Re: About that sintering question......

From: Stephen J Rock (rocks@cat.rpi.edu)
Date: Tue Nov 05 1996 - 19:14:23 EET


Regarding the discussion on sintering,
Will Pattison, Applications Manager, DTM Corporation wrote:

> First of all, let me point out that in the strictest technical sense
> of the word, our process is not true sintering. As I believe the
> gentleman from Japan was trying to point out, true sintering takes
> place at some temperature below the melting point of the material in
> question. Adjacent particles are actually joined when their surfaces
> become soft due to the effects of heat and pressure. Since there is
> no pressure involved in SLS, you can see how we have a slight
> misnomer.

Sintering does not necessarily require both elevated temperature AND pressure
at the same time. Powder can be poured into a furnace boat and sintered
without ever being compacted (known as loose powder sintering); however,
this generally results in a rather porous sintered body.

Sintering typically occurs mainly as solid state atomic transport events driven
by the systems tendancy to reduce surface free energy cause interparticle
welds to form. This is not an instantaneous process and generally requires
times far longer than point-wise laser exposure times found in SLS.
 
I suggest the SLS misnomer stems from the fact that SLS isn't truly
"sintering", as pointed out -- but it has nothing to do with the absense
of consolidation pressure.

Those people interested in learning more about sintering may wish to consult
German, R., "Powder Metallurgy Science," 2nd. ed., Metal Powder Industries
Federation, Princeton, N.J., 1994 or other publications on sintering.

You can contact the MPIF at (609)452-7700.

Regards,
Steve
 
=====================================================================
Stephen J. Rock rocks@cat.rpi.edu
CII8015 (518)276-2280
NYS Center for Advanced Technology 276-8652
in Automation, Robotics & Manufacturing fax 276-4897
Rensselaer Polytechnic Institute
Troy, NY 12180 USA http://cat.rpi.edu/~rocks
=====================================================================



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