In many composite technologies such as HP-RTM and Prepreg moulding, high productivity derives from the availability of near-net shape, dimensionally stable preforms feeding the presses. In giving the part an initial shape through preforming, the insertion of the reinforcement into the mould cavity (the bottleneck of the process) becomes less time consuming and permits to occupy for lower times the injection and/or curing station.
Furthermore, injecting through a dimensionally stable preform (instead of carbon fibre plies) will enhance the final part quality, facilitating the resin flow and lowering the fibre washout. Preforming is obtained by opportunely draping the reinforcement stack in a dedicated mould through a press. In order to “freeze” the obtained shape, a binder (previously deposed on the reinforcement) is used. The process is therefore accounting for a first phase of heating (necessary to activate the binder) followed by the draping and forming phases. Among the different preform trimming solutions, in order to obtain a near-net shape before the insertion into the mould, Cannon selects ultrasonic cutting for its extreme flexibility, ideal in case of frequent production changes, and punch pressing for its low cycle times, ideal for long production batches.