Manufacturing of prepregs

Fibers and base resins are supplied against certificates of conformance and often property test certificates. On-line control during the manufacture of prepreg revolves around the correct ratio of fiber to resin. This is done by a traversing Beta-gauge, which scans the dry fiber (either unidirectional of fabric) and then the impregnated fiber and provides a continuous real-time plot of the ratio across the width of the material. This can be linked back to the resin system application point for continuous adjustment. 

The cost of epoxies is higher than polyesters but they are very versatile and widely used in filament winding, pultrusion, resin injection and in the manufacture of prepregs. 

A solid isophthalic alkyd for the manufacture of prepreg moulding compounds. 

A styrene free maleic acid resin for the manufacture of prepregs used for electrical purposes. 

Fig. 9. The effect of voids due to poor wetting on adhesive strength, (a) The zippering effect of voids aligned in the plane of shear, (b) Macro-voids in the resin formed during the manufacture of a carbon fiber reinforced prepregs. (c) Micro-voids caused by axial crenulations along carbon fiber surfaces.

Thorfinnson, B., Biermann, T.F. Measurement and Control of Prepreg Impregnation for Elimination of Porosity in Composite Parts, Society of Manufacturing Engineers, Fabricating Composites 88, Anaheim, September 1988... 

A model has been developed for the prediction of the lay-up consolidation process during the lamination of prepreg lay-ups for the manufacture of printed circuit boards. This model can be used advantageously in prepreg material screening and in the optimization of lamination schedules for high-performance structural composites. 

After its manufacture, the prepreg is backed with release film for storage in a cool dry place or in a refrigerator until its use. Typically prepregs have a guaranteed shelf life of 12 months at -18 °C. Tack life at 23 °C depends on the thermosetting polymer. 

Vacuum bag and autoclave processing are the two main methods for the manufacture of final parts from prepregs. Consolidation involves the cutting and stacking of prepreg... 

The use of prepreg in the manufacture of a composite components offers several advantages over the conventional wet lay-up formulations ... 

Manufacturers of composite structures have traditionally used prepreg tape to manufacture structural components. Fibres are initially combined into unidirectional tows (bundles) of fibres combined into fabrics, e.g. by weaving or knitting. The vast majority of the tows employed in woven, braided or knitted reinforcements comprise low twist or untwisted continuous filament yams. Three-dimensional technical textiles can be produced by weaving [5], knitting [6] and braiding [7] or as non-crimp fabrics. 

In the AFP process, multi-headed robot machinery lays down multiple strands of prepregged fibre on either flat tools, curved mandrels or complete cylindrical mandrels or drums (as applied in manufacture of fuselage sections of the Boeing 787). The process is shown in Figure 3.4. The ATL variant of the process lays down tapes of unidirectional prepreg up to 300 mm wide across the mandrel. The AFP process uses smaller width ribbons of prepreg a few millimetres wide and can... 

The cost limitations of prepreg processing have led to the development of alternative techniques in which dry fabric is infused with resin as part of the manufacturing... 

A cheaper alternative is the cold temperature hardening prepreg system. As opposed to heat-hardening prepregs, where the prepreg fabrication can take place at a different place and time than the manufacture of the ultimate component, in the cold temperature process the fabric or rovings are coated with the matrix at the point where the component itself is made. 

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