The just-concluded Society of Plastics Engineers’ (SPE) Automotive Composites Conference & Exhibition (ACCE), held at the Michigan State University’s Management Education Center in Troy, Mich., USA, included two facility tours: the Fraunhofer Project Center in London, Ontario, Canada, and Plasan Carbon Composites’ (Wixom, Mich.) technical development center, which opened in 2011. CompositesWorld had the opportunity to visit the Plasan facility and see first-hand the results of radical strides that the company has made over the past several years in reducing carbon prepreg cure cycle time.
Plasan Carbon Composites, formerly known as Vermont Composites Industries, which was purchased by ballistic armor giant Plasan Sasa in 2006, produces composite body panels for the Corvette, Dodge Viper and Ford Shelby GT sports cars. Gary Lownsdale, Plasan’s CTO, explains that initial processing included an autoclave cure, with a total cycle time on the order of 90 minutes even with optimizing tweaks. Fast by aerospace standards, he believed there had to be a better solution for producing prepreg panels for the faster-paced automotive arena.
“We undertook a $6 million gamble to develop out-of-autoclave technology for our commercial future,” he states. That gamble involved a Vermont winter of painstaking study of various resin chemistries and prepreg styles using thermal and dynamic mechanical analysis (DMA) techniques, as well as correlations between various processing methods and resulting laminate properties. What the research ultimately showed was that a seven-minute cure time was possible, using the group’s existing primary prepreg system, if the right process could be developed.
After the move to Michigan from Vermont, to be closer to the OEMs’ engineering centers, Plasan looked for a collaborative equipment partner to help realize its fast-cycle production vision. It found Globe Machine (Tacoma, Wash., USA), known for industrialization of wood processing, including oriented strand board. What the two companies ultimately developed is remarkable for its simplicity and elegance, which was demonstrated during the tour using sample parts.
“What we have is essentially a small autoclave inside a press, but without the energy needs, nor the nitrogen nor the consumables,” comments Lownsdale. The process consists of automated cutting of plies and layup of the four-layer prepreg kit on a tool, then positioning of the tool on the Globe Machine’s shuttle mechanism. At this point, workers place a “canopy” or reuseable silicone rubber membrane over the layup, and clamp it to the tool. The tool itself, which has been reported previously by CompositesWorld as supplied by Weber Manufacturing Technologies Inc. (Midland, Ontario Canada), has a very thin nickel-shell tool face backed with heating and cooling tubing and sensors, and is equipped with a large, single “smart” connector. This means that once the tools shuttles into the Globe machine, dubbed a “pressure press,” and the connection is made between the tool and the press via the connector, the machine automatically identifies the part and cure recipe and saves the production data for manufacturing quality control.
In place inside the press, the canopy-covered tool is then enveloped by a steel hood or “box” that moves downward hydraulically and locks into place, forming an airtight enclosure. Vacuum is pulled beneath the tool and the heat cycle begins, to bring the tool face up to temperature within a few seconds, heating the prepreg and causing the resin to flow (important to achieving a Class A finish). Meanwhile, compressed air is pumped into the box, exerting downward pressure against the canopy for consolidation during the cure, which Lownsdale asserts is currently between 7 and 9 minutes: “We believe that we have the capability of achieving a 2-minute cycle, with an alternative resin system.”
For now, the company is operating a 17-minute part cycle, from start to finish, which includes automated cutting of plies and ply layup, cure in the pressure press, demolding and any finishing steps, which Lownsdale claims is a “balanced” production flow that is sufficient for an approximate 50,000 vehicles per year scenario. “We don’t want to build up excess parts at any one step in the process and become like a supermarket — we are operating in a lean manner.”
Seven work cells have been built and delivered so far, each of which includes a pressure press, to Plasan’s new manufacturing plant in Walker, Mich., slated to open in January 2013, for an as-yet-undisclosed program. But, watch for announcements of a much faster rate approaching that of thermoplastic processes.