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By Mark McCollough
3D
Rapid Modeling Instructor
Art
Center College of Design
Pasadena, California
Utilizing
CNC machining instead of clay modeling makes it possible to
significantly reduce vehicle modeling time while substantially
increasing the accuracy of the model.
Previously, it took Art Center students hundreds of hours to
produce clay models of their concept car designs by hand sculpting.
With a CNC router, they produce designs that represent their
concepts within a much smaller margin of error in much less time. By
reducing the manual labor associated with vehicle design, CNC
technology potentially gives the students much more time to spend on
the creative process -– which is why they came here in the first
place.
Art Center
College of Design is an international center for art and design
education located in Pasadena, California. An independent,
nonprofit, four-year college, Art Center offers a bachelor of fine
arts or bachelor of science degree in nine majors: Advertising,
Environmental Design, Film, Fine Art, Graphic Design, Illustration,
Photography, Product Design, and Transportation Design. Master's
degrees (MA, MFA and MS) are given in Art Theory and Criticism,
Film, Fine Art, Illustration, Photography, Digital Media,
Transportation, Environmental Design and Product Design.
In
the first four semesters of Art Center’s Transportation Design
program, fundamental skills are developed including concept
sketching and 3D rendering. Principles of ergonomics, aerodynamics,
research into new energy sources, and computer applications to the
design process are also investigated. There is also a strong
emphasis on marketing and consumer preferences. In later semesters,
students simulate professional design activity by completing
projects sponsored by North American, European and Japanese auto
manufacturers. Students collaborate with designers from these
companies, who guide and critique their work. This exchange of ideas
makes for an invaluable forum in automobile design, engineering and
materials.
The traditional
method of styling began with hand-drawn sketches which were
eventually made into renderings. The more promising designs were
fashioned as one-fifth scale models in clay by students in a process
that was both labor intensive and highly iterative. It would
typically take students up to 700 hours to create their clay models.
Once they were satisfied with the model, they could use it to
produce a form that later might be used to produce a durable
fiberglass model. It was particularly difficult to maintain a
symmetrical relationship between the different sides of the vehicle.
Through his work in private industry prior to joining the staff of
Art Center, the author became familiar with the trend towards CNC
machining as a replacement for hand-built models. This trend draws
its strength from several factors that apply equally well to private
industry as well as educational institutions. First of all, most
current design work is, if not originally created with CAD,
duplicated in CAD soon after it is created. Second, the price and
ease of use of CNC machinery suitable for producing models has been
dramatically reduced in the last several years. Finally, the
increased use of CNC machining to produce models has driven up
expectations concerning the accuracy and symmetricity of models.
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Not long after
joining Art Center, the author proposed purchasing a light CNC
machine suitable for model building. After getting approval to move
ahead, he examined several different CNC approaches to determine
which would best fit the needs and budget of the school. He first
considered stereolithography apparatus (SLA), a commonly used method
of producing prototype models, but determined that aesthetically
critical parts with complex surfaces couldn't be produced with SLA
since this technology makes tiny steps or facets in a curved
surface. Next, he considered a traditional CNC machine tool. These
machines, made by companies such as Bridgeport, start at $50,000,
not including the CNC programming software. To get a model with a
working area large enough to produce one-fifth scale models, Art
Center College would have had to buy one of the larger machines
costing at least twice that.
Then, the author
remembered a machine that he had used in an earlier position at
another workplace with considerable success.
The Techno Series III
gantry router from Techno-Isel, New Hyde Park, New York is similar
in function to a CNC machining center. At about $22,000, the machine
is considerably less expensive and designed for lighter duty work.
Yet, it provides the same surface finish and accuracy as a machining
center. Its working
area of 49 inches by 41 inches with a Z-axis height of 10
inches, is larger than nearly all machining centers in the
under-$100,000 price range. And the machine can handle virtually any
type of material although it is limited to relatively small depths
of cut in ferrous and other tough-to-machine materials.
Based on his
recommendation, the college purchased the Techno machine and gave
students the option of using it for the design projects. Most Art
Center students were able to learn to operate the new machine in a
day or so. This was largely because the Mastercam CNC programming
software, from CNC Software Inc., Tolland, Connecticut, supplied
with the machine was easy to learn. Although originally designed for
metal working, Mastercam is also well-suited for industrial design
models because of its ability to generate the most complex contours
with little programming effort. Mastercam includes IGES, DXF and
CADL converters so that geometry can be uploaded from many CAD
systems such as Pro/ENGINEER.
Art Center
students begin by defining their concept design in a computer aided
industrial design software package such as Alias, FormZ and
SolidWorks. They export their model in the IGES format and import it
into a CNC programming package called Mastercam from CNC Software,
Tolland, Connecticut, to produce a file that the router understands.
They generate the CNC program, then use the Techno machine to cut
patterns from 3-inch thick sheets of 4-foot by 8-foot 7-pound or
15-pound density polyurethane foam. They machine the top and bottom
halves of the car separately, drilling alignment holes in each half.
Then they marry the two halves by inserting steel rods into the
holes and gluing them together. The foam model is then used as the
pattern to produce a mold that casts the fiberglass model. The time
needed to produce detail components, such as tires, is also
dramatically reduced.
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The Techno
machine's .0002 inch resolution and repeatability and 0.003 inch
absolute accuracy ensure that the foam models are faithful
representation of the designs created on the computer. This is
critical in an industrial design application since the models must
give the client an accurate likeness of the eventual end product.
The Techno machine's accuracy is the result of several features
inherent to the table, such as the use of ball screws and servo
motors. For example, anti-backlash ball nuts permit play-free motion
that makes it possible to produce accurate circles and inlays. The
ballscrews have excellent power transmission due to the rolling ball
contact between the nut and screw. This rolling contact also ensures
longer life and greater rigidity during the life of the system
because of the reduced wear as compared to ACME screws and nuts or
rack and pinion systems, which have a sliding friction contact.
In approximately
300 hours of operation, Art Center College has had no problems with
the Techno machine. This is partly due to the strength and rigidity
of the table, which is constructed from extruded aluminum profiles
that provide easy clamping capability. The machine also has four
ground and hardened steel shafts and eight recirculating bearings in
each axis. This shaft and bearing system produces very smooth
play-free motion and an extremely rigid system that produces
high-quality cuts.
Art Center
College students have found that the new approach to model building,
while seemingly addressing the mechanical aspects of design,
actually has a major impact on the creative process. First, the
Techno CNC machine gives the students unlimited freedom because they
know that they can build anything that they can draw on the
computer. Most important,
the Techno CNC takes much
of the drudgery out of model building and can save them about 400
hours per model that they can put to good use in developing new
concept designs.
Perhaps the
greatest benefit of the new CNC approach comes after the initial
design is complete. Because the design is produced in electronic
format and the modeling process is largely automated, students can
easily change their designs and generate a model. In the past, the
amount of time required to make changes was so great that it often
couldn't be done.
By reducing cycle times and giving
students the opportunity to improve their designs, the new approach
lets students take advantage of the latest "design to model"
techniques that reduce time to market in the industrial world.
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