Re: Green-body fabrication technique comparison

From: Rajeev Garg (rgarg@sut1661.Princeton.EDU)
Date: Wed Nov 12 1997 - 18:54:48 EET

It is a very interesting question raised here and I am sure we will hear
different opinion from different groups. Here is mine. As I work mostly on
SLA so I start with SLA. Any suggestions corrections are welcome

SLA provides an excellent way of fabricating green bodies with good
dimensional control. Especially with the models we have developed we can
control the dimensions within 2 mils. So, once a good ceramic resin has
been developed quality ceramic green bodies can be fabricated by SLA.

Developing a resin for SLA is more difficult than any other. There are #
of restrictions on photopolymers that can be used with ceramic
dispersions, especially at high solids loading. Even after having a good
ceramic resin, there are only limited # of ceramics which can be processed
by SLA. That is because the ceramics like boron carbide and PZT are so
absorbing that one will not be able to get good cured depths. Besides, SLA
in its present form can only be used for making monolithic green bodies.

LOM: This technology has the potential to overcome above drawbacks. AS one
can fabricate composite green bodies and any ceramic by this technique.
The ceramics tape can be processed from high solids loading as is the case
in SLA. The question here is the selective interlaminate adhesion
required. This will affect the quality of the green body. the work need to
be done in developing the dimensional accuracy.

SLS: Any ceramic can be processed by this technique but still the
monolithic ceramic. The quality of the green bodies fabricated by SLS is a
question. The powder processing always leads to flaws in the ceramic green
bodies, eventually decreasing the mechanical properties. Also, not enough
work has been done to develop models for precise dimensional controls of
the ceramic green bodies.

FDM: This is the only non laser based technology in the four technologies
being compared here. There is always problem in high solids loading of the
ceramic powders in polymers. This limits the quality and the mechanical
properties.My opinion is the dimensional accuracy of this technolgy will
not be as good as the laser based technologies. As the optics can be
focussed on much finer length scales.

Rajeev Garg

On Tue, 11 Nov 1997, Marshall Burns wrote:

> 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
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