Following a path well-worn by their counterparts in aerospace and automotive design, off-highway engineers seem to be readying themselves to replace metal with thermoplastics. A primary reason is to reduce weight, and a key secondary reason is for controlling noise and vibration.
With more than a half century of application in aerospace (and nearly as many years in automotive), reinforced and rigid engineering plastics have produced a track record for reducing weight and cost. During the same span, foams and elastomeric polymers have found widespread application in absorbing vibration and noise. (For basic types and applications, see SOHE June/July 2009, p. 32, “Plastics expand their range.”)
Applications of all forms of plastics run from unstressed trim panels to functional parts designed for light stress (shrouds, heat shields) to those for moderate and heavy stress (powertrain components).
But even if the lightness of plastics is proving attractive, there is no doubt that off-highway engineering is slow to adopt them. “There is an innate conservatism in heavy equipment,” said Dr. Robert Malloy, Professor and Chairman of the Plastics Engineering Department, University of Massachusetts, Lowell. “If something’s not broken, why fix it?”
History and tradition play strong roles: mobile heavy equipment emerged in the golden age of iron and steel.
Malloy also cites engineering academic traditions. “Until recently, mechanical engineering students were given only limited training in plastics.” Designers are naturally reluctant to adopt unknowns.
“The rugged life of off-highway equipment drew on the strengths of steel from the start,” said Karl P. Maurer, Off-Highway Segment Leader, DuPont Performance Polymers. “There’s a bit of a push into polymeric body panels and other applications where components don’t have to take the brunt of the workload. But at the same time, there’s plenty of investigation of plastics going on. There are plenty of opportunities to replace metal with plastic for fuel efficiency and for weight and cost reduction.”
Weight savings, the holy grail of aerospace, has only recently entered the world of off-highway equipment, where it has become part of an overall design push to increase fuel efficiencies and decrease environmental impact. Per-part savings, a key driver in automotive, is less attractive to off-highway designers. Saving a few cents makes a huge difference when millions of car parts are to be made, but it draws little interest when yearly production is in the thousands—or far less. Still, any production savings could be useful, either as a response to competitive price pressures or a means for greater profit.
Fortunately, time and history are on the side of designers as thermoplastics make their way into off-highway equipment. “Polymeric material behaviors are well known, especially around high-temperature exposure to fluids, including transmission fluids, oils, and fuels,” said Maurer.
As a result, according to John Gavenonis, Nylon Application Development Leader for DuPont, “if designers want to see how plastics behave in off-highway uses, they don’t have to start from scratch—they can look at the existing performance data in automotive and trucking.”
Maurer offers a list of components that have offered a relatively easy transition from metal to plastics in commercial and off-highway designs: valve covers, oil pans, fuel injectors, throttle bodies, fuel pump components, even exhaust systems. “Air-induction systems are especially attractive because they can be designed with fewer components and cleaner, less restrictive passages," he said. "Fewer components mean lower assembly costs and fewer warranty issues. Better airflow can mean improved engine efficiencies.”
“There is a lot of promise in what you could call translations,” said Hansel Ramathal, Product Marketing, Celstran, at Ticona. “Aerospace comes up with something that works. Before long, automotive translates it into mass vehicle production. It’s only a matter of time before off-highway equipment will translate these into its own efficient systems, both in terms of performance and in cost engineering.”