RTM: the next generation targets body panels.

A new generation of resin-transfer molding (RTM) technology for processing low-volume thermoset-composite auto body panels will see its North American debut on Chrysler Corp.'s 1995 Viper roadster. The panels are the result of a strategic partnership of APX International (formerly Aero Detroit) of Madison Heights, Mich., the primary RTM molder of Viper body panels, with Sora Composites a French firm with an office in Birmingham, Mich. In July, Sora began production of a Viper door-hinge cover, using its patented technique, similar to RTM, known as ICS ("Injection-Compression System").

The ICS technology builds upon RTM processing advances pioneered by APX for the Viper (PT, March '94, P. 38). This new process was developed by Sora Composites of Meslay-du-Maine, France. The process has been used in Europe for production of body panels, spoilers, and exterior trim for various automotive platforms during the last four years. Philippe Houchois, North American project manager for Sora, says ICS provides true net-shape molding with reduced scrap levels and minimal part finishing compared with traditional RTM techniques.

The hinge covers are located in the "gill" of the vehicle (the car's characteristic slot where the door panel meets the inner fender). They are being molded by Sora at its Chambery production facility in southern France. Parts are shipped to APX for final inspection and painting. APX plans eventually to produce the hinge cover itself, and perhaps other body panels too, with the ICS process. Chrysler produces about 15 Viper models daily at its New Mack facility in Detroit.

NOW IT WORKS

Like standard RTM, the ICS process begins with placing glass reinforcement in a mold-in this case, mounted in a vertical 150-ton press. The key difference, Houchois says, is that the tool is held "slightly" open (he declines to specify how much) during the initial resin injection and subsequently closed using compressive force. Overall molding pressure is low (70 psi), as is usual for RTM.

The computer-controlled ICS process modulates the speed of the resin being injected into the mold - fast at first, then slower to complete the filling of the tool. As the resin enters the mold cavity it pushes out air, but doesn't displace the glass perform.

The two-cavity tool for the right and left hinge covers is oil heated to 180-205 F. Total cycle time is about 3 min. System automation and integration of the resin pumping system and press was supplied to Sora by Aplicator AB, a Swedish firm represented in North America by Euromer Polymers Inc., Grand-Mere, Quebec.

Sora originally devised the technology for thermoset polyester, but the Viper application makes use of a new batch-mixed, single-component version of Modar thermosetting acrylic resin from Ashland Chemical, Inc., Columbus, Ohio. Modar is also used by APX in RTM body panels for the Viper. The new Modar grade is described as a quick-curing material with a thermoplastic low-profile additive that reduces surface porosity and eliminates the need for a gel coat. (Ashland declines to offer further details.) The part also makes use of Unifilo 750 E-glass mat, supplied here by Vetrotex Certain Teed Corp., Valley Forge, Pa.

INTERNAL RELEASE: A KEY

ADVANTAGE

John Moore, APX R&D manager for molded composite manufacturing, stresses the benefits of using an internal release agent with the ICS process. He explains that in traditional RTM, mold temperatures are too low to activate an internal release agent in the resin and bring it to the surface of the part.

In his view, the ability to use hotter "hard" tooling and a premixed internal release agent in the ICS process defines a new generation of RTM technology. Benefits include faster cycles, reduced scrap rates, better part surface, less post-mold rework, and improved part quality. It also means the process is more machine driven and compatible with automation techniques and statistical process control (SPC).

Another key point is that while a typical RTM process involves polymer/catalyst blending at the resin mix-head, the ICS technology can utilize a premixed, batch-blended resin system with the built-in release agent. This eliminates the need for constant flushing to prevent resin crosslinking inside the pumping apparatus.

An internal release agent developed by Sora for the current tool temperature will be used initially to process the Viper hinge covers. Meanwhile, APX is testing a different, proprietary release agent that can be used at lower molding temperatures (160-175 F), providing an option to employ water-heated tooling. While be declines to be specific, Moore says the new release agent is based on existing chemistry now used for sheet molding compound (SMC) but requires reformulation to make adjustments for the viscosity and gel time of the Modar resin.

A LEAP IN TOOL TECHNOLOGY

The ICS process also represents a major advance for RTM in terms of being accessible to higher quality "hard" tooling. "The true technology leap for ICS is in the tool design for this part and the ability to mold to net shape." Houchois says. "We began the design of this tool based on the work done by APX, then made enhancements to complement our ICS process."

Sora builds the all-steel tooling for the hinge cover, which features a shearedge design. Originally, the first-generation tool was made of steel with an epoxy core. Chrysler recently gave final approval on the steel tool with a new steel core.

Houchois says the more precise, net-shape molding capability of the ICS process reduces trim scrap and does away with the "overkill" practice of venting excessive amounts of waste resin to ensure the removal of air pockets and dry spots inside the tool. He estimates average scrap rates for the ICS process at about 3%, extremely low compared with traditional RTM processing scrap rates of up to 25%. ICS parts generally have only a slight flash, which can be removed manually.

Prior to using the ICS process, APX manufactured this hinge cover via a traditional RTM process with epoxy tooling. Walter A. Bartkowiak, v.p. and general manager of composites manufacturing for APX, points out that the hinge cover's complex shape presented significant processing challenges in terms of resin flow and distribution. It originally required extensive hand finishing and trimming via a waterjet cutter.

Moore says he welcomes the advent of the ICS technology primarily for the enhancements it offers in tooling design. He says that, generally speaking, the RTM process never has had the "luxury" of utilizing higher-quality, hard tooling, which accounts for the quirky reputation sometimes associated with the RTM process.

COMING TO AMERICA

APX recently signed a cooperative licensing agreement with Sora Composites to utilize its technology in North America and jointly develop and fine tune ICS processing. While arrangements have yet to be finalized, it's anticipated that once the manufacturing system for the hinge cover has been proven out in France, APX will assume production responsibility for this part - and potentially others - made with the ICS process. The plan calls for the tooling and processing equipment to be transferred to APX's Madison Heights installation sometime next year.

If the Viper door-hinge application proves successful, APX and Sora hope the ICS technology can be used for other automotive parts, such as doors, spoilers, and fenders, and perhaps even body panels for trucks, marine craft, and agricultural equipment. Bartkowiak says the current tooling economics for ICS would be appropriate for niche vehicles with annual volumes of up to 15,000 units.

Bartkowiak sees near-term opportunity for the ICS technology on the new Viper hard-top coupe slated for introduction in 1996. He notes that Chrysler must design new tooling for the coupe's quarterpanels and doors. "Tooling will dictate the choices Chrysler makes for these parts," he says.

Another opportunity for ICS technology may come from the global marketing capabilities afforded by the Apx/Sora alliance. Next year, Sora will begin production of a rear spoiler for Ford Motor Co.'s 1995/96 European Fiesta model. Houchois says Sora will use ICS to produce up to 800 parts per day in a three-cavity tool.

The Fiesta spoiler has a polyurethane foam core wrapped with glass mat. The wrapped core is placed into the ICS tool and molded in one piece using unsaturated polyester resin. Houchois says the success of this European contract could translate into North American business with Ford.