Preforming Process Design

According to the pre-forming process design, the second and third steps can be changed. The heating or melting of the fiber mat mainly depends on the properties of the resin used. The temperature setting of the oven (such as a high-efficiency infrared heater) should take into account the glass transition temperature (Tg) of the resin and the cooling rate at which the fiber mat is taken out of the oven and placed in the punching station. In addition, the friction between the fiber mat and the tool surface will seriously affect the strain and the quality of the preform. Reducing the friction at the fiber/resin interface will make the fiber distribution more uniform, which can prevent positioning thinning and fiber breakage. Conversely, increasing the friction will reduce the bendability of the fiber. After closing the mold, the resin can be used to bond the fiber to the fiber contact point to give the preform dimensional stability, and then compact it. The cooling effect is to turn the resin into a solid state, helping to keep the preform with a similar geometry to the mold.

Because RTM mostly uses glass fiber reinforced epoxy composite mold, this kind of mold has poor thermal conductivity compared with metal mold, so the cooling rate is slow. If a perforated metal mold is used and vent holes are provided, the cooling rate will be increased. After demolding, the preform can be trimmed. Although the large-scale structure of stamping technology is fast and the process is simple, because it is reinforced by random fibers, its performance is not on the same level as that of textile stitched preforms, and the overall performance is relatively low.