Page 60 - 3D Fibre Reinforced Polymer Composites

Preform Consolidation 49

and presses with sufficient load capacity limits the size of component that can be
economically produced via the RTM process. Cheaper tooling can be used but this often
restricts the compaction pressure that can be applied and can potentially reduce the
surface quality. These and other tooling issues are discussed further in Section 3.6.

Heating
Preforming Mould filling Releasing
& Curing

Figure 3.1 Schematic of the RTM process

There are a number of liquid moulding processes related to RTM. Vacuum Assisted
RTM (VARTM) is the same as RTM except that vacuum is applied to preform. This
aids in consolidation quality through removal of air and speeds up the resin infiltration
through an increased pressure differential. Structural Reaction Injection Moulding
(SRIM) is similar to RTM and is used primarily in the automotive industry. The main
difference is that much higher injection pressures are used to fill the preform quickly as
the resin systems are generally fast curing and short cycle times are crucial in
automotive production.

3.2.2 Resin Film Infusion
The process of Resin Film Infusion (RFI) is different from the RTM technique in two
ways. Firstly, as the name suggests, the resin is initially present within the process as a
film rather than a liquid. Secondly, the movement of the resin after heat and pressure is
applied and the film melts, is in the thickness direction of the preform not in the plane
of the preform as in the RTM process. The essential details of this technique are shown
in Figure 3.2. In the RFI process the resin film is placed against the prepared tool
surface, covering the necessary part surface area, and the preform is placed on top of the
film. A release film, to aid in part removal, and a breather material, to enable the
generation of vacuum within the bagged area, is then laid on top of the preform. This
lay-up is then bagged in a similar process to prepreg components and can be heated
within an oven or autoclave, depending upon the requirement for externally applied
pressure. The molten resin is sucked into the fibre preform through capillary effects and
the careful placement of vacuum outlets. External pressure can be used to compact the