Toray announces new out-of-autoclave CFRP technology

Toray Industries, Inc. (Chuo-ku, Tokyo) announced March 28 that it succeeded in developing a new fabrication technology for carbon fiber reinforced plastics (CFRP) that enables both improved dimensional accuracy and energy savings. Toray is working to mature this new technology and broadly deploy it for aircraft applications as well as the automobile and industry sectors.

CFRP is usually fabricated using an autoclave (high temperature and high pressure furnace) or an oven where prepreg (intermediate material in sheet form) is placed on a mold of predetermined shape and the resin in the prepreg is cured using heated air for fabrication. The conventional fabrication technology has disadvantage that requires long time for heating up and curing due to inefficient heat transfer of heated air and large heat capacity of the mold. 

There is also a dimensional accuracy problem particularly for large, complex-shaped parts with variable thickness from location to location. This is due to the difficulty in control of temperature distribution in the part, which could in turn generate variable residual stresses and sometimes deform the part. Due to this, extensive labor is often required during final assembly of parts to manually insert filler materials called shims.

Toray’s newly developed fabrication technology provides a solution to the problem with a number of embedded sheet heaters on the mold’s surface. Each heater is individually controlled and the part under vacuum is heated effectively from direct contacts with the heaters. Controlling individual heaters and allowing optimum heat distribution at each location provides even residual stress throughout the fabricated part. As a result, the part can be fabricated as close to the original design with minimal dimensional inconsistencies.

In order to effectively control this heating system, Toray carried out a joint research program with Ehime University (Matsuyama, Ehime Prefecture, Japan) and Tokyo University of Science (Tokyo, Japan) to establish simulation technologies to predict part deformation and optimize heater temperature. Toray combined them into a program for designing heating conditions that would effectively minimize fabrication time and dimensional errors of the parts. Toray installed a prototype fabrication device and is currently conducting demonstration trials.

Using conventional autoclaves and ovens it takes about nine hours to fabricate a large CFRP part for aircraft – depending on the part shape and dimension. The newly developed fabrication technology is expected to reduce the fabrication time to about four hours. In addition, the technology achieves about 50% energy saving compared to conventional fabrication methods because pressure and heating media – such as heated air – are no longer required. The new technology is also expected to save time during assembly as the improved dimensional accuracy during fabrication can decrease the amount of correctional work needed.

This article is based on results obtained from the Cross-ministerial Strategic Innovation Promotion Program (SIP) for "Structural Materials for Innovation" (managed by Japan Science and Technology Agency). The program is led by the Council for Science, Technology and Innovation (CSTI).