Method of manufacturing a composite turbomachine blade, and a blade obtained by the method

1. A method of manufacturing a composite turbomachine blade, the method comprising the following steps:

a) making a preform by three-dimensional weaving of yarns, said preform comprising both the airfoil and the root of the blade, the yarns including tracer yarns that are visually identifiable and that are disposed at least on the surface of the preform;

b) cutting out said preform while leaving intact a series of tracer yarns situated along a reference face of the preform, thereby providing a cut-out preform suitable for taking the shape and the dimensions of portions constituting the blade;

c) pre-deforming said cut-out preform so as to provide a pre-deformed preform;

d) compacting and stiffening said pre-deformed preform;

e) providing an injection mold in which said stiffened preform is placed;

f) injecting into said injection mold a binder comprising a thermosettable resin so as to impregnate the entire stiffened pre-deformed preform and maintain the relative disposition between the yarns of the preform;

g) heating said injection mold; and

h) extracting from the mold a composite molded part presenting substantially the shape and the dimensions of said blade.

2. A method according to claim 1 , wherein the tracer yarns are of different nature from that of the other yarns.

3. A method according to claim 1 , wherein, during step c), said pre-deformation is performed by placing the cut-out preform in a shaping mold.

4. A method according to claim 3 , wherein the shaping mold puts the cut-out preform in a configuration that deforms it in rotation about an axis parallel to its main direction.

5. A method according to claim 4 , wherein, during step c), prior to placing the cut-out preform in the shaping mold, preliminary pre-deformation is performed that consists in applying shear in a direction parallel to the main direction of the cut-out preform, while maintaining the cut-out preform in a plane.

6. A method according to claim 5 , wherein, during step d), before or after stiffening, the following sub-steps are performed:

d1) supercompacting the pre-deformed preform at the location of the leading edge; and

d2) mounting a metal, leading edge protector element on the pre-deformed preform at the location of the leading edge, the protector element presenting two flanges for receiving a portion of the pressure-side and suction-side walls.

7. A method according to claim 6 , wherein, during step d2), said protector element is placed in a mounting device suitable for splaying apart said flanges of said protector element, and then said mounting device is placed on the pre-deformed preform in such a manner that the two flanges of said protector element are fitted onto the supercompacted leading edge of the pre-deformed preform, and then said flanges are released.

8. A method according to claim 6 , wherein, prior to step d2), a protective film is secured on the pre-deformed preform over a portion of the outside surface of the pressure-side wall that includes the leading edge.

9. A method according to claim 8 , wherein the protective film is made of polyurethane.

10. A method according to claim 8 , wherein an interface element is interposed between the protective film and the pre-deformed preform, the interface element forming extra thickness on the yarns of the preform.

11. A method according to claim 1 , wherein, during step e), at least one spacer is also placed in said injection mold against the surface of the stiffened preform that is to form the bottom of the blade root.

12. A method according to claim 11 , wherein, during steps f) and g), said spacer is maintained under constant pressure against the surface of the stiffened preform that is to form the bottom of the blade root.

13. A blade according to claim 1 , wherein said preform is made up of warp yarns and weft yarns, the direction of the warp yarns forming the longitudinal direction of the preform, wherein said preform comprises at least a first portion made with a first weave forming the airfoil of the blade, and a second portion made with a second weave forming the root of the blade, and wherein the first and second portions are united by a transition zone in which the first weave is modified progressively to become the second weave, thereby obtaining a reduction at least in the thickness of the blade between the second portion and the first portion.

14. A blade according to claim 13 , wherein the yarns belong to the group constituted by: carbon fibers; glass fibers; silica fibers; silicon carbide fibers; alumina fibers; aramid fibers; and aromatic polyamide fibers.

15. A blade according to claim 14 , wherein the warp yarns and the weft yarns are carbon fibers, and wherein the tracer yarns are glass fibers.