Process for manufacturing homogeneously needled three-dimensional structures of fibrous material

A process for manufacturing homogeneously needled three-dimensional structures of fibrous material to be used as reinforcing structures in composite materials, said process comprising the steps of:

• superposing on a support layer after layer of fibrous material in sheet form;
• individually needling each layer with a substantially same and constant needling density per unit of surface by thrusting needling needles through said layer and to a predetermined depth below said layer;
• increasing the distance between the support and the needles by a value substantially equal to the thickness of a needled layer each time a new layer is superposed so as to keep said depth at a substantially constant value with each newly superposed layer;
• and
• after a final layer has been superposed and needled, carrying out additional finishing needling steps with the distance between the support and the needles being increased after each finishing needling step during which the structure is once needled over the whole outer surface of the final layer so as to have a needling density in the last superposed layers substantially equal to the inside the other layers, whereby a substantially uniform needling density is achieved through the structure.