Low-Cost Composite Profiles in Small Quantities
At the Institute for Design and Composite Structures (Institut für Konstruktion und Verbundbauweisen e.V.), Chemnitz, a new method for producing glass fibre-reinforced composite profiles has been developed. The laminate makeup and wall thickness can be matched to the load regime of the supporting structure.
In the so-called successive (or multi-step) compression moulding technique, the profile is pulled or pushed through a mould. Prepared cores covered with the laminate are calibrated in the mould and cured by heat. In this way, rigid yet lightweight beams that can be dynamically loaded can be produced inexpensively in small quantities. The thickness of the laminate can vary over the part length and thus be matched to the load.
To match the laminate makeup locally to the load regime, e.g. in a bent beam, a test profile was produced. During the trials, it was determined that the frictional forces act primarily between the mould and outer laminate layer, so that no internal shifting within the laminate occurred. The individual fabric layers thus do not need to be sewn together or joined by other means.
The working group built a mould that can process a profile with a maximum cross-section of 300 mm x 220 mm. For the trials, an inner profile with a wall thickness of 3 mm was fabricated from glass fibre-reinforced plastic (GFK) and coated on all sides with a 20 mm thick layer of foam. The outer CFK layers were applied to the core as wet laminate. The mould temperature ranged between 90 and 140°C; the feed rate varied between 5 and 15 mm/s. With increasing laminate wall thickness, the temperature must be raised or the feed rate reduced to guarantee complete heating of the profile throughout. To date, profiles up to 2 m in length have been produced.
For production of larger quantities, an impregnation zone in the mould can replace manual preparation of the laminate. Moreover, production of profiles that curve along the lengthwise axis is, in principle, also conceivable.
In the trials, the component was pushed through the mould hydraulically. Alternatively, the profile can be pulled through the mould by a steel cable, for instance. There is also the possibility of keeping the part stationary and moving the mould.