Hello listers,
To the existing prototyping technologies comes this one, developed at the
University of Southern California.
The following is a USC press release.
Enjoy!
--Bryan Bashin
---------- Forwarded message ----------
>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 Newly Patented 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
EDITOR: Dr. Khoshnevis is a resident of West Los Angeles (90064).
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