Jon Rittle
Designer
Mark Bringle
Technical Sponsor Manager
Joe Gibbs Racing
joegibbsracing.com
Edited by Leslie Gordon
leslie.gordon@penton.com
As a NASCAR race-car manufacturer,
we call our main vision
“concept to car.” The phrase sums
up our push to keep a competitive
edge by moving from idea to
physical component as swiftly as
possible. Race cars are no different
from many engineering endeavors
in that designs often require
several changes before approval.
So our shop makes lots of prototypes
to test on cars for form and
fit. About five years ago, to speed
the prototyping phase, we started
using direct-digital-manufacturing
(DDM) technology called fuseddeposition
modeling (FDM) from
Stratasys Inc. Today, we use the
FDM 400mc, one of the company’s
recent machines.
Examples of parts we prototype
include alternator brackets, oil-pan
pieces, and steering mechanisms.
In one design, a complex steering
mechanism with six separate
machining operations needed
changes five times before it was
approved. What would have taken
weeks with our old method took
only a few days because FDM can
run 24/7. The prototype provided
a part to bolt on to the car to see if
the piece would fit in with the rest
of the steering components.
Also, we are one of the few
NASCAR shops that runs a scalemodel
wind-tunnel program. Most
of the parts for scale models come
off the FDM machine. A recent
example is a 40%-scale header, a
component with a complex shape
and small internal holes.
Another example comes from a
fixture intended to hold an engine
for testing in the dynamometer.
Technicians made up the prototype
piece just to check for fit before
cutting such a large piece of
steel. The FDM machine build envelope
is 16 14 16 in., so when
parts are bigger than that, we can
create a tongue-and-groove design
comprising two pieces that
get fabricated in the same build.
Previously, the making of prototypes
necessitated having
a programmer write code
for the CNC and an operator
run parts. This process took
a lot of time, tied up valuable
personnel, and usually provided
only about 75 to 100 prototypes
annually. Today, though, we basically
just dump STL files from CAD
models to our file server or internal
Internet. An operator downloads
a file from the server to the
FDM and the machine produces
sample pieces in about a day.
(Files can also queue to the FDM in
an automated fashion.) Last year,
we made 750 pieces this way.
The FDM process is straightforward.
First, the machine’s
Insight software takes STL files
and figures out how to layer
models, where boundaries reside,
and where to put support
material. The software lets users
rotate parts, specify surfaces,
and even overlap parts with
the work rectangle to get more
parts in one build.
The material the shop uses is
PC-ABS plastic. The form it comes
in looks like twine on a spool in
a canister. There are canisters
for the support and part material, with a backup for each. The software warns if a newly loaded job will run out of material. Also, a flashing red light on the machine indicates the need for a swap-out.
Once inside the machine, the material feeds through a nozzle, which melts the plastic and extrudes
a line of material about 0.010-in. high and 0.20-in. wide with the largest tips offered, while moving back and forth to build the part. The machine extrudes the boundary layer first from support material, a soluble resin, and then fills the part interior. Parts sit on a sheet which, in turn, sits on a steel platen held down by a vacuum.
We use a polycarbonate sheet because parts are a polycarbonate blend of ABS. Fully built parts go into a tank containing water and a soaplike substance to dissolve the support material.
The shop picked FDM for several
reasons. First, other DDM techniques
require a controlled environment
that allows only so much UV. In contrast, the FDM can go anywhere on the shop floor. Also the machine is affordable. Equipment
from another developer cost $900,000. The FDM 400mc was about $225,000. Other technology used a liquid photopolymer that costs about $2,700 a gallon. Canisters
for the FDM machine cost $400 to $500 each.
A
handy feature: Each machine comes with a little “cheat sheet” with magnetic strips. Just place it on the machine for readily available
information on everything from how to replace a canister to how to identify and replace tips. There is also an integrated Help Function in the user interface to diagnose problems on-the-fly.
In manufacturing, the absolutely
best way of doing anything is rarely needed. Companies are only successful when they manufacture
products as cheaply as possible. For example, to make a door wedge out of titanium is overkill. So we bypassed technologies
that would be overkill for the shop. Some DDM techniques allow building parts and bolting them, say, directly to a motorcycle for running. But NASCAR likes keeping
things plain and simple, so it probably will not allow the building
of functional parts for race cars anytime soon. The organization
doesn’t want to run the cost of manufacturing so high that smaller guys go out of business.
The FDM 400mc machine comes from Stratasys Inc., 7665 Commerce Way, Eden Prairie, MN 55344, (800) 937-3010, stratasys.com.