5, 1998 Design News
ANNUAL AUTO ISSUE
Polymers help put vehicles on a lightweight
Plastics infiltrate more
Gary Chamberlain, Senior Editor
As part of a design and light-weighting trend that
began back in the 1970s with the oil embargo, plastic
use in automotive applications has grown from a meager
70 lb per vehicle at that time to more than 230 lb today.
Industry experts predict that the trend will continue,
with another 30 lb or more of plastic components installed
in each vehicle by the year 2002. This translates into
some 1.04 billion lb of engineering plastics alone for
automotive uses as the new century gets underway, according
to industry research analyst The Freedonia Group (Cleveland).
Why the switch away from traditional materials for
automotive applications? "Vehicle light-weighting
and energy efficiency will help lower energy consumption
and, in turn, air emissions," reports John McAuley,
manager of environmental programs for Montell USA (Wilmington,
DE). "Moreover, source reduction or less material
usage, post-industrial and post-consumer recycling,
and use of recycled content resins will greatly contribute
to resource conservation." Plastics can best meet
these design goals, says McAuley.
In a recent Ford Motor Co. seminar on the company's
"Materials Recycling Partnership for the Environment,"
McAuley stressed that because of key environmental issues
facing the auto industry, fewer materials and parts
are being used in applications to make disassembly and
recycling of post-industrial and post-consumer materials
Ford brought the environmental/recycling message into
perspective when the company, along with its former
automotive-components maker Visteon, walked off with
the Grand Award at last year's Society of Plastics Engineers
automotive awards ceremonies. The award-winning program,
"Carpets to Car Parts Recycling," uses 25%
post-consumer recycled content in all nylon air cleaners
installed in Ford's North American cars and trucks.
DuPont reclaims the nylon and other materials from used
carpeting--enough to cover all floors of the New York
World Trade Center and the U.S. Capital Building.
Chrysler also deserves acclaim for its decision to
use recycled polyethylene terephthalate (PET) in headliners
for the 1999 Jeep Grand Cherokee. Johnson Controls Automotive
Systems Group (Plymouth, MI) and Prince Corp. (Holland,
MI), a Johnson Controls subsidiary, developed the material,
called CorteXr, and sold Chrysler on its use. The process
involves using recycled carpets and soft-drink bottles.
Since CorteX uses less space than current-generation
products, according to its developers, it offers more
vehicle interior design flexibility and more room for
occupants. In the Grand Cherokee, the material provides
additional head-impact protection as an energy-absorber
under the headliner.
These recycling efforts illustrate in only a small
way why plastics continue to make inroads into the automotive
arena. Freedonia analysts list these other advantages
for plastics and elastomers versus metals and glass
for automotive uses:
Lighter weight without sacrificing strength.
Putting plastics to work. Here's a
sampling of innovative projects in 1999-model-year cars:
The Beetle is back, and it's creating a buzz among
new car buyers across North America. But this is not
the same Beetle that provided basic transportation at
a bargain price for millions of drivers from the '50s
to the '70s. The new Beetle incorporates the latest
automotive technology, including dual airbags, front-wheel-drive,
four-wheel disc brakes--and 14 applications of engineering
plastics, polyurethane foams, and polyurethane raw materials.
The car features engineering plastics in the headlights
and taillights, diisocyanate in the auxiliary springs,
and a polyurethane coat to protect the finish on plastic
and metal components inside and out. Engineering plastics
also are used in the inner door panels, instrument panel,
glove box, and center console. Polyurethane foam resides
inside the doors and instrument panel to control noise
Bayer Corp. supplied all of the materials. "To
have our materials used so broadly in this new version
of a classic automobile is indeed a compliment,"
says H. Lee Noble, president of Bayer's Polymers Div.
Here's another design challenge for polymers: converting
an automotive air brake valve from a cast-metal component
to molded plastic. The new design had to function identically
and be completely interchangeable with the current product.
It also had to reduce cost, part count, and assembly
Early attempts by the manufacturer to redesign the
valve involved replacing a cast-metal body with a molded
plastic body made from acetal. However, the material
failed to achieve the desired cost reduction. Teaming
with UFE Product Engineering (Stillwater, MN), the valve's
engineers and UFE technicians re-engineered the product
to better utilize the properties of plastics by switching
to Capronr, a glass- and mineral-filled nylon supplied
by AlliedSignal Plastics (Morristown, NJ).
UFE turned to design-for-assembly concepts to optimize
the final product design to meet the customer's cost-cutting
Eliminating the mechanical fasteners and O-ring
seals by using spin-welding to attach the lower
housing to the body.
The result: a weight reduction of 60% over the previous
design, and a reduction in parts from 16 to six. You
can find the new valves on Mack and Navistar trucks.
More sensitive sensors. Lucas Control
Systems (Hampton, VA) had a different challenge to meet:
protecting the delicate circuitry of a new mini-sized
wheel-speed sensor. It accomplished this by using an
advanced thermoplastic encapsulation technology.
Mounted on a fixed member close to a car's wheel-bearing
seal or another rotating part fitted with magnets, the
electronic sensor uses either the Hall- or magneto-resistive
effect to determine wheel speed. This, in turn, generates
digital signals for antilock braking, traction control,
and other automotive systems.
"With assistance from DuPont, we developed an
extremely compact, reliable, and economical sensor,"
says Kim Smith, a principal product development engineer
at Lucas. The sensor's lead frame assembly is encapsulated
by placing it in an injection mold fitted with retractable
support pins and overmolding it with Zytelr nylon resin
supplied by DuPont Engineering Polymers (Wilmington,
DE). The formulation: a nylon 612 with a 33% glass reinforcement.
The sensor's internal electrical/electronic assembly
consists of an IC chip, and a capacitor, and may contain
a diode welded to a lead frame. It is terminated through
a pre-molded connector covered by overmolding or by
lead wire, depending on the application.
Precise positioning of the IC within the envelope proved
crucial to accurate speed sensing, according to Smith.
The nylon resin avoids displacement or damage to the
delicate parts thanks to its ability for slow, low-pressure
mold fill at moderate melt temperature.
Sealing out moisture is also critical. The resin's
slow crystallization rate helps Lucas achieve complete
fill and void-free sealing in areas where the mold's
support pins retract. This blocks moisture penetration
and avoids the need for a separate sealing step.
The sensor measures 1 inch long by 0.25 inch in diameter.
Its size enables it to be mounted in locations where
conventional coil-type sensors won't fit.
Initially, Lucas expects to supply the sensors for
use in European automobiles with magnets mounted on
wheel-bearing seals. Planned developments include modification
for use with a toothed wheel that rotates with road
wheels, a popular design in the U.S. In the future,
Lucas envisions adapting the sensor to provide even
greater sensitivity, along with information about direction
Instrument panels (IPs) also offer bountiful opportunities
for plastics. To reduce weight and cost on IPs and other
interior components, Ford switched from a polycarbonate
(PC) for its F-Series trucks to a PC and acrylonitrile-butadiene-styrene
(ABS) blend. The material, Dow Chemical's PULSE 2000,
is the first PC/ABS to be approved under a new Ford
Ford supplier Visteon (Dearborn, MI) uses the resin
primarily for instrument panels and knee bolsters on
the popular Ford trucks, resulting in a reduction in
cost and weight while still meeting all performance
requirements. "Visteon and Ford have a strong commitment
to continuous improvements in manufacturing