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Recent innovations in hardware and software have opened new horizons
in the way technology educators can approach the curriculum.
As our world becomes increasingly more high tech, fast paced, and
competitive, many middle and high school teachers have
decided to update parts of their manual technology programs with
automated technology. One good example involves transforming the C02
car curriculum into a CAD/CAM/CNC based process.
The C02
curriculum has traditionally served as an early exposure to
technology for middle and high school students. The activity begins
with students receiving a kit with a block of wood, four wheels, two
axles, and a booklet that gives design parameters and process
instructions. Each student then studies design principles, carves a
car body, assembles the car, and races it in the school gym.
Although this
activity has proved motivational and successful, it can be improved
by updating the design and production process with CAD/CAM/CNC
(computer-aided drafting/computer-aided manufacturing/computer
numerical control). This approach teaches the skills needed in
high-tech manufacturing careers and stimulates student interest.
Benefits of CNC.
Students will work hard for
something they want to own. Few at the middle school level have the
carving skills needed to produce a good product from raw stock. Some
lose interest when they see that they can’t compete with other
students who have more shop experience or access to tools at home.
Frustration arises when expectations exceed abilities. Early
failures can steer students away from pursuing a technology career.
Thus, the very mechanism that teachers use to motivate students
toward work in technology may backfire if it produces disappointing
early experiences.
The use of CAD/CAM/CNC can "level
the playing field" and motivate students.
With
a CNC machine doing the carving, cars come out perfectly bilateral
and even the wildest designs can achieve the "concept car" look.
Students
want these cars, and they know that winning this activity depends
more on their minds than their hands. Fortunately, technology has
advanced to a point where students can delegate laborious manual
tasks to a machine. Producing high-quality projects no longer
requires superior dexterity. Also, if the C02 competition
is a public event, the sharp appearance of high-tech race cars will
give a good impression to parents and the public.
More
than 50 middle and high school technology education programs in
south Florida have converted to building C02 race cars
with CAD/CAM/CNC, using Techno’s IMS C02 system. With the
system, students can produce C02 metric 500 cars in less
than an hour.
The cars not only satisfy Technology Student Association (TSA)
specifications, but they also have placed high in state, regional,
and national competitions. In the 1996 TSA national competition,
juniors with CAD/CAM/CNC cars placed first and third. A highly
motivated and enthusiastic special education student took fourth
place.
In the 1997 competition, four
CAD/CAM/CNC-produced cars placed in the top 10, with one taking
first place.
Background:
The concept of producing C02 cars with CAD/CAM/CNC has
been possible for years, though not plausible. CAD systems could
describe complex 3-D shapes, but it took too long to get a student
up to speed to draw a car. CAM systems could generate the toolpath,
but problems arose in cutting out a car from the top, because the
cutter got buried too deep and there was little or no side
definition. Cutting from the side addressed tool burial concerns,
but it posed indexing problems
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The
DaVinci XYZ System
CNC machines
could cut a car, but slow feeds and speeds made the process so time
consuming that not everyone in the class could use it. No text
existed for guiding students through all of the integrated
processes.
Three companies, CNC Software (Mastercam), Techno, and IMS
Technologies have worked together to address these challenges. The
technology has come of age and pricing has fallen to under $10,000
for a complete system.
One package can process an entire class, though some
instructors add additional software stations to allow more
experimentation with design.
How the process
works:
Software and
template.
The part is designed and toolpathed, and NC-code is generated in
Mastercam integrated CAD-CAM software. The average student can
quickly design complex 3-D shapes because of a software template
system and curriculum developed by IMS Technologies.
The template is
a file that resides in the CAM software and coaches the student
through the design process. It gives the student a cross-sectional
slice through the C02 blank, every inch showing what to
avoid. The student simply draws one-half of the cross-section shape
of the C02 car by charting points with the mouse. The
software then creates a spline through those points. The student
changes levels, changes depth, hides the old template, and activates
the new one.
After all the
cross sections are drawn, the part is mirrored to complete the
design and then rendered. The rendered image lets the student check
the design form and determine whether it meets TSA specifications. A
window is put around the cross sections and the toolpath is
generated.
The generated
toolpath is for the right side of the car. This toolpath is mirrored
to produce the left-side toolpath. Two toolpaths are necessary as
the car is cut from the right side then indexed to the left side.
Precision indexing is the key to cutting the car from the side.
The fixture.
A fixture is integral to the success of this process. Cutting the
car from the side eliminates cutter burial problems, and the fixture
addresses indexing problems.
The C02
canister hole on the blank is placed on a shaft on the back of
the fixture, and the shaft is pushed forward. The front of the blank
fits in a holder on the front of the fixture. A few taps with a
soft-blow hammer secures the blank. The car is machined on one side,
then the fixture is loosened, indexed 180, and the other side is
machined. This produces a bilaterally perfect car.
The
CNC machine
The DaVinci CNC
machine works well for making C02 cars. It has a work
envelope and feedrates (140 ipm) that produce C02 cars
efficiently enough to run the whole class through the
curriculum. The average car takes from 8 to 10 minutes per side at
80 ipm. An average educational machine that has feedrates of 10-15
ipm would take 80 minutes or longer. The machine has a high 24,000
rpm spindle that machines wood well. Like industrial machines, it
has ball screws on all three axes, which increases power and
accuracy.
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The curriculum.
The IMS C02 curriculum integrates all aspects of the
procedure from machine and fixture setup to software instructions.
Students and teachers receive instructional training videos and
curriculum guides, step-by-step instructions for assemble and use,
clamps, fixtures, and software. The basic system includes CAD
software. CAM toolpath generation software, and a CNC machine.
The CAM software
eliminates hand carving by creating tooling instructions for the CNC
machine, based on the CAD drawing specifications.
The three-axis CNC machine
performs the manual labor with precision, speed, and reliability.
The only manual work left for students is finishing touches, such as
light sanding, painting the car, and adding wheels. This approach
saves students time and lets them focus on learning new skills and
experimentation.
The speed of the CNC machine also allows students to produce more
than one race car, experimenting with different materials and
designs and testing aerodynamic differences. This freedom to
experiment encourages innovative thinking, creative problem solving,
and collaborative brainstorming efforts.
This activity results in students learning transferable
skills by using the same prototype and design software and machines
found in high-tech industrial workplaces.
Students also benefit from
having the luxury of performing trial-and-error learning and
discovery.
Other options.
Advanced secondary students can go beyond defining their cars with
simple cross-sectional slices. Cars can be designed using full
surface modeling, which allows for greater detail and more variation
in shape.
Students might
also take on the engineering challenge of designing a car/boat/plane
body. Here, they would take into consideration the particular
requirements of each type of vehicle:
Car
– The most critical design factor here is weight, then aerodynamic
shape, then friction and alignment of mechanical parts, wheels, and
axles. Points would be awarded for speed.
Boat
– The first consideration is hydrodynamic shape (water flow), then
the amount of water the shape displaces, then the placement of the
mast. The boat competition would use the same C02 body,
with a spent C02 cartridge as ballast. A mast hole would
be drilled into the bottom of the car to hold a standard sail. The
race would take place in a vinyl rain gutter filled with water, and
the student would provide power with air from a portable fan. Points
would be awarded for speed and straightness of course.
Plane
– The critical design factor is placement of the wings at the center
gravity, then trimming of the tail, body shape, and fuselage. The C02
cartridge would be removed for this competition and a special plug,
with tail fin support and adjustment mechanism, would be placed in
the hole. The body would be slotted to accept prefabricated wings.
The wings would slide forward and back to adjust for center of
gravity. Competition would use a mechanical launcher and points
would be awarded for straightness of flight and distance.
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