I saw this in sci.engr.manufacturing...thought it might be of interest
to some. Actually, there is a familiar name in here too!
-Justin
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Justin Kidder, Research Asst. | Automation and Robotics Laboratory
jrkst34+@pitt.edu | University of Pittsburgh
Home page: http://www.pitt.edu/~jrkst34
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"If at first you don't succeed, skydiving is not for you"
Subject: New Rapid Prototyping Technique/USC PRESS RELEASE
Date: Thu, 19 Jun 1997 16:47:17 -0700
From: mankin@usc.edu (Eric Mankin)
Organization: University Of Southern California
Newsgroups: sci.engr.manufacturing
>From the University of Southern California News Service
3620 South Vermont Avenue, Los Angeles, CA 90089-2538
Tel: 213 740 7600 Fax: 213 740 7600 http : / /
www.usc.edu
Contact: Eric Mankin (213-740-9344)
0697008 email: mankin@usc.edu
A Novel Rapid Prototyping Technique Allows Quick
Fabrication of Large, Highly Finished, Computer-Designed
Objects
One of mankind's oldest tools was the inspiration for
the improvement of mankind's newest manufacturing
process.
The trowel - the simple flat blade used by artists
and builders for millennia to shape fluid materials like
clay or plaster - is the key element in a new
rapid-prototyping technology called "Contour Crafting,"
recently patented by University of Southern California
researcher Behrokh Khoshnevis.
"Rapid prototyping" is the general name for a group
of novel manufacturing processes that have come into
commercial use in the last decade. In all of them, a
computer controls a continuous feed of raw material to
build up complex three-dimensional objects. Such
objects are typically then used as prototypes to create
molds or jigs for traditional mass-production techniques.
Khoshnevis believes Contour Crafting has significant
advantages over existing rapid-prototyping processes.
It can create much larger objects more quickly out of a
greater variety of material - including standard, widely
used structural plastics or even metals - and the objects
created require less final finishing.
"Contour Crafting may even have potential not just
as a rapid- prototyping process, but as a manufacturing
process," said Khoshnevis, an associate professor in the
USC School of Engineering's department of industrial and
systems engineering.
Like other rapid-prototyping processes, Contour
Crafting is a way to realize a three-dimensional object
designed with a Computer Aided Design (CAD) system.
Most existing prototyping processes work by first
having computers analyze a CAD representation into a
stack of flat, thin sections. A cone, for example, is
visualized as a stack of disks of constantly increasing
size; a hollow cylinder as a stack of identically sized
rings.
Then, various techniques are used to create these
visualized layers, one by one. Some rapid-prototype
systems use ultraviolet light or lasers to harden soft
plastic or plastic powder layer by layer onto rising
platforms; some use a computer-controlled laser to cut
glued-together layers of special fiber paper, one layer at
a time. One technique, called "three-dimensional
printing," uses an ink-jet-printer-like nozzle to spray
layers of glue on plastic powder, one layer at a time.
All of these layering techniques share a common
problem - rough edges. If the layers are thick, the side
edges of the resulting shape show laddering effects on
what should be smooth surfaces, so that what should be
a cone looks instead like a stack of discreet,
differently-sized disks. The effect can be minimized by
making the layers thinner; but doing so makes the rapid
prototyping much less rapid, because it takes more
layers to create a finished product. Making even a
relatively small part can take hours or even days with
existing machines. Since such machines cost $100,000 or
more, the time factor sharply increases the cost of parts.
Even when cost is not a factor, all existing systems
have physical limits on the size of the objects that can
be created. The maximum size is about one cubic meter -
a box 39 inches on a side.
Khoshnevis' Contour Control system breaks those
boundaries. It improves on an existing technique in
which a computer-controlled extrusion nozzle squirts out
plastic to build up layers, somewhat like the way a cake
decorator squeezes out patterns.
Khoshnevis has added to this setup a pair of
movable, flat control surfaces that Khoshnevis calls
trowels - just above and to the side of the nozzle. The
trowel movements, shaping the material coming out of
the nozzle before it sets, are controlled by the computer.
In Khoshnevis' system, the nozzle and trowel
arrangement creates the object's outside walls as a thin
but strong shell. A separate pouring mechanism fills in
solid objects by adding material in bulk, layer by layer.
Khoshnevis said he got the idea smoothing plaster on his
house.
The inventor acknowledges that programming the
Contour Control system is more complex than with
existing rapid-prototyping systems. Such systems need
only describe the fabrication of the object using three
control parameters - the three dimensions of space,
represented as the x, y, and z axes of a CAD
representation.
Contour Crafting programming needs to specify not
just the three spatial coordinates, but three more control
parameters - the desired orientation of both the trowels,
plus a flow-rate for the extrusion nozzle.
"These are not trivial problems," Khoshnevis said,
"but they are solvable, and the solutions are becoming
easier as we gain experience."
Against this difficulty, he ticks off the advantages:
A wide variety of materials can be used.
Khoshnevis' extrusion nozzles can use polyethylene, ABS,
nylon or other strong, common synthetics or specialized
plastics that harden when exposed to ultraviolet light.
The fact that the nozzle can be large allows the use of
ultra-strong new fiber-composites, as well as such
traditional materials as plaster or concrete. Khoshnevis
is experimenting with metal powder carried in a plastic
binder. Subsequent heat treatment "sinters" the work -
burns off the binder and fuses the metal.
The process is much more rapid than any existing
rapid- prototyping system, building parts in less than
one-tenth the time. At the same time, extremely large
parts are possible. "If you install the extrusion nozzles
on a gantry assembly," Khoshnevis said, "it is completely
feasible to build items as big as boats, all in one piece."
Large auto or airplane parts could be created in a single
process.
High-value items like boats are candidates for
production by the new method, the researcher believes.
"As we gain expertise in this method," Khoshnevis said,
"machines improve and cost falls. I believe this method
will be competitive with some manufacturing processes."
In the meantime, Khoshnevis wrote recently, "We
believe that the [positive] attributes [of Contour
Crafting] are desperately needed in the manufacturing
community, and the idea has been well-received by both
large and small manufacturing companies in the Los
Angeles area. Many of these companies are not content
with methods currently available, either because of cost,
surface finish, component size, material limitations or
some combination thereof. But there is little doubt that
better prototyping methods are needed, especially given
increasingly competitive world markets."
The National Science Foundation and private industry
have supported Khoshnevis' work. His collaborators
include professor Steven Nutt of the School of
Engineering department of materials science, Ph.D.
candidates Rick Russell and Zheng-Ha Yeh, and master's
degree candidates Majid Aghababazadeh, Dmitri Landos
and Steve Farentino. (Farentino currently works in the
Southern California-rapid prototyping industry.)
Khoshnevis received patent #5,529,471 in June 1996
for Contour Crafting technology and has another patent
pending.
EM.KHOSHNEVIS -USC- JUNE 11, 1997
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