Method for manufacturing a stiffened panel made from composite material

1. A method for manufacturing a stiffened panel made from composite material comprising a skin and elongated reinforcing elements located on the skin, said elongated reinforcing elements comprising at least a web and wherein some of the elongated reinforcing elements cross each other, the method comprising the following steps:

a.) laying up a flat laminate comprising stacked plies of composite layers for forming a structure comprising the elongated reinforcing elements of the stiffened panel,

b.) cutting the flat laminate along intersection lines of planes defining the webs of two crossing elongated reinforcing elements,

c.) cutting in said flat laminate an outline of the elongated reinforcing elements in their position in the stiffened panel,

d.) providing the flat laminate, previously generated, over a tooling base for forming the structure comprising the elongated reinforcing elements of the stiffened panel,

e.) applying a forming process for forming the elongated reinforcing elements structure,

f.) laying up plies of composite layers for forming the skin,

g.) providing the laid-up plies of the skin and the formed structure, comprising the elongated reinforcing elements of the stiffened panel, on an integrating tool by curing,

h.) integrating together, with the integrating tool, the skin and the formed structure, comprising the elongated reinforcing elements, by curing,

i.) obtaining a cured panel made of skin and elongated reinforcing elements in which some of the elongated reinforcing elements cross each other,

wherein during the cutting step at the intersections of the planes defining the webs of two crossing elongated reinforcing elements, the cuts are performed in each ply in a different position so that the cuts are not coincident,

wherein plies of the flat laminate each exhibit a plying direction in a Cartesian Coordinates System,

wherein the flat laminate incorporates a ply having a unique plying direction relative to another ply,

wherein the ply having a unique plying direction relative to another ply has a plying direction which is coincident or nearly coincident with a direction of the intersection line of the planes defining the webs of two crossing elongated reinforcing elements, does not have cuts in the plying direction.

2. The method for manufacturing a stiffened panel made from composite material, according to claim 1 , wherein the integrating tool is a curing tool and the skin and the formed structure comprising the elongated reinforcing elements are co-cured.

3. The method for manufacturing a stiffened panel made from composite material, according to claim 1 , wherein one of the skin or the formed structure comprising the elongated reinforcing elements is independently cured while the other of the skin or the formed structure is uncured and afterwards both the skin and the formed structure comprising the elongated reinforcing elements are provided on a co-bonding tool such that they are co-bonded together.

4. The method for manufacturing a stiffened panel made from composite material, according to claim 1 , wherein the elongated reinforcing elements are longitudinal and transversal reinforcing elements.

5. The method for manufacturing a stiffened panel made from composite material, according to claim 1 , wherein the cuts are out of phase with respect to the intersection line.

6. The method for manufacturing a stiffened panel made from composite material, according to claim 1 , wherein the tool for integrating together the skin and the formed structure comprising the elongated reinforcing elements comprises longitudinal cores with the cross-sectional shape of the elongated reinforcing elements which are provided into the cavities between the elongated reinforcing members and the skin.

7. The method for manufacturing a stiffened panel made from composite material, according to claim 6 , wherein some of the cores are continuous and some of the cores are divided into several parts that extend between the continuous cores.

8. The method for manufacturing a stiffened panel made from composite material, according to claim 7 , wherein the parts in which the discontinuous cores are divided are joined among them to allow their extraction by pulling from one of the cores located in the edge of the panel.

9. The method for manufacturing a stiffened panel made from composite material, according to claim 6 , comprising the following steps for providing the laid-up plies of the skin and the formed structure comprising the elongated reinforcing elements of the panel on the integration tool,

providing the structure of elongated reinforcing elements,

providing a hollow inflatable core having the shape of a first part of the cross-sectional shape of the elongated reinforcing elements into the cavities of the elongated reinforcing elements,

providing a solid core having the shape of a second part of the cross-sectional shape of the elongated reinforcing element not covered by the hollow inflatable core such that the solid core and the hollow inflatable core cover the entire cross-sectional shape of the elongated reinforcing element,

providing the laid-up plies of the skin onto the structure of the elongated reinforcing elements,

inserting a vacuum bag inside the hollow inflatable core,

applying pressure in the vacuum bag such that the vacuum bag presses against the hollow inflatable core.

10. The method for manufacturing a stiffened panel made from composite material, according to claim 9 , further comprising a step of demolding the cured stiffened panel in which the hollow inflatable cores are reduced to pull them out firstly and afterwards the pulling out of the solid cores is performed.

11. The method for manufacturing a stiffened panel made from composite material, according to claim 1 , wherein cuts is in successive plies have a common vertex close to the head joining adjacent webs.