New high-pressure RTM process for carbon fiber composites promises economies of scale

The German affiliate of Japanese carbon fiber concern Toho Tenax has developed an integrated production system for CFRP.

Combining a high-pressure resin transfer molding (HP-RTM) process with carbon fiber pre-processed to incorporate a binder resin has reportedly realized an an integrated production system for carbon fiber-reinforced plastic (CFRP) that enables manufactured composite parts to be optimized for required shapes and properties. Development of the process was undertaken by Toho Tenax Europe GmbH (TTE), the German subsidiary of Japan’s Toho Tenax, itself part of the Teijin Group.

The new production system uses the HP-RTM process coupled with TTE’s one-step carbon fiber to part technology, known as Part via Preform (PvP), which it developed in 2014. One European automaker has already adopted this system and other projects are under way in the automotive industry. Research and development for the mass production of visually appealing Class-A surface parts also has been launched.

A cost-effective process for CFRP.

The system is based on automated PvP technology utilizing Tenax Binder Yarn, which combines carbon fiber with binder resin placed on the preform. Preforms can be manufactured without requiring intermediate steps. The yarn can be processed by random fiber placement for isotropic behavior, or by aligned uni-directional fiber placement in areas where higher mechanical performance is required.

Both technologies — random and aligned uni-directional fiber placement — can be combined to meet cost and mechanical needs in any desired geometry. Further, PvP considerably reduces carbon-fiber waste compared to conventional preform production. The result is an automated, cost-effective solution for optimized manufacturing of CFRP parts tailored to the specific customer needs. The newly introduced system allows integrated production, from carbon fiber to CFRP part. The integration of PvP and HP-RTM reportedly enables the production of composite parts in large volumes that are priced very competitively to metal materials.

As efforts continue to reduce the weights of automobiles, it is vital that tenacity and stiffness be maintained at safe levels. Existing metallic materials lose tenacity at thin gages according to Toho Tenax. Structural designing, such as u-shaping using high-tensile steel plate, is commonly used to achieve weight reduction and stiffness, but metallic materials with added tenacity are not suitable stamping due to their low elasticity.

Reducing joint positions through large-scale integral molding is one method for reducing weight, but greater levels of formability, tenacity and stiffness are still required. CFRP is generally based on thermoset resins cured in an autoclave. A prepreg, or carbon fiber sheet pre-impregnated with matrix resin, is layered in the mold, covered by baggings, vacuumed and then pressurized at high temperature. Autoclaved CFRPs have high strength, but they necessitate an extended manufacturing cycle.

Preformed RTM processing is common, but it requires intermediate steps, higher production costs and requires chopped fiber placement on the form, which produces large amounts of carbon fiber waste. In addition, it is not suitable for forming complicated or thick shapes.

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