PRODUCT
RAYITE™ 100 Machinable Media
PROJECT
Cessna
Aircraft Company
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"We've reduced our cutting time by 50 percent and our finishing
time by 75 percent."
 Larry
Stephens
Superintendent of Tooling
Cessna Corporation
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Gypsum-Based Machinable Media Takes Off at Cessna
Cessna
Aircraft Company, one of the largest light-aircraft manufacturers in the world,
prides itself on having an innovative outlook. The company established itself
more than 70 years ago as the creator of the first strut-free single-wing
airplane and now features a broad line of business and personal aircraft
favored throughout the world.
That spirit of innovation carries through
to the Cessna composites and tooling group, which is part of the company's
research and development organization, where the staff develops and refines
individual parts for Cessna airplanes. In fact, employees in the pattern bond
shop and plastic and composite operations constantly seek new materials to
improve machining speed and design flexibility in making prototypes, according
to Larry Stephens, superintendent of tooling for Cessna.
"We are quite
open to tooling change and improvement as a group," he said. "We pride
ourselves on thinking out of the box."
But "in the box" is where
Stephens' group ended up, so to speak, with the latest change they made to
their tooling operations. The group switched from using pulp board to
gypsum-based RAYITE™ 100 Machinable Media from USG Corporation Industrial
Products to create temporary and limited-production parts and quick turnaround
tools. Pulp board, similar to phenolic board, was cumbersome to handle. It
required extensive storage space and then had to be glued together before
machining. During one of the group's last experiences with the material, it
came apart and its abrasiveness slowed the machining process.
RAYITE
100 Machinable Media appealed to Stephens and his staff because of the many
efficiencies it offered. Since Stephen's team was already accustomed to mixing
plasters and resins, switching to this gypsum-based media was easy. Shop
personnel mix any size batch they need and pour the water and gypsum-based
RAYITE 100 product into a plywood box used as a containing mold. Because the
product is a slurry, it quickly cures into any size or shape mold. After
removing the cured Rayite 100 after one hour, the billet cures overnight. The
media is then machined primarily using an HSS (high speed steel) or carbide
tipped [need explanation], two-fluted, 2-inch end mill. The prototype is
lightly sanded with 100-200 grit sandpaper and sealed with USG-1 Sealer
developed for the chemistry of RAYITE 100 machinable media. [need product
information].
"We produce billets in various sizes using 5- to
30-gallon plywood boxes," explained Stephens. "The largest batch we've made so
far was a 195-pound slurry to build a 500-pound tool."
To date, Stephens
and his staff have used the USG product to make patterns for landing gear
(which are eventually produced from polyester), wheel covers, wing tips,
struts, inlet caps and speed fairings (which are all manufactured from epoxy).
They've also used RAYITE 100 Machinable Media as a vacuum mold for interior
parts such as dashboards and panels. These parts have gone into Cessna's 172
Skyhawk, 182 Skyline, 206 Stationair, 560 Encore and Sovereign models.
Stephens and his staff like RAYITE's advantages.
"The main
reason we switched to the product was that it's castable and offers greater
versatility than board," said Stephens. "It allows for faster machining and
less cleanup. And it doesn't restrict the size or shape we need and reduces
waste and labor."
RAYITE 100 Machinable Media is dimensionally stable
for production of patterns to exacting dimensions. It does not require
lubricating fluids during machining and is not highly abrasive on cutting
tools. In fact, it not only reduces wear and tear, it does not require
carbide-tipped tools for milling.
"We've reduced our cutting time by 50
percent and our finishing time by 75 percent," said Stephens. Once machining is
complete, cleanup is easier, too, since RAYITE media is mixed with water.
The machinable media cost savings that Cessna has realized by using
RAYITE 100 are probably as important as the time and labor savings. Compared to
resin-type or phenolic-core board, which runs approximately $15 per board foot,
RAYITE 100 Machinable Media costs about $11 per board foot. The product is also
less expensive than urethane, resins or aluminum, which runs $3 to $4 per
pound, compared to RAYITE's $1 to $2 per pound. After working with RAYITE 100
Machinable Media for about one year, Stephens and his staff began using it in a
way he has not seen elsewhere in his industry: in one pattern, they integrate
pattern material produced from both RAYITE 100 and the stereo lithography
process (SLA). "We like to improvise, and this combination seemed like a
natural step for us to take," Stephens said.
The group uses the RAYITE
100 Machinable Media/SLA combination to produce parts such as wing tip vacuum
molds, a baggage door interior part and other components. In these cases, a
section of the part requires the intricate details that SLA technology can
produce, while other, larger parts were produced with the gypsum-based media.
Stephens reports that using stereo lithography for the entire part would have
been prohibitively expensive because this method involves injecting an
ultraviolet-sensitive liquid polymer onto a tray, where it is hardened by laser
light in layers that are .0005 of an inch thick. The process is slow and
costly, but produces the finer, thinner parts that can't be machined. These
parts are then inserted into a machined pocket in the RAYITE 100 Machinable
Media-produced portion of the pattern.
"Overall, the benefits of the
RAYITE 100 machinable media have helped us increase the speed of our product
development here at Cessna, and helped us save money," said Stephens. "We are
always trying to deliver products to the market faster and more effectively and
see more opportunities for using this machinable media in the future."
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