Deactivator > PPS PROVIDES CRITICAL FLATNESS NEEDED FOR FORD ENGINE HOUSING
Release 2/28/1997 PPS PROVIDES CRITICAL FLATNESS NEEDED FOR FORD ENGINE HOUSING
DETROIT, Mi. -Ford Motor Company's latest switch to plastic involves the intake manifold runner control (FMRC) housing of its 4.6-L four-valve engine.
Previously, the 420 mm x 89 mm x 29 mm part, called a deactivator, was cast from aluminum, then machined to required tolerances. The new part has been injection molded from Ryton® PPS (polyphenylene sulfide) in commercial quantities only since mid- 1996, Ford reported. The company projects a significant savings in both cost and weight over the cast aluminum version.
The change, however, required a lot of imaginative engineering to mold the plastic MMC with the same tolerances that machining gave to the aluminum part. Tier One supplier, Tomco Plastic, Inc. (Bryan, Ohio) developed a proprietary process to make a mold that could give the deactivator critical flatness 'right off the press,' which Ford required.
Since mid 1996, Ford Motor Company has been using a deactivator made from Ryton® PPS polyphenylene sulfide, an engineering thermoplastic from Phillips Chemical Company, in its 4.6-L four-valve engine. The component, shown here, was previously cast from aluminum. Converting to Ryton® PPS eliminated the secondary and expensive machining operation required to bring the aluminum-cast part to spec.
The deactivator is a throttle device in the intake system of an automobile engine that restricts air flow and increases air velocity to the combustion chamber at low engine speeds - generally below 3,000 RPM. As a result, the combustion process is enhanced, improving fuel economy and low-end torque, and reducing emissions. At high engine speeds, the throttles open for an added air flow to maximize engine power.
To make the transition to Ryton® PPS from aluminum, Tomco first created product from an uncontoured mold. This rough tooling was then contoured to exact specifications using data generated from the pinpoint accuracy of a coordinate measurement machine (CMM). The company then applied their proprietary formulas for converting the CMM data to tool steel dimensions in the mold.
"If it wasn't for Tomco's ability to be innovative in its mold-building technique, the IMRC would still be made from aluminum," said Walt Fedison, Ford's Electrical and Fuel Handling Division design engineer.
"We knew that the flow pattern in a traditional mold would not produce a part that would match the machined aluminum tolerances, regardless of the polymer," said Bob Wisler, market development manager for Tomco Plastic. "The computerized mold contouring process that we developed goes well beyond what current mold-flow analysis is capable of achieving."
Tomco developed and perfected this new process for depicting the contours in the mold that would allow the Ryton® PPS to flow, cool and form a stress-free, dimensionally stable product that matched the machined aluminum tolerances.
"The fact that Ryton® PPS itself provides a high degree of dimensional stability was definitely a plus," explained Wisler.
"In the past the perception was that an as-molded plastic component could not obtain the tolerances of traditional machined metal components," he said. "But for many years we have been able to mold engineering-grade polymers to reach those tolerances in the as-molded state. The deactivator has created an opportunity for our technology to allow plastic to move into metal-dominated areas such as motor housings, manifold components and fuel delivery systems."
Ford's Fedison headed the team which started in 1992 to study the complexities of making the switch. He brought in experts from Tomco and material supplier Phillips Chemical Company, a division of Phillips Petroleum Company. Kellems and Coes Tool Corporation built the mold to Tomco's specifications.
"This engineering team was able to produce a new housing that is an exact replica of the aluminum part, and add some significant improvements as well," Fedison said.
In addition to achieving the primary goal of cost and weight reduction, the new deactivator now incorporates sealing gaskets into the molded assembly. And, since it is possible to use Tomco's existing presses, capital equipment investment was kept to a minimum.
"Injection molding of the part had to match the old part exactly, or it would have leaked," Fedison explained. "We have a plus/minus 0.20mm tolerance for the sealing surface height over a 60-square-inch surface area (420mm x 89mm). If this tolerance could not be met, we would have to scrap the entire project."
Fedison and the Ford design team examined virtually all thermoplastic alternatives to aluminum. "Only Ryton® PPS could provide the dimensional stability over the engine operating temperatures. Plus it is non-hygroscopic and has high resistance to chemicals, with no known solvent below 450°F. Tomco also favors Ryton® PPS because of its low creep."
Ryton® R-4 02XT, a 40-percent-glass-filled grade, is used. Molding is done on a 300-ton Van Dom HT single-cavity injection molding press.
Tomco's Wisler said, "We worked with Ford to establish a tight, reliable datum system in accordance with Geometric Dimensional Tolerancing (GDT) international standards. Our mold contouring process allows us to confidently measure all features of this part and enter precise contours into the mold steel.
"To achieve the correct height and flatness, and without abrupt peaks and valleys, the tool shop used our formulated computerized data to complete the mold."
DETROIT, Mi. -