FR3074444A1 - METHOD FOR MANUFACTURING AN ORDINARY ORDER OF ACOUSTIC CHANNELS IN ABRADABLE MATERIAL - Google Patents

Abstract

A method of manufacturing an ordered array (10) of acoustic channels, the method of depositing on a substrate surface (12) a filament of a thermosetting material while simultaneously providing relative displacement between the substrate and the filament in a defined deposition path and solidification of the filament to create a three-dimensional scaffold of filaments, the thermosetting material being a thixotropic solvent-free mixture of a polymer base and a crosslinking agent in a weight ratio of polymeric base to the crosslinking agent of between 1: 1 and 2: 1, and a flow facilitating component, typically a petroleum jelly has between 5 and 15% by weight of the total weight of said thixotropic mixture.

Description

Invention background

The present invention relates to the general field of the manufacture of parts made of polymeric materials, in particular thermosetting, of metal parts, of metal alloy or of ceramic by additive manufacturing and it relates more particularly, but not exclusively, to the manufacture of an abradable coating turbomachine wall such as an airplane turbojet.

The control of noise pollution caused by airplanes around airports has become a public health issue. Increasingly stringent standards and regulations are being imposed on aircraft manufacturers and airport managers. Therefore, building a silent aircraft has become a selling point over the years. Currently, the noise generated by aircraft engines is attenuated by acoustic coatings with localized reaction which make it possible to reduce the sound intensity of the engine over one or two octaves on the principle of Helmholtz resonators, these coatings conventionally occurring under the form of composite panels composed of a rigid plate associated with a honeycomb core covered with a perforated skin and arranged at the level of the nacelle or the upstream and downstream propagation conduits. However, in new generation engines (for example in turbofans), the areas available for acoustic coatings are reduced considerably as in UHBR (Ultra-High-BypassRatio) technology.

It is therefore important to propose new processes and / or new materials (in particular porous materials) making it possible to eliminate or significantly reduce the level of noise produced by aircraft engines, especially during the takeoff phases and landing and over a wider frequency range than currently including low frequencies while maintaining engine performance. This is the reason why today we are looking for new acoustic treatment surfaces and this with a minimal impact on other engine functions such as specific fuel consumption which constitutes an important commercial advantage.

In addition, it is now common and advantageous to use additive manufacturing processes instead of traditional foundry, forging or mass machining processes to easily, quickly and inexpensively produce complex three-dimensional parts. The aeronautical field also lends itself particularly well to the use of these processes. Among these, there may be mentioned in particular the process of direct energy deposition by wire (Wire Beam Deposition).

Subject and summary of the invention

The present invention therefore aims to provide a method of shaping a new material, which can significantly reduce the noise generated by aircraft turbojets. The control of the parameters of the material allows a reduction of the noise on a range going from low to high frequencies. The products resulting from this method are intended to be mounted on a wall of a turbojet engine in contact with a fluid flow and more particularly in place of an abradable cartridge of a fan casing.

To this end, there is provided a method of manufacturing an ordered network of acoustic channels, the method consisting in depositing on a substrate surface a filament of a thermosetting material while ensuring both a relative displacement between said substrate and said filament according to a determined deposition trajectory and a solidification of said filament in order to create a three-dimensional scaffolding of filaments, characterized in that said thermosetting material is a thixotropic mixture devoid of solvent and consisting of a polymer base and of a crosslinking agent in a weight ratio of said polymer base to said crosslinking agent of between 1: 1 and 2: 1, and of a flow-facilitating component, typically a petroleum jelly present between 5 and 15% by weight by weight total of said thixotropic mixture.

Thus, a porous microstructure with regular and orderly porosity is obtained which ensures significant absorption of the acoustic waves by visco-thermal dissipation within the channels while retaining its abradable nature due to the material constituting it.

Preferably, said thixotropic mixture is obtained by coextrusion of said components in a conical extrusion screw and deposited on said substrate surface by means of an ejection nozzle of calibrated shape and size, the outlet section of which has a greater width. less than 250 microns.

Advantageously, the relative movement between said substrate and said cylindrical filament is ensured by a machine at least three axes or a robot controlled from a computer and the solidification of said cylindrical filament is ensured by a heating element mounted at the outlet of said ejection nozzle. calibrated.

According to the embodiment envisaged, said three-dimensional scaffolding can be constituted:

• superimposed layers whose filaments of a given layer are oriented alternately at 0 ° or 90 ° without offset in the superposition of filaments in the same direction;

• superimposed layers whose filaments of a given layer are oriented alternately at 0 ° or 90 ° having an offset in the superposition of filaments in the same direction;

• superimposed layers having directions of orientation of the filaments Di offset by the same angular deviation, between 20 ° and 40 °, typically 30 °, at each layer i;

• or superimposed layers of filaments having, for each of the layers, both an orientation of filaments at 0 ° and an orientation of filaments at 90 °, so as to form vertical perforations of square sections between the filaments.

The invention also relates to the ordered network of acoustic channels obtained from the aforementioned method and to the abradable coating of the wall of a turbomachine comprising this network.

Brief description of the drawings

Other characteristics and advantages of the present invention will emerge from the detailed description given below, with reference to the following figures which are devoid of any limiting nature and in which:

FIG. 1 illustrates in exploded perspective the mounting of a three-dimensional scaffolding of filaments of abradable material according to the invention,

FIG. 2 illustrates the filament deposition system for the construction of the three-dimensional scaffolding of FIG. 1, and

FIGS. 3A to 3D show four examples of three-dimensional scaffolds having acoustic properties.

Detailed description of the invention

The method according to the invention allows the printing of an abradable material on a substrate in order to achieve a three-dimensional scaffolding of filaments forming between them an ordered network of channels having acoustic properties.

By abradable material is meant the ability of the material to dislocate (or erode) in operation when it comes into contact with a facing part (low shear strength) and its resistance to wear following the impact of particles or foreign bodies that it has to take in operation (compromised with abradability). Such a material must also keep or even promote good aerodynamic properties (roughness criterion: Ra on surface condition), have sufficient resistance to oxidation and corrosion and a coefficient of thermal expansion of the same order as the layer or the substrate on which it is deposited.

FIG. 1 illustrates in exploded perspective part of a three-dimensional scaffolding 10 of filaments 100, 200, 300, advantageously cylindrical, of an abradable material allowing, in accordance with the invention, the production of a coating in the form of an ordered network of channels capable of imparting acoustic properties to a wall (the substrate) 12 intended to receive this coating. Depending on the network configuration envisaged, interconnections between the channels may exist regularly during the superposition of the different layers of the abradable material intended to generate these different channels. This wall is preferably, without this being limiting, a wall of a turbomachine such as an airplane turbojet engine and more particularly a 3D woven composite casing disposed on the periphery of the fan blades and usually intended to receive a cartridge of abradable.

The printing of such an ordered network of channels is carried out by additive manufacturing according to the method described below with reference to FIG. 2. This printing requires precision equipment making it possible to control the deposition of the abradable material and thus ensure tolerancing final dimensional. This requires at least a 3-axis machine of the ABG10000 type from Aerotech Incorporation or a robot with precision "digital axes" (positioning on the order of 5 microns) allowing, via appropriate software, to control the printing according to a user-defined deposition trajectory. Thanks to this equipment, it is therefore possible to guarantee a precise deposit of filaments in a determined three-dimensional space, by controlling the printing parameters such as the speed of flow of the material, the position and speed of displacement of the printing.

As shown in FIG. 2, a filamentary deposition system, at least a 3-axis machine or a robot 20, preferably deposits, in connection with a pressure and temperature control circuit internal to the system, the material abradable by extrusion via a ejection nozzle 22 of shape and size calibrated first on the substrate 12 and then successively on the various superimposed layers created in succession until the desired thickness is obtained. The filament deposition system follows a deposition path controlled by a calculator (computer or microcontroller 24) to which it is connected ensuring control of the filament deposition system and controlling at all points of the treated surface both the filament arrangement and the porosity of the medium necessary to guarantee the desired abradability.

The supply of abradable material is ensured from a conical extrusion screw 26 making it possible to mix several components to form a thixotropic mixture having the appearance of a paste. The conical extrusion screw which has at least two separate inlets 26A, 26B for the simultaneous introduction of at least two components makes it possible to ensure an adequate and homogeneous mixing of the components throughout the deposition operation, to obtain ultimately a fluid material with high viscosity which will be deposited by the calibrated ejection nozzle 22 whose outlet section in its greatest width is less than 250 microns. During this operation, avoid the generation of air bubbles which form as many defects in the filament during printing and it is therefore necessary to push the material very gradually while controlling the pressure in the nozzle. ejection and its speed of movement, so as to obtain a filament whose section is uniform and the position conforms. It will be noted that by checking the components introduced into the conical extrusion screw, it is possible to change the constitution of the material deposited.

A heating lamp 28 or any similar device can be mounted at the outlet of the ejection nozzle 22 to stabilize the material deposited and to prevent creep during deposition. The abradable material is deposited up to a specified thickness. To accelerate the deposition of the material, the filamentary deposition system 20 can comprise several independently adjustable nozzles or include a multi-nozzle of calibrated diameter such as that described in the application US 2017/203566.

This gives a controlled deposition of abradable material in the thickness and on the surface allowing the abradable to be functionalized in particular with a view to giving it acoustic properties.

For this, the ordered network of channels advantageously has a scaffolding having one of the configurations illustrated in FIGS. 3A, 3B, 3C and 3D, namely:

In FIG. 3A, a three-dimensional scaffolding of filaments 100, 200 consists of superimposed layers, the filaments of a given layer being oriented alternately at 0 ° or 90 ° without offset in the superposition of filaments in the same direction.

In FIG. 3B, a three-dimensional scaffolding of filaments 100, 200 consists of superimposed layers, the filaments of a given layer being oriented alternately at 0 ° or 90 ° and have an offset in the superposition of the filaments in the same direction . This offset is, as illustrated, preferably equal to half the distance between two filaments.

It will be noted that for these two configurations the angular difference between the two directions of filaments can be different and less than 90 °, for example 45 °.

In FIG. 3C, a three-dimensional scaffolding of filaments 100, 200, 300, 400, 500, 600 consists of superimposed layers having directions of orientation of the filaments Di offset by the same angular deviation, between 20 ° and 40 ° , typically 30 °, at each layer i (i between 1 and 6 for an angular difference of 30 °).

And in FIG. 3D, a three-dimensional scaffolding of filaments 100, 200 consists of superimposed layers of filaments having, for each of the layers, both an orientation of filaments at 0 ° and an orientation of filaments at 90 °, so that forming vertical perforations 700 of square sections between the filaments.

An impression on a housing sector with these different structures showed the feasibility of such a robotic deposition of abradable material according to the aforementioned additive manufacturing process. Mechanical behavior tests in compression and bending were also carried out as well as samples intended for a low energy impact test or for a characterization of the acoustic impedance in normal incidence.

In particular, it has been observed that the acoustic energy is transmitted through the scaffolding and that part of this acoustic energy has been absorbed by modification of the aero-acoustic sources or absorption of the propagating sound waves.

The abardable material extruded by the calibrated nozzle (s) is advantageously a thermosetting material with high viscosity (also called fluid) which is devoid of solvent, the evaporation of which generates, as is known, a strong shrinkage. This material is preferably a resin with slow polymerization kinetics and stable filamentary flow in the form of a thixotropic mixture which therefore has the advantage of a much lower shrinkage between printing on the substrate (just after extrusion of the material) and the final structure (once heated and complete polymerization).

An example of an abradable material used within the framework of the process is a material in pasty form and consisting of three components, namely a polymer base, for example an epoxy resin (presenting itself as a blue plasticine), a crosslinking agent. or accelerator (presenting itself as a white plasticine) and a translucent petroleum jelly (for example vaseline ™). The accelerator / base components are distributed according to a weight ratio of the base to the accelerator of between 1: 1 and 2: 1 and the petroleum jelly present between 5 and 15% (typically 10%) by weight of the total weight of the material. . The base may also include microspheres of hollow glasses of a determined diameter to ensure the desired porosity while making it possible to increase the mechanical performance of the printed scaffolding. The advantage of the introduction of petroleum jelly lies in the reduction in the viscosity of the resin as well as in the reaction kinetics of the abradable, which makes its viscosity more stable during the time of printing. (The viscosity is directly related to the extrusion pressure necessary to ensure the adequate extrusion speed to maintain the quality of the print).

For example, such a ratio of 2: 1 gives an abradable material comprising 0.7g of accelerator and 1.4g of base, to which 0.2g of petroleum jelly should be added.

Thus, the present invention allows rapid (30mm / s) and stable printing allowing effective reproduction of controlled efficient acoustic structures (roughness, appearance, opening rate) having a small filament size (<250 microns in diameter) and a low weight (improved porosity rate> 70%) particularly interesting in view of the severe constraints encountered in aeronautics.

Claims (10)

1. A method of manufacturing an ordered network (10) of acoustic channels, the method consisting in depositing on a substrate surface (12) a filament (100, 200, 300) of a thermosetting material while ensuring both a relative displacement between said substrate and said filament according to a determined deposition trajectory and a solidification of said filament in order to create a three-dimensional scaffolding of filaments, characterized in that said thermosetting material is a thixotropic mixture devoid of solvent and consisting of a polymer base and of a crosslinking agent in a weight ratio of said polymer base to said crosslinking agent of between 1: 1 and 2: 1, and of a flow-facilitating component, typically a petroleum jelly present between 5 and 15% by weight of the total weight of said thixotropic mixture. 2. Manufacturing method according to claim 1, characterized in that said thixotropic mixture is obtained by co-extrusion of said components in a conical extrusion screw (26) and deposited on said substrate surface (12) by means of a ejection nozzle of calibrated shape and dimension (22), the outlet section of which has a greater width of less than 250 microns. 3. Manufacturing process according to claim 1 or claim 2, characterized in that the relative movement between said substrate and said filament is provided by a machine at least three axes or a robot (20) controlled from a computer (24). 4. Manufacturing method according to any one of claims 1 to 3, characterized in that the solidification of said filament is ensured by a heating element (28) mounted at the outlet of said calibrated ejection nozzle. 5. Manufacturing method according to any one of claims 1 to 4, characterized in that said three-dimensional scaffolding of filaments consists of superimposed layers whose filaments of a given layer (100, 200) are oriented alternately at 0 ° or at 90 ° without offset in the superposition of filaments in the same direction. 6. Manufacturing method according to any one of claims 1 to 4, characterized in that said three-dimensional scaffolding of filaments consists of superimposed layers whose filaments of a given layer (100, 200) are oriented alternately at 0 ° or at 90 ° and have an offset in the superposition of the filaments in the same direction. 7. The manufacturing method according to any one of claims 1 to 4, characterized in that said three-dimensional scaffolding of filaments consists of superimposed layers of filaments (100, 200, 300, 400, 500, 600) having directions of orientation of the filaments Di offset by the same angular deviation, between 20 ° and 40 °, typically 30 °, at each layer i. 8. Manufacturing method according to any one of claims 1 to 4, characterized in that said three-dimensional scaffolding of filaments consists of superposed layers of filaments (100, 200) having, for each of the layers, both an orientation of filaments at 0 ° and an orientation of filaments at 90 °, so as to form vertical perforations (700) of square sections between the filaments. 9. Ordered network of acoustic channels obtained from the manufacturing process according to any one of claims 1 to 8. 10. Abradable coating of a turbomachine wall comprising an ordered network of acoustic channels according to claim 9.