a commercial machine is possible in a couple of years,
priced at well under US$50 000 (based on the use of off-the-shelf
components
and a substantial price markup by the yet-to-be-determined manufacturer).
Brock Hinzmann
bhinzmann@sric.sri.com
Marshall Burns wrote:
>Guy Allen Brady wrote:
>
>> Well, now, this is a nice surprise. I've been working on
>> Stereolithography of Ceramics for the past 2+ years. My suspensions
are
>> 50vol% Alumina in a photocurable resin. There are two others groups
(at
>
>Dear Allen and others,
>
> I wonder if I might ask a question that could spark some
interesting
>technical debate.
>
> What are the relative pros and cons of the various techniques for
>fabricating green bodies of either ceramics or metals? The techniques
that must
>be considered include direct fabrication of the green body:
> - Selective photocuring of a photopolymer/powder suspension
(SLA)
> - Laser sintering of polymer-coated powders (SLS),
> - Extrusion of a polymer/powder paste (FDM),
> - Lamination of polymer/powder tapes (LOM),
> - and perhaps some other direct techniques.
>And one should also include indirect techniques of:
> - Fabricating a mold or master which is used to mold a powder
system
>(old fashioned P/M as well as Keltool, etc.).
>
> What do people think about how these various techniques campare?
>
>Best Regards,
>Marshall Burns
>marshall@ennex.com
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