High-pressure resin transfer molding slashes cycle times, boosts lightweighting efforts

Those familiar with the i3 electric vehicle from BMW may also be aware of the extensive use of carbon-fiber composites to realize lightweighting. They may not be so up to speed on one of the key processes employed to mold the passenger compartment and other components: High-pressure resin transfer molding, or HP-RTM.

The automotive conference—Lightweighting Strategy & Drivetrain Efficiency for All Supplier Tiers & OEMsto be held in conjunction with Advanced Design & Manufacturing (ADM) Cleveland, March 29–30 at the Huntington Convention Center of Cleveland, OH, will feature a presentation on HP-RTM from Frank Henning, Director of the Fraunhofer Project Center, Composites Research, Western University, on this very subject.

High-pressure resin transfer molding will be described in detail in a presentation at the automotive conference during ADM Cleveland.

The HP in HP-RTM refers to the elevated pressure, in general around 120 bar, at which the typically epoxy resin-based system is formulated at the mixing head with catalyst and mold release agent to form a homogenous system for injection into the mold. The tool contains a draped woven or non-crimpled carbon fiber fabric as the reinforcing material. This processing approach allows industrially viable cycle times of around five minutes to be realized versus several hours to several days for standard RTM processes for fabricating large components such as aircraft frames and wind turbine blades. “We have already achieved two-minute cycle times in development, and a bit above a minute for simple parts using a polyurethane system,” notes Henning. “And new generation materials are about to be introduced which will achieve one-minute cycles.”

According to Henning, in platforms developed from the ground up such as the BMW i3 and i8, use of composites can save up to 50% in weight for the vehicle as a whole, whereas for lightweighting existing designs such as the BMW 8 series, where a steel-composite hybrid approach is adopted, the weight savings are of the order of 20-40%.

Additional weight savings will be possible if parts are not over-engineered according to Henning. “Nowadays parts are still very much over-engineered, as OEMs want to be on the safe side so there is a huge opportunity to cut down weight and cost, especially since carbon fiber is expensive.” Here simulation tools are playing an important role, as Henning will describe in his presentation.

The automotive supply chain has a new rendezvous. UBM America’s newest design and manufacturing trade show and conference debuts in Cleveland, OH, on March 29 and 30, 2017. On one show floor, Advanced Design & Manufacturing (ADM) Cleveland showcases five zones—packaging, automation and robotics, design and manufacturing, plastics and medical manufacturing. Hundreds of suppliers and numerous conference sessions offer sourcing and educational opportunities targeted to the automotive and other key industry sectors. Go to the PLASTEC Cleveland website to learn more and to register to attend.

The resin system can be injected into a fully closed mold or an partially open mold, the latter case known as compression RTM. Compression RTM is generally better suited to the molding of larger components, but the fibers tend to be moved around and displaced more during the resin infiltration stage. Simulation is important here to minimize these effects.

Germany’s Fraunhofer Institute established the Fraunhofer Project Center (FPC) at Canada’s Western University, London, ON, five years ago as North America’s largest composite manufacturing center housing real industrial scale processes. The focus is on the automotive sector, with the FPC capable of manufacture complete automotive structures including roofs, underbodies and side frames, seats, and tailgates.

Besides RTM, the FPC is also capable of processing sheet molding compounds (SMC), injection molding of long fiber reinforced thermoplastics, and fabricating composite foams. The latest initiative is to install capability for rapid placement of unidirectional thermoplastic tape. “In this way, we are working with both thermoplastic and thermoset resins, and discontinuous and continuous fibers,” says Henning, who adds that a similar center will start up next year in Ulsan, South Korea, while a third center in Jiangsu, China is in the planning phase.

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