Plastics vs. Metals in
Automobiles
Greg Boehm
Kendall Chapman
Gordon Clarke II
Gary Gomlak
April 10, 2001
General Overview
• History / Background
• General Design Characteristics
• Select Parts for Comparision
– Fuel Tanks
– Interior / Exterior
– Cooling and Air Intake Systems
History
• History
– Polymers first use in vehicles
• Tires.
• Rubber in bumpers. (1940’s)
• Electrical wiring.
– Interior (late 60’s – 70’s)
• Upholstery cushioning.
• Dashboard / Instrument Panels.
• Electronic components and housings.
History
– Exterior
• Body panels – from composites (fiberglass) on the
Corvette.
• Bumper fascias on almost all models today.
• Compression molded polyester body panels.
– Highly sophisticated polymers, such as
injection molded nylons, are now being
developed for mechanical and operational
systems.
General Design Characteristics
• Mechanical Strength
– Weight
– Temperature
• Material Cost and Manufacturability
• Coatings Applications
• Recyclability
Mechanical Strength
• Temperature
– Plastics making inroads to high temperature
engine accessory applications.
• Corrosion
• Weight
• Permeability
– Issue in fuel and high pressure systems.
Materials Cost
• Biggest barrier to plastic in automobiles.
• Raw material cost.
– Basic polyethylene to specialty plastics.
• Strength and weight to cost ratio.
• Cost in manufacturing.
– Challenge in high end parts.
• Recyclability.
Coatings Applications
• Materials and manufacture.
– Economical raw material costs.
– Lower “tooling” costs.
• Coating Process.
– Greatest expense lies with paint materials and
their adhesion difficulties with plastics.
Introduction to Fuel Tanks
•
•
Terne-coated steel mainstay for
automotive for automotive gas tanks.
Drivers for change include:
1.
2.
3.
4.
5.
Legislation
Permeability
Weight
Safety
Cost
Plastic Fuel Tanks
• Since mid 1980’s plastic replacing steel fuel tanks.
• HDPE is the resin of choice for plastic gas tanks.
• Barrier technology enables plastic fuel tank
manufacturers more stringent emission standards.
• Some see multi-layer tank technology as the
answer to stricter emission standards
Steel Fuel Tanks
• Currently a steel substrate coated with zincnickel or terne.
• Stainless steel tested but are difficult to
form without severe breakage. Also very
expensive.
• Testing painted galvanneal found it
effective for resisting corrosion on both
sides of the tank.
Performance Attributes
Manufacturability
•
•
•
Terne plate holds a cost advantage over
HDPE.
Cost not the only driver: reliability within
the total fuel system.
Plastic tanks need to be chlorinated or
fluorinated to retard permeation. Can be
toxic if mishandled.
Performance Attributes
Features and Weight
• Plastics have the ability to meet packaging
constraints.
• Design engineers have flexibility in the car
design without worry of fitting the gas tank
• Plastic tanks can boast of weight savings of
up to 30%. New permeability requirements
diminish weight savings.
Performance Attributes
Safety and Corrosion
• Ability to meet crash requirements is the key.
• Plastic considered safer because they are seamless.
• Plastic are also not a source of sparks. Retard heat
transfer to the fuel.
• When deformed they have the ability to rebound.
• Thermal properties are an issue in determining
material.
Interior
• Polyurethane foam has long been used due
to design and economic benefits.
• ABS plastic instrument panels reduce
production costs and weight of autos.
• Seamless, single units are easier to assemble
and install.
• Steering wheels made from molded vinyl
resins or pigmented urethanes.
Interior
• HVAC vents and control consoles produced
from ABS and polypropylene resins.
• Key parameters to all plastics in this area
are:
– Reduced weight.
– Reduced noise and vibration.
– Reduced manufacturing costs.
Exterior
• Materials and manufacture.
– Cost effective.
• Highly filled and cross-linked polyesters.
• Premium mechanical Properties.
• Compression molding process.
• Coating process.
– Unique problems to solve.
• Adhesion problems with paints.
• High cost of coatings and “off-line” preparation.
Cooling and Intake Systems
• Cooling Systems
– Radiator end caps
– Radiator fan
– Water pump
• Air / Fuel Intake Manifolds
– Fuel injectors
• Temperature resistance and cost drivers.
Cooling
• Radiator end caps injection molded Nylon
– 30% weight savings.
– Molded into complex shapes to save space.
– High resistance to corrosion and temperatures.
• Water pumps also made of Nylon.
– Withstand high pressures.
• Radiator fans from Nylon.
– Mechanical strength to avoid warping.
• Short molding cycle for Nylon.
Air / Fuel Intake Systems
• Air intake manifold
– Nylons again used for its flexibility in design.
– Smooth interior surfaces to allow for better
flow of air into engine.
• Fuel intakes now emerging with integrated
injectors, filters and sensors.
• Cost is still a barrier to widespread use.