Carbon Fiber/Epoxy Mold with Embedded Carbon Fiber Resistor Heater - Case Study

The article presents a complete description of the design and manufacturing of a Carbon Fiber/epoxy mold with an embedded Carbon Fiber resistor heater, and the mold performances in terms of its surface temperature distribution and thermal deformations resulting from the heating. The mold was designed for manufacturing aileron skins from Vacuum Bag Only prepreg cured at 135°C. The glass transition temperature of the used resin-hardener system was about 175°C. To ensure homogenous temperature of the mold working surface in the course of curing, the Carbon Fiber heater was embedded in a layer of a highly heat-conductive cristobalite/epoxy composite, forming the core of the mold shell. Because the cristobalite/epoxy composite displayed much higher thermal expansion than CF/epoxy did, thermal stresses could arise due to this discrepancy in the course of heating. Therefore, to lower these stresses, the Carbon Fiber/epoxy faces were separated from the cristobalite/epoxy core containing the heating element by the buffer layer of carbon nanotubes/epoxy displaying intermediate thermal expansion. The determined mold surface thermal deformation was in the range of 1 mm in 20°C-135°C temperature range and, at 135°C, the mold surface temperature unevenness was in the range of 10°C. Despite such temperature unevenness, the Tg values determined with the help of the specimens cut out from the different parts of the cured skin were of satisfactory values.