Fiber preform for a turbine engine blade made of composite material and having an integrated platform, and a method of making it

1. A method of making a fiber preform for fabricating a turbine engine blade out of composite material, the blade including an airfoil extending in a longitudinal direction and presenting two opposite side faces and at least one platform extending from a side face, the method comprising:

making a single-piece fiber blank by three-dimensional weaving with a plurality of longitudinal yarns extending in a direction corresponding to the longitudinal direction of the blade that is to be fabricated and interlinked by yarns of a plurality of transverse layers of yarns; and

shaping the fiber blank to obtain a single-piece fiber preform including a first portion forming an airfoil preform and at least one second portion forming a platform preform,

wherein, during the weaving of the fiber blank, yarns of a first group of longitudinal yarns are extracted from the fiber blank beside at least one of side faces of the fiber blank to form a portion of the blank corresponding to a blade platform preform, and yarns of a second group of longitudinal yarns are inserted into the fiber blank with mutual crossing between the yarns of the first group and the yarns of the second group, and

wherein the yarns of the second group of yarns that are inserted into the fiber blank come from layers of longitudinal yarn previously extracted from the fiber blank to obtain a reduction in thickness of the blank over a width of the blank.

2. A method according to claim 1 , wherein the crossing between the yarns of the first group and the yarns of the second group takes place close to a connection between the portion of the blank corresponding to the blade platform preform and the portion of the blank corresponding to the airfoil preform.

3. A method according to claim 1 , wherein the shaping of the fiber blank includes cutting away portions of the yarns of the second group of yarns that are situated between zones where the yarns of the second group of yarns are extracted from and inserted into the fiber blank.

4. A method according to claim 1 , wherein at least some of the yarns of the second group of yarns are extracted from the fiber blank downstream from a zone where the yarns of the second group of yarns are inserted into the fiber blank to reduce thickness of the blank over the width of the blank downstream from the portion of the blank that corresponds to the blade platform preform.

5. A method according to claim 1 , wherein at least some of the yarns of the second group of yarns that are inserted into the fiber blank come from additional layers of longitudinal yarns.

6. A method according to claim 1 , wherein the yarns are extracted from and inserted into the fiber blank on each of the side faces of the fiber blank to form portions of the blank that correspond to two blade platform preforms.

7. A method according to claim 1 , wherein the shaping of the fiber blank includes cutting the portion of the blank that corresponds to the blade platform preform to have desired dimensions, and deploying the portion of the blank in a direction that is substantially orthogonal to a side face of the blank.

8. A method according to claim 1 , wherein the longitudinal yarns extending in a direction corresponding to the longitudinal direction of the blade that is to be fabricated are warp yarns.

9. A method according to claim 1 , wherein the longitudinal yarns extending in a direction corresponding to the longitudinal direction of the blade that is to be fabricated are weft yarns.

10. A fiber preform for a turbine engine blade including an airfoil extending in a longitudinal direction and presenting two opposite side faces together with at least one platform extending from a side face, the preform comprising:

a fiber blank woven as a single piece by three-dimensional weaving with a plurality of layers of longitudinal yarns extending in a direction corresponding to the longitudinal direction of the blade that is to be fabricated and interlinked by yarns of a plurality of layers of transverse yarns,

wherein yarns of a first group of longitudinal yarns are extracted from the fiber blank beside at least one of the side faces of the fiber blank to form a portion of the blank corresponding to a blade platform preform, and yarns of a second group of longitudinal yarns are inserted into the fiber blank, with mutual crossing between the yarns of the first group and the yarns of the second group, and

wherein the yarns of the second group of yarns that are inserted into the fiber blank come from layers of longitudinal yarn previously extracted from the fiber blank to obtain a reduction in thickness of the blank over a width of the blank.

11. A preform according to claim 10 , wherein the crossing between the yarns of the first group and the yarns of the second group takes place close to a connection between the portion of the blank that corresponds to a blade platform preform and the portion of the blank that corresponds to the airfoil preform.

12. A preform according to claim 10 , wherein yarns are extracted from and inserted into the fiber blank on each of side faces of the fiber blank to form portions of the blank that correspond to two blade platform preforms.

13. A turbine engine fan blade made of composite material and comprising a fiber preform according to claim 10 densified by a matrix.

14. A turbine engine fan comprising at least one blade according to claim 13 .