RE: Green-body fabrication technique comparison

From: Brent Stucker (stucker@egr.uri.edu)
Date: Wed Nov 12 1997 - 21:06:46 EET


Marshall and the RPML,

As a person who has focused the last 4 years of his life on the merits and
drawbacks of fabricating green bodies of ceramics and metals using RP,
I have some thoughts.

For SLA:
        Mixing dark and/or non-reflective powders in your resin won't work,
so that eliminates most potential ceramics/metals. If you get the ceramic
and/or metal of choice to work as a green body, you will have a difficult time
burning out the polymer because there is no porosity in the part and thus the
burnout phase must proceed very slowly. If you want to do an infiltration of
your part after polymer burnout, the amount of residue in the part may affect
the wetting characteristics. On the plus side, SLA has some of the best
accuracies and surface finishes in the industry.

For SLS:
        There are some distinct benefits to using SLS. First of all, it is a
powder process, so it lends itself naturally toward green body fabrication.
When the green body is created there is continuous porosity throughout
the green body, so the binder burnout phase proceeds at a more rapid
rate. The trick is finding the right binder that will give the green strength
you want, sinter in the SLS machine at room temperature and burnout clean
in the furnace.

For FDM:
        You can use either a ceramic/metal loaded filament or a "syringe"
full of extrudable binder and ceramic/metal. The solids loading appears to
be quite good. The drawback is that there is often segregation between binder
rich and solids rich sections during the extrusion. In addition, FDM often leaves
internal voids (although this has been addressed in the recent past) and that
is a big drawback for certain materials. Lastly, we again have all of the area
between the ceramic/metal particles full of binder, so the binder removal is
more difficult. The benefit is this is an expensive process.

For LOM:
        You can apply ceramic tape technology. The machines are relatively
inexpensive. The drawbacks are, again, lots of binder that is difficult to remove.
In addition, you have a lot of "waste" material that needs to be recycled,
because, unlike the paper that is thrown away, the extra ceramic/metal tape is
probably too expensive to just put in the trash.

For 3DP:
        This process, like SLS, is a powder-based process. It has the
same benefits as SLS. The drawback is that you can't order your own
machine, yet, and produce your own parts in-house.

For molds:
        This is a good process as well. Georgia Tech has done good work with
low pressure injection molding of ceramics into SLA tools to make green
parts. It seems to be a great process. In addition, you could injection mold
into an SLS nylon part. Also, the "replication" processes such as ExpressTool
and Keltool use this technique well. For service bureaus, this is a good
way to create good ceramic/metal parts from RP masters. The main drawbacks
of these processes are that they entail a number of steps and thus
tolerance buildup becomes an issue. In addition, they often use binders that
totally fill the voids between the ceramics/metals and thus they can be
difficult to burn out.

Those are my two cents worth. I could write a lot more, but I don't want
to bore anyone more than I already have.

Brent

P.S. For those of you who have been following my work on EDM electrodes,
there is a company that has recently been licensed to make available this
new Zyrkon material for EDM electrodes. Contact me for more information

_________________________________________________
Dr. Brent Stucker
University of Rhode Island
Dept. of Industrial and Manufacturing Engineering
Gilbreth Hall, 2 East Alumni Ave.
Kingston, RI 02881
ph: (401)874-5187
fax: (401)874-5540
stucker@egr.uri.edu

----------
From: Marshall Burns[SMTP:marshall@ennex.com]
Sent: Tuesday, November 11, 1997 4:21 PM
To: Guy Allen Brady
Cc: Murphy, Matt; RP Mailing List
Subject: Green-body fabrication technique comparison

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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