RE: Green-body fabrication technique comparison

From: Guy Allen Brady (
Date: Wed Nov 12 1997 - 22:24:02 EET

RP folks,

Ok, I suppose I should place my 2cents worth now. I've spent the last
2.5years on Ceramic SLA, so that's what I know the most. I'm in the midst
of writing my thesis and will provide a web copy and I hope other students
will do likewise. Btw, if anyone is interested, I'm searching for career
opportunities as early as Jan. '98. Hope that wasn't out of line.

First of all, no matter what you use with a given RP technology,
traditionally supplied material or crushed moonrocks, you'll not get
around the limitations inherent to that process. Most ceramics are not
magic. Most.

For SLA: Can only use particles which have low index of refraction at UV
wavelengths. The particles cannot absorb UV. While this may make really
neato ceramics like SiC or Graphite out of the question, there are many
that fit the bill. I've made aluminum oxide parts which look very nice,
for example (couldn't help that one). There is the issue of binder
removal (not exclusive to SLA, but I'll talk about it here) which is
something ceramic/powder metal folks deal with on a daily basis. To us,
24hr binder removal (burnout) runs are quick and quite the norm, so if you
think this is unreasonable, get used to it. Of course the time depends
upon the thickness of the thickest section on the part (i.e. it's a mass
transport thing...). Some of the hardest things to tackle are combining
many requirements: high solids, >50vol%, ceramic/metal suspensions + low
viscosity + photopolymerizable suspensions + friendly shrinkage + descent
burnout. But it can be done, it has been done and there's more to come.

For SLS:
There will be difficulties in getting 100% dense parts without some
secondary process (infiltration or HIPping - oh, Hot Isostatic Pressing).
Can use a much wider variety of materials, ceramic-metal-polymer in this

For FDM: Again, a wide variety of materials, more freedom with rheology -
which means the requirement for the polymeric+solvent binder is only
mechanical, and not necessarily chemical (a la SLA). There are
densification issues here, but the folks at Rutgers are getting that down.
Notice I ignored burnout here because this is a solvable issue. High
solids loading in extrudable mixtures is easier - makes burnout easier.

For LOM: This is the farthest along, commercially than all others, thanks
to Lone Peak Engineering. Again, many materials can be fabricated into
tape for use in this process. There is the issue of lamination of the
tape which is probably the biggest difficulty with this technique. The
need for some pseudo CIP (Cold Isostatic Pressing) before and/or after
binder removal may preclude some geometries from being built easily.

For 3DP: This powder process great, but surface finish isn't the best -
this is the fastest technique for ceramics - or does Formus do ceramics??.
The MIT group has done marvelous things on the materials science side of
this technique, which means if I start to talk about it, I'll get excited
and you'll fall asleep.

IMHO, other deposition techniques, like Sanders, has the most potential.
I'll not say much more, but from a materials processing point of view, its
the most flexible, material independent and robust building technique.

          G. Allen Brady -- Graduate Research Assistant
Materials Science and Engineering - The University of Michigan
2219 H.H. Dow Bldg. 2300 Hayward Street Ann Arbor, MI 48109-2136
work: 313/936-0177 fax: 313/747-4807 email:

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