Method for manufacturing composite material blades for aircraft engines

Abstract

This disclosure discloses a method for manufacturing a composite material blade (10) for a turbine, particularly an aircraft turbine engine, the blade comprising an airfoil (12) having a pressure side (14) and a suction side (16) extending from a leading edge (12a) to a trailing edge (12b) of the airfoil, the blade further comprising a metal shroud (22) extending along the leading edge of the airfoil, the method comprising the steps of: a) arranging a preform made of three-dimensional woven fibers in a mold, a polymerizable adhesive (24) being inserted between the shroud and the edge of the preform; b) injecting a polymerizable resin into the mold to impregnate the preform to form the airfoil after curing, characterized in that, in step b), the resin is injected at time intervals during which the adhesive reaches its solidification point.

Description

Technical Field

[0001] This invention relates to a method for manufacturing blades made of composite materials for aircraft turbines. Background Technology

[0002] The prior art specifically includes documents FR-A1-2 956 057, FR-A1-3 029 134 and FR-A1-3 051386.

[0003] The use of composite materials is advantageous in the aerospace industry, especially because these materials have beneficial mechanical properties at relatively low mass.

[0004] The method known to those skilled in the art for manufacturing composite material components for the aerospace industry is the RTM method, which stands for Resin Transfer Molding.

[0005] This is a method for producing parts made of resin-impregnated fiber composite materials. This method is used, for example, in the manufacture of fan blades and includes multiple sequential stages.

[0006] First, fibers are woven to obtain a three-dimensional preform blank, which is then cut to obtain a preform that roughly has the desired blade shape. The preform is then placed in an injection mold, which is closed. Resin is then injected into the mold while maintaining pressure on the resin in a liquid state, and the part is polymerized by heating.

[0007] The resin used is a highly fluid resin, capable of penetrating the fibers of the preform even when injected under reduced pressure. During the polymerization process, under the influence of heat, the injected resin sequentially changes from a liquid state to a gel state, and finally to a solid state.

[0008] To manufacture blades, for example, for turbine fans, preforms are made by weaving and then impregnated with resin to form a blade. The blade includes a pressure side and a suction side extending from the leading edge to the trailing edge.

[0009] Composite blades are relatively fragile and particularly sensitive to impact, and it is known to protect composite blades by attaching and securing metal shields to the leading edge of the blade.

[0010] The shield can be attached to the impeller in two ways. The first way is to glue the shield onto the impeller after the resin has polymerized. The glue is then in the form of a paste.

[0011] Another method is to fix the shield by co-molding it with a fiber preform. The preform is arranged in a mold, and the shield is positioned on the edge of the preform that forms the leading edge of the impeller. Injected resin impregnates the preform and makes contact with the shield to ensure that the shield is fixed to the impeller after polymerization and curing.

[0012] The present invention relates to an improvement of the second technology, wherein the shield and the preform are co-molded.

[0013] The applicant seeks to optimize the attachment of the shroud by combining two existing technologies and therefore using an adhesive in addition to co-molding the shroud with the impeller. The adhesive is inserted between the leading edge of the shroud and the impeller.

[0014] In this case, both the resin and the adhesive are polymerizable. The adhesive has different rheological properties than the resin. The adhesive typically begins to cure at a lower temperature than the resin. This temperature is reached when the mold is heated to the high temperature required for resin injection. Adhesives that polymerize too quickly during resin injection cannot achieve effective co-bonding between the resin and the adhesive, and reduce the mechanical strength of the shield on the impeller.

[0015] This invention provides a simple, effective, and economical solution to ensure the proper positioning and optimal mechanical strength of the shroud on the impeller. Summary of the Invention

[0016] This invention proposes a method for manufacturing composite material blades for turbines, particularly aircraft turbines, the blades comprising a rotor blade, the rotor blade including a pressure side and a suction side extending from the leading edge to the trailing edge of the rotor blade, the blade also including a metal shroud extending along the leading edge of the rotor blade, the method comprising the following steps:

[0017] a) A preform made of three-dimensional woven fibers is arranged in a mold, a shield is positioned on the leading edge of the preform for forming the impeller, and a polymerizable adhesive is inserted between the shield and the edge of the preform.

[0018] b) Injecting polymerizable resin into a mold to impregnate the preform, so that it forms a blade after curing.

[0019] The characteristic feature is that, in step b), resin is injected at time intervals during which the adhesive reaches its gel point.

[0020] Therefore, this invention proposes to attach the shroud to the blade by co-molding and by using an adhesive film. The adhesive film is inserted between the edges of the shroud and the preform, designed to improve and maintain the position of the shroud on the edge of the preform, and also designed to improve the fixation and tear resistance of the shroud relative to the blade. Thus, it can be understood that during the injection of resin into the manufacturing mold of the blade, the resin will impregnate the preform and will also come into contact with the film or even the shroud, thus ensuring optimal attachment of the shroud to the blade.

[0021] The present invention also proposes a resin injection cycle suitable for the presence of an adhesive. The aim is to inject the resin within a time interval at which the viscosity of the adhesive allows for satisfactory co-adhesion. Injecting the resin before the adhesive becomes too viscous, which would prevent good co-adhesion between the products, is not recommended. This is achieved by injecting the resin within the time interval during which the adhesive reaches its gel point.

[0022] Gels are formed by two media dispersed together: the first medium is called a "solid" or "gel" and consists of long molecules connected to each other through cross-linking points to form a three-dimensional (3D) network. Conversely, the second medium is a liquid medium called a "solvent" or "sol" and consists of individual molecules.

[0023] The state change of a system from a single-phase sol to a sol-gel two-phase system is called the sol-gel transition. Typically, the state of the gelation process is characterized by its degree of advancement, p, where p varies between zero and one between the beginning and end of the polymerization process. At the gel point, or "gel point," the value of the degree of advancement is p. c The "gel point" is the instant when the viscosity of a medium changes abruptly. Therefore, for 0... <p<p c The reaction bath is where the viscosity η increases to p. c The liquid. For 1 ≥ p > p c The reaction bath is an elastic body with an increasing shear modulus μ. At point p... c At this point, gel formation occurs. However, polymerization continues, and viscosity increases. In the context of this invention, the concept of the gel point is paramount, and it is a fact that once gelation (solid state) has occurred, it cannot be injected again or densified further. The gel point is the channel from multiple 3D macromolecules to a single 3D macromolecule, and the presence of solvent has no effect on viscosity (molecules are independent of the 3D network).

[0024] Therefore, this invention proposes adjusting the resin injection time and duration based on the progress of the adhesive polymerization, and particularly the change in the adhesive's viscosity. Injecting the resin for a certain period (including the time required to reach the adhesive's gel point) specifically ensures good co-adhesion between the resin and the adhesive.

[0025] The method according to the invention may include one or more of the following features, which may be used individually or in combination:

[0026] - Adhesives are adhesive films, especially double-sided adhesive films;

[0027] - In step b), resin is injected at time intervals in which the adhesive reaches its gel point in the middle of the time interval;

[0028] - The time interval begins at least 5 minutes before the adhesive reaches the gel point, and preferably 10 minutes before it ends at least 5 minutes after the adhesive reaches the gel point, preferably 10 minutes;

[0029] - Begin resin injection when the adhesive reaches its gel point;

[0030] - Adjust the temperature of the mold to keep it constant within a time interval;

[0031] - The temperature of the mold is maintained at at least 160°C during the time interval;

[0032] -The resin is epoxy resin;

[0033] - The adhesive is an epoxy adhesive;

[0034] - The adhesive was manufactured by Solvay under the number [number missing]. 309-1 Adhesives sold. Attached Figure Description

[0035] In the following detailed description, reference is made to the accompanying drawings, in which other features and advantages of the invention will become apparent:

[0036] [ Figure 1 ] Figure 1 This is a schematic perspective view of a composite material aircraft turbine blade.

[0037] [ Figure 2 ] Figure 2 This illustrates the use of the present invention for manufacturing such as Figure 1 The flowchart illustrates the steps of the method for the blade shown.

[0038] [ Figure 3 ] Figure 3 This is a schematic perspective view of the mold, showing the preforms and guards intended to be arranged within the mold, and the resin intended to be injected into the mold.

[0039] [ Figure 4 ] Figure 4 It is a graph showing the changes in viscosity of resin and adhesive over time, as well as the changes in temperature over time, during the manufacturing process. Detailed Implementation

[0040] First refer to Figure 1 , Figure 1 A composite blade 10 for a turbine is shown, the blade 10 being, for example, a fan blade.

[0041] The blade 10 includes a wheel blade 12 connected to a root 16 by a support 14, the root having, for example, a dovetail shape and being shaped to engage in a complementary-shaped recess in a rotor disk in order to hold the blade on the disk.

[0042] The blade 12 includes a leading edge 12a and a trailing edge 12b for allowing gas to flow into the turbine. The blade 12 has a curved or even twisted aerodynamic profile and includes a pressure side 18 and a suction side 20 extending between the leading edge 12a and the trailing edge 12b.

[0043] The blade 12 is made of a fiber preform obtained by three-dimensionally weaving fibers (e.g., carbon).

[0044] The leading edge 12a of the impeller is reinforced and protected by a metal shield 22 attached to the leading edge 12a. The shield 22 is made, for example, of a nickel and cobalt-based alloy.

[0045] In this invention, such attachment is achieved on the one hand by co-molding the preform with the cover 22, and on the other hand by bonding the cover 22 with at least one adhesive 24 (preferably in the form of a film).

[0046] Figure 2 It shows the use of manufacturing such as Figure 1 A flowchart of the steps in the method for the composite material blade 10 shown.

[0047] The method may include multiple steps, some of which are optional.

[0048] The first step a) of this method comprises several sub-steps or operations. In the first operation a1) discussed above, the fiber preform is made by weaving fibers. The resulting preform is unprocessed and can be subjected to operations such as cutting or compression.

[0049] In a further step a2) of this method, one or more adhesive films are prepared. The resin is injected into, for example... Figure 3 Before being inserted into the mold 30 shown for manufacturing the blade, the adhesive film is intended to be inserted between the shield 22 and the preform.

[0050] The adhesive film is, for example, a double-sided film, meaning it is adhesive on both sides. Therefore, both sides of the film are coated or impregnated with adhesive, such as epoxy resin-type adhesive. For example, this is manufactured by Solvay under the serial number... 309-1 Adhesives sold.

[0051] The adhesive film has, for example, a thickness between 0.1 mm and 0.2 mm. The adhesive film can be in the form of a strip. Therefore, the adhesive film can have an elongated shape, the dimensions of which vary with the size of the cover 22.

[0052] The shield 22 typically has a dihedral shape and defines a V-shaped groove into which the edge of the preform is inserted.

[0053] The adhesive film is preferably adhered to the cover 22 within the groove.

[0054] Then, another operation of the method (a3) ​​includes positioning the preform equipped with the adhesive film and the cover 22 in the mold 30. Figure 3 Then, for example, use a reverse mold to close mold 30.

[0055] The consecutive operations a1) to a3) represent the first step a) of the manufacturing method.

[0056] In the second step b) of the method, resin is injected into mold 30, and the resin is intended to impregnate the preform and bring it into contact with the adhesive film and the shield 22. After the resin polymerizes and cures, the shield 22 is attached to the impeller via the adhesive film and the resin.

[0057] After the resin is polymerized, the resulting blade 10 has the advantage that the shroud 22 of the blade is perfectly positioned and held on the impeller 12.

[0058] Figure 4 The invention is shown to have features related to the time of resin injection into the mold.

[0059] Figure 4 It is a graph that includes three curves, C1, C2 and C3.

[0060] Curve C1 represents the change in resin viscosity over time. Curve C2 represents the change in adhesive viscosity over time, and curve C3 represents the change in mold temperature over time.

[0061] In practice, curve C1 depends on the resin used. The resin is injected at time T0 and experiences a decrease in viscosity. Then, the viscosity of the resin increases due to polymerization and reaches the gel point G1 at T1. For example, the resin is injected at a pressure between 5 bar and 15 bar and continues for approximately 120 minutes.

[0062] The temperature of mold 30 (curve C3) is adjusted according to the resin to optimize resin polymerization. The temperature is gradually increased from time T2 until a threshold is reached at T3 at a temperature greater than or equal to 160°C, which corresponds to the resin polymerization temperature. This threshold is maintained until T4, and then the temperature is increased from T4 to T5 until a new threshold is reached at a temperature greater than or equal to 180°C.

[0063] T3 occurs earlier than T0, meaning the threshold temperature is reached at 160°C before the resin is injected into the mold. Furthermore, T4 and T5 occur before T1. Therefore, the resin's gel point G1 occurs during the second temperature threshold period.

[0064] Curve C2 depends on the adhesive used. The adhesive viscosity begins to decrease from T2, i.e., from the heating of the mold. Then, the viscosity begins to increase from T6 and continues to rise past the gel point G2 at T7. T7 lies between T3 and T4. The glass transition V1 of the adhesive is reached at T8. T8 is later than T5 but earlier than T1.

[0065] According to the present invention, resin is injected into the mold within a time interval ΔT around the gel point G2 of the adhesive. This time interval ΔT is... Figure 4 The rectangle is defined by double lines. Therefore, it can be understood that, advantageously, the resin is injected into the mold during a period when the adhesive viscosity is not too high. This ensures optimal co-bonding between the adhesive and the resin.

[0066] In the example shown, times T0 and T7 coincide, meaning that resin injection occurs or begins at the gel point G2 of the adhesive.

Claims

1. A method for manufacturing a turbine blade (10) made of composite material, the blade comprising a vane (12) having a pressure side (14) and a suction side (16) extending from a leading edge (12a) to a trailing edge (12b) of the vane, the vane further comprising a metal shroud (22) extending along the leading edge of the vane, the method comprising: A preform made of three-dimensional woven fibers is arranged in a mold (30), the metal shield is positioned on the edge of the preform for forming the leading edge of the blade, and a polymerizable adhesive (24) is inserted between the metal shield and the edge of the preform. A polymerizable resin is injected into the mold to impregnate the preform, thereby forming the blade after curing. The resin is characterized by being injected during a time period during which the adhesive reaches its gel point, such that injection begins before the gel point of the adhesive and stops after the adhesive reaches its gel point.

2. The method according to claim 1, wherein, The adhesive (24) is in the form of an adhesive film.

3. The method according to claim 1 or 2, wherein, In the middle of the time period, the adhesive reaches the gel point.

4. The method according to claim 3, wherein, The time period begins at least five minutes before the adhesive reaches the gel point and ends at least five minutes after the adhesive reaches the gel point.

5. The method according to claim 1 or 2, wherein, The temperature of the mold is adjusted so that the temperature of the mold remains constant during the time period.

6. The method according to claim 5, wherein, The temperature of the mold is maintained at at least 160°C during the time period.

7. The method according to claim 1 or 2, wherein, The resin is epoxy resin.

8. The method according to claim 1 or 2, wherein, The adhesive is an epoxy adhesive.

9. The method according to claim 1, wherein, The turbine in question is a turbine used in aircraft.

10. The method according to claim 2, wherein, The adhesive (24) is in the form of a double-sided adhesive film.

11. The method according to claim 4, wherein, The time period begins ten minutes before the adhesive reaches the gel point and ends ten minutes after the adhesive reaches the gel point.

12. A method for manufacturing a turbine blade made of a composite material, the blade having a vane having a pressure side and a suction side extending from a leading edge to a trailing edge of the vane, the blade further having a metal shroud extending along the leading edge of the vane, the method comprising: Obtain a preform made of three-dimensional woven fibers in a mold; Position the metal shield on the edge of the leading edge of the preform used to form the blade; A polymerizable adhesive is disposed between the metal shield and the edge of the preform, the adhesive having a gel point; Arrange the preform, the metal shield, and the adhesive into the mold; as well as Before the gel point of the adhesive, a polymerizable resin is injected into the mold to impregnate the preform, so as to form the blade after curing. The resin is characterized by being injected continuously over a period of time during which the adhesive reaches the gel point.

13. The method according to claim 12, wherein, The adhesive is in the form of an adhesive film, and the adhesive film is disposed in a groove in the metal shield, the groove being configured to receive the edge of the preform.

14. The method according to claim 12, wherein, The time period begins at least five minutes before the adhesive reaches the gel point and ends at least five minutes after the adhesive reaches the gel point.

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