Patent Publication Number: US-2020276641-A1

Title: Method for manufacturing a cellular core for an acoustic panel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/FR2018/052159, filed on Sep. 4, 2018, which claims priority to and the benefit of FR 17/58216 filed on Sep. 6, 2017. The disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to a method for manufacturing a cellular core for an acoustic panel. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     An aircraft is propelled by one or several propulsion unit(s) each comprising a turbojet engine/turboprop housed within a tubular nacelle. Each propulsion unit is attached to the aircraft by a pylon generally located below a wing or at the level of the fuselage. 
     A nacelle generally has a structure comprising an air inlet upstream of the engine, a middle section intended to surround a fan of the turbojet engine, a downstream section accommodating thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and generally terminates in an ejection nozzle whose outlet is located downstream of the turbojet engine. 
     The air inlet comprises, on the one hand, an air inlet lip adapted to enable the optimum collection towards the turbojet engine of air desired for feeding the fan and the inner compressors of the turbojet engine, and on the other hand, a downstream structure on which the lip is affixed and intended to channel air towards the blades of the fan. The set is attached upstream of a casing of the fan belonging to the upstream section of the nacelle. 
     In flight, depending on the temperature and humidity conditions, ice may form on the nacelle, in particular at the level of the outer surface of the air inlet lip. The presence of ice or frost modifies the aerodynamic properties of the air inlet and disturbs the channeling of air towards the fan. In addition, the formation of frost on the air inlet of the nacelle and the ingestion of ice by the engine in case of detachment of ice blocks may damage the engine, and threaten the safety of the flight. 
     A solution for deicing the outer surface of the air inlet lip consists in avoiding that ice forms on this outer surface by maintaining the concerned surface at a sufficient temperature. 
     Thus, it is known, for example from the U.S. Pat. No. 4,688,757, to collect hot air at the level of the compressor of the turbojet engine and to bring it at the level of the air inlet lip in order to heat up the outer surface of the lip. 
     Also, it is known to equip the air inlet lip of the nacelle with an acoustic panel adapted to absorb a portion of the noise emitted from the inside of the nacelle towards the outside of the nacelle. 
     Typically, the acoustic panel comprises a perforated acoustic skin which is arranged opposite the air inlet flow path of the nacelle and a cellular core which is assembled on the acoustic skin. 
     The cellular core comprises a plurality of acoustic cells, forming Helmholtz resonators, which are separated from one another by peripheral partition walls. 
     The acoustic cells extend across the thickness from a front end bearing on the acoustic skin, up to a rear end sealed by a rear face. 
     The cellular core is generally made flat and has a high mechanical resistance to compression and to bending, which makes the forming of the acoustic panel difficult, in particular to form the acoustic panel according to the geometry of an air inlet lip of a nacelle. 
     The document WO 2009/081020 describes and represents a structure for acoustic treatment which integrates both an acoustic treatment and a deicing treatment. 
     According to this document, the structure comprises an acoustic skin, a cellular core comprising strips of cells, a reflective skin and a plurality of channels which are interposed between the cells and which are intended to channel the hot air of a deicing system. 
     It should be noted that the channels and the strips of cells form distinct subassemblies which are manufactured independently and which are assembled together. 
     The manufacture of such a structure turns out to be time-consuming and expensive. 
     In addition, the strips of cells that form the cellular core do not seem to have a high mechanical strength, the cellular core therefore barely contributes to the mechanical strength of the air inlet lip. 
     SUMMARY 
     This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all of its features. 
     The present disclosure relates to a method for manufacturing a cellular core for an acoustic panel, the cellular core comprising at least: 
     a plurality of acoustic cells each being delimited by peripheral longitudinal partition walls and by peripheral transverse partition walls, the acoustic cells extending vertically across the thickness from an open front end intended to bear vertical on an acoustic skin, up to a rear end sealed by a rear face, and 
     a plurality of deicing channels which extend longitudinally, each deicing channel being interposed transversely between two successive cells, the deicing channels being adapted to channel a deicing fluid, 
     characterized in that it comprises a manufacturing step which consists in making the acoustic cells and the deicing channels integrally in one-piece, the cellular core thus manufactured during the manufacturing step forming an integral part. 
     An integral cellular core can offer a high mechanical strength, or conversely the integral cellular core can be flexible so as to conform to a complex shape, depending on the material used for the manufacture thereof and depending on needs. 
     In addition, the present disclosure allows making simultaneously, in one single manufacturing step, both the channels and the cells of the cellular core, in order to reduce the manufacturing cycle of an acoustic panel. 
     According to a first form of the present disclosure, each deicing channel extends longitudinally from a front end of the longitudinal partition walls of the cells. 
     According to this first form, the manufacturing step is an additive manufacturing step. 
     According to a second form, each deicing channel is interposed between a first longitudinal partition wall of a first acoustic cell and a second longitudinal partition wall of a second acoustic cell, said acoustic cells being directly adjacent, the acoustic cells and the deicing channels being designed without any undercut face. 
     This feature allows making the cellular core by molding in one single manufacturing step. 
     According to a third form, each deicing channel is delimited by a rear face which is flush with the rear face of the acoustic cells. 
     This feature allows facilitating the demolding of the cellular core. 
     According to the second and third forms, the manufacturing step is a step of manufacturing by molding. 
     According to another feature, the manufacturing step is a step of manufacturing by deformation of a sheet metal. 
     According to another feature, the material used for the manufacture of the cellular core during the manufacturing step is a substantially elastically-deformable material adapted to facilitate demolding and to enable the cellular core to conform to complex shapes. 
     According to another feature, the manufacturing step consists in making the cellular core shaped as a sector of a rotationally-symmetric part. 
     This feature allows obtaining the final shape of the cellular core and allows getting rid of a step of forming the cellular core. 
     According to another feature, the method comprises an assembly step which consists in assembling the cellular core on a front acoustic skin, to form an acoustic panel. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
         FIG. 1  is a schematic longitudinal sectional view, which illustrates a turbojet engine nacelle comprising an air inlet lip equipped with an acoustic panel made according to the manufacturing method according to the present disclosure; 
         FIG. 2  is a schematic detail longitudinal sectional view, which illustrates the acoustic panel of  FIG. 1  integrated into the air inlet lip; 
         FIG. 3  is a schematic detail perspective view which illustrates the acoustic panel of  FIG. 1  forming an angular sector; 
         FIG. 4  is a schematic sectional and perspective view which illustrates a portion of the acoustic panel of  FIG. 1  according to a first form of the present disclosure; 
         FIG. 5  is a schematic sectional and perspective view which illustrates a portion of the acoustic panel of  FIG. 1  according to a second form of the present disclosure; and 
         FIG. 6  is a schematic sectional and perspective view which illustrates a portion of the acoustic panel of  FIG. 1  according to a third form of the present disclosure. 
     
    
    
     The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     In the description and the claims, the expressions “front” and “rear” will be used in a non-limiting manner respectively with reference to the lower portion and to the upper portion of  FIGS. 4 to 6 . 
     In addition, in order to clarify the description and the claims, the terminology longitudinal, vertical and transverse will be adopted locally and in a non-limiting manner with reference to the trihedron L, V, T indicated in  FIGS. 4 to 6 , whose axis L is parallel to the axis A of the nacelle. 
     It should be noted that the vertical axis V extends generally radially with respect to the longitudinal axis A of the nacelle and the transverse axis T extends generally tangentially with respect to the longitudinal axis A of the nacelle. 
     In addition, in order to facilitate the understanding of the description, the acoustic panel portions illustrated in  FIGS. 4 to 6  are represented planar, without taking into account the radius of curvature of the acoustic panel in its entirety. 
     In all of these figures, identical or similar reference numerals represent identical or similar members or sets of members. 
     In  FIG. 1 , there is represented a nacelle  10  with a generally annular shape which extends around a longitudinal axis A. 
     The nacelle  10  comprises an air inlet  12  upstream of the engine  14 , a middle section  16  intended to surround a fan  18  of the turbojet engine, a downstream section  20  accommodating thrust reversal means and intended to surround the combustion chamber of the turbojet engine, and an ejection nozzle  22  whose outlet is located downstream of the turbojet engine. 
     As shown in  FIG. 2 , the air inlet  12  comprises an air inlet lip  24  which forms an annular shaped volume around the axis A of the nacelle  10 , having a “D” shaped section. 
     The air inlet lip  24  is delimited by an upstream outer wall  26  to be deiced, forming a leading edge, and a downstream partition wall  28  which separates the volume delimited by the air inlet lip  24  and the section of the nacelle  10  that is connected on the lip  24 . 
     The lip  24  is equipped with an acoustic panel  30  which comprises a perforated front acoustic skin  32  which forms a portion of the outer wall  26  of the lip  24  and a cellular core  34 . 
     Referring to  FIG. 4 , the cellular core  34  comprises a plurality of acoustic cells  36  which are bonded to one another and which are arranged in a checkerboard-like fashion. 
     Each of the cells  36  has a generally parallelepiped shape and each is delimited by two peripheral longitudinal partition walls  38  facing each other and by two peripheral transverse partition walls  40  facing each other. 
     Also, the acoustic cells  36  extend vertically, or radially, across the thickness from an open front end  42  which bears vertical on the acoustic skin  32 , up to a rear end  44  sealed by a rear face  46  of the associated cell  36 . 
     In order to allow channeling a deicing fluid, such as hot air for example, the cellular core  34  comprises a plurality of deicing channels  48  which extend longitudinally. 
     Each deicing channel  48  is interposed transversely between two successive cells  36 . 
     As shown in  FIG. 2 , each channel  48  has a hot air inlet  52  which is connected to a hot air source, in the vicinity of the partition wall  28  of the lip, and a hot air outlet  54  which opens in the vicinity of the leading edge of the lip  24 , such that the passage of the hot air through the channels heats up the outer wall of the lip  24  which is arranged under the channels  48 . 
     The circulation of the hot air in the lip  24  is illustrated by arrows in  FIG. 2 . 
     The manufacturing method according to the present disclosure comprises a manufacturing step which comprises in making the acoustic cells  36  and the deicing channels  48  integrally in one-piece, the cellular core  34  thus manufactured during the manufacturing step forming an integral part. 
     According to a first form of the present disclosure illustrated in  FIG. 4 , each deicing channel  48  extends longitudinally from a front end  56  of the longitudinal partition walls  38  of the cells  36 , each channel  48  connecting all of the longitudinal partition walls  38  which are aligned so as to form a row. 
     Each channel  48  has a half-circle like cross-section, which has two longitudinal edges  58  bearing on the acoustic skin  32  and a convex central portion  60  from which extends the longitudinal partition wall  38  of the associated cell  36 . 
     In a non-limiting manner, the cross-section of the channels  48  may have a triangular shape to facilitate an additive-type manufacture. 
     According to this first form, the step of manufacturing the cellular core  34  is a step of additive manufacturing by material addition. For example, the cellular core  34  is made of an aluminum alloy. 
     The additive manufacture is also known by the expression “three-dimensional printing” or “3D printing”. 
     The additive manufacturing step allows making integrally in one-piece the cellular core  34  which comprises the cells  36  formed by the partition walls  38 ,  40  and by the rear face  46 , and the channels  48 . 
     Referring to  FIG. 3 , the integral cellular core  34  obtained following the manufacturing step is shaped as a sector of a rotationally-symmetric part about the axis A of the nacelle  10 , whose generatrix G illustrated in  FIG. 3 , shaped as a curved rectangle, conforms to the curvature of the air inlet lip  24 . 
     Thus, the cellular core  34  perfectly conforms to the shape of the lip  24  and of the acoustic skin  32 , without any additional forming step. 
     According to a second form of the present disclosure illustrated in  FIG. 5 , each deicing channel  48  extends longitudinally and is interposed between a first longitudinal partition wall  38  of a first acoustic cell  36  and a second longitudinal partition wall  38  of a second acoustic cell  36 , said acoustic cells  36  being directly adjacent transversely, such that the acoustic cells  36  and the deicing channels  48  are designed without any undercut face. 
     By “without any undercut face”, it should be understood that the rear face formed by the cells  36  and the channels  48  are adapted to enable the removal from a manufacturing mold. Similarly, the front face formed by the cells  36  and the channels  48  is adapted to enable the removal from a manufacturing mold. 
     Each channel  48  has a half-circle like cross-section, which has two longitudinal edges  58  bearing on the acoustic skin  32 . 
     The two longitudinal edges  58  of each channel  48  are common to the front ends edges of the longitudinal partition walls  38  of the associated cells  36 . 
     According to this second form, the step of manufacturing the cellular core  34  is a step of manufacturing by injection molding of a flexible polymer, the cellular core  34  being designed so as to be substantially deformed in order to conform to the curves of the air inlet lip  24  and to facilitate the demolding of the cellular core  34 . 
     Thus, the cellular core  34  may be molded into a generally planar shape, to facilitate demolding. 
     In addition, manufacturing in a polymer enables the use of a material suited to the external environment and without any risk of galvanic coupling with another metallic part. 
     Still according to this second form, the cellular core  34  is made of silicone for example. 
     In a non-limiting manner, according to this second form, the cellular core  34  may also be made by injection molding of a metal, which method is known under the acronym MIM standing for “Metal Injection Molding”. 
     Similarly, in a non-limiting manner, the cellular core  34  may be made of polyether ether ketone (also referred to as PEEK), or of Polyphenylene Sulfide, for example, despite the fact that these materials are not flexible. 
     In addition, according to this second form, the cellular core may also be made by stamping of a sheet metal. 
     According to a third form of the present disclosure illustrated in  FIG. 6 , each deicing channel  48  extends longitudinally and is interposed between a first longitudinal partition wall  38  of a first acoustic cell  36  and a second longitudinal partition wall  38  of a second acoustic cell  36 , said acoustic cells  36  being directly adjacent transversely. 
     In addition, according to this third form, each deicing channel  48  is delimited by a rear face  62  which is flush with the rear face  46  of the acoustic cells  36 . 
     Thus, the rear face of the cellular core  34  is generally planar, which facilitates the demolding of the cellular core  34 . 
     Also, according to the three forms described hereinabove, the material used for the manufacture of the cellular core  34  during the manufacturing step is a material which is adapted to withstand a high temperature in order to withstand the passage of the hot air, for example a temperature close to 180 degrees Celsius. 
     In addition, the method for manufacturing the cellular core comprises an assembly step, which is common to the three previously-described forms and which consists in assembling the cellular core  34  on the acoustic skin  32 , to form the acoustic panel  30 . 
     For example, the assembly step is carried out by gluing, by soldering or by welding, depending on the material used to make the cellular core  34 . 
     The present description of the present disclosure is provided as a non-limiting example. 
     Unless otherwise expressly indicated herein, all numerical values indicating mechanical/thermal properties, compositional percentages, dimensions and/or tolerances, or other characteristics are to be understood as modified by the word “about” or “approximately” in describing the scope of the present disclosure. This modification is desired for various reasons including industrial practice, material, manufacturing, and assembly tolerances, and testing capability. 
     As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A OR B OR C), using a non-exclusive logical OR, and should not be construed to mean “at least one of A, at least one of B, and at least one of C.” 
     The description of the disclosure is merely exemplary in nature and, thus, variations that do not depart from the substance of the disclosure are intended to be within the scope of the disclosure. Such variations are not to be regarded as a departure from the spirit and scope of the disclosure.