Forged part for the manufacture of a structural arm for the intermediate casing of a turbofan engine and method for manufacturing such a structural arm

Abstract

The invention relates to a forged part (20) for manufacturing a structural arm of an intermediate casing of an aircraft turbojet engine, the structural arm comprising a body having a cavity opening onto an external surface of the body and a closing cover closing said cavity, the forged part (20) comprising a body intended to form, after machining, the body of the structural arm, the body of the forged part (20) comprising a cavity blank (290) intended to form, after machining, the cavity of the body of the structural arm. Figure 5.

Description

Title of the invention: Forged part for the manufacture of a structural arm of an intermediate casing of a dual-flow turbojet engine and method of manufacturing such a structural arm Technical field

[0001] The present invention relates to the aeronautical field, and more precisely to the manufacture of intermediate casing arms for a dual-flow turbojet. State of the art

[0002] Aircraft are known that are powered by at least one propulsion unit comprising a dual-flow turbojet engine housed in a nacelle. Each propulsion unit is attached to the aircraft by a mast generally located under or on a wing, or at the level of the fuselage of the aircraft. A dual-flow turbojet engine mainly comprises a gas generator and a fan.

[0003] In operation, an air flow enters the propulsion unit through an air inlet of the nacelle, is accelerated by the fan, and then splits into a primary flow and a secondary flow. The primary flow flows in a primary gas circulation vein passing through the gas generator of the turbojet engine. The secondary flow flows in a secondary vein surrounding the gas generator. The secondary vein is delimited, radially inwardly, in part by an internal structure of the nacelle which envelops the gas generator, and radially outwardly, in part by an external structure of the nacelle which surrounds the turbojet engine. A portion of the secondary vein is further delimited radially outwardly by a fan casing surrounding the fan, and by an intermediate casing, located downstream of the fan casing.

[0004] The intermediate casing generally comprises a hub and an external shroud, connected to the hub by structural arms. The structural arms are parts which are hollow, to optimize their mass and / or to allow the passage of elements necessary for the operation of the turbojet. The structural arms are generally metal parts, obtained by machining a forged part.

[0005] The objective of the present invention is to propose a structural arm whose manufacturing costs are lower. Statement of the invention

[0006] To this end, the invention relates to a forged part for the manufacture of a structural arm of an intermediate casing of an aircraft turbojet, the structural arm comprising a body comprising a cavity opening onto an external surface of the body and a closing cover closing said cavity, the forged part comprising a body intended to form, after machining, the body of the structural arm, the body of the forged part comprising a cavity blank intended to form, after machining, the cavity of the body of the structural arm.

[0007] Thus, by providing a forged part comprising a cavity blank intended to form, after machining, the internal cavity of the structural arm, the quantity of material required to obtain the forged part from which the finished part, i.e. the structural arm, will be obtained is reduced. It is thus possible to manufacture the forged part using a starting billet of lower mass. In addition, the forged part will be lighter and easier to handle. In addition, the quantity of material to be removed from the forged part to obtain the finished part is reduced, which makes it possible to reduce the machining time of the forged part. By lightening the forged part and reducing the machining time, the manufacturing costs of a structural arm are significantly reduced.

[0008] According to other characteristics of the invention, the forged part may comprise one or more of the following optional characteristics, considered alone or in all possible combinations.

[0009] According to one characteristic, the cavity blank comprises a bottom wall in which at least one recess is formed, intended to form, after machining, a recess located in the cavity of the body of the structural arm and delimited by reinforcing elements extending in projection from a bottom wall of the cavity of the body of the structural arm.

[0010] According to one characteristic, the forged part comprises at least two recesses formed in the bottom wall, and intended to form respectively, after machining, two indentations located in the cavity of the body of the structural arm and delimited by reinforcing elements extending in projection from a bottom wall of the cavity of the body of the structural arm.

[0011] According to one characteristic, the external contour of the body of the forged part has, relative to the external contour of the body of the structural arm, an excess thickness greater than a minimum excess thickness, the minimum excess thickness being between 3 mm and 6 mm, and preferably between 3.5 mm and 4.5 mm.

[0012] According to one characteristic, a concave zone of the forged part has a clearance angle relative to a vertical direction of the forged part, the clearance angle being greater than or equal to 20°, and preferably greater than or equal to 25°.

[0013] According to one characteristic, a curved zone of the forged part has a radius of curvature greater than or equal to 6 mm, and for example greater than or equal to 7 mm.

[0014] The invention also relates to a dual-flow turbojet comprising an intermediate casing and at least one intermediate casing structural arm obtained from a forged part conforming to that defined above.

[0015] The invention also relates to an aircraft comprising one or more turbo- double-flow reactors conforming to that defined above.

[0016] The invention also relates to the use of a forged part conforming to that defined above for the manufacture of a structural arm of an intermediate casing of an aircraft turbojet.

[0017] The invention also relates to a method for manufacturing a structural arm of an intermediate casing of an aircraft turbojet, the structural arm comprising a body comprising a cavity opening onto an external surface of the body and a closing cover closing said cavity, the method comprising: - a forging step of a forged part conforming to that defined above; - a step of machining the forged part; - a step of fixing the closing cover, for example by welding. Brief description of the drawings

[0018] [Fig-1] [Fig.l] is a schematic half-sectional view of a propulsion unit in accordance with the invention.

[0019] [Fig.2] [Fig.2] is a top view of an intermediate casing structural arm according to the invention.

[0020] [Fig.3] [Fig.3] is a partial perspective view of the structural arm of [Fig.2], without the closing hood.

[0021] [Fig.4] [Fig.4] is a top view of a forged part according to the invention, making it possible to obtain the structural arm of [Fig.2].

[0022] [Fig.5] [Fig.5] is a perspective view of the forging of [Fig.4].

[0023] [Fig.6] [Fig.6] is a sectional view of the forging of [Fig.5], in the plane CC of [Fig.5].

[0024] [Fig.7] [Fig.7] is a diagram illustrating the steps of a manufacturing method according to the invention. Description of the embodiments

[0025] [Fig.l] represents an aircraft propulsion unit 1 comprising a double-flow turbojet 2 and a nacelle 3.

[0026] The turbojet engine 2 has a central axis, or longitudinal axis X, around which its various components extend. The turbojet engine is, in the example, a twin-spool, dual-flow turbojet engine. It comprises, from upstream to downstream along a main direction F of gas flow through this turbojet engine, a fan 4, a low-pressure compressor 5, a high-pressure compressor 6, a combustion chamber 7, a high-pressure turbine 8 and a low-pressure turbine 9.

[0027] Conventionally, after passing through the blower 4, the air divides into a primary flow A and a secondary flow B. The primary flow A flows in a primary gas circulation vein, passing through the compressors 5, 6, the combustion chamber combustion 7 and the turbines 8, 9, before being ejected towards the rear of the propulsion unit 1. The secondary flow B flows in a secondary vein surrounding the primary vein. The secondary vein is delimited, radially inwards, partly by an internal structure 10 of the nacelle 3 which surrounds a part of the turbojet, and, radially outwards, partly by an external structure 11 of the nacelle which surrounds the internal structure 10. A part of the secondary vein is further delimited radially outwards by a fan casing 12 surrounding the fan 4, and by an intermediate casing 13, located downstream of the fan casing 12.

[0028] The intermediate casing 13 comprises an outer shroud 14 located in the downstream aerodynamic extension of the fan casing 12. The intermediate casing 13 also comprises a hub 15, formed by transverse flanges 16, 17 arranged radially internally relative to the outer shroud 14, the intermediate casing 13 further comprising structural arms 18 distributed angularly and extending radially to connect the outer shroud 14 and the hub 15. The turbojet engine may for example comprise two, three or four structural arms 18.

[0029] [Fig.2] is a schematic side view of a structural arm 18. The structural arm 18 comprises a body 180 and a closing cover 182 fixed to the body 180, for example by welding. The body 180 extends in a longitudinal direction L, the longitudinal direction L being parallel to a radial direction of the turbojet engine 2 when the structural arm 18 is mounted on the turbojet engine 2.

[0030] The structural arm 18 comprises a central portion 184 which is in operation arranged in the secondary vein. The central portion 184 extends in the longitudinal direction L between a first radially internal end portion 186, or foot 186, and a second radially external end portion 188, or head 188. The central portion 184 extends in a transverse direction T from a leading edge 184a towards a trailing edge 184b, the leading edge 184a being arranged in the turbojet 2 upstream of the trailing edge 184b.

[0031] As visible in [Fig. 3], which is a perspective view of the structural arm 18 of [Fig. 2] without the closing cover 182, the structural arms 18 form hollow parts, in order to optimize the mass of these parts and / or to allow the passage of elements necessary for the operation of the turbojet, such as electrical cables (not shown). Thus, the body 180 comprises a cavity 190 opening onto an external surface 184c of the central part 184. The cavity 190 is delimited at the external surface 184c by an opening whose external contour 190a is of a shape complementary to the closing cover 182. The cavity 190 comprises a bottom wall 190b, and, in the example, two opposite transverse walls 190c and two opposite longitudinal walls 190d. In order to optimize the mechanical behavior of the structural arm 18, reinforcing elements 191a, 191b, such as ribs 191a, 191b, are provided. The reinforcing elements 191a, 191b are elements extending in projection from the bottom wall 190b of the cavity 190. In the example, the reinforcing elements comprise a longitudinal rib 191a, extending in a direction parallel to the longitudinal direction L of the structural arm 18 (or in a direction slightly inclined relative to this direction, for example inclined by less than 10°, or even less than 5°). In the example, the reinforcing elements also comprise transverse ribs 191b, extending in a direction parallel to the transverse direction T of the structural arm 18 (or in a direction slightly inclined relative to this direction, for example inclined by less than 10°, or even less than 5°). In the example, three transverse ribs 191b are provided, each joining, at one of its ends, the longitudinal rib 191a.Thus, the set of transverse ribs 191b and longitudinal rib 191a delimit, with the bottom wall 190b of the cavity 190, two recesses 192.

[0032] Figures 4 to 6 show a forged part 20 according to the invention, used for the manufacture of a structural arm 18. The forged part 20 is obtained by forging a billet and constitutes a rough forging, that is to say that the forged part 20 shown in the figures is directly produced by forging. The body 180 of the structural arm 18 of [Fig. 2] is obtained from the forged part 20 of [Fig. 3], after one or more additional manufacturing steps, including at least one machining step.

[0033] The forged part 20 comprises a body 280 comprising a central part 284, forming, after machining the central part 284 and fixing a closing cover 182, the central part 184 of the structural arm 18. The central part 284 extends in the longitudinal direction L between a first radially internal end part 286, and a second radially external end part 288. The first end portion 286 and the second end portion 288 of the body 280 of the forged part are intended to form respectively, after machining, the first end portion 186 and the second end portion 188 of the body 180 of the structural arm 18. The central portion 284 extends in the transverse direction T from a front edge 284a to a rear edge 284b, intended to form respectively, after machining, the leading edge 184a and the trailing edge 184b of the central portion 184 of the structural arm 18.

[0034] As can be seen more particularly in [Fig. 5], which shows the forged part 20 in perspective, the body 280 comprises a hollow 290, or blank of a cavity 290. The cavity blank 290 is intended to form, in particular after a machining step, the cavity 190 of the body 180 of the structural arm 18. The cavity blank 290 forms a cavity open on an external surface 284a of the central part 284 of the forged part 20, and is delimited at this external surface 284a by an external contour 290a. The cavity blank 290 comprises a bottom wall 290b, and may comprise one or two transverse peripheral walls and / or one or two longitudinal peripheral walls. In the example, the cavity blank 290 comprises only one bottom wall 290b. Advantageously, two recesses 292 are provided in the bottom wall 290b of the cavity blank 290. The two recesses 292 are intended to form respectively, after machining, the recesses 192 delimited by the reinforcing elements 191a, 191b arranged in the cavity of the body 180 of the structural arm 18. Alternatively, it may be provided that the cavity blank 290 comprises a single recess 292, intended to form after machining a single recess 192, or that the cavity blank 290 comprises more than two recesses 292 (for example, three recesses), intended to form respectively, after machining, as many recesses 192.

[0035] By providing a forged part comprising a cavity blank 290 intended to form, after machining, the internal cavity 190 of the structural arm 18, the quantity of material required to obtain the forged part, from which the finished part, i.e. the structural arm 18, will be obtained, is reduced. It is thus possible to manufacture the forged part 20 using a starting billet of lower mass, which is more economical. In addition, the forged part will be all the lighter, and therefore easier to handle. For example, a forged part produced in accordance with the invention in a titanium-based alloy may have a difference in mass with a conventional forged part of more than 900 grams. In addition, the quantity of material to be removed from the forged part to obtain the finished part is reduced, which makes it possible to reduce the machining time of the forged part.By lightening the forging and reducing the machining time, the manufacturing costs of a structural arm are reduced.

[0036] [Fig. 6] represents a sectional view of the forged part 20 along the plane CC of [Fig. 5], on which is represented, in thin line, the external contour 280a of the body of the forged part 20 and, in strong line, the external contour 180a of the corresponding body 180. As shown in [Fig. 6], in order to guarantee good quality machining, an excess thickness E is provided at each location of the contour 290a of the body 280 of the forged part 20 relative to the external contour 180a of the body 180 obtained after machining. The value of the excess thickness E is not necessarily the same at all points of the external contour 180a of the body 180. On the other hand, the excess thickness E is at all points greater than or equal to a minimum excess thickness Emin. The minimum excess thickness Emin is for example between 3 mm and 6 mm, preferably between 3.5 and 4.5 mm, and for example between 3.8 and 4.2 mm, and for example equal to approximately 4 mm.Preferably, the excess thickness E is less than or equal to a maximum excess thickness Emax which is for example equal to 6 mm. Furthermore, in order to guarantee that the forged part 20 is easily forged, while avoiding premature wear of the forging tools, the following will preferably be provided: . at the level of the curved areas: a radius of curvature R greater than or equal to 6 mm, preferably greater than or equal to 7 mm; at the level of the concave zones: a clearance angle D relative to a vertical direction of the part (i.e. the direction perpendicular to the longitudinal L and transverse T directions) which is greater than 20° and preferably greater than or equal to 25°.

[0037] [Fig. 7] is a diagram illustrating a manufacturing method 100 of a structural arm according to the invention. The manufacturing method 100 comprises a step 102 of forging a forged part 20 according to the invention. The manufacturing method 100 then comprises a machining step 104, during which the forged part 20 is machined to obtain the body 180 of the structural arm comprising the cavity 190. The manufacturing method 100 then comprises a step 106 of fixing a closing cap 182, for example by welding. The step 106 of fixing the closing cap may be followed by a finishing step, in particular in order to obtain an outer surface of the structural arm 18 which has the desired surface condition.

[0038] The forged part according to the invention is preferably forged from a piece of metal alloy, such as an aluminum-based or titanium-based alloy.

Claims

Claims

1. Forged part (20) for the manufacture of a structural arm (18) of an intermediate casing (13) of an aircraft turbojet (2), the structural arm (18) comprising a body (180) comprising a cavity (190) opening onto an external surface (184a) of the body (180) and a closing cover (182) closing said cavity (190), the forged part (20) comprising a body (280) intended to form, after machining, the body (180) of the structural arm (18), the body (280) of the forged part (20) comprising a cavity blank (290) intended to form, after machining, the cavity (190) of the body (180) of the structural arm (18).

2. Forged part (20) according to the preceding claim, in which the cavity blank (290) comprises a bottom wall (290b) in which at least one recess (292) is formed, intended to form, after machining, a recess (192) located in the cavity (190) of the body (180) of the structural arm (180) and delimited by reinforcing elements (191a, 191b) extending in projection from a bottom wall (190b) of the cavity (190) of the body (180) of the structural arm (18).

3. Forged part (20) according to the preceding claim, comprising at least two recesses (292) formed in the bottom wall (290b), and intended to form respectively, after machining, two indentations (192) located in the cavity (190) of the body (180) of the structural arm (180) and delimited by reinforcing elements (191a, 191b) extending in projection from a bottom wall (190b) of the cavity (190) of the body (180) of the structural arm (18).

4. Forged part (20) according to one of the preceding claims, in which the outer contour (280a) of the body (280) of the forged part has, relative to the outer contour (180a) of the body (180) of the structural arm (18), an excess thickness (E) greater than a minimum excess thickness (Emin), the minimum excess thickness (Emin) being between 3 mm and 6 mm, and preferably between 3.5 mm and 4.5 mm.

5. A forging (20) according to any preceding claim, wherein a concave area of ​​the forging (20) has a clearance angle (D) relative to a vertical direction of the forging, the clearance angle (D) being greater than or equal to 20°, and preferably greater than or equal to 25°.

6. A forging (20) according to any preceding claim, wherein a curved area of ​​the forging (20) has a radius of curvature (R) greater than or equal to 6 mm, and for example greater than or equal to 7 mm.

7. Double-flow turbojet (2) comprising an intermediate casing (13) and at least one structural arm (18) of the intermediate casing obtained from a forged part (20) according to one of the preceding claims.

8. Aircraft comprising one or more dual-flow turbojets (2) according to the preceding claim.

9. Use of a forged part (20) according to one of claims 1 to 6 for the manufacture of a structural arm (18) of an intermediate casing of an aircraft turbojet.

10. Method for manufacturing (100) a structural arm (18) of an intermediate casing of an aircraft turbojet, the structural arm (18) comprising a body (180) comprising a cavity (190) opening onto an external surface (184a) of the body (180) and a closing cover (182) closing said cavity (190), the method comprising: - a step of forging (102) a forged part (20) according to one of claims 1 to 6; - a step of machining (104) the forged part (20); - a step of fixing (106) the closing cover (182), for example by welding.

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