Feature article on composite pickup boxes writtern by
Richard Stewart for Composites Technology magazine.
Truckmakers Go Different Routes for Cargo Boxes
Ford favors SMC for unique Explorer cargo box while GM selects SRIM and preforms for Silverado.
By Richard Stewart
GM and Ford have been researching structural polymeric
composite pickup boxes since the 1980s, but it has taken until
now for them to decide to bite the bullet and introduce the
lightweight, durable boxes on their light trucks. Each company
has selected a different molding process to manufacture these
large, single-piece components.
Ford has revived SMC processing technology developed for
a composite pickup box pilot program in the late ‘80s. GM has
selected structural reaction injection molding (SRIM), adapting
preforming and liquid composite molding processing technology
developed by the automaker and its supplier partners. GM has
also been involved in research on a similar program with the
Automotive Composites Consortium (ACC) at the National
Composites Center in Kettering, Ohio.
Starting this fall, GM will offer a 6.5-foot-long composite
pickup box as an option for the Chevy Silverado, its most
popular full-size pickup truck. The single-piece PRO-TEC(tm)
box is molded of 50% glass-filled polyurethane, using a single
directed-fiber preform. Ford is introducing a composite box on
an all-new Explorer model called the Sport Trac. Designed for
a young, niche market, the vehicle features a four-foot-long
composite cargo box at the rear of a four-door sport utility
vehicle. The SMC box is molded of 50% glass-filled vinyl
ester. A lockable SMC tonneau cover will also be available
for the Sport Trac.
Both Ford and Chevy have done extensive testing on their
composite boxes and both claim that the lightweight compon-
ents have proven to be far more durable than conventional
steel cargo boxes. Customer research has shown that truck
buyers appreciate the ability of composite materials to resist
scratches, dents and rust – and eliminate the need to buy an
aftermarket bed liner.
Significant weight reduction was also realized with the
composite boxes. GM, which also has a composite tailgate
in its PRO-TEC package, claims a savings of some 50 lbs.
over the Silverado's steel-bed version. Ford estimates an
equivalent steel box on the Explorer Sport Trac would
weigh about 20% more than the composite box.
BACKBONE OF SRIM PROCESS
The SRIM process and preforming technology used for
GM's box evolves from a three-year research and develop-
ment project with Molded Fiber Glass (Ashtabula, Ohio).
Eight-foot pickup boxes were molded in 1997 to demonstrate
process capability. GM has also been involved with an R&D
program on a composite box with the ACC, under the
umbrella of the U.S. Council for Automotive Research
(USCAR), an organization formed by GM, Ford and
Chrysler in 1988. ACC's mission is to conduct research to
produce large composite structural parts for automotive use.
That included a pickup box and tailgate. The group worked
with several preforming processes, including one developed
in 1993 in Belgium by Owens Corning (Toledo, Ohio).
Known as the Powdered Programmable Preform Process
or simply P4, the technology utilizes robotically controlled
chopper guns to cut and spray up inexpensive glass tow onto
a metal preform molding screen that is in the shape of the
final part. A powdered heat-setting binder is also applied to
the fibers during the P4 deposition process. Hot air causes
the binder to set and hold the fibers in the shape of the screen
after cooling, producing a net-shape preform. Other binder
systems, including liquid emulsions, have been utilized in the
preforming process. Today, the system used to produce
the Silverado's composite box by GM's Tier One composite
box supplier, Cambridge Industries (Madison Heights, Mich.),
is even more advanced.
Developed by Owens Corning, the new binder technology
completely eliminates the need for the processor to handle
binder material. Called the OC ( tm) Preformable System, the
binder is applied to a certain portion of the glass fiber strands
by the manufacturer during the final stage of glass roving
production. The coated strands are integral to the glass roving
package that is supplied to Cambridge's Huntington, Ind.
production facility, where the PRO-TEC boxes are molded.
As the roving is chopped, both fibers and binder are
deposited onto the screen at the same time.
“With the OC Preformable System, no further application
of powdered or liquid binder is required. That's a significant
advantage in processing and throughput,” says Tom Ketcham,
GM pickup box project manager for Owens Corning. The
company partnered with Cambridge Industries, GM and
Cannon Tecnos USA (Seven Fields, Pa.), manufacturer of
the chopper gun equipment, to bring the preforming process
from the P4 concept to the current production-ready system.
“This is a very clean and efficient way to make a preform,” he
The preforming process used for the GM box starts at the
glass deposition station. Roving doffs are fed through program-
mable robot-controlled chopper guns, which direct the orien-
tation and depth of the chopped glass, spraying the fibers onto
a perforated screen. In the Cambridge plant, glass is deposited
on the screen by four robots, each controlling a chopper gun.
The glass is chopped and sprayed on the preforming screen in
less than three minutes. Air flowing through the screen holds
the fibers against it.
Consolidation screens hinged to the base screen are closed
over top of the fibers on the vertical walls to hold them in place
as the screen moves on a conveyor into the oven chamber.
The binder, a heat-activated polyester thermoset material, sets
the shape of the glass fibers after crosslinking occurs in the
450 degree F. oven. Total cycle time is about six minutes, but
Cambridge expects to increase throughput with additional oven
capacity. The objective is a throughput of three minutes for each
finished preform, according to Pat DePalma, Operations Man-
ager at the 140,000-square-foot Huntington facility. Cambridge
reportedly spent nearly $8 million on preforming, molding,
bonding and painting equipment for the plant.
PRESS SHUTTLES MOLDS
FOR FASTER THROUGHPUT
The completed preform is automatically removed from the
screen and manually transported to the molding station and
loaded into the mold. Transport of preforms and loading into
the mold will eventually be automated, as will the closing and
opening of the consolidation screens, says GM's Jensen. For
molding, Cambridge uses a dual shuttle-type SRIM press
that has the top half of the tool attached to the upper platen
and two identical bottom halves mounted on a shuttle below it.
The duel shuttle enables the press operator to both load the
preform and unload the molded part outside the press while a
second part is curing in the press, for improved throughput,
During the injection/compression molding operation, a
preform is loaded into the outside bottom mold and it is
shuttled into the press. The press closes, bringing the top half
down to meet the bottom half. When they are about 5mm
from final close, the resin -- roughly 40 lbs. of polyurethane,
supplied by Bayer Corp. (Pittsburgh, Pa.) -- is injected into
the mold cavity. After filling, the press closes the rest of the
way, promoting a uniform flow of the resin across all surfaces
of the preform, DePalma explains.
The part is left in the press to cure while the operator loads
a preform into the second mold bottom. After several minutes
of curing, the press opens, the first mold shuttles out for
unloading, positioning the second mold in the press for the
process to continue. DePalma expects to achieve a consistent
four-minute molding cycle by the time production starts to
ramp up in June. Drilling and trimming operations come next
and are followed by 45 minutes of post curing in a
285-degree F. oven.
After curing, where steel components such as cross sills,
extension rail supports, D-pillars at the tailgate, and other
reinforcements are attached using a two-part epoxy adhesive
system from SIA Adhesives, Inc. (Akron, Ohio). The cross
sills and box mounts interface with the vehicle in the same
locations as the steel pickup box, so GM has not had to
redesign the vehicle attachment points to accommodate the
After the bonding process, the parts are power washed
and put through a paint line that applies a black spatter-type
paint to surfaces that are visible after final assembly. The paint
is baked at 180 degrees F. The tailgate is installed, metal
tie-down hooks and some other components are attached,
and the module is ready for shipping to GM's truck assembly
plant in Ft. Wayne, Ind.
To produce the tailgate, preparation of the preform and the
molding closely follow the process used to produce the cargo
box. Both have a 50/50 ratio of glass to resin. Over 50 lbs. of
glass are used to manufacture the box and tailgate assembly,
says DePalma. The composite tailgate is 15 lbs. lighter than the
Silverado's steel tailgate, making it easier to open and close.
The composite tailgate has a designed load-carrying capacity
of 1,000 lbs. vs. 600 lbs. for the steel tailgate, GM reports.
On the assembly line, the composite box is attached to the
chassis with mechanical fasteners. The fenders, molded from
20% mica-filled polyurea, are attached to the box assembly
with fasteners and can be removed in 10 minutes for repair or
replacement if damaged, relates Tom Beaman, a spokesman
for GM's Truck Group. The fenders and the tailgate panel
are molded using the reinforced reaction injection molding
process (RRIM) by the Plastics Division of the Budd Com-
pany (Troy, Mich.).
Budd uses Dow Automotive's (Southfield, Mich.) high-
temperature Spectrim HH 365 polyurea to mold the fenders
and tailgate panel. The two-part chemistry is mixed in the mold
nozzle and requires separate tanks, recirculation pumps and
plumbing to transfer the liquids to the press.
The GM Truck Group has been using fenders of RRIM
polyurea since 1999. The high-temperature polymer enables
the fenders and tailgate panels to go through GM's Fort
Wayne Assembly Plant paint ovens. Budd added 5 RRIM
clamps (presses) and a 20,000-square-foot RRIM post-
curing oven to handle the GM contract. Fenders are molded
in 500-ton clamps; tailgate panels require only 125-ton clamps.
Beaman emphasizes that the PRO-TEC pickup box avoids
the need to buy and install a protective bedliner, as the
majority of pickup owners do. GM offers an aftermarket
bedliner for about $250, he notes. “People who work their
pickups hard often end up replacing the bedliner every two
or three years. And when they do, they often find corrosion
or other damage underneath from dirt and grit that can require
some work on the bed,” he says. “The Silverado composite
box eliminates that. It's guaranteed for the life of the truck
and saves the cost of having to replace the bedliner X number
SMC components for the Ford Explorer Sport Trac are also
manufactured by the Budd Plastics Division, at its North
Baltimore molding facility. Budd recently expanded the
250,000-square-foot plant with an additional 100,000 square
feet of manufacturing space, largely due to contracts for the
new Ford and Silverado truck parts, relates Mike Dorney,
Plastics Division vice president of sales and marketing. The
company molds the Sport Trac's single-piece cargo box inner
panel of structural grade vinyl ester SMC (50% glass by weight)
in a 2,500-ton press.
Budd also molds the box outer panels or fenders for the
Sport Trac of 27% glass-reinforced SMC. Both the right- and
left-side fenders are molded together in a 2,000-ton press. In
addition, Budd molds the unique foldable hard tonneau cover
of 27% glass-filled SMC. The formulation for the Sport Trac
cargo box was set at 50% by weight to meet Ford's durability
requirements. Budd produces its own SMC material at the
Plastics Division's Van Wert, Ohio compounding plant, using
fiberglass from Owens Corning and resins from Alpha Owens
Corning (East Collierville, Tenn.) and Union Carbide Corp.
On the Budd production line, few operators are involved in
molding the cargo box. Two operators at the front of the press
pull the SMC material off the roll, lay it on a table where an
automatic slitter cuts it to length, and place it on an automated
loader. Two plies of SMC material, cut in the same rectangular
shape and size are used for each cargo box. The loader positions
each sheet on the mold before the press closes. An automated
picker pulls the finished part out of the mold and places it in a
cooling nest, where it remains through a three-stage cooling
period. Another operator deflashes the box with a sander before
it moves on to other secondary finishing stations, some of which
Bill Mellian, Owens Corning's Ford North American business
manager, says he is very impressed by the high level of automation
that Budd Plastics Division has attained in the production of the
cargo box. “Minimal handling leads to better part consistency
and higher throughput,” he says. “The automated charge loading
and placement are very critical in terms of producing the right
flow pattern and glass orientation. That and the rest of the
automation speaks highly of Budd and the progress the industry
Secondary operations include drilling holes in the cargo box,
including four in the bed for the attachment of the box to the
truck's frame with bolts. A steel D-pillar assembly is bolted to
the rear of the box to reinforce the tailgate opening, enabling it
to remain square and upright through repeated slamming of the
tailgate, explains Dorney. The box is painted a flat black with a
finish designed to replicate the look of plastic bedliners. It is
baked in a 300-degree F. oven before shipping to Ford's Truck
Assembly Plant in Louisville. At the plant, the box is lowered
onto the frame and attached at the end of the trim assembly line.
Conversely, the SMC fenders are attached in the plant's body
shop at the front of the assembly process and go through the
normal paint system.
The Sport Trac's tonneau cover is assembled by Budd from
four molded panels – two outers and two inners. Molded
two-up on the press, the panels are bonded together to form
two halves of the cover, then painted flat black, and assembled
into the final product. That includes attaching a long piano hinge
that joins the halves in the middle, adding seals around the
periphery, locks, handles, an inside safety cable release, and
bungy cords to hold the cover partially opened if desired, notes
Dorney. Warranted by Ford, the tonneau cover was designed
to endure the OEM's same durability testing that the rest of the
vehicle had to go through, he adds.
EARLIER FORD PICKUP BOX
PROVED SMC DURABILITY
Ford first used SMC pickup boxes in 1989 to demonstrate the
technology in a Ford Ranger pilot program. Those boxes were
molded from SMC with glass content as high as 67%, recalls
Peter Miskech, technical specialist at Ford's Research and
Vehicle Technology (RVT) group in Dearborn, Mich. He
played a major role in the development of the box for the
Ranger program and was instrumental in promoting the use of
composites for the Sport Trac box.
“With the Ranger, we showed that this was a material whose
time had come,” he says. “We knew that pound-for-pound,
SMC was stronger than steel and that it provided excellent
dimensional stability, even in extreme temperatures. The box
we delivered for that program was fully assembled with body
side outer panels, and it went through the paint shop like a
normal sheet metal box.” The pilot build totaled about 400
units, the majority of which went to a private fleet. Others
went into Ford's engineering fleet and some went to the general
public. “The technology was put on the shelf, where it stayed
until the Sport Trac version of the Explorer was being
discussed,” recalls Miskech.
As a result of the pilot program, Ford was able to collect
excellent long-term durability and corrosion data. “Even after
the surface was scratched, we did not see any UV effects on
the structure of the box,” he notes. “Originally people feared
that there would be excessive chalking and deterioration of
the structural integrity. But none of that was apparent in the
10-year-old boxes that went through normal service in the
Ford fleet.” He adds that the performance of those early
boxes was a major factor in the decision to produce a
composite box for the Sport Trac.
The ability to consolidate parts is an important advantage
of the composite cargo box, Miskech says. A conventional
steel box is constructed from stamped steel parts that are
welded together. Major parts include the floor pan, body
side inner panels, headboard, wheel houses, cross members
with butterfly spacers, and sills. Those parts are all consoli-
dated into the one-piece molded composite cargo box.
The dramatically lower cost of tooling for compression
molding vs. metal stamping tools (plus labor in welding) is
another significant advantage of composites. Producing a
sheet metal box for this relatively low-volume version of the
Explorer would have been cost-prohibitive, notes Miskech.
Not wanting to be critical of GM's decision to use the SRIM
process for the Silverado box, he characterized the preforming
technology as highly complex and far more expensive than
SMC. He believes that the successes Ford has had with SMC
makes it a better choice for the Sport Trac. Ford is the
automotive industry's largest user of SMC.
BOTH BOXES SURVIVED
MOST RIGOROUS TESTING
Testing of the composite cargo boxes by both automakers
has been exhaustive and torturous. Ford engineers put the
equivalent of 450,000 miles of durability testing on the Sport
Trac's composite cargo area, the company says. Some of
the same tests if performed on steel pickup beds would
cause severe damage. That did not occur on the composite
bed, Ford adds.
“Not only is the inside durable as can be, but the inner
and outer panels of the cargo area won't dent and won't
rust,” comments David Paul, Ford systems engineer for the
composite area. “If someone heaves their bike into the
cargo box, it will not damage the inside of the box like a
painted steel box,” he adds. All of the required Ford tests
were run on the composite box, including dropping a 55-
gallon drum on it and extreme temperature testing. In
addition “typical customer tests” were conducted such as
dragging cinderblocks across the floor and throwing in
steel pipes and 35-lb. angle irons and stirring them around
in the cargo area, Ford says.
The Silverado's composite pickup box was installed on
48 Chevy C/K pickups and operated in “real-world”
conditions for more than two million miles in some of the
most severe operating environments in North America. All
of them came back unscathed, says GM's Beaman. “We
took a front-end loader full of boulders and dropped them
into the composite box. Except for a little paint flaking, the
box was undamaged,” he recounts. “Try that with a steel
box and you're going to have major damage.” As for the
future of composites in automotive applications? “For
selected applications like pickup boxes and fenders, I think
the future is very, very bright,” says Beaman.
In January, GM introduced a one-of-a-kind auto show
version of the Chevy Avalanche, which featured PRO-TEC
components. Promoting it as the “Ultimate Utility Vehicle,”
GM says the Avalance was designed to be configured as a
pickup truck with an eight-foot-long bed, an SUV, or both
at the same time with a 5' 3” molded cargo box. The
tailgate, a midgate (between the passenger compartment
and the cargo box) and cargo cover are also molded of
PRO-TEC composite materials. The Avalance is scheduled
to go on sale in early 2001.
The 2000 Ford Excursion SUV features an SMC rear
closure system consisting of a liftgate and two cargo doors.
The “Tri-door” system is assembled from inner and outer
body panels bonded together with epoxy adhesive, reports
Cambridge Industries, the supplier. The doors are 15%
lighter than a comparable sheet metal system to facilitate
opening and closing, says Cambridge. The supplier notes
that tooling costs for the molded doors were about 75%
less than costs associated with stamping and assembling
ON CONTINUED GROWTH
Owens Corning forecasts that the use of composites for
open cargo areas and pickup truck boxes will go from zero
to more than 50,000 metric tons by 2004. Budd's Dorney
is also optimistic about the future of composites in cars and
trucks. “I fully expect that there will be additional SMC
applications in the arena of pickup boxes in the future,” he
says. “A lot of OEMs are interested.” He notes that Budd
has equipment large enough to compression-mold six- and
eight-foot pickup boxes from SMC.
Dorney, chairman of the executive council of the Auto-
motive Composites Alliance (ACA), reports that the group
has revised its production forecast of reinforced thermoset
composites for automotive use since these new composite
applications were announced. The ACA has increased its
total projected automotive usage for 2003 from 380 million
lbs. to 456 million lbs. For 2004, the total amount is
expected to climb to 468 million lbs., Dorney reports.
Among the next likely candidates for composite use in
automotive products are large structural floor pans and
front-end supports, suppliers agree.
GM has not released pricing or projected numbers yet
for the 2001 model composite box Silverado. Ford's pro-
jected first-year volume of the 2001 Explorer Sport Trac
is 65,000 units. Customer demand will determine the success
of these programs, but both companies feel that truck buyers
will appreciate the durability advantages that composite
materials provide and be willing to pay the extra cost for the