Low-pressure molding trims part costs at Ford Utica

When the Taurus/Sable platform underwent its last redesign, Ford Automotive Component Div.'s Utica plant did a little redesigning of its own. ACD Utica used a new padded trim laminate with olefin foam from Toray Plastics in its low-pressure molding (LPM) lines to produce door trim panels that were cost competitive, lighter, and easier to manufacture than previous incarnations.

According to Ford's Aashir Patel, LPM originated in Japan when Sumitomo Chemical developed a high-melt-flow PP that could be used in such a process, then patented the method, calling it Sumitomo press molding. It has been licensed to Kasai Kogyo, a Tier One supplier to Nissan. Ford ACD acquired the technology from Kasai, launching the first door panel at Utica in 1993 for the Thunderbird and making Ford the first to bring LPM to North America.

Patel related the equipment setup for Utica's LPM during a recent phone interview. Initial door panels are molded on an imported vertical press. A robotic sheet feeder places laminate sheets into the mold prior to each molding cycle.

From a processing standpoint, ACD technicians combine a vinyl skin/olefin foam laminate and PP substrate in one shot. The precut skin/foam laminate material is inserted robotically on the cavity side of an open mold. The mold closes partially, leaving a gap, and molten PP is injected behind the laminate at low pressure and 200C. No adhesives are required to bond the two materials, because the molten PP resin combines readily with the olefin foam during molding.

"Also," says Patel, "we are able to get all backside details in one shot - attachments for locator pins, wiring harnesses, hooks, etc. - Compare this to the traditional vacuum forming process: first, a rigid substrate is molded with vacuum holes, coated with adhesive, and transferred to the vacuum forming tool. A trim pad laminate is then placed above the adhesive-coated substrate, and a vacuum is drawn to bond the two components together. The additional handling increases the chance of damage to the PVC skin, says Patel, and adds time and cost.Closed loop controls maintain mold and resin temperatures and other parameters in the LPM process. "While we don't consider this a tricky process," Patel says, "doing it properly requires a certain amount of expertise. "All LPM molding at Ford Utica is performed in a building dedicated to that purpose.

Another secret to LPM success lies in the laminate material. For the Taurus/Sable panels, olefin foam used to make the laminate was developed by Toray Plastics' PEF Div. (Front Royal, VA). According to Patel, the most common alternative to olefin foam is expanded PVC, a foam with densities four times higher than that of olefins. In addition, PP will not adhere to PVC without a synthetic backing, adding further to weight penalties. "Toray worked closely with us to meet our requirements for design and processing flexibility, weight reduction, and system cost efficiency," Patel notes, "then joined us in production start-up to ensure the foam processed properly in the tool."

Chris Workman of Toray explains how the unique foam chemistry makes it suitable for padded trim applications. "The foams are blends of two olefins - PP and PE - that are first lightly crosslinked to increase mechanical and thermal properties, then foamed into sheet stock ranging from 2 to 5 mm," he says. "They provide thermal performance to 200C, and have a specific gravity less than 1.0, making them the lightest foams available for padded trim."