Objet and the "It's a Small World Dept."

From: EdGrenda@aol.com
Date: Tue Mar 28 2000 - 23:31:23 EEST

Hi Folks:

Thought you would get a kick out of this article that appeared in NASA Tech
Briefs this month. The device described is nearly identical to Objet's and
the language sounds a lot like it comes from a patent disclosure. You can
get the entire disclosure at www.nasatech.com after signing up.

I've attached the abstract below for your perusal since it doesn't carry a
copyright notice.

Let the food fight begin.

Ed Grenda
Castle Island Co.
19 Pondview Road
Arlington, MA 02474 USA
781-646-6280 (voice or fax)
EdGrenda@aol.com (email)

Molecular structures would be tailored to obtain superior structural
NASA's Jet Propulsion Laboratory, Pasadena, California

Several improvements have been pro-posed for the fabrication process known as
"rapid prototyping." In this process, a model or prototype of a solid object
is built up by controlled ejection of molten poly-meric material through
programmed ori-fices to form patterned layers. The second layer is deposited
on top of the first layer, the third layer is deposited on top of the second
layer, and so forth, until the stack of layers reaches the desired final
thick-ness and shape.

In rapid prototyping according to cur-rent practice, the polymeric material
is one of that has low molecular weight, little or no cross linking, and few
(if any) active functional groups in its molecular struc-ture. Such a
material is used because (1) it lends itself readily to melting and
solidifi-cation over a narrow temperature range and (2) when molten, it has a
relatively low viscosity that make it amenable to pas-sage through small
orifices. The disadvan-tage of such a material is that the low mol-ecular
weight and absence of cross link-ing result in a model that has very little
strength; this characteristic limits the utility of models fabricated by
rapid prototyping.

The first proposed improvement would be the addition of photoactive
functional groups to the polymer. The second pro-posed improvement a
concomitant of the first would be provision of a radiant source to blanket
the model with ultraviolet light to activate the photoactive functional
groups. The photoactive functional groups and their locations in the
molecular struc-ture of the polymer would be chosen so that upon exposure to
ultraviolet light of selected wavelengths, the molecular struc-ture would
become lengthened and cross-linked in such ways as to impart greater strength
and other structural benefits.

In rapid prototyping incorporating the first and second improvements, each
layer of the photoactive-modified polymer would be printed in the same manner
as in current practice. However, prior to deposi-tion of the next layer, each
layer would be exposed to the ultraviolet illumination to obtain a
higher-molecular-weight, cross-linked molecular structure. Subsequent layers
would be treated similarly, so that the completed solid model would be
stronger and more useful, in comparison with the corresponding model
fabricated by conventional rapid prototyping.

The first and second improvements would offer other advantages in addition to
increased strength and utility of models. One advantage pertains to molecular
weight: In a typical instance of current prac-tice, the molecular weight is a
compromise between (a) one that is large enough that the polymer has at least
minimum accept-able hardness and strength and (b) one that is small enough
that when the polymer is molten, its viscosity is small enough to allow
ejection through small orifices. Because the desired high molecular weight
could be obtained in the photoactivation step, the proposed first and second
improvements would make it possible to start with a base polymer of lower
molecu-lar weight and thus lower viscosity; this, in turn, would make it
possible to use smaller ejecting orifices, thereby improving the reli-ability
and increasing the level of detail achievable in the deposition of each layer.

Another improvement also made possible by the first and second
improve-ments would be the addition of nonre-active plasticizers and/or
solvents to the base polymer. Solvents could be used to enhance ejection.
Solvents could be removed by heating each layer immedi-ately after deposition
and before expos-ing it to ultraviolet light. Plasticizers could be used,
along with suitable amounts of molecular lengthening and cross linking, to
tailor the mechanical properties of the finished model.

This work was done by Frank Hartley
and Steve Bolin of Caltech for NASA's
Jet Propulsion Laboratory.

For more information about the rp-ml, see http://ltk.hut.fi/rp-ml/

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