Box-shaped monolithic structure in composite material for fuselages and wings of aircraft and method for manufacturing said structure

A method for manufacturing a box-shaped monolithic structure for fuselages and wings of an aircraft comprising:

• a) providing at least two elongated support tools that are formed of a reinforcement material and a polymer, whereby the polymer transitions from a rigid state to a flexible elastomeric state upon a heating and transitions from the flexible elastomeric state to the rigid state upon a cooling, each of the elongated support tools are internally hollow and extend along a longitudinal axis, the elongated support tool comprising a plurality of walls extending along the longitudinal axis and include at least a first external surface, a second external surface, and a third external surface, whereby the first external surface is orthogonal to the second external surface, and whereby the second external surface is orthogonal to the third external surface,
• b) externally disposing an initial layer of a prepreg material comprising a fiber-reinforced polymer matrix material onto the second external surface of each elongated support tool and subsequently shaping the initial layer of the prepreg material in-situ on the elongated support tool to form a shaped prepreg material that conforms to the plurality of walls of the elongated support tool, the shaped prepreg material having a C-shaped cross-section and the combination of the shaped prepreg material and elongated support tool resulting in an elongated profiled bar that comprises:
• a back of the shaped prepreg material adjacent to the second external surface of the elongated support tool,
• a first end appendices of the shaped prepreg material adjacent to first external surface of the elongated support tool, and
• a second end appendices of the shaped prepreg material adjacent to the third external surface of the elongated support tool;
• c) joining said elongated profiled bars along the respective backs placing side by side said elongated support tools so that the elongated profiled bars themselves have opposing concavities to form an assembly;
• d) laminating one or more lower layers of said prepreg material on a lower plate of a forming mold to form a lower skin;
• e) inserting the assembly of step c) on said lower skin carried by said lower plate of said forming mold and between respective side plates delimiting the forming mold itself;
• said profiled bars being arranged with respective end appendages coplanar in contact with said lower skin;
• f) laminating one or more upper layers of said pre-impregnated material on an upper plate of said forming mold to form an upper skin;
• g) mounting said upper plate on said side plates of said forming mold in a position facing said lower plate so that said upper skin is placed in contact with the end appendages of said profiled bars opposite the end appendages in contact with the lower skin;
• h) bringing to autoclave the forming mold thus prepared and filled with the upper and lower skins and with the profiled bars to carry out a curing operation at predefined curing temperature and pressure;
• wherein the elongated support tools transition into the flexible elastomeric state at a temperature lower than the predefined curing temperature and higher than 50° C.;
• step b) is carried out by laminating the said initial layer of prepreg material directly onto the second external surface said elongated support tools in a rigid state;
• and
• during phase h), the curing pressure is applied both inside the forming mold and inside said elongated support tools, whereby the plurality of walls transition to the flexible elastomeric state and are therefore pushed by the curing pressure to adhere to said elongated profiled bars and to said lower and upper skins.

A method for manufacturing a box-shaped monolithic structure for fuselages and wings of an aircraft:

• a) providing at least two elongated support tools each being internally hollow and having an external polygonal profile defined by plurality of external walls, the elongated support tool comprising a polymer and reinforcing material, wherein the polymer transitions from a rigid state to a flexible elastomeric state upon heating and transitions from the flexible elastomeric state to the rigid state upon cooling;
• b) laminating a layer of a prepreg material having a first geometry onto at least one of the plurality of external walls of the elongated support tools and subsequently shaping the layer of prepreg material into a second geometry that conforms to the external polygonal profile of the elongated support tool, thereby forming an elongated profiled bar, whereby the second geometry is different from the first geometry;
• c) forming an assembly by positioning a plurality of the elongated profiled bars adjacent to each other such that the prepreg material of each elongated profiled bar contacts the prepreg material of an adjacent-most elongated profiled bar;
• d) laminating to the assembly one or more lower layers of said prepreg material on a lower plate of a forming mold to form a lower skin;
• e) laminating to the assembly one or more upper layers of said pre-impregnated material on an upper plate of said forming mold to form an upper skin;
• f) curing the assembly, one or more lower layers, and one or more upper layers in a curing operation in a mold at predefined curing temperature and pressure to form the box-shaped monolithic structure;
• wherein the elongated support tools transition into the flexible elastomeric state at a temperature lower than the predefined curing temperature and higher than 50° C.;
• wherein step b) is carried out by laminating the said initial layer of prepreg material directly onto the external surface said elongated support tools in a rigid state;
• and
• during step f), the curing pressure is applied both inside the mold and inside said elongated support tools, and wherein the plurality of walls transition to the flexible elastomeric state and are therefore pushed by the curing pressure to adhere to said elongated profiled bars and to said lower and upper skins.