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December 3, 1999

6 Min Read
Hardtops today, entire car bodies to come

No matter how you celebrate the end of this millennium, you have to appreciate the way that Husky and DaimlerChrysler are ringing in the new one, albeit a little early. Last month, the two companies unveiled the 100,000-sq-ft Husky Technical Center in Novi, MI, built to develop automotive plastic body panels. It's a forward-thinking venture that gives credence to the contention by industry experts that replacing steel panels with molded plastic is, in fact, the future of automotive exteriors (see "Molding the Future of Auto Exteriors," April 1999 IMM, pp. 40-46).

Owned by Husky Injection Molding Systems (Ontario) and leased in part by DaimlerChrysler, the tech center not only will provide the research required to mold entire car bodies, but also will serve as a small production center for Jeep Wrangler hardtops. This is an entirely new development from our April report on the center, which was testing body parts for the Composite Concept Vehicle (CCV) at the time.Fifty prototype hardtops are due to be tested on vehicles later this year; if the tests are positive, the Husky Technical Center will begin molding up to 5000 white hardtops for 2001 model year Wranglers. DaimlerChrysler President Bill Holden explains, "If customers are as satisfied with the Jeep hardtops as we are, we will move forward with concepts for complete vehicle construction using injection molding technology. We're essentially changing a fundamental aspect of making cars and trucks."Injection Molding vs. SMC
At the unveiling ceremony, Husky's E8000 (an 8800 tonner built specifically for molding large automotive body panels) was up and running, producing the outer half of the prototype hardtop at molding cycle times of less than 3 minutes. (Inner halves require a similar cycle time.) After the 18-minute cooling time, the tops were transported robotically to an adhesive station for bonding to the inner halves, another 3-minute-or-less operation. Doing the math, that's a 27-minute total cycle time, or 30 percent less time than it takes to compression mold and paint the current SMC hardtop.To mold the hardtop outers, the press supplies 4000 to 7000 psi of injection pressure. According to Larry Oswald, director of body engineering, this much pressure over such a large surface area would have required a 12,000-ton machine. Instead, Husky designed the hot runner system with sequential drops to cut the tonnage needed. The molds fill from edge gates in several patterns, including front-to-back.Eliminating the paint cycle is a major driver behind DaimlerChrysler's investment in molding technology. Oswald estimates that a typical paint shop costs between $200 million and $400 million to install, including expenses for emissions control equipment. "We can now mold virtually any color without painting," he explains, "although we are still working on inmold surface coatings to create a Class A finish within the mold."Other reasons for DaimlerChrysler's molding enthusiasm are evident when making comparisons between the molded and SMC hardtops. Molded hardtops weigh only 47 lb (23 lb less than SMC versions), cost 10 percent less to produce, and generate no trimming waste. They can also be made with 25 percent recycled content. In addition, molding the hardtop requires only two pieces, while the SMC model requires five. Fewer parts, and thus tools, mean less capital investment. In terms of safety, the molded hardtop ranks equally with its SMC counterpart in both actual and simulated test results.Replacing Steel
Translating the hardtop project's benefits to an entire vehicle body opens the door for even greater cost savings and styling flexibility. According to Holden, DaimlerChrysler estimates that a molded body could be produced in six to 12 parts vs. the current 75 to 100 pieces of steel required today. This part reduction alone could bring as much as 70 percent reduction in tooling cost.With lighter weight and less cost, plastic bodies could also offset the additional weight and expense of a hybrid powertrain. "This is a combination gasoline and electric engine that DaimlerChrysler is developing to meet Partnership for a New Generation Vehicle (PNGV) standards of 80 mpg vehicles," explains Holden. "We are closer to bringing PNGV concept vehicles, such as the Pronto Spyder, to reality, and molding was the enabling technology we envisioned when we introduced it two years ago."Rather than hanging the thermoplastic panels from a steel skeleton or spaceframe, DaimlerChrysler's approach involves the use of metal reinforcement in structural plastic panels. "Our crash tests have shown that plastic-bodied cars can meet federal crash requirements with minimal use of metal for reinforcement only," says Oswald. "How and where the metal is placed is part of the developing science for this technology."Showcase for E8000
According to Husky President and CEO Robert Schad, the E8000 is the world's largest dual-platen injection molding machine. Unibody construction dictated that eight tiebars would be needed to minimize platen deflection. The platens themselves range from 180 to 207 tons, and the larger moving platen is believed to be the third largest modular iron casting in the world. Says Schad, "We were pushing the envelope here and in other areas, but the advantage to making a one-piece machine is that the platens are much more accurate."To accommodate the crane used to lower molds into the press, three of the top four tiebars are retractable. This allows unobstructed entry to the stationary platen's mold mounting face. The unit contains a Siemens controller and a fully articulated robot (Kuka), which picks the part out of the mold and places it on the cooling fixture.Shot size can range from 20 to 145 lb, thanks to a two-stage injection unit-an extruder with 6.7-inch screw that feeds a shooting pot below. Other benefits of using this technology rather than two standard reciprocating screws, according to Husky sources, is that the material comes from one source for color stability, and there is less glass fiber damage because no check valve is required.Four arrays of variable displacement pumps provide just the power demanded by the press for greater energy efficiency. Only three arrays are actually required to run the machine-a fourth was installed for redundancy. An Extended Enterprise
Current contenders for production resins include Montell's Hivalloy, a 30 to 40 percent glass-filled PP/PS alloy, and Ticona's 15 to 20 percent glass-filled PET. Oswald confirms that the automaker is still evaluating the two materials for the hardtop project, and will make a decision in less than six months.Molding partner Decoma Intl. (Ontario) is managing production on the project, and toolmaker Paragon Die & Engineering (Grand Rapids, MI) designed and built the huge hardtop molds. Project manager Russell Fielding of DaimlerChrysler put some additional constraints on the mold design. "We asked Paragon to machine the show surface of the outer half mold from one piece of steel," he recalls.Contact information
Husky Injection Molding Systems
Novi, MI
Trefor Jones
Phone: (248) 735-6326
Fax: (248) 735-6423
Web: www.husky.ca

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