COMPOSITE PREFORM DRIVERS

Though not insurmountable, the analysis required can seem daunting to manufacturers just entering the HP-RTM arena.īMW Group, however, is already well-versed in this optimization, and thus seeks more flexibility via advanced process control. Typical of composites, the abundance of material and process choices makes optimizing parameters more complex. Numerous studies over the past several years have explored mold filling simulation and optimized temperature, pressure and preform binder configurations to avoid fiber washout while decreasing cycle time.

Indeed, preform permeability must be high (i.e., resin flows through easily) if resin viscosity is high, and both must be balanced with injection and mold pressure to achieve a successful part. Also, if injection pressure is too high it can move the fabric preform and you get fiber washout,” Taillemite adds. “But Elium is 100 cps at room temperature, so you can inject it without heating.

He points out that epoxies are higher in viscosity so they must be heated for HP-RTM. “Technical experts recommend resin viscosity between 50 and 200 cps to get good injection speed and impregnation,” advises Sebastien Taillemite, business manager for Arkema and its Elium liquid thermoplastic polymer (LTP). So everyone, now, is using HP mixing and injection heads.”Īnother option is to reduce resin viscosity. “This causes high pressure to build up in the mold, but you must still fill the cavity, so pressure up to 110 bar is required.” He claims that while low-pressure machines using gear pumps can run against pressures up to 40 bar, “we use HP axial piston pumps which can go against 200 bar. “Now, we are seeing different parts, with very high fiber content,” says Fries. This increased structural and geometrical complexity has posed additional challenges. “Now we are able to volume-produce these to a high quality and with high process stability, cutting manufacturing costs for CFRP body components by around 50%.” That’s compared to roof production, he notes, assuming the same boundary conditions and process chain. HP-RTM also offered the potential to produce large, complex structural components, such as sideframes (see photo). Wolff relates that cost and cycle-time reduction were key issues that BMW Group faced with the intricate geometry of the i3 and i8 body components. Thus, it was useful to keep with this process as we faced the challenge to step from small quantities to fully industrialized production.” “During this time we have gained valuable experience for volume production of CFRP components. Thomas Wolff, head of CFRP technology development at BMW. “For more than 10 years BMW Group has used CFRP in the roof of its M3 and M6 models, opting for HP-RTM for reasons of cycle time, surface quality and industrialization,” explains Dr.

COMPOSITE PREFORM DRIVERS

Three elements - reduced cycle time, automation and carbon fiber - have been the key drivers in the transformation to HP-RTM. Then, in 2008, carbon fiber producer Toray (Tokyo, Japan) listed “faster-cycling RTM” in its presentation, “CFRP: What Is Needed Next For Mass Production In The Automobile?” Preceding all of this work, however, was the BMW Group, which has a decade of production experience with RTM for carbon fiber/epoxy roofs in its M3 and M6 models. Although not necessarily an HP-RTM process, RocTool (Le Bourget du Lac, France and Charlotte, NC, US) introduced its induction-heated molds as “high-speed RTM” at JEC 2007, touting a cut in cycle time by as much as 50%. The process also was gaining traction in heavy trucks where Class A requirements are less rigorous. (Dearborn, MI, US) and Aston Martin (Gaydon, Warwick, U.K.). In fact, metering/mixing/injection suppliers for the PU and reaction injection molding (RIM) industries were among the early developers of HP-RTM, including KraussMaffei (Munich, Germany), Hennecke (Sankt Augustin, Germany), FRIMO (Lotte, Germany) and Cannon SpA (Borromeo, Italy).īy 2005, RTM had been used heavily in the Dodge Viper and also by Sotira Composites (Meslay du Maine, France) for a wide range of OEMs, including a joint development effort with Ford Motor Co. HP-RTM still comprises a fiber preform, a closed mold, a press and a resin injection system, but the latter is now an impingement mixing head, like that first developed for polyurethane (PU) foam applications in the 1960s. The goal: integrated, lightweight structures with cycle times of less than 10 minutes. According to equipment suppliers, that investment is indeed being made. “High pressure,” says Mayr, “means up to 150 bar in the mixing head and from 30 to 120 bar inside the mold, depending on part size and geometry.” Automation is also key to HP-RTM, but that demands an increased investment in both capital and process control. CompositesWorld, Plataine launch composites technology survey

Composite preform