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 manufacturing a structural arm of an intermediate casing of a turbofan engine and method for manufacturing such a structural arm. Technical field

[0001] The present invention relates to the aeronautical field, and more specifically to the manufacture of intermediate casing arms for turbofan engines. Prior art

[0002] Aircraft are known that are propelled by at least one propulsion system comprising a turbofan engine housed in a nacelle. Each propulsion system is attached to the aircraft by a mast located generally under or on a wing, or at the level of the aircraft fuselage. A turbofan engine primarily comprises a gas generator and a fan.

[0003] During operation, an airflow enters the propulsion assembly through an air inlet in 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 channel through the turbojet's gas generator. The secondary flow flows in a secondary channel surrounding the gas generator. The secondary channel is delimited, radially inward, partly by an internal structure of the nacelle that encloses the gas generator, and radially outward, partly by an external structure of the nacelle that surrounds the turbojet. A portion of the secondary channel is further delimited radially outward 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 outer shell, connected to the hub by structural arms. The structural arms are hollow parts, designed to optimize their mass and / or to allow the passage of components necessary for the operation of the turbojet engine. The structural arms are generally metal parts, obtained by machining a forging.

[0005] The objective of the present invention is to provide a structural arm with lower manufacturing costs. Description of the invention

[0006] To this end, the invention relates to a forged part 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 comprising a body intended to form, after machining, the body of the structural arm, the body of the forged part having a rough cavity intended to form, after machining, the cavity of the body of the structural arm.

[0007] Thus, by providing a forging with a blank cavity designed to form, after machining, the internal cavity of the structural arm, the amount of material required to obtain the forging from which the finished part, i.e., the structural arm, will be produced, is reduced. It is therefore possible to manufacture the forging using a lower-mass blank. Furthermore, the forging will be lighter and easier to handle. In addition, the amount of material to be removed from the forging to obtain the finished part is reduced, which in turn reduces the machining time of the forging. By lightening the forging and reducing machining time, the manufacturing costs of a structural arm are significantly reduced.

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

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

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

[0011] According to one feature, the outer contour of the body of the forged part has, in relation to the outer contour of the body of the structural arm, an overthickness greater than a minimum overthickness, the minimum overthickness being between 3 mm and 6 mm, and preferably between 3.5 mm and 4.5 mm.

[0012] According to one feature, a concave area of ​​the forged part has a draft angle with respect to a vertical direction of the forged part, the draft angle being greater than or equal to 20°, and preferably greater than or equal to 25°.

[0013] According to one feature, a curved area 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 turbofan engine comprising an intermediate casing and at least one structural arm of the intermediate casing obtained from a forged part conforming to that defined above.

[0015] The invention also relates to an aircraft comprising one or more turbofan engines 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 engine.

[0017] The invention also relates to a method for manufacturing a structural arm for 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 method comprising: - a forging step of a forged part conforming to that defined above; - a machining step of the forged part; - a step of fixing the closing cover, for example by welding. Brief description of the drawings

[0018] [Fig-1] Fig. 1 is a schematic half-view in cross-section of a propulsion assembly in accordance with the invention.

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

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

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

[0022] [Fig.5] The [Fig.5] is a perspective view of the forged part of the [Fig.4].

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

[0024] [Fig.7] The [Fig.7] is a diagram illustrating the steps of a manufacturing process according to the invention. Description of the implementation methods

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

[0026] The turbojet 2 has a central axis, or longitudinal axis X, around which its various components extend. In this example, the turbojet is a twin-spool, turbofan engine. It comprises, from upstream to downstream along a principal direction F of gas flow through this turbojet, 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 splits into a primary flow A and a secondary flow B. The primary flow A flows into a primary gas circulation channel, passing through the compressors 5, 6, the combustion chamber 7 and the turbines 8, 9, before being ejected towards the rear of the propulsion assembly 1. The secondary flow B flows into a secondary channel surrounding the primary channel. The secondary stream 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 stream 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 includes an outer ferrule 14 located in the downstream aerodynamic extension of the fan casing 12. The intermediate casing 13 also includes a hub 15, formed by transverse flanges 16, 17 arranged radially inwardly with respect to the outer ferrule 14, the intermediate casing 13 further including structural arms 18 distributed angularly and extending radially to connect the outer ferrule 14 and the hub 15. The turbojet engine may, for example, include two, three or four structural arms 18.

[0029] Figure 2 is a schematic side view of a structural arm 18. The structural arm 18 comprises a body 180 and a closing cover 182 attached to the body 180, for example by welding. The body 180 extends along 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 part 184 which is in operation and disposed in the secondary flow. The central part 184 extends along the longitudinal direction L between a first radially internal end part 186, or foot 186, and a second radially external end part 188, or head 188. The central part 184 extends along a transverse direction T from a leading edge 184a to a trailing edge 184b, the leading edge 184a being disposed in the turbojet 2 upstream of the trailing edge 184b.

[0031] As can be seen in [Fig. 3], which is a perspective view of the structural arm 18 of [Fig. 2] without the closing cowl 182, the structural arms 18 are 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 engine, such as electrical cables (not shown). Thus, the body 180 has a cavity 190 opening onto an external surface 184c of the central part 184. The cavity 190 is delimited at the level of the external surface 184c by an opening whose external contour 190a is complementary in shape to the closing cowl 182. The cavity 190 has a bottom wall 190b, and, in the example, two opposing transverse walls 190c and two opposing longitudinal walls 190d. 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 projecting from the bottom wall 190b of the cavity 190. In the example, the reinforcing elements include 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 with respect to this direction, for example inclined at less than 10°, or even less than 5°).In the example, the reinforcing elements also include 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 at 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 transverse ribs 191b and the longitudinal rib 191a together with the bottom wall 190b of the cavity 190 define two recesses 192.

[0032] Figures 4 to 6 show a forged part 20 according to the invention, used for manufacturing a structural arm 18. The forged part 20 is obtained by forging a billet and constitutes a forging blank, i.e., the forged part 20 shown in the figures is directly from the forging process. 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 having a central part 284, forming, after machining of the central part 284 and fixing of a closing hood 182, the central part 184 of the structural arm 18. The central part 284 extends along the longitudinal direction L between a first radially internal end part 286, and a second radially external end part 288. The first end part 286 and the second end part 288 of the body 280 of the forged part are intended to form, after machining, respectively, the first end part 186 and the second end part 188 of the body 180 of the structural arm 18. The central part 284 extends in the transverse direction T from a front edge 284a to a rear edge 284b, intended to form, after machining, respectively, the leading edge 184a and the trailing edge 184b of the central part 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 has a hollow 290, or a rough cavity 290. The rough cavity 290 is intended to form, particularly after a machining step, the cavity 190 of the body 180 of the structural arm 18. The rough cavity 290 forms a An open cavity 290 is formed on an external surface 284a of the central portion 284 of the forged part 20, and is delimited at this external surface 284a by an external contour 290a. The cavity blank 290 has a bottom wall 290b, and may have one or two transverse peripheral walls and / or one or two longitudinal peripheral walls. In the example, the cavity blank 290 has only a bottom wall 290b. Advantageously, two recesses 292 are formed in the bottom wall 290b of the cavity blank 290. After machining, the two recesses 292 are intended to form, respectively, the indentations 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 has a single recess 292, intended to form after machining a single indentation 192, or that the cavity blank 290 has more than two recesses 292 (for example, three recesses), intended to form respectively, after machining, as many indentations 192.

[0035] By providing a forged part comprising a blank cavity 290 intended to form, after machining, the internal cavity 190 of the structural arm 18, the amount 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. Furthermore, the forged part will be lighter and therefore easier to handle. For example, a forged part made according to the invention in a titanium-based alloy can have a mass difference of more than 900 grams compared to a conventional forged part. In addition, the amount 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 machining time, the manufacturing costs of a structural arm are reduced.

[0036] Figure 6 shows a sectional view of the forged part 20 along plane CC of Figure 5, on which the outer contour 280a of the body of the forged part 20 is shown in thin lines, and the outer contour 180a of the corresponding body 180 is shown in thick lines. As shown in Figure 6, to ensure high-quality machining, a certain amount of extra thickness E is provided at each point along the contour 290a of the body 280 of the forged part 20, relative to the outer contour 180a of the body 180 obtained after machining. The value of this extra thickness E is not necessarily the same at all points along the outer contour 180a of the body 180. However, the extra thickness E is at all points greater than or equal to a minimum extra thickness Emin. The minimum overthickness 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 about 4 mm.Preferably, the extra thickness E is less than or equal to one. Maximum overhang Emax, which is, for example, equal to 6 mm. Furthermore, in order to ensure that the forged part 20 is easily forged, while avoiding premature wear of the forging tools, it is preferable to provide: - at the level of 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 concave areas: a draft angle D with respect to a vertical direction of the part (i.e. the direction perpendicular to the longitudinal direction L and transverse direction T) which is greater than 20° and preferably greater than or equal to 25°.

[0037] Figure 7 is a diagram illustrating a manufacturing process for an arm. structural according to the invention. The manufacturing process 100 includes a forging step 102 of a forged part 20 according to the invention. The manufacturing process 100 then includes a machining step 104, during which the forged part 20 is machined to obtain the body 180 of the structural arm having the cavity 190. The manufacturing process 100 then includes a step of attaching a closing cover 182, for example by welding. The step of attaching the closing cover 106 may be followed by a finishing step, in particular to obtain an external surface of the structural arm 18 that has the desired surface finish.

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

Claims

Demands

1. A method for manufacturing (100) a structural arm (18) of an intermediate casing of an aircraft turbojet engine, the structural arm (18) comprising a body (180) having 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 forging step (102) of a forging (20), the forging (20) having a body (280) intended to form, after machining, the body (180) of the structural arm (18), the body (280) of the forging (20) having a cavity blank (290) intended to form, after machining, the cavity (190) of the body (180) of the structural arm (18); - a machining step (104) of the forging (20); - a fixing step (106) of the closing cover (182), for example by welding.

2. A manufacturing method (100) according to the preceding claim, in which the cavity blank (290) has a bottom wall (290b) in which is formed at least one recess (292), 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. A manufacturing method (100) according to the preceding claim, wherein the forged part (20) has 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. A manufacturing method (100) according to any one of the preceding claims, wherein the outer contour (280a) of the body (280) of the forging has, relative to the outer contour (180a) of the body (180) of the structural arm (18), an overthickness (E) greater than a minimum overthickness (Emin), the overthickness minimum (Emin) being between 3 mm and 6 mm, and preferably between 3.5 mm and 4.5 mm.

5. A manufacturing method (100) according to any one of the preceding claims, wherein a concave area of ​​the forged part (20) has a draft angle (D) with respect to a vertical direction of the forged part, the draft angle (D) being greater than or equal to 20°, and preferably greater than or equal to 25°.

6. A manufacturing method (100) according to any one of the preceding claims, wherein a curved area of ​​the forged part (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. Turbofan engine (2) with a double-flow design comprising an intermediate casing (13) and at least one structural arm (18) of the intermediate casing obtained from a forged part (20) by means of the manufacturing process (100) according to any one of the preceding claims.

8. Aircraft comprising one or more turbofan engines (2) according to the preceding claim.

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