Re: SLS of ceramics

From: Holger Wirtz (wirtz@indy.ipt.rwth-aachen.de)
Date: Tue Dec 22 1998 - 11:23:11 EET


Hello list

Oops, sorry, almost missed that discussion (I only read
the digest). About SLS of ceramics and our work:

We have been investigating SLS of ceramics for several
years, either trying to sinter the ceramic directly or
using a binder (organic, inorganic). Just by trying different
materials we got some interesting results. SiC for example
does not melt but dissociates at temperatures around
2300 degrees C, thus you would never think SLS of SiC would
work. Well it does amazingly well. When dissociating, the Si
is oxidized, yielding SiO2 as a glassy phase acting as a
binder. We have produced parts with layer thicknesses as small
as 0.05 mm and superior surface finish and detail. Now one
might argue that SiO2 is not the type of material you want
in your SiC ceramic. Infiltrating the laser sintered SiC parts
with molten silicon leads to an elimination of the SiO2 and
the classical Si-infiltrated SiC ceramic.

Concerning SLS of investment casting shells (ZrSiO4) we recently
made a huge leap forward and are now able to produce shells
with layer thicknesses of 0.1 mm. The surface finish of cast
parts has improved dramatically and is in the range of
Rz=30 to 50 micro meters. We received a scientific award for
our work from the Materialica in October in Munich, a fair and
conference on developments and processing of advanced/new
materials.

Other experiments included alumina and zirconia with much less
success. I believe these materials may have to be laser sintered
using a binder. However, even then the biggest problem is
getting green densities around 70% so that green parts will
sinter to full density later. The MIT has used an interesting
approach for increasing green density: Since tap densities of
powders are quite low they use a recoating technique with which
they deposit layers of slurry. The particles rearrange in the
slurry yielding high green densities.

That's it for now. If anyone would like more information or to
comment on this please send email to wirtz@ipt.fhg.de because
I do not read rp-ml on a regular basis.

Holger

-- 

---------------------------------------------------------------------- "Opinions expressed are solely my own and thus do not represent or are in line with those of my employer ..." Dipl.-Ing. Holger Wirtz email: wirtz@indy.ipt.rwth-aachen.de Research engineer at the Fraunhofer Institute of Production Technology Steinbachstr. 17, 52074 Aachen, F.R.G. phone: +49 (0)241 8904-120

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