Composite material moulding by simultaneous projection

Simultaneous spraying is a technique for manufacturing composite parts that simultaneously supplies, or sprays, the two basic components of these materials: the reinforcement in the form of chopped fibers, and the matrix in the form of a jet of reactive liquid resin. This stream of mixed materials is directed into a mold cavity to create a compact layer.

In principle, this process produces a material similar to that obtained by contact molding, and can be seen as a step towards industrialization with substantial productivity gains.

In the strict application of the technique, the reinforcements are only chopped fibers, and the parts come from open molds, a characteristic that has forced an evolution in practice to meet today's hygiene and safety requirements.

Being essentially a manual operation, the process is suitable for the manufacture of any type of part with a relatively open shape, either hollow or bumpy, and where all surfaces can be reached in a straight line from the gun.

Nevertheless, continuous closed shapes such as tubes or tanks can be produced using a cleverly removable mold.

Simultaneous projection took its first steps in the 1950s in response to the particular demands of the post-war period: firstly, growing public and industrial interest in these new, tried-and-tested composite materials based on glass fibers and polyester resins, and secondly, the feverish demand for basic necessities, equipment and leisure products.

The projection of materials, such as sand and cement mortar onto a metal frame, had been exploited during the 1939-45 war, with the construction of large, thin-walled pieces such as caissons and barges, which proved both fast and solid. Compressed-air paint spraying, meanwhile, benefited from technical advances developed thanks to the enormous industrialization effort during this period.

Anyone who has manufactured composite parts by contact molding will realize that preparing the resin with its catalytic system, and then applying it, is an obstacle to speed of execution and therefore to productivity. With a few modifications, the conventional spray gun is quickly put to use to prepare the resin (mixing the resin with its catalytic system) and apply it to the glass-fibre reinforcements of the mat and/or fabric type previously placed in a mould.

By adding a lightweight, high-performance device for cutting the glass fibers and directing them into the mold, the simple spray gun becomes a real tool for producing the complete raw material for the future part, paving the way for semi-industrial composite manufacturing.