On Tue, 16 Sep 1997 ralott@CCGATE.HAC.COM wrote:
> 4. The FDM hasn't piqued the interest of the academics the way SLA's have.
> I guess without lasers and exotic chemicals, the FDM's are just too
Just a few observations on FDM:
a. The envelope conditions are far from mundane, Altough envelope
temperature is more or less homogeneous throughout the volume;
air velocities are not, due to complicated flow patterns generated
by two planar jets located at the sides of the hardware, and
their interactions with machine components (foam platform, elevator
guides, ...). More on the structure of velocity distributions, if
there will be interest.
To test the effects of the air velocity distributions,
construct a 0.5"diameter x 2" long cylinder *without* containment
supports at NW/W/SW/N/O/S/NE/E/SE corners of the foam.
The cylinders on the east/west side of the foam would have more
shrinkage on the west/east side. Why? differential cooling rates
imposed with stagnation flow/wake structure would force the
wake side to remain at elevated temperatures longer.
Cylinders along N/O/S axis would have reproducible kinks located
around half an inch from the foam. The air velocities at the foam
surface near the center are significantly lower for the first
half an inch of the build, due to the blocking of side jets
by the foam platform. The sudden change in air velocities-> cooling
rate may be the cause of the problem.
(N:north(back), S:south(front), E:east(right), W:west(west),
b. Imagine you have a 6"x1"x0.26" rectangular prism to be built.
Let's assume that 6" direction is
aligned with x axis, and cooling is uniform throughout the
workvolume. If one would embed thermocouples to the foam or into
the part, the measurements will indicate that the E side
of the part will be hotter relative to the W side. The presence
of the support liquefier and radiative heat transfer from it
does pre/post-heat the part and surroundings during the build.
Since the thermal footprint of the traveling extrusion head
has a non-spherical and rather large spatial extent, thermal
analysis of the problem becomes significantly involved.
c. Why do road cross-sections look like a rectangle + two semi-circles?
Can the answer lie in injection molding? in injection molding
polymeric melts/liquids injected in-between parallel walls produce an
elegant flow structure at the flow front, called 'fountain
flow'. previous experience in this field points that the flow front
will be near to a semi-circle for most instances. Do the
thermoplastic melts experience a combination
of 'fountain-flow'+couette flow between liquefier tip at the top
and previously deposited material at the bottom?
d. If one wishes to do adaptive slicing, hence generate a family
of roads of different thicknesses stacked onto eachother at
arbitrary angles; how does the microstructure look like? Some
of the experiments show increased sensitivity of
thinner roads to substrate topography. Depending on the ratio
of the slice thicknesses and local stack angle, roads may decide to
follow the valleys and hills rather than forming a planar surface,
resembling rivers that meander through the topography at
well defined wavelengths if viewed from the top.
e. The build file of FDM is in ASCII, hence it comes with a built-in
API. i believe it is unique in this aspect among other RP vendors
and the guys in Stratasys should be encouraged to keep it in an
open platform. what else can a graduate student ask for?
Manufacturing Processes Laboratory +1-312-355-0478 / +1-312-413-7408 [voice]
Mechanical Engineering Department +1-312-413-0447 [fax]
University of Illinois at Chicago e-mail: firstname.lastname@example.org
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