Method for integrating a stiffener into a thermoplastic matrix composite part

1. A method for manufacturing a composite part comprising a fibrous reinforcement and a thermoplastic polymer matrix, the composite part comprising:

a substrate part made of a composite material comprising a continuous fibrous reinforcement in a matrix made of a first thermoplastic polymer having a first melting point comprised in a first melting temperature range; and

a stiffener integral with the substrate part, made of a fibrous-reinforced composite material in a matrix made of a second thermoplastic polymer, the stiffener comprising at least one flange and at least one web, the second thermoplastic polymer having a second melting point comprised in a second melting temperature range; wherein:

the second melting point is higher than the first melting point; and

the first thermoplastic polymer is miscible with the second thermoplastic polymer at the second melting point;

the method comprising the steps of:

I) obtaining a non-consolidated preform of the substrate part;

II) obtaining a preform of the stiffener comprising a layer comprising the first thermoplastic polymer at a location of a flange of the stiffener configured to be in contact with the substrate part;

III) placing and assembly of the non-consolidated preform of the substrate part and the preform of the stiffener contacting the substrate part in a tooling comprising a molding surface reproducing a shape of the substrate part and comprising means for positioning the stiffener relative to the molding surface; and

IV) subjecting the assembly to a consolidation thermomechanical cycle comprising heating under pressure up to a first temperature that is higher than the first melting temperature range but lower than the second melting temperature range in order to consolidate the preform of the substrate part and to weld the flange of the stiffener on the substrate part.

2. The method of claim 1 , wherein the first thermoplastic polymer is of a Low Melting Polyaryletherketone type (LMPAEK®) and the second thermoplastic polymer is of a Polyetheretherketone (PEEK) type.

3. The method of claim 2 , wherein the first melting temperature range is comprised between 285° C. and 320° C., the second melting temperature range is comprised between 294° C. and 354° C., and the second melting point is 343° C.

4. The method of claim 3 , wherein the first temperature is 335° C.

5. The method of claim 1 , wherein the first thermoplastic polymer is of the LMPAEK® type and the second thermoplastic polymer is of a Polyetherketoneketone (PEKK) type.

6. The method of claim 1 , wherein the first polymer is of a Polyetherimide (PEI) type and the second polymer is chosen among PEKK, LMPAEK® and PEEK.

7. The method of claim 1 , wherein step III) comprises interposing a film comprising the first thermoplastic polymer between the stiffener flange and the preform of the substrate part.

8. The method of claim 1 , wherein the fibrous reinforcement of the stiffener comprises fibers selected among continuous fibers, long fibers and short fibers.

9. The method of claim 1 , wherein the stiffener preform is obtained by a method selected from injection molding, additive manufacturing, and thermo-compression.

10. The method of claim 1 , wherein the substrate part is a skin and the stiffener is a profile, wherein integration of the stiffener with the skin making a stiffened panel.

11. The method of claim 1 , wherein the substrate part is a profile having a U-shaped cross section and the stiffener comprises at least two flanges, at least one of these two flanges being configured to be integrated with the profile, and a member extending from at least one of the at least two flanges of the stiffener and integral with this flange.

12. The method of claim 1 , wherein step I) comprises a layup by automated fiber placement of fibers pre-impregnated with the first thermoplastic polymer on the molding surface of the tooling so as to obtain the non-consolidated preform of the substrate part.

13. The method of claim 12 , wherein the layup by automated fiber placement of pre-impregnated fibers of with first thermoplastic polymer is carried out while the preform of the stiffener is held in the means for positioning the stiffener relative to the molding surface so that the flange of the stiffener configured to be in contact with the substrate part is flush with the molding surface.

14. The method of claim 1 wherein step II) comprises the steps of:

obtaining a non-consolidated preform of the stiffener;

integrating a layer made of the first thermoplastic polymer into the non-consolidated preform of the stiffener at a location of a flange of the stiffener configured to be in contact with the substrate part; and

consolidating the non-consolidated preform of the stiffener comprising the layer made of the first thermoplastic polymer, thus obtaining the preform of the stiffener.

15. The method of claim 1 , wherein step II) comprises the step of:

a layup of a non-consolidated preform of the stiffener by automated fiber placement; and

hot-stamping the non-consolidated preform of the stiffener and consolidating the preform of the stiffener during the stamping, thus obtaining the preform of the stiffener.

16. The method of claim 15 , wherein the flat layup step of the non-consolidated preform of the stiffener comprises the layup of a ply comprising fibers pre-impregnated with the first thermoplastic polymer.