Process for manufacturing a fibrous preform for reinforcement of parts made of composite material with a high local variation in thickness

1. A manufacturing process of a fibrous preform for a composite material part, the process comprising:

creating a fibrous texture by three-dimensional or multilayer weaving between a plurality of weft layers and warp layers, the fibrous texture comprising an extra-thick portion having a sacrificial portion and a useful portion adjacent to said sacrificial portion in the warp direction,

placing the fibrous texture in a forming toolset,

shaping the fibrous texture so as to obtain a fibrous preform having a sacrificial portion and an adjacent useful portion, and

removing the sacrificial portion from the fibrous preform, process in which, when weaving the fibrous blank, one or more expansion elements are inserted into the weft layers located at the core of the sacrificial portion of the fibrous texture, each expansion element having a first cross-section greater than the cross-section or count of the weft threads or strands present in the useful portion,

wherein all of the one or more expansion elements having said first cross-section are confined solely in the sacrificial portion and each weft thread or strand of the weft layers of the useful portion of the extra-thick portion has a count that is smaller than the count of any of the expansion elements, and

wherein all of the one or more expansion elements inserted into the weft layers and having said first cross-section are removed-during said removing and prior to any densification of the fibrous preform.

2. The manufacturing process according to claim 1 , wherein when weaving the fibrous blank, braids are inserted into the weft layers located at the core of the sacrificial portion of the fibrous texture to form said one or more expansion elements, each braid having a cross-section greater than the cross-section or count of the weft threads or strands present in the useful portion.

3. The manufacturing process according to claim 2 , wherein weft layers located near weft layers comprising the braids comprise threads or strands having a count greater than the count of the threads or strands of the weft layers located in the skin of the sacrificial portion.

4. The manufacturing process according to claim 3 , wherein the braids have a cross-section corresponding to a count of 5 K, the threads or strands of the weft layers located near the weft layers comprising the braids comprise threads or strands having a count comprised between 1 K and 4 K, the threads or strands of the weft layers located in the skin of the sacrificial portion having a count of 0 . 5 K.

5. The manufacturing process according to claim 2 , wherein the sacrificial portion and the useful portion comprise the same number of warp threads woven continuously between said sacrificial portion and said useful portion.

6. The manufacturing process according to claim 1 , wherein when weaving the fibrous blank, at least one pin is inserted into the weft layers located at the core of the sacrificial portion of the fibrous texture, each pin having a cross-section greater than the cross-section or count of the weft threads or strands present in the useful portion.

7. A process for manufacturing a composite material part comprising:

creating a fibrous preform conforming to the manufacturing process for a fibrous preform according to claim 1 ,

injecting a liquid composition comprising at least one matrix material precursor into the fibrous preform,

transforming the liquid composition into matrix so as to obtain a composite material part comprising a fibrous reinforcement densified by a matrix.

8. A method comprising manufacturing a turbomachine blade of composite material with the process of claim 7 .