FR3118900A1 - PROCESS FOR MANUFACTURING A HOLLOW PIECE IN COMPOSITE MATERIAL - Google Patents

Abstract

The invention relates to a method for manufacturing a hollow part (1) made of composite material comprising a polymer matrix and fibers embedded in the polymer matrix, the part (1) comprising an envelope (2) delimiting an internal cavity (3) , the manufacturing process comprising the following steps: - (a) Providing a preform (4) of the part (1) comprising adjoining plies (4a) formed from the fibers and the polymer matrix; - (b) hydrating the preform (4); - (c) Heat treating the preform (4) at a temperature higher than an initial ambient temperature to create a gas evolution within the matrix, the gas evolution having the effect of causing the preform (4) to swell by moving the folds ( 4a) from each other to create said internal cavity (3). Abstract Figure: Figure 1

Description

PROCESS FOR MANUFACTURING A HOLLOW PIECE IN COMPOSITE MATERIAL

Technical field of the invention

The invention relates to the technical field of the manufacture of hollow parts in composite material, more particularly in composite material with an organic matrix (CMO). The invention relates more particularly to hollow parts made of composite material whose firing temperature is greater than 300°C.

The parts are intended in particular for the aeronautical and aerospace industry.

Technical background

A composite material is generally formed of a matrix reinforced by fibers embedded in the matrix. More particularly, in the context of composites with an organic matrix, called CMO composite, the organic matrix is formed of a thermoplastic or thermosetting material. The fibers are for example long or short fibers such as carbon fibers, glass fibers or any fiber suitable according to the applications.

Given their low weight compared to metallic material such as steel, organic matrix composite materials find many applications in the aeronautical or aerospace industry. Thus, many structural parts of aircraft, for example, are made of these composite materials.

In order to further reduce the weight of aircraft and increase its overall performance, it has been proposed to make hollow structural parts. Hollow composite parts typically include an envelope defining an internal cavity. The section of the structural part can be circular, rectangular or of any geometry depending on the part.

These hollow structural parts made of composite material are manufactured in several stages. Generally, a first step of supplying a preform is carried out. During this stage, plies formed from a prepreg are draped around a core. The core is for example a flexible bladder made of silicone material. The flexible bladder also has an interface capable of cooperating with an external pressurizing device. The folds are then placed in a removable mold having an internal surface with a geometry that conforms to the geometry of the desired part.

Then, pressure is applied inside the core. This makes it possible to inflate the core so as to press the plies against the internal surface of the mold and to form a preform having an envelope and an internal cavity occupied by the core. Moreover, during this pressurization, the preform is subjected to a heat treatment, called curing, during which the material of the matrix of the preform is completely hardened. The core is capable of withstanding the pressures and temperatures necessary for curing the composite preform.

Given certain temperature levels, some resins cannot be used to form the matrix of the composite by the core method formed by the flexible silicone bladder. For example, polyimide resins cannot be used because their polymerization temperature is around 350°C. However, a core made of a silicone resin cannot withstand such temperatures. In addition, pre-impregnated polyimide resins contain solvents that must be evacuated in volatile form during curing, which is not feasible with such a method. Such a manufacturing process is therefore unsuitable for polyimide prepregs.

Furthermore, when the hardening of the resin is complete, the demolding of the preform can take place. Once the preform has been demoulded, the core must be removed to obtain the final hollow part. The core must be removed through a hole in the preform envelope. The size of the orifice must be at least equal to the size of the core to allow its passage. This step is therefore complex to implement.

There is therefore a need to provide a method for manufacturing a hollow part in composite material, in particular at high temperature, which is simple to implement.

To this end, the invention proposes a method for manufacturing a hollow part made of composite material comprising a polymer matrix and fibers embedded in the polymer matrix, the part comprising an envelope delimiting an internal cavity, the method of manufacture comprising the steps following:

-(a) providing a preform of the part comprising adjoining plies formed from the fibers and the polymer matrix;

-(b) hydrating the preform;

-(c) heat treating the preform at a temperature above an initial ambient temperature to create a gas evolution within the matrix, the gas evolution having the effect of causing the preform to swell by moving the plies away from each other to create said internal cavity.

Thus, according to the invention, once the preform has been formed, the latter is hydrated. The preform thus comprises water molecules. During the heat treatment of step (c) the water adsorbed by the preform becomes gaseous and concentrates in the less cohesive zone of the preform until it delaminates and creates a cavity in the preform by pushing the delaminated parts. A hollow part is thus obtained.

Consequently, the method according to the invention makes it possible to dispense with a core to form the internal cavity of the part. Also, it is no longer necessary to apply high pressure to create the cavity, which facilitates the implementation of the process. The method is all the more simplified in that according to the invention, it is no longer necessary to carry out a step of removing the core.

The method according to the invention comprises the following characteristics, taken alone or in combination with each other:

- the mass concentration of water in the preform is greater than 0.5% and less than 2%, preferably less than 1% at the end of step (b) of hydration;

- the heat treatment of the step is carried out at a plateau temperature of between 300°C and 400°C, preferably between 300°C and 380°C;

- step (c) includes the following sub-steps:

- (c1) increase the initial temperature by 1 to 2°C per minute until a first temperature is reached;

- (c2) increase the first temperature by 0.5°C per minute until the plateau temperature is reached;

- (c3) maintain the plateau temperature for a period of between 0 hours and 6 hours.

- step (a) includes the following sub-steps:

- (a1) draping within a mold the folds formed from the fibers impregnated with a resin intended to form the matrix;

- (a2) optionally, insert a separator between the folds;

- (a3) heat treating the plies in order to polymerize the resin to form the matrix and the preform;

- the preform comprises at least one end flange making it possible to delimit the swelling of the preform;

- during step (c), the preform cooperates with a mold to delimit the swelling of the preform;

- the cavity has a height of between 5 mm and 200 mm;

- step (b) is carried out at an initial temperature of between 20°C and 80°C and at a relative air humidity of between 50% and 90%.

- the material of the polymeric matrix is chosen from resins of the polyimide family, for example of the PMR-15 type or resins of the phthalonitrile family or a mixture thereof.

Brief description of figures

Other characteristics and advantages will emerge from the following description of a non-limiting embodiment of the invention with reference to the appended drawings in which:

there is a schematic cross-sectional representation of a hollow part made of composite material;

there is a schematic cross-sectional representation of a preform according to the invention;

there is a schematic representation of a preform after the hydration and heat treatment step;

there is a schematic representation of an exemplary embodiment of a preform with a separator according to a first exemplary embodiment;

there is a schematic representation of another embodiment of a preform with a separator;

there is a schematic representation of an example of holding a preform before the heat treatment step;

there is a schematic representation of the example of the in another step of the process;

there is a schematic representation of another embodiment of holding a preform before the heat treatment step;

there is a schematic representation of the example of the in another step of the process;

there is a schematic representation of a method according to the invention.

Detailed description of the invention

An example of a hollow part 1 made of composite material is for example shown in cross section on the .

Part 1 is for example a structural part intended to equip a turbomachine of an aircraft (not shown). Part 1 is for example a vane or a casing arm.

Part 1 present in the example of the a rectangular section. However, part 1 can be of circular section, or of any other section depending on the applications.

Part 1 is made of a composite material. The composite material includes a matrix and fibers embedded in the matrix. Optionally, the composite material also includes additives.

The fibers are for example glass, quartz or carbon fibers. Preferably, the fibers are woven.

The matrix is a polymer matrix. The material of the polymeric matrix is chosen from resins of the polyimide family, for example of the PMR-15 type or of the RM1100 type or the resins of the phthalonitrile family or a mixture thereof. The polymerization temperature of the polymeric matrix material is between 300°C and 400°C, preferably 350°C.

Part 1 is a monolithic part. Part 1 comprises an envelope 2 delimiting an internal cavity 3. The thickness of envelope 2 is constant or variable. It is generally between 1 mm and 10 mm, and preferably between 1 mm and 5 mm. Preferably, the casing 2 of part 1 has two side walls 2a, 2b and possibly two transverse walls 2c, 2d extending transversely relative to the side walls 2a, 2b.

The distance D between the side walls 2a, 2b is preferably between 5 mm and 200 mm. This represents the height of cavity 3.

The hollow part 1 made of composite material is made according to a process shown in the . The method comprises a first step (a) of supplying a preform 4 of the part 1, a step (b) of hydrating the preform 4 and a step (c) of heat treatment.

The preform 4 corresponds to the part 1 during the manufacturing steps, before obtaining the part 1. Advantageously, the preform 4 comprises at least one end flange 5, for example two end flanges 5 as represented on the .

The preform 4 is composed of an assembly of plies 4a. In a manner not shown, the preform 4 comprises for example thirteen plies 4a. The folds 4a are formed from the fibers and the matrix. Folds 4a are in step (a) contiguous. According to the present invention, a ply 4a corresponds to a thickness or a layer of fibers impregnated with the matrix.

Advantageously, the supply of the preform 4 in step (a) is carried out in several sub-steps. A first sub-step (a1) in which the folds 4a are draped within a mold (not shown) is carried out. In this first sub-step (a1) the plies are formed from fibers impregnated with a resin intended to form the matrix, called pre-pregs. The resin is in an uncured state in step (a1) draping.

As shown in Figures 3a and 3b, optionally, during a sub-step (a2), a separator 6 is inserted between the folds 4a. As shown on the , the separator 6 is for example a segment 7. The segment is for example metallic or polymer having a non-stick surface. The non-stick surface comprises for example a polymeric coating chosen from silicones or fluorinated polymers such as polytetrafluoroethylene (PTFE). According to another exemplary embodiment shown in the , the separator 6 is formed of a foaming element 8. The foaming element 8 is able to react on contact with the gases released during the process and to swell according to the concentration of the gases. The separator 6 being arranged between the plies 4a, it makes it possible to control and target the separation of the plies 4a from the preform 4 during the manufacturing process.

At the end of step (a1) of draping, the plies 4a are heat-treated in a step (a3) in order to polymerize the resin to form the matrix. Such heat treatment is called baking. The heat treatment is carried out at a temperature between 300°C and 400°C, preferably 350°C. This thus makes it possible to form the preform 4. Preferably, the heat treatment in step (a3) is carried out under pressure and under vacuum for a period of between 1 hour and 5 hours, for example 3 hours. The heat treatment in step (a3) is for example carried out in an autoclave.

According to another embodiment of step (a), the provision of the preform 4 is made by resin transfer molding (RTM for “resin transfer molding” in English).

Then, in a step (b) of the method, the preform 4 is hydrated. During this step, water molecules are fixed to the preform 4 by adsorption. The water adsorbed by the preform 4 becomes gaseous and concentrates in the less cohesive zone of the preform 4 until it allows delamination and creates a cavity by pushing the parts thus delaminated.

Preferably, step (b) of hydrating the preform 4 is carried out at an initial temperature of between 20°C and 80°C. The initial temperature is for example equal to the ambient temperature. Ambient temperature means the temperature in the air of the surrounding environment. By convention, this temperature is generally between 20°C and 25°C, for example 23°C.

Preferably, in step (b), the relative humidity (RH) of the air, also called hygrometric degree, is between 50% and 90% and preferably 55% as measured at ambient temperature and atmospheric pressure. Step (b) can be carried out in a room with controlled hygrometry or in a climatic chamber. Such a temperature and relative humidity makes it possible to accelerate the hydration of the preform 4. Possibly, the temperature in the room with controlled hygrometry or in the climatic chamber can be around 70° C. and 85% relative humidity in order to further accelerate the hydration step.

Advantageously, at the end of step (b) of hydration, the mass concentration of water in the preform 4 is greater than 0.5% and less than 2%, preferably less than 1%. Such a concentration makes it possible to ensure sufficient gas release to move the folds 4a away and form the cavity 3.

Then, in a step (c) the preform 4 is subjected to a heat treatment. This heat treatment takes place on the preform 4 in which the material of the matrix is hardened. Thus, this heat treatment is called post-bake heat treatment. The heat treatment during step (c) is advantageously carried out for a period of less than or equal to 20 hours, preferably at atmospheric pressure. This heat treatment is advantageously carried out at a plateau temperature of between 300°C and 400°C, preferably between 300°C and 380°C, advantageously 350°C. By plateau temperature, it is understood a temperature maintained constant for a determined time.

More particularly, step (c) of heat treatment can be broken down into several sub-steps. A first sub-step (c1) is carried out, in which the initial temperature, which is for example the ambient temperature, is increased by 1°C to 2°C per minute until a first temperature is reached. The first temperature is for example between 200°C and 300°C.

A second sub-step (c2) in which the first temperature is increased by 0.5°C per minute until the plateau temperature is reached can then be performed. ;

Then, the plateau temperature can be maintained in a step (c3) for a period of between 0 hour and 6 hours.

The heat treatment makes it possible to create a gaseous release such as water vapor for example within the matrix, the release of gas having the effect of moving the plies 4a away, in other words of delaminating the plies 4a, to create said internal cavity 3 of the part 1 as represented on the .

The hollow part 1 thus formed is allowed to drop in temperature to the initial ambient temperature. For example, the plateau temperature is reduced by 0.5°C to 5°C per minute down to ambient temperature.

According to an exemplary embodiment, represented for example in FIGS. 4a, 4b, 5a and 5b, during the heat treatment of step (c), the preform 4 cooperates with a mold 9 to delimit the swelling of the preform 4. The mold 9 is preferably removable.

According to a first embodiment shown in Figures 4a, 4b, the mold 9 is a counter mold 10 formed by two end jaws 10a, 10b. The end jaws 10a, 10b are intended to grip the ends of the preform 4. More particularly, the end jaws 10a, 10b grip the flanges 5 of the preform 4. The end jaws 10a, 10b grip the preform 4 for example with a clearance allowing the delamination of the plies 4a at the ends of the preform 4 to be authorized during the heat treatment as represented on the or alternatively without backlash as required. The end jaws 10a, 10b are, for example, interconnected to ensure the position of the flanges 5 relative to each other. Preferably, the end jaws 10a, 10b comprise a clamping means 10c such as a set of screws and nuts allowing the opening and clamping of the counter mold 10.

According to another exemplary embodiment represented in FIGS. 5a, 5b, the mold 9 is a complete mold 11 comprising a wall delimiting an internal space receiving the preform 4. The internal space of the complete mold 11 has a surface of the geometry of the part 1. The complete mold 11 preferably comprises two parts to facilitate the demolding of part 1 after the heat treatment of step (c). The delamination of the plies 4a of the preform 4 is thus limited by the wall of the complete mold 11 as shown in the .

According to yet another example not shown, the end flanges 5 alone make it possible to delimit the swelling of the preform 4.

An additional step (d) (not shown) of machining part 1 can be performed. For example, the flanges 5 can be removed by machining to form a part (1) without flanges.

Claims (10)

Method of manufacturing a hollow part (1) made of composite material comprising a polymer matrix and fibers embedded in the polymer matrix, the part (1) comprising an envelope (2) delimiting an internal cavity (3), the method of manufacturing including the following steps:
- (a) Providing a preform (4) of the part (1) comprising adjoining plies (4a) formed from the fibers and the polymer matrix;
- (b) hydrating the preform (4);
- (c) Heat treating the preform (4) at a temperature above an initial ambient temperature to create a gas evolution within the matrix, the gas evolution having the effect of causing the preform (4) to swell by moving the folds ( 4a) from each other to create said internal cavity (3). Manufacturing process according to Claim 1, characterized in that the mass concentration of water in the preform (4) is greater than 0.5% and less than 2%, preferably less than 1% at the end of the step (b) hydration. Manufacturing process according to any one of the preceding claims, characterized in that the heat treatment of step (c) is carried out at a plateau temperature of between 300°C and 400°C, preferably between 300°C and 380°C. °C. Manufacturing process according to the preceding claim, characterized in that step (c) comprises the following sub-steps:
- (c1) Increase the initial temperature by 1 to 2°C per minute until a first temperature is reached;
- (c2) Increase the first temperature by 0.5°C per minute until the plateau temperature is reached;
- (c3) Maintain the plateau temperature for a period between 0 hours and 6 hours. Manufacturing process according to any one of the preceding claims, characterized in that step (a) comprises the following sub-steps:
- (a1) Drape within a mold the folds (4a) formed of the fibers impregnated with a resin intended to form the matrix;
- (a2) Optionally, insert a separator between the folds (4a);
- (a3) Heat treating the plies (4a) in order to polymerize the resin to form the matrix and the preform (4). Manufacturing process according to any one of the preceding claims, characterized in that the preform (4) comprises at least one end flange (5) making it possible to delimit the swelling of the preform (4). Manufacturing process according to any one of the preceding claims, characterized in that during step (c), the preform (4) cooperates with a mold (9) to delimit the swelling of the preform (4). Method according to any one of the preceding claims, characterized in that the cavity (3) has a height of between 5 mm and 200 mm. Manufacturing process according to any one of the preceding claims, characterized in that step (b) is carried out at an initial temperature of between 20°C and 80°C and at a relative humidity of the air of between 50% and 90%. Manufacturing process according to any one of the preceding claims, characterized in that the material of the polymeric matrix is chosen from resins of the polyimide family, for example of the PMR-15 type or resins of the phthalonitrile family or a mixture of these.