The RTM process, or low pressure injection molding of liquid resin, consists in filling the cavity of a rigid and closed mold by injection of resin at one or more points. Among the many advantages, the high productivity induced by this system allows the production of large series parts. In addition, the flexibility of implementation, and the ease of adjusting process parameters (cycle time, shape of parts, injection positions, reinforcement rate, etc.) make it a very flexible process.
The RTM is available in three main processes:
- RTM injection
- RTM assisted by vacuum
- The RTM Light
The RTM (Resin Transfert Molding) process should develop at a rate of 8% per year in Europe, in particular for the production of small series, thanks to the improvement of resin injection simulation methods.
The RTM process ensures the transformation of approximately 5% of composites in France against 8% in Europe; it tends to replace manual technologies for the following reasons:
- The process is in a closed mold (therefore, no release of harmful vapors).
- The rates are higher, from 10 to 100 pieces per day.
The progress in the use of RTM technology comes up against a number of technological difficulties:
- A better knowledge of the injection process and simulation must be developed, for example by the use of conductive carbon wicks to follow the injection front;
- Current piston pumps only inject the resin intermittently and in too small a quantity, hence:
- Difficulty controlling the injection flow and pressure;
- appearance of defects in the structure of the composite following discontinuous injection.
The RTM process is used for various applications (this list being non-exhaustive):
- Sports and leisure: bicycle frame and fork, ski, etc.
- Public transport: seat, door, bumpers, rear panels ...
- Automotive: hood, door, deflectors, spoiler ...
- Aeronautics: window panel, rear jet cone, etc.
- Agricultural equipment: cowling, wing, roof ...
- Boating: Sailboat hull