Hollow side member for manufacturing a composite blade with resin injection

Abstract

The invention relates to a spar (82) for a turbomachine blade, comprising a body (85) elongated along a principal axis (Z) along which it comprises a first portion (86) configured to be inside a blade of the blade (58), and a second portion (67) configured to be outside the blade (62) and to form a root (66) of the blade (58), characterized in that the body (85) comprises a cavity (98) which opens into an external surface (100) of said first portion (86) through an opening (102), and a plug (104) received in the cavity (98) and closing the opening (102) which delimits a first conduit (106) of an internal cooling circuit (96) which comprises at least a second conduit (108) which passes through at least the second portion (67) and opens to the outside of the second portion. (67). Figure for the abstract: Figure 8

Description

Title of the invention: HOLLOW LEG FOR MANUFACTURE OF A COMPOSITE BLADE WITH RESIN INJECTION Technical field of the invention

[0001] The invention relates to a spar used in the manufacture of an aircraft turbomachine blade and a method for manufacturing such a spar. Technical background

[0002] The state of the art includes documents WO-2010 / 061139-A2 and FR-3.109.115-A1.

[0003] New generations of engines require blades with compact feet because their blades are designed to pivot around their radial axes to adapt their angle of attack to different flight regimes. This is the case, for example, in a ducted turbomachine, for the outlet guide vanes (OGVs) located downstream of the fan blades. It is also the case for the propeller blades of unducted, open-rotor turbomachines.

[0004] This feature adds to the need to attach the blade to the disc or hub that carries it as deeply as possible, that is, as close as possible to the axis of the disc or hub. It is therefore necessary to significantly reduce the overall size of the blade's base.

[0005] However, the operating blade is subjected to numerous stresses. Indeed, the blade root is primarily subjected to bending and tensile stresses, notably due to centrifugal forces on the blade and potential impacts with birds. Furthermore, the blade roots of "open rotor" type turbomachines can be subjected to alternating bending stresses caused by intense bending vibrations exerted on the blades due to the absence of a nacelle to control the airflow, as is usually the case on enclosed engines. In order to counteract these alternating bending moments, the roots are prestressed in the hub and are therefore subjected to an additional circumferential mechanical load.

[0006] The blades used in this type of application generally have blades made of a composite material in order to improve their thermomechanical resistance and reduce their mass. The composite material can be made from a preform obtained by three-dimensional (or 3D weaving) or two-dimensional (2D weaving) weaving of fibers. This weave is intended to form a fibrous reinforcement and is embedded in a matrix formed by injecting a resin during an RTM (resin transfer molding) or VARTM (vacuum assisted resin transfer molding) injection process.

[0007] Three-dimensional weaving is generally preferred in this type of application because it offers better resistance to delamination. The term "three-dimensional weaving" or "3D weaving" refers to a weaving method in which warp yarns are bonded to weft yarns in several layers. Preferably, but not exclusively, 3D weaving has an interlock structure (or reinforcement). Interlock weaving offers improved impact resistance, particularly compared to 2D weaving. Similarly, the preform is woven in a single piece.

[0008] The composite material can be monolithic or include a core, for example made of foam, to form a composite sandwich material. The latter provides rigidity and lightness to the final part. Indeed, the interposition of a cellular core, such as a honeycomb or foam, between two monolithic fibrous reinforcement skins or layers (densified by a resin or not impregnated with a resin) makes it possible, on the one hand, to considerably increase the flexural stiffness of the final part and, on the other hand, to simultaneously control the mass by introducing a low-density material in the core, where the mechanical load is low.

[0009] Finally, the blade has a cavity intended to receive a first part of a metal spar, a second part of which, external to the blade, forms the foot of the blade.

[0010] During its manufacture, the first part of the spar is coated with glue and then inserted into the blade preform. The assembly is then placed in a two-part mold, which is closed. The mold is then heated to an injection temperature that allows for good diffusion of the resin, generally an organic resin, into the fibers. In the case of a VARTM process, a vacuum is created in the mold, and then the resin is injected. This is followed by a consolidation step during which the mold is maintained at a curing temperature, generally higher than the injection temperature, to ensure the resin crosslinks.

[0011] This conventional design carries a risk of adhesive film thinning. Indeed, the vacuum created in the mold cavity at -1 bar (= -1 x 10⁵ Pa) and the concomitant decrease in viscosity of the adhesive film exposed to the temperature rise of the preform before consolidation tend to cause the adhesive to flow deeply into the fiber strands of the preform by capillary action. This dispersion of the adhesive, or thinning, within the preform reduces the thickness of the adhesive joint and compromises the bond between the spar and the preform.

[0012] Such dispersion is therefore to be avoided in the context of structural bonding. Summary of the invention

[0013] To overcome this drawback, it is proposed to cool the spar after it has been placed in the mold and throughout the resin injection process. Cooling the spar advantageously maintains it at a temperature lower than the injection temperature, thus preventing the adhesive from thinning and dispersing within the composite material of the preform. To achieve this, the invention provides a hollow spar that can be easily cooled.

[0014] To this end, the invention proposes a spar for a turbomachine blade, in particular for an aircraft, said spar comprising a body having an elongated shape along a principal axis and comprising along said principal axis a first part configured to be inside a blade of the blade, and a second part configured to be outside the blade of the blade and to form a root of the blade, characterized in that the body comprises a cavity which opens into an external surface of said first part by forming an opening, and in that the spar further comprises: - a plug which is fixed to the body, this plug being engaged in the cavity and closing the opening, and - an internal cooling circuit comprising at least a first conduit which is delimited between the plug and the walls of said cavity and at least a second conduit which communicates with said at least first conduit, which passes through at least the second part and which opens outside the second part.

[0015] According to other characteristics of the longeron: - said at least one second conduit is arranged near a median axis of the second part, - the longeron comprises at least two secondary conduits, each communicating with opposite ends of said at least one primary conduit, - said at least two secondary conduits open through orifices on the same internal face of the cavity, - the stopper comprises a operculum which seals the opening of the cavity, a pad which extends into the cavity from said operculum, and a rib which extends from said pad to the inner face of the cavity between said orifices, hermetically delimiting two chambers within the cavity, - at least one passage through said buffer puts said chambers in fluidic communication, - the inner face is opposite the opening, - the external surface of the first part is arranged substantially transversely with respect to the axis of the body, at an end of said body which is opposite its second part, According to a first embodiment of the invention, the pad comprises: two lateral edges arranged in a watertight manner in contact with the lateral surfaces of the cavity, the rib, joining the two lateral edges, light passing through said buffer and forming the passage, the stamp is plate-shaped, According to the second and third embodiments of the invention, the pad is of a shape complementary to the cavity and it comprises at least one helical groove which is cut into the periphery of the pad along a whole length of said pad, this helical groove comprising a first end opening opposite the operculum on a first side of the rib into a first of the two chambers, and a second end located near the operculum, The passage extends through the buffer and has a first end that communicates with the second end of the helical groove and a second end that communicates with a second of the two chambers. More particularly, in the second embodiment of the invention, the passage crosses the buffer along the entire length of the buffer and its second end opens opposite the operculum on a second side of the rib in the second of the two chambers, In the third embodiment of the invention, the pad comprises two helical grooves which are cut into its periphery, which are of the same pitch and which are arranged in a double helix arrangement along the entire length of the pad, and which comprise first ends which open opposite the operculum, each on one side of the rib respectively in the first and second chambers, and second ends located near the operculum, The passage crosses the buffer transversely and opens at its first and second ends into the second ends of the gutters. The operculum is formed in a lid that extends over the external surface of the first part, sealing the opening, said lid being glued to said external surface. The external surface of the first part is flat and machined, The cap is made of thermoplastic material, preferably by injection molding using additive manufacturing. The stopper is made by molding and machining a foam, in particular polymethacrylimide, having a density between 0.15 and 0.5 kg / m3, - the first part of the body and the cavity have respective cross-sections that are elongated transversely with respect to the main axis, - the sections of the first part of the body and the cavity have edges that are substantially homothetic to the intrados and extrados edges of the blade of the vane, - in the three embodiments of the invention, preferably, at least one first conduit extends only in the first part, at least one second conduit extends only in the second part, and at least one first conduit and at least one second conduit are connected at the junction of the first and second parts.

[0016] The present invention also relates to a blade for an aircraft turbomachine, comprising a blade and a foot, this blade comprising a spar as described above, a first part of which is inside the blade and a second part is outside the blade to form said foot.

[0017] The invention also relates to a method for manufacturing a spar for a turbomachine blade of the type described above, characterized in that it comprises the steps of: - A) supply of a plug, and supply of a spar blank having an elongated body along a principal axis and comprising along said axis a first part configured to form the first part of the spar body and a second part configured to form the second part of the spar body, said first part comprising a cavity which opens into an external surface of said first part by forming an opening, - B) machining of at least a second conduit until it opens into said cavity, - C) Insertion of the plug into the cavity, - D) fixing the cap to the body. Brief description of the figures

[0018] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the accompanying drawings in which: - [Fig.1] The [Fig.1] is a schematic axial cross-sectional view of an example of a turbomachine to which the invention applies; - [Fig.2] The [Fig.2] is a side view of a turbomachine blade according to the invention; - [Fig.3] The [Fig.3] is a detailed view of the foot of the dawn of the [Fig.2]; - [Fig.4] The [Fig.4] is a perspective view cut by a transverse plane of the dawn of the [Fig.2]; - [Fig.5] The [Fig.5] is a schematic view of a molding installation for molding a turbomachine blade using a spar according to the invention; - [Fig.6] The [Fig.6] is a cross-sectional view of the body of a spar according to the invention; - [Fig.7] The [Fig.7] is a side view of the plug of a first embodiment of a longitudinal member according to the invention; - [Fig.8] The [Fig.8] is a cross-sectional view of the first embodiment of a longitudinal member according to the invention; - [Fig.9] The [Fig.9] is a cross-sectional view of a second embodiment of a longeron according to the invention; - [Fig. 10] The [Fig. 10] is a cross-sectional view of a third embodiment of a longeron according to the invention; - [Fig. 11] The [Fig. 11] is a schematic view of the helical grooves and the passage of the plug of the third embodiment of the spar according to the invention; - [Fig. 12] The [Fig. 12] is a block diagram illustrating the manufacturing steps of a process for manufacturing a spar according to the invention; - [Fig. 13] The [Fig. 13] is a block diagram of a manufacturing process for a turbomachine blade comprising a spar according to the invention. Detailed description of the invention

[0019] The invention which will now be described here applies here to a spar for a turbomachine blade but it will be understood that it can be applied to any spar used in the manufacture of any type of parts which can be made of composite materials, without limitation of the invention.

[0020] A turbomachine 10 with longitudinal axis X is shown in the axial and partial cross-sectional view of [Fig. 1] which includes various components that can be made of composite materials, such as blades.

[0021] The turbomachine 10 of [Fig. 1] is, without limiting the scope of the invention, a twin-shaft turbomachine 10 with a doublet of counter-rotating propellers 12, 14 of the "open rotor" type, intended for mounting on an aircraft. The invention applies here, for example, to the blades of these propellers, but it could just as easily apply to other types of blades, such as outlet guide vanes (OGVs) used in a flow channel secondary of a ducted twin-flow turbomachine, without fundamentally changing the nature of the invention.

[0022] The turbomachine 10 represented here comprises mainly, along a central longitudinal axis X and the airflow F circulating in the turbomachine turbomotor from upstream to downstream, a gas generator assembly 16, a propulsion assembly 18 comprising the pair of counter-rotating propellers 12, 14 constituting the unfaired fan (“open rotor”) and, between the gas generator 16 and the propulsion assembly 18, a transmission assembly 20 of the power delivered by the gas generator 16 in the direction of the propellers 12, 14, at the output of which are driven, respectively, in opposite rotation to each other, two concentric output shafts external 46 and internal 48 integral with rotating housings 50, 52 respectively of the upstream 12 and downstream 14 propellers of the propulsion assembly 18.

[0023] For each propeller 12, 14, a respective device 54, 56 is provided for changing the pitch of the blades of each propeller in order to independently vary the pitch of the blades according to the different operating phases of the turbomotor, in order to optimize its aerodynamic performance.

[0024] As illustrated in [Fig.2], the propellers 12, 14 each have blades 58, 60 with each blade 62, 64 oriented substantially along a radial axis Z and a foot 66, 68 which is rotatably mounted in a pivot (not shown) of axis Z of the associated housing 50, 52. This foot 66, 68 is driven by the respective device 54, 56 for changing the pitch of the blades 58, 60 of each propeller.

[0025] In this embodiment example, the blades 58, 60 of the propellers 12, 14 are made of a composite material with a fibrous blade preform embedded in a resin.

[0026] As can be seen in [Fig.4] which more specifically represents a blade 58, each blade 58 comprises an aerodynamic blade 62 which extends along an axis which is parallel here to the radial axis Z. The blade 62 comprises an intrados surface 70 and an extrados surface 72 which are opposed along a transverse axis Y (perpendicular to the longitudinal axis X) and which are connected upstream by a leading edge 74 and downstream by a trailing edge 76.

[0027] The blade 62 comprises a casing 78 made of composite material produced from a preform of the blade 62 stiffened by injection of a resin into said preform of the blade 62. The external walls of the casing 78 form the intrados surface 70 and the extrados surface 72. The casing 78 comprises a central cavity 80 receiving a spar 82, preferably metallic.

[0028] Optionally, the cavity 80 can also receive a foam core 84, interposed between the spar 82 and the envelope 78, as shown here in [Fig.4], but this configuration is not limiting of the invention, the spar 82 being able to occupy the entire cavity 80 of the envelope, the blade 62 then being devoid of foam.

[0029] The spar 82 comprises a body 85 which has a first part 86 which occupies the cavity 80 of the envelope 78 and a second part arranged outside the envelope 78 which forms the foot 66 of the blade 58.

[0030] The composite material of the preform is obtained from a three-dimensional (or 3D) or two-dimensional (2D) weave of yarns. In the present invention, the expression "three-dimensional weave" or "3D weave" refers to a weaving method in which warp yarns are bonded to weft yarns in several layers. Preferably, the weave of the composite material of the preform is three-dimensional because it offers better resistance to delamination. Preferably, but not exclusively, the 3D weave has an interlock structure (or reinforcement). The interlock weave offers improved impact resistance, particularly compared to a 2D weave. Similarly, the preform is woven in a single piece.

[0031] The preform is woven using a weaving installation (not shown) comprising a loom configured for three-dimensional and / or two-dimensional weaving. The composite material comprises a plurality of warp yarns and a plurality of weft yarns oriented in perpendicular directions (in the plane or even in the thickness for 3D weaving). The weaving is advantageously carried out flat along a general longitudinal direction.

[0032] The yarns or strands used to carry out the weaving include, for example, carbon, glass, ceramic, silica, silicon carbide, Kevlar, polyamide, alumina fibers or a mixture of these fibers.

[0033] As illustrated in Figures 5 and 13, to obtain such a turbomachine blade 58, a method for manufacturing an aircraft turbomachine blade 58 comprising a composite material blade 62 and a metal base 66, includes at least the following steps:

[0034] - a step a) of supplying a preform 88 of a blade by weaving fibers, and of supply of a metal spar 82 whose body 85 comprises a first part 86 configured to be inserted into a cavity 80 of said preform and a second part 67 configured to remain outside the preform and to form the foot 66 of the blade 58,

[0035] - a step b) of applying glue to the first part 86 of the longeron 82,

[0036] - a step c) of introducing the first part 86 of the body 85 of the longeron 82 covered with glue in cavity 80 of the preform 88,

[0037] - a step d) of depositing the longitudinal member 82 and the preform 88 into a mold 90 in two parts 90A, 90B and mold closure 90,

[0038] - a step e) heating the mold 90 to a first temperature predetermined using a means 91 for heating the mold 90,

[0039] - a step f) of injecting a resin into the mold 90 using an injector cylinder 92 in order to impregnate the preform 88,

[0040] - a step g) of resin consolidation during which the mold 90 is maintained at a second cooking temperature, generally higher than the first temperature, for a determined period of time to ensure the cross-linking of the resin.

[0041] This configuration corresponds to the basic configuration of an RTM (Resin Transfer Molding) process. Preferably, the process is a VARTM (Vacuum Assisted Resin Transfer Molding) process which generally includes an additional step 1) of vacuuming the mold 90 which begins after step d) and before step f) during which a vacuum pump 94 performs a vacuum in the mold 90 prior to the injection of the matrix into it.

[0042] A problem arises due to the difference between the application temperature of the adhesive used to bond the spar 82 and the initial temperature at which the resin is injected. Indeed, the resin injection temperature to which the mold 90 is subjected is a specific, relatively high temperature (around 160°C for an epoxy resin) which tends to thin the adhesive previously applied to the spar 82 before the matrix consolidates. Consequently, the adhesive tends to flow from the spar 82 and penetrate the fibers of the composite material of the preform 88, thus weakening the bond between the spar 82 and the preform 88.

[0043] As shown in [Fig. 3], a blade 58 is subjected during operation, at the junction of its blade 62 with the spar 82, to significant tensile stresses T and bending stresses F. Any weakening of the bonded connection between the spar 82 and the preform 88 must be avoided.

[0044] The invention therefore proposes a spar 82 which makes it possible to remedy this drawback by preventing such a thinning of the glue during the heating of the mold 90.

[0045] In this context, the longeron 86 allows for the implementation in the process of a step i) of cooling the longeron 82.

[0046] As illustrated in [Fig. 13], the process according to the invention comprises a step i) of cooling or holding the spar 82 at a third temperature that is lower than the first temperature. This step i) begins before step e) and ends after step f). This is followed by step g) of consolidation during which the mold 90 is held at the second curing temperature for a determined period, for example 2 hours, to ensure the crosslinking of the resin.

[0047] It will be understood that this step can begin at any time before step e). However, for practical reasons, as illustrated in [Fig. 13], this step i) intervenes preferentially after step d), that is to say after the introduction of the preform 88 and the spar 82 into the mold 90.

[0048] In practical terms, the temperature of the longeron 82 must be well below the first injection temperature. For a given injection temperature of around 160°C, during step i) the longeron 82 is maintained at a third temperature which corresponds to the ambient temperature, i.e. a temperature of approximately 20°C.

[0049] As illustrated in [Fig.5] which relates to a molding installation 104 and in Figures 8 to 10 relating to a spar 82 according to the invention, a spar 82 is used which is traversed by at least one internal cooling circuit 96, in which a cooling fluid is circulated.

[0050] More particularly, as illustrated in figures 8 to 10, the body 85 of the spar 82 has an elongated shape along the main axis Z and it comprises successively along this axis Z the first part 86 which is configured to be inside the blade of the blade, and the second part 67 configured to be outside the blade of the blade and to form the foot 66 of the blade.

[0051] According to the invention, as illustrated in Figures 6 to 10, the body 85 has a cavity 98 which opens into an external surface 100 of the first part 86 by forming an opening 102, and the spar 82 further has a plug 104 which is fixed to the body 85. This plug 104 is engaged in the cavity 98 and closes the opening 102.

[0052] According to the invention, as illustrated in Figures 8 to 10, the internal cooling circuit 96 comprises at least a first conduit 106, which is delimited between the plug 104 and the walls 110 of the cavity 98, and at least a second conduit 108 which communicates with said at least first conduit 106, which passes through at least the second part 67 and opens out of this second part.

[0053] Preferably and without limiting the invention, at least one first conduit 106 passes through the first part 86 and at least one second conduit 108 passes through the second part 67. More particularly, at least one first conduit 106 extends only in the first part 86, at least one second conduit 108 extends only in the second part 67 and at least one first conduit 106 and at least one second conduit 108 are connected at the junction of the first and second parts 86, 67.

[0054] This configuration is not limiting of the invention and it could for example be envisaged that the first conduit extends into the second part 67, the cavity 98 extending into the second part 67. Similarly, at least one second conduit 108 could extend into the first part 98, for example by extending into the thickness of the body 85 and opening laterally into the cavity 98.

[0055] The longeron 85 could have only one second conduit 108 communicating with the first conduit 106, these conduits being filled with a cooling fluid. However, in this configuration, the fluid could only dissipate the heat received by the longeron 82 by conduction since it could not circulate.

[0056] Also, preferably, the spar 82 has at least two second conduits 108 which each communicate with opposite ends of an associated first conduit 106.

[0057] Figures 8 to 10 show three embodiments of a spar 82 comprising only two secondary conduits 108 communicating with the ends of a first conduit 106, but it will be understood that, without changing the nature of the invention, the spar 82 could comprise a greater number of pairs of secondary conduits 108, each associated with a first conduit. For example, the spar 82 could comprise two cavities 98, two plugs 104 delimiting two first conduits 106, and four secondary conduits 108 associated in pairs with the ends of a first conduit 106.

[0058] Preferably also, each second conduit 108 is arranged near the median axis Z of the second part 67. Indeed, as we have seen, the blade 58 is subjected in operation, at the junction of its blade with the spar 82, to significant tensile stresses T and bending stresses F, and the most critical areas for the mechanics are close to the external surface of the foot 66, it is desirable that the second conduits 108 be as far away as possible from the external surfaces of the second part 67.

[0059] We will now describe, with reference to figures 7 to 10, the first to third embodiments of the invention.

[0060] Generally, the second conduits 108 open through orifices 112 into the same internal face 114 of one of the walls 110 of the cavity. Preferably, and without limiting the invention, the external surface 100 of the first part 85 is arranged substantially transversely with respect to the Z-axis of the body 85, at an end of said body that is opposite its second part 67. The internal face 114 into which the conduits 108 open is opposite this external surface 100 and also extends substantially transversely with respect to the Z-axis of the body 85. In the examples shown here, the first part 86 of the body 85 and the cavity 98 have respective cross-sections elongated transversely with respect to the principal Z-axis. The cross-sections of the first part 86 of the body 85 and of the cavity 98 have edges that are substantially homothetic to the intrados 70 and extrados 72 surfaces of the blade of the previously described turbine.

[0061] Generally, the stopper 104 comprises a operculum 116 which closes the opening 102 of the cavity 98, a pad 118 which extends into the cavity 98 from said operculum 116 and a rib 120 extending from the buffer 118 to the inner face 114 of the cavity between the orifices 112 of the second conduits 108, thus hermetically delimiting two chambers 98a, 98b within the cavity 98. The buffer 118 further comprises at least one passage 124 through the buffer 118 which connects said chambers 98a, 98b in fluidic communication. In this way, the two chambers 98a and 98b define the first conduit 106, the ends of which are connected to the second conduits 108.

[0062] In the first embodiment of the plug 104 which was shown in [Fig.7], the plug 118 has two lateral edges 122 arranged in a sealed manner in contact with lateral surfaces of the walls 110 of the cavity 98, and the rib 120, which joins the two lateral edges 122. The plug 118 further has a light 123 forming the passage 124.

[0063] Without limiting the invention, the buffer 118 can be made in the form of a plate. The light 123 is in this case formed in the plate.

[0064] According to second and third embodiments of the invention which have been represented in figures 9 and 10 the pad 118 is of complementary shape to the cavity 98 and it includes at least one helical groove 126, 126a, 126b which is cut into the periphery of the pad 118 along a whole length of the pad 118. This helical groove 126 has a first end 128 opening opposite the operculum 116 on a first side of the rib 120 into a first 98a of the two chambers 98a or 98b, and a second end 130 located near the operculum 116.

[0065] The passage 124 extends through the buffer 118 and it has a first end 132 which communicates with the second end 130 of the helical groove 126 and a second end 134 which communicates with the second of the two chambers 98b.

[0066] More particularly, according to a second embodiment of the invention which has been represented in [Fig.9], the pad 118 is of complementary shape to the cavity 98 and it has a single helical groove 126, which is cut into the periphery of the pad 118 along a whole length of the pad. This helical groove 126 has a first end 128 opening opposite the operculum 116 on a first side of the rib 120 into a first 98a of the two chambers 98a, 98b, and a second end 130 located near the operculum 116. The passage 124 extends for the most part along the Z axis through the buffer 118 and has a first end 132 which communicates with the second end 130 of the helical groove 126 and a second end 134 which opens directly into the second of the two chambers 98b.

[0067] In this case, the helical groove 126 and the passage 124 form the first conduit 106.

[0068] More particularly, according to a third embodiment of the invention which has been represented in [Fig. 10], the pad 118 is also of complementary shape to the cavity 98 but it has two helical grooves 126a, 126b which are cut into its periphery, which are of the same pitch and which are arranged in a double helix arrangement along the entire length of the pad 118, and which have first ends 128a, 128b which open opposite the operculum each on one side of the rib 120 respectively into the first and second chambers 98a, 98b and, second ends 130a, 130b located near the operculum 116.

[0069] In this embodiment, the passage 124 crosses transversely the buffer 118 and it opens at its first and second ends 132, 134 into the second ends 130a, 130b of the channels 126a, 126b.

[0070] In this case, the two helical channels 126a, 126b and the passage 124 which connects them form the first conduit 106, as schematically represented in [Fig.1 1].

[0071] In the three embodiments described herein, the function of the operculum 116 is to close the opening 102. For this purpose, it could fit exactly into the opening 102. However, preferably in the invention, the operculum 116 is formed in a cover 136, and preferably of one piece with this cover, this cover 136 extending over the external surface 100 of the first part, closing the opening 102. This cover 136 is bonded to the external surface 100.

[0072] As regards the material of the cap 104, it can be made of a thermoplastic material, preferably by injection, or by additive manufacturing, for all embodiments of the invention.

[0073] With regard more specifically to the second and third embodiments of the plug 104, it can alternatively be made by molding and machining a foam, in particular polymethacrylimide, having a density between 0.15 and 0.5 kg / m³. In particular, the helical grooves 126, 126a, 126b are formed by machining. An example of a material used that meets these characteristics is ROHACELL HERO foam (registered trademark).

[0074] As illustrated in [Fig. 12], the spar 82 can thus be obtained by a process which first comprises a step A) of supplying a plug 104, and supplying a spar blank having an elongated body similar in shape to that of the spar body 85 along a principal axis Z and comprising along said axis a first part configured to form the first part 86 of the spar body 85 and a second part configured to form the second part 67 of the spar body 85. This first part comprising the cavity 98 which opens into an external surface of said first part, forming an opening. This opening will form the opening 102 of the spar body 85.

[0075] Then the process includes a step B), of machining at least a second conduit 108 until it opens into said cavity 98. Depending on how the spar blank was obtained, the external surface 100 will also be faced.

[0076] Then the process includes steps C) of inserting the plug 104 into the cavity 98 and D) of fixing the plug 104 to the body 85. Generally the fixing will be carried out very simply by applying glue to the external surface 100 or under the cover 136.

[0077] The invention therefore makes it possible to obtain in a very simple way a longitudinal member 82 comprising an integrated cooling circuit.

Claims

1. Demands A longeron (82) for a turbine blade (58), particularly for an aircraft, said longeron (82) comprising a body (85) having an elongated shape along a principal axis (Z) and comprising along said principal axis (Z) a first part (86) configured to be inside a blade (62) of the turbine blade (58), and a second part (67) configured to be outside the blade (62) of the turbine blade (58) and to form a foot (66) of the turbine blade (58), the body (85) comprising a cavity (98) which opens into an external surface (100) of said first part (86) by forming an opening (102), and in that the longeron (82) further comprises: - a plug (104) which is fixed to the body (85), this plug (104) being engaged in the cavity (98) and closing the opening (102), and - an internal cooling circuit (96) comprising at least one first conduit (106) which is delimited between the plug (104) and the walls (110) of said cavity (98) and at least two second conduits (108) which each communicate with opposite ends of said at least first conduit (106), which pass through at least the second part (67) and which open outwards from the second part (67), characterized in that: - said at least two second conduits (108) open through orifices (112) into the same internal face (114) of the cavity (98), - the stopper (104) includes a operculum (116) which closes the opening (102) of the cavity (98), a pad (118) which extends into the cavity (98) from said operculum (116), and a rib (120) which extends from said pad (118) to the contact of the inner face (114) of the cavity (98) between said orifices (112) by hermetically delimiting two chambers (98a, 98b) in the cavity (98), - at least one passage (124) through said buffer (118) puts said chambers (98a, 98b) into fluidic communication.

2. Longeron (82) according to the preceding claim, characterized in that the inner face (114) is opposite the opening (102).

3. Longeron (82) according to any one of the preceding claims, characterized in that the external surface (100) of the first part (86) is arranged substantially transversely with respect to the axis (Z) of the body (85), at an end of said body (85) which is opposite its second part (67).

4. Longeron (82) according to any one of claims 1 to 3, characterized in that the buffer (118) comprises: - two lateral edges (122) arranged in a sealed manner in contact with lateral surfaces of the cavity (98), - the rib (120), joining the two lateral edges (122), - a light (123) passing through said buffer and forming the passage (124).

5. A spar (82) according to any one of claims 1 to 3, characterized in that: - the pad (118) is complementary in shape to the cavity (98) and comprises at least one helical groove (126, 126a, 126b) which is cut into the periphery of the pad (118) along a length of said pad (118), this helical groove (126, 126a, 126b) having a first end (128, 128a, 128b) opening opposite the operculum (116) on a first side of the rib (120) into a first (98a) of the two chambers (98a, 98b), and a second end (130, 130a, 130b) located near the operculum (116), - the passage (124) extends through the buffer (118) and has a first end (132) which communicates with the second end (130, 130a, 130b) of the helical groove (126, 126a, 126b) and a second end (134) which communicates with a second (98b) of the two chambers (98a, 98b).

6. Longeron (82) according to the preceding claim, characterized in that the passage (124) crosses the buffer along the entire length of the buffer (118) and in that its second end (134) opens opposite the operculum (116) on a second side of the rib (120) in the second (98b) of the two chambers (98a, 98b).

7. Longeron (82) according to claim 5, characterized in that: - the buffer (118) comprises two helical grooves (126a, 126b) which are cut into its periphery, which are of the same pitch and which are arranged in a double helix arrangement along the entire length of the buffer (118), and which have first ends (128a, 128b) which open opposite the operculum (116) each on one side of the rib (120) respectively in the first and second chambers (98a, 98b) and second ends (130a, 130b) located near the operculum, - the passage (124) crosses transversely the buffer (118) and opens at its first and second ends (132, 134) into the second ends (130a, 130b) of the channels (126a, 126b).

8. Longeron (82) according to any one of claims 1 to 7, characterized in that the operculum (116) is formed in a cover (136) which extends over the external surface (100) of the first part (86) by closing the opening (102), said cover (136) being glued to said external surface (100).

9. Longeron (82) according to any one of the preceding claims, characterized in that the plug (104) is made: - of thermoplastic material, preferably by injection, or by additive manufacturing, or - by molding and machining of a foam, in particular polymethacrylimide, having a density between 0.15 and 0.5 kg / m3.

10. Longeron (82) according to any one of the preceding claims, characterized in that the first part (86) of the body (85) and the cavity (98) have respective sections elongated transversely with respect to the main axis (Z).

11. Longeron (82) according to any one of the preceding claims, characterized in that: - at least one first conduit (106) extends only in the first part (86), - at least one second conduit (108) extends only in the second part (67), and - at least one first conduit (106) and at least one second conduit (108) are connected at the junction of the first and second parts (86, 67).

12. Blade (58) for an aircraft turbomachine, comprising a blade (62) and a foot (66), this blade (58) comprising a spar according to any one of the preceding claims, of which a first part (67) is inside the blade (62) and a second part is outside the blade (62) to form said foot (66).

13. A method for manufacturing a longeron (82) according to any one of claims 1 to 11, characterized in that it comprises the steps of: A) supplying a plug (104), and supplying a spar blank having a body (85) elongated along a principal axis (Z) and comprising along said axis a first part configured to form the first part (86) of the body (85) of the longeron (82) and a second part configured to form the second part (67) of the body (85) of the longeron (82), said first part having a cavity (98) which opens into an external surface (100) of said first part by forming an opening (102), B) machining at least one second conduit (108) until it opens into said cavity (98), C) inserting the plug (104) into the cavity (108, D) fixing the plug (104) to the body (85).

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