Meridian makes a midgate for GM

A divider between the cab and the cargo box when upright, the midgate serves as an extension to the cargo bed when folded flat, as shown here.

The all-new 2002 Chevrolet Avalanche showcases the exclusive Convert-A-Cab System via a midgate transformation, which enables reconfiguration from a six-passenger SUV with a 1600-mm (63-in) cargo box into a full-size pickup truck with a 2460-mm (97-in) box.

"This is a brand new concept," said Larry Rood, Director of General Motors Sales at Meridian Automotive Systems, molder/assembler of the composite midgate. The midgate is composed of a structural reaction injection molding (SRIM) exterior panel—bonded to sheet molding composite (SMC) reinforcement—and a polypropylene interior trim panel. SRIM has been used for seat frames and engine covers, but the Avalanche's pass-through cab/cargo panel marks a milestone. "This is really the first major high-volume production application of SRIM for an exterior product," said Rood, noting that SRIM has better toughness and durability compared to most plastics. (Meridian also provides the SRIM interior tailgate of the Avalanche.)

A new pre-form technology is being used to produce the midgate. To meet quality and throughput requirements, a patents-pending string-binder technology called OC-Preforming System was co-developed by Owens Corning and Meridian. "In string-binder technology, the adhesive, which functions as a binding agent, is carried along with the glass roving," Ashish Diwanji, Director of Structural Solutions for Owens Corning Automotive, explained.

Because of string-binder technology, the pre-form process is cleaner (no solvents used) and more efficient than the conventional pre-form process. In a conventional pre-form process, "due to the nature of the spraying operation, the liquid or the powder binder gets sprayed onto more areas than just the screen and requires frequent cleaning, especially after multiple passes through the baking oven," Diwanji said. Even more fundamental than the operations, parts molded using these pre-forms exhibit blistering, which results in scrapping of the product.

Meridian was involved in the Avalanche's midgate design by virtue of having been involved in work on the Silverado 1500 extended pickup cab. Those pickup trucks, via special order, use SRIM on the inner structures for the cargo box and tailgate. "That project really gave us the technology to do the midgate," said Rood.

The Avalanche midgate separates the rear seat from the cargo box. It can be folded flat via a single handle. The rear glass window, which has handles at the top of an encapsulation, can be removed and stored in the midgate. The 60/40 split-folding rear seat's rubber bumpers carry the midgate when it's lowered.

Molded components, hardware, reinforcements, latches, spacers, springs, screws, and rivets compose the 30 different pieces of the midgate, which is assembled at a Meridian plant in Huntington, IN.

- Kami Buchholz

Thermoplastic intake manifold from DuPont

A cutaway of GM's Vortec 4200 inline six shows the internal structure of the thermoplastic intake manifold, which is also shown as a ready-to-install unit.

The power behind General Motors Corp.'s new midsize SUVs—the Oldsmobile Bravada, GMC Envoy, and Chevrolet TrailBlazer—is the biggest inline six-cylinder engine to feature a composite manifold, according to DuPont. The high-compression Vortec 4200 engine that produces 200 kW (270 hp)—the highest rating in its class, according to GM—and 373 N•m (275 lb•ft) at 3600 rpm is made of DuPont Zytel welding-enhanced nylon. The one-piece manifold, compared to a non-thermoplastic version composed of 20 or more parts, has a mass of about 3.6 kg (8 lb).

Vibration welding is used to join two shells that form the manifold. A vibration-welded thermoplastic manifold on a North American vehicle is a GM first. Montaplast of North America designed the manufacturing process and produces the part. "This is one of the best manifolds we have developed in recent years because it is incredibly robust, but best of all, the design is simple yet highly functional," said Montaplast's Michael Ellenbeck. No support brackets are required because it is a very stiff, self-supporting design, and the part's geometry makes warping less of a concern than it otherwise would be, according to DuPont.

The air-intake manifold underwent extensive pre-production analysis. "FEA modeling was used for vibration and noise analysis, along with mold flow and warp analysis to enhance the design," said DuPont Automotive's Ken Nelson, Senior Technical Consultant. "FEA was also employed to make sure the part could successfully pass overpressure (backfire) events without breaking. The FEA work influenced the part design, and we contributed early on to strengthening the overall design with burst pressure testing in our lab."

- Kami Buchholz