DETROIT — After several years seeking out alternative materials, General Motors Corp. has become the first automaker to make a wholesale switch in its pickup truck beds to reinforced reaction injection molded parts.
The project is touted by Detroit-based GM as the largest production application of RRIM technology ever used on a body panel. The world's No. 1 carmaker will debut its 1999 fleet of pickup trucks, which includes the Chevrolet Silverado and GMC Sierra, with an optional, RRIM sport-side fender.
The fenders will replace GM's current sporty fender made with sheet molding compound, another thermoset plastic material. The newer models will use a newly developed polyurethane-based substance from Dow Automotive in Troy, Mich.
Rather than being a blow to the SMC market, the move widens the universe of thermoset plastics as a substitute for steel, said Maryann Combs, director of body engineering for the GM Truck Group, based in Pontiac, Mich.
``When we want to get into something that is highly curved and styled, we like the [RRIM] plastic better than SMC,'' Combs said. ``It's a transition for us that we think could work well for any vertical body panel. But SMC still has its place in the market in areas where RRIM would not survive.''
Yet the use of RRIM could also turn the heads of other carmakers who have been loathe to change from metal or SMC fenders. With more than 870,000 trucks produced last year, GM's pickups are the automaker's top-selling vehicles.
Sales numbers were not available for those trucks sold with the more-rounded, sport-side fenders as opposed to the flatter, traditional fleet-side versions made from steel.
``It would be my guess that sporty fenders would be a growing segment for us,'' said GMC spokesman Dan Flores. ``The buying public has changed quite a bit, and they want a truck with more flair.''
Styling was a major reason for the switch, Combs said. With RRIM's one-piece molding process, the material can easily be curved and designed in virtually any configuration without added cost, she said. The new fenders include a step-up area allowing easy entry to the vehicle's rear cargo space.
In the past, the material's problem with painting and vulnerability to dents and scratches kept it from pickup box consideration, she said. However, a team that included engineers from GM, Dow and RRIM molder Decoma International Inc. of Markham, Ontario, spent two years looking for ways to improve the current product.
The result was a material more resistant to high heat of more than 300° F, said Dow Automotive commercial manager Ronald Parker. That opened the door for the RRIM fenders to move through an in-line paint oven and allow them to be easily painted during the assembly process, he said. The parts must sustain 330° F for 20 minutes while in the ovens.
``It's a real breakthrough for RRIM,'' Parker said. ``Now, it makes no difference whether the material is steel or plastic. Either can be painted in a similar manner on an assembly line.''
The material's chemistry also offered scratch resistance while significantly lowering cost and weight, Combs said. The RRIM fenders are 38 percent lighter than SMC, dropping the fenders in weight from 33 pounds to 20.5 pounds. ``We had new strict mass reduction goals to meet to improve fuel economy,'' she said.
Ultimately, the molding process reduced the number of fasteners by 53 percent, leading to a 4 percent reduction in piece cost, she said. And while the compression molded SMC part took more than 4 minutes in production cycle time, the new parts can be made in less than 20 seconds, Combs said.
Yet, the time might not be right for the industry to leap into RRIM, said plastics automotive consultant Mark Opalewski of Phillip Townsend Associates Inc. of Houston. Automakers have been known to change their minds quickly about materials.
``I'm curious how it will stand up when the trucks hit rocks or when a rake or shovel gets thrown into the back,'' he said. ``It's a good alternative for fuel efficiency if it can hold up. Sometimes, it's difficult to really know until a part is in production.''
Whether the move is a grand experiment or a permanent change doesn't necessarily affect the market for SMC parts, said President Kevin Alder of Cambridge Industries Inc. in Madison Heights, Mich. The company is a major supplier of SMC and RRIM automotive parts.
``RRIM has been challenging SMC for quite some time,'' Alder said. ``There are not always significant advantages for one or the other. It can depend more on customer preferences.
``What's more important is that both materials have evolved to where there are fewer restrictions for them as a replacement for metal exteriors.''
Currently, Ford Motor Co.'s popular F-series pickup trucks use an SMC sport-side box. SMC, a thicker material, is also used frequently for heavy truck applications and for horizontal body parts such as truck hoods.
Other RRIM fender applications have slowly taken hold with smaller-volume niche vehicles, such as GM's Pontiac Firebird and Chevrolet Corvette.
Besides the development by GM, plastic pickup beds are going under the microscope at the National Center for Composite Systems Technology in Dayton, Ohio. The composites research group is working with Big Three automakers to fabricate prototype carbon-fiber composite beds. Production has not yet begun on the pickup beds.