Injection Molding for Low-Cost High Mileage

For years, the argument's been "steel versus aluminum" for taking body and chassis construction into a new era. But Daimler-Chrysler AG's recent unveiling of its latest Partnership for a New Generation of Vehicles (PNGV) prototype may change that discussion to "steel and aluminum versus plastic."

Quietly but resolutely, DC is pushing the envelope in plastic-body engineering. It's latest ESX3 - a prototype built to show the PNGV industry/government coalition's progress towards the goal of developing an 80-mpg (3L/100 km) midsize family sedan by 2004 - relies heavily on expected advances in injection-molding for large, structural body panels.

DaimlerChrysler is keenly interested in large, injection-molded body panels and is fostering a serious development history with the process. The former Chrysler Corp. initiated its public dialog about the production-car possibilities when it showed the CCV (China Concept Vehicle, later Composite Concept Vehicle) circa 1996. The simple and elemental CCV was meant as an emerging-market car, so the bodywork didn't offer much promise for the structural support necessary to meet developed-market safety regulations.

No matter, as DaimlerChrysler went on to show more complex concept vehicles, like the Pronto Spyder and the previous PNGV interation, the ESX2. And late last year, DC announced it would use the process to produce a limited run of injection-molded tops for the Jeep Wrangler - the first production-vehicle application (see WAW - Dec.'99, p.119).

"We're essentially inventing a new way to make automobiles," said DaimlerChrysler President Jim Holden last November at a press conference showing off pilot production of the Wrangler hardtops at Husky Injection Molding Systems' new Detroit Technical Center in Novi, MI. "Today, everyone knows how to make lightweight vehicles with exotic composite materials, they just happen to be terribly expensive. Now, we're developing a technology to make cars lighter and less expensive than traditional steel vehicles."

Up to 5,000 hardtops will be produced with the new material for 2001 model year Wranglers.

Not only does the new process have the potential to improve fuel economy and cut vehicle body weight up to 50%, it also could reduce tooling costs by up to 70%, Mr. Holden says.

The new Husky Technical Center is equipped with the world's largest dual-platen injection molding machine. It is twice the size of the largest molding machines used in the automotive industry today and exerts 8,800 tons of clamp force and weighs 650 tons. Less than a dozen 4,400-ton machines exist, which are large enough to mold fascias. The Husky molding machine is designed specifically for DaimlerChrysler's needs and can inject more than 100 lbs. (45 kg) of thermoplastic at one time - enough to create half of a car body in one shot.

But the ESX3's use of the process adds another dimension to DC's ongoing crusade, because its experience with injection-molded body panels helps the company to answer two of PNGV's most vexing design and development problems: reducing weight and cutting costs.

First, the ESX3's "total body system" - that is, the structural injection-molded body panels and the unique aluminum "sparse frame" (you read that right: "sparse," not "space") - is a meaningful 46% lighter than a typical Dodge Intrepid body-in-white, crows Larry Oswald, DC's director of advanced body engineering (the total vehicle weighs in at just 2,250 lbs. [1,021 kg]).

That sort of weight reduction, of course, is a crucial element to arriving at a midsize car that achieves 80 mpg; PNGV says an 80-mpg "supercar" will have to weigh at least 40% less than today's sedans.

The injection-molded plastic panels and the floorpan-like elements are bonded to the aluminum sparse frame, says Mr. Oswald, in a process that ensures incredible strength. DC obviously has come a long way since the CCV: the ESX3 is fully ready to meet U.S. crash-safety requirements. And Mr. Oswald says that original fears have been dispelled about the effects of extreme cold on the panels - some mules have been crashed to satisfaction at temperatures of -40degreesF (-40degreesC), and the company's computer-simulated similar tests for the ESX3.

Meanwhile, the cost thing. Here, injection-molded panels help to cut basic sheetmetal bodywork costs by about 10% and also contribute to an overall labor-cost reduction, as a few plastic panels replace several conventional sheet pieces. But the real cost-cutting grail is tantalizingly close, yet still unattained: molding the panels with the "Class A" finish today's customers demand. If that can be accomplished, plastic-paneled vehicles can be built in factories without expensive paint shops.

To now, DC had not achieved Class A finish with large panels. The upcoming Jeep tops are a small step in that direction, coming through the process with basic colors, but finishes that are hardly world-class.

Mr. Oswald gives hope, however. "We have molded small pieces with a Class A finish," he asserts, but cautions that the company hasn't yet perfected the process for anything like the size of even the tiny CCV.

"We haven't molded whole CCVs with Class A finish," he continues, "but one whole CCV bodyside will be done (with a fine finish) this summer."

DaimlerChrysler technical honchos still harbor the secret hope, too, that customers might be trained to accept the dullish, matte finishes now so popular on a variety of other consumer products. That would make customer-ready plastic vehicles easier to bring to market in a more expedient timeframe.

"I like it (matte finish)," claims Bernard Robertson, senior vice president, engineering technologies and general manager, truck operations. But Mr. Robertson concedes that a run of matte-finish Jeep Wranglers a few years ago left a rather, uh, "dull" impression on the market. "The dealers kept trying to buff them out," he quips.

But the prospect of molded-in Class-A finish seems a possibility, at least judging by Mr. Oswald's confidence in the ongoing development.

"If we can't make it work, we can't make it work," admits Mr. Robinson. But he reminds that very little that DC does is sheer experimentation - virtually every advanced-technology program is geared toward the ultimate goal of production-vehicle programs, and the large, injection-molded body panel process is no exception.

As for its PNGV ramifications, Mr. Robinson says that DC's experience with the process has put it at an advantage the other "competing yet cooperating" PNGV participants, Ford Motor Co. and General Motors Corp., don't enjoy. He believes plastic paneled vehicles are "a better shot" at low-cost, lightweight body structures. And that's just what the PNGV program must have.