Improved method for manufacturing a metal annular part

Abstract

Improved method for manufacturing a metal annular part. Method for manufacturing a metal annular part (10) comprising at least one diameter (De) having a predetermined value, the method comprising a forging step (S110) in which a rough blank of the annular part (10) is produced, at least one heat treatment step (S120, S130), a machining step (S200) comprising, on the one hand, the fit turning (S220') of the blank to adjust the diameter (De) of the blank to the predetermined value of the part to be manufactured, and on the other hand, the material removal (S210') of the blank in which at least 50% of the mass of the rough blank is removed and comprising at least the drilling of holes (14) and / or a groove (17, 19) in the rough blank, the material removal (S210') of the roughing being done before the adjustment turning (S220'). Figure for the abbreviation: Fig. 5.

Description

Title of the invention: Improved method for manufacturing a metal annular part technical field

[0001] This presentation relates to the field of industrial production, in particular the forging and machining of aeronautical parts. More specifically, this presentation relates to a manufacturing process for an annular part, for aeronautical engines but not exclusively. Previous technique

[0002] In the field of industrial production, the manufacture of metal parts includes, as is known, a forging range and a machining range, these ranges generally coming from different and independent sources (forger source and machinist source).

[0003] During the forging of the part, a metal block, or blank roughly representing the shape of the final part to be produced, is manufactured using a high-temperature furnace (between 900 and 1000°C) to shape the blank. The heated and shaped blank is then quenched in a coolant to solidify the shape and achieve the desired metallurgy. One or more additional heat treatments may also be performed.

[0004] The resulting rough blank is then machined to obtain the final part with the desired dimensions. During machining, some of the material forming the blank is removed by turning the part to adjust its dimensions (diameters, dimensions, etc.) to the desired values. The three-dimensional ("3D") parts of the part, in particular holes, grooves, or scallops where applicable, are also produced, for example by milling.

[0005] However, during the manufacture of large-diameter annular parts, for example, those exceeding 50 cm, using the machining described above, geometric defects may appear in the final part. This is the case, for example, for ferrules used to couple two turbomachine modules, such as a high-pressure turbine and a low-pressure turbine. Such ferrules require tight tolerances, with a maximum tolerance range, for example, of 0.05 mm, particularly at the shrink-fit interfaces between the ferrule and the turbomachine modules it joins. Failure to comply with this tolerance range results in defects in the final assembly, or even the rejection of the manufactured ferrules.

[0006] However, these large-diameter ferrules, for example about 1 m, have the characteristic of being flexible, given their dimensions and their material, generally A refractory metal alloy, such as a nickel alloy like Waspaloy®, is often used. However, the processes described above (forging and machining) for manufacturing this ferrule frequently result in geometric defects in the final part, making it impossible to meet the aforementioned tolerance ranges.

[0007] These defects can be caused, in particular, by residual stresses remaining in the blank after heat treatments, especially hardening, carried out after forging, and released during machining. These defects concern the circularity and average diameter of the ferrule at the shrink-fit interfaces. In other words, these parts are often produced with a lack of ovality and diameter sagging, leading to potential non-conformities during assembly and a high scrap rate.

[0008] There is therefore a need to address at least some of the aforementioned disadvantages. Description of the invention

[0009] The present description relates to a method for manufacturing a metallic annular part comprising at least one diameter having a predetermined value, the method comprising: - a forging stage in which a rough blank of the annular piece is manufactured, - at least one heat treatment step, - a machining step comprising on the one hand the fit turning of the blank to adjust the diameter of the blank to the predetermined value of the part to be manufactured, and on the other hand the removal of material from the blank in which at least 50% of the mass of the rough blank is removed and comprising at least the drilling of holes and / or a groove in the rough blank, the removal of material from the blank being carried out before the fit turning.

[0010] It is understood that the part to be manufactured is annular, for example a ring, and therefore necessarily comprises at least one diameter, for example at least one internal diameter and one external diameter with respect to the radial direction of the part, the part possibly exhibiting rotational symmetry. However, the annular part may have a more complex shape than a ring, and include one or more flanges, grooves, or shoulders. Such a more complex geometry implies several internal and external diameters.

[0011] Furthermore, "predetermined value" of diameter means the diameter value that the annular part must respect at the end of the manufacturing process to conform to the quality requirements, subject to a tolerance interval that is also predetermined.

[0012] It is further understood that the rough blank is a rough annular metal block obtained at the end of the forging stage, for example a ring, roughly showing the shape and dimensions of the final part, before the finishing stages by machining.

[0013] To this end, in a manner known per se, the rough blank is usually machined first by turning. For this purpose, the blank is rotated to machine its internal and / or external diameter, in order to adjust these diameters to the desired dimensions, i.e., the predetermined dimensions. Once this step is completed, the blank is then usually machined, notably by milling, to create the so-called "3D" parts, in particular the holes and / or grooves.

[0014] This manufacturing method, comprising these different steps carried out in this order, constitutes the usual practices encountered in industrial production, and is based on the optimization of the implementation of manufacturing, in order to reduce the number of steps and costs.

[0015] However, the inventors observed, through experiments and simulations carried out at each stage of the process, a significant release of residual stresses present in the blank after heat treatment, particularly during material removal from the blank, including drilling and milling of holes, which usually constitute the last stage of the machining operation and thus the finishing of the part. The deformation of the part, resulting in irregularities in its circularity, therefore occurs to a significant extent during milling.

[0016] Conversely, the inventors found, surprisingly, that by removing a maximum of material, in particular at least 50% of the mass of the blank and by making the holes and / or grooves in the first stage, and then making the geometries of revolution (diameters, faces) in the second stage to adjust the part to the dimensions desired by the adjustment turning stage usually carried out first, the defects observed in the resulting part decreased significantly.

[0017] Thus, reversing the material removal step, in which a significant amount of material is removed and at least some holes and / or grooves are formed in the blank initially, and the fitting turning step, in which at least one diameter of the blank is adjusted to the predetermined value of the part to be manufactured, makes it possible to considerably improve the circularity of the annular part thus manufactured, consequently reducing the scrap rate. In particular, this solution, although contrary to traditionally employed cutting strategies, makes it possible to reduce the scrap rate from approximately 90% to 10%.

[0018] In certain embodiments, during material removal from the blank, at least 90% of the initial mass of the rough blank is removed. This makes it possible to remove a maximum amount of material at the beginning of machining, and thus to minimize the effects of releasing residual stresses during the adjustment turning stage.

[0019] In some embodiments, the material removal includes the formation of scallops intended to be distributed circumferentially along an external face of the annular piece.

[0020] The scallops can be notches or slots distributed circumferentially around the annular part, preferably with holes allowing the part, for example a ferrule, to be attached to another part, for example a turbine module. The inventors found that machining scallops was responsible for a significant portion of the stress relief, and therefore of the deformation, in the final part. Consequently, performing the material removal, including scallop formation, before the final fitting and finishing turning of the part further improves the quality of the resulting part.

[0021] In certain embodiments, the diameter of the annular part is greater than or equal to 50 cm. It is understood that the larger the diameter of the annular part, the more flexible and relatively thin it is, and consequently, the more susceptible it is to deformation. Therefore, this solution, when applied to large-diameter parts, greater than or equal to 50 cm, significantly improves the circularity, and thus the quality of the resulting part.

[0022] In some embodiments, the process includes, after the step of forging the rough blank, then heat-treating the rough blank by quenching in a coolant, an expansion step, during which a diameter of the rough blank is increased relative to its initial diameter after quenching.

[0023] The inventors have observed that, particularly on flexible annular parts of large diameter (> 50 cm) and in particular in nickel alloy which only allows rapid quenching that freezes strong stress gradients, the heat treatments of de-icing usually carried out do not allow a return to a situation without residual stresses.

[0024] Conversely, the inventors have observed that stretching the rough blank by increasing its initial diameter, for example its initial internal diameter, during the expansion step after hardening, allows for the redistribution of stresses within the blank. Indeed, increasing the initial diameter of the blank induces plastic deformation, which helps to even out the stresses within the blank, and thus reduces significant local stress concentrations. This expansion step, in addition to reversing the machining steps described above, further improves the circularity and quality of the resulting annular parts.

[0025] In certain embodiments, during the expansion step, the diameter of the rough blank is increased by a value between 0.1% and 0.8% of its initial diameter.

[0026] These diameter expansion values, for example of the internal diameter of the rough blank, are sufficient to considerably reduce residual stresses and improve the quality of the parts obtained.

[0027] In some embodiments, the expansion step is carried out by means of a jack pushing the rough blank radially outwards so as to enlarge said rough blank.

[0028] For example, it is possible to use a jack with pads arranged against the radially internal face of the annular part at several equidistant places along this face, thus uniformly pushing the annular part outwards so as to stretch and widen it, and thus substantially increase the diameter of the annular part.

[0029] In certain embodiments, the annular part is a ferrule for coupling two aircraft engine modules. The aircraft engine modules could be, for example, the high-pressure and low-pressure turbines of the engine. Since the tolerance ranges for such a ferrule are very tight, implementing a process according to the present description is therefore particularly advantageous, as it allows for more efficient compliance with these tolerance ranges while significantly improving the circularity and thus the quality of the parts. Brief description of the drawings

[0030] The invention and its advantages will be better understood upon reading the following detailed description of various embodiments of the invention, given by way of non-limiting examples. This description refers to the accompanying figure pages, on which:

[0031] [Fig-1] Fig. 1 represents a perspective view of an annular ferrule coupling manufactured by a process according to the present description;

[0032] [Fig.2] [Fig.2] represents a section of the ferrule of [Fig.1] in a plane parallel to the central axis of the shell;

[0033] [Fig.3] Fig.3 is a diagram schematically representing the different steps of a process for manufacturing an annular part according to the prior art;

[0034] [Fig.4] Fig.4 is a graph representing the evolution of the number of parts per nuculars manufactured by the process of [Fig.3], depending on the differences between a diameter measured on these samples and the predetermined theoretical value of this diameter;

[0035] [Fig.5] Fig.5 is a diagram schematically representing the different steps of a manufacturing process for an annular part according to a first embodiment of the present presentation;

[0036] [Fig.6] Fig.6 is a graph (full on the left, and detailed on the right) representing the evolution of the number of annular pieces manufactured by the process of [Fig.5], as a function of the differences between a diameter measured on these samples and the predetermined theoretical value of this diameter;

[0037] [Fig.7] Fig.7 is a diagram schematically representing the different steps of a manufacturing process for an annular part according to a second embodiment of the present presentation;

[0038] [Fig.8] Fig.8 is a graph (full on the left, and detailed on the right) representing the evolution of the number of annular pieces manufactured by the process of [Fig.7], as a function of the differences between a diameter measured on these samples and the predetermined theoretical value of this diameter. Description of the implementation methods

[0039] In the following description, a method for manufacturing a coupling ferrule 10 of two aeronautical engine modules (not shown) will be described with reference to figures 1 to 8. The invention is not, however, limited to the manufacture of such a ferrule, but can be applied to all flexible metallic annular parts having a diameter greater than or equal to 50 cm.

[0040] Such a ferrule 10, shown in perspective in [Fig. 1], measures, for example, 1 m in internal diameter, and comprises a refractory nickel alloy, for example Waspaloy®. The ferrule 10 extends around an axial direction X, corresponding to the center of the ferrule 10, a radial direction R of the ferrule 10 being perpendicular to the axial direction X. The terms "internal", "external" and their derivatives are therefore considered in relation to this radial direction R, "internal" being understood as closer to the axis X, and "external" being understood as further from the axis X.

[0041] The ferrule 10 comprises a plurality of scallops 12, that is to say, notches distributed circumferentially around the ferrule 10, along its radially external face. Each of these scallops 12 is traversed by an orifice 14. The ferrule 10 also has a complex shape, clearly visible in the section shown in [Fig. 2].

[0042] The ferrule 10 includes, in particular, on a first axial face, a first annular flange 15, and a first annular groove 17. On a second axial face, the ferrule 10 includes, in particular, a shoulder 18 and a second annular groove 19. A second annular flange 16 is further formed at the radially internal end of the ferrule.

[0043] Each of these geometric structures comprising the ferrule 10 implies dimensions that must comply with predetermined values. In particular, the internal and external diameters of these different portions, notably the first annular flange 15 constituting a shrink-fit interface with an aeronautical module, must have predetermined values, which must respect a restricted tolerance range.

[0044] The following example focuses on the external diameter De of the first annular flange 15 (hereafter referred to simply as "flange 15"). However, the description could also apply to other portions of the part. It is understood that the external diameter De is the distance between the X-axis and the external surface of the first annular flange 15, identified by the dashed line in [Fig. 2].

[0045] Figure 3 is a diagram representing the different stages of a manufacturing process for such a ferrule 10 according to the prior art. Such a process comprises, firstly, a manufacturing stage (stage S100) in which a rough blank of the part is produced by forging, and secondly, a machining stage (stage S200) in which the rough blank obtained in stage S100 is machined to obtain the desired shape and dimensions of the ferrule 10.

[0046] The manufacturing step S100 comprises forging, which initially involves shaping a rough metal block. In a manner known per se, the block is placed in a furnace at 900-1000°C, and then a significant force is applied to the hot block to give it the desired shape (step S10). The shaped block is then placed back in the furnace at approximately 1000°C and subsequently quenched in a coolant (step S120), which may be water, oil, or a polymer liquid. During this step, due to the high cooling rate, quenching creates significant stress gradients within the part. In particular, the edges of the metal block cool faster than the core, resulting in strong stress gradients. An additional stress-relieving heat treatment is then performed to attempt to reduce these residual stresses (step S130).

[0047] Such a heat treatment for detention may include, in a manner known per se, tempering treatments, in particular by subjecting the part for 4h to a temperature of 850°C±10 and for 16h to 760°C±10, allowing the part to cool in open air.

[0048] At the end of the manufacturing step S100, which includes forging and heat treatments, a rough blank of the ferrule is obtained. This rough blank has, for example, the shape of a metal ring with a rectangular cross-section. During the machining step S200, this metal blank is first placed on a tool allowing it to be rotated, in order to adjust the diameters, in particular the external diameter De, to predetermined values ​​(fit turning step S210).

[0049] Once the diameters have been adjusted to the desired dimensions, the blank is then machined to form the highly 3D parts of the ferrule 10, in particular the grooves 17, 19, the orifices 14 and the scallops 12 (material removal step S220), by through the intermediary of a milling cutter, for example.

[0050] Figure 4 is a graph showing the distribution of the measurement results for diameter De, at a given location, on 67 samples, and in particular the deviation E in mm (millimeters) between the measured diameter De and the predetermined value that this diameter De must meet, for example, 958.1 mm. The interval I between the two dashed lines represents the tolerance interval that the diameter De must meet after the manufacturing process described above, this interval I being 0.05 mm. The solid curve represents the average variations in the number of samples as a function of the deviation E.

[0051] The graph in [Fig.4] shows a large number of samples with different deviations E, indicating a large dispersion of the measured diameter De values, and therefore a non-repeatability of the results obtained by this process, and further shows that the vast majority of the measured deviations E are beyond the tolerance interval I.

[0052] Figure 5 is a diagram representing the various stages of a manufacturing process for a ferrule 10 according to a first embodiment of the present description. The manufacturing step S100 in this first embodiment is identical to step S100 of the prior art process. However, the machining step S200 differs from step S200 of the prior art process in that steps S210 and S220 are reversed.

[0053] More specifically, during the machining step S200, the metal blank is first machined to form the strongly 3D parts of the ferrule 10, in particular the grooves 17, 19, the orifices 14 and the scallops 12 (material removal step S210'), and to remove a large part of the mass of the blank, in particular at least 50% of its mass, preferably at least 90%.

[0054] Next, the metal blank is placed on a tool allowing it to be rotated, so as to adjust the diameters, in particular the external diameter De, to predetermined values ​​(step S220' of adjustment turning). Thus, step S210' constitutes a roughing of the part in which the majority of the mass of the blank is removed, making it possible to obtain a ferrule 10 having overall the desired final shape, including in particular the orifices 14, scallops 12 and grooves 17, 19, and step S220' constitutes a finishing step in which the diameters are adjusted by a suitable tool.

[0055] It should be noted that the material removal step S210' may also include turning the blank, the latter constituting, however, a roughing turn (in addition to the milling of holes and / or grooves) allowing material to be removed to approach the final shape and dimensions of the ferrule 10, but which is different from the fitting turn (step S220'), allowing the adjustment of the diameters to the precise dimensions desired and predetermined.

[0056] Figure 6 is a graph showing the distribution of the diameter measurement results De, at a given location, on 18 samples, in particular the difference E in mm (millimeters) between the measured diameter De and the predetermined value of this diameter. In particular, the graph on the right represents the one on the left in more detail, with the x-axis scale enlarged.

[0057] The graph in [Fig. 6] shows a lower dispersion of the measured diameter values ​​De compared to the result of the prior art process ([Fig. 4]), demonstrating better repeatability of the results, and shows a larger proportion of the measured deviations E below the tolerance interval I of 0.05 mm. It should also be noted that reversing steps S210 and S220 results in a rate of 64.5% of the ferrules exhibiting circularity that meets quality requirements after machining step S200, compared to 1% without such a reversal in the prior art process. Thus, releasing a large portion of the residual stresses by performing the material removal and roughing step S210' first, before the diameter adjustment finishing step, improves the circularity of the ferrules 10.

[0058] Figure 7 is a diagram representing the various stages of a manufacturing process for a ferrule 10 according to a second embodiment of the present description. The machining step S200 in this second embodiment is identical to the step S200 of the process according to the first embodiment. However, the manufacturing step S100 differs from the step S100 of the prior art process according to the first embodiment in that it includes, after the quenching step S120 of the blank in a coolant, an expansion step S140, during which an initial diameter of the blank after the quenching step S120 is increased.

[0059] Thus, according to this second embodiment, the process includes on the one hand the expansion step S140 during the manufacture of the blank, and on the other hand carrying out the material removal step S210' of the blank before the fitting turning step S220'.

[0060] The expansion step S140 is carried out by means of a jack (not shown), for example a jack with pads arranged against the radially inner face of the annular blank at several equidistant points along this face, thus uniformly pushing the blank outwards so as to stretch and widen it, and thus substantially increasing the diameter of the annular part. The internal diameter of the rough blank can be increased by a value of between 0.1% and 0.8% of its initial diameter, for example by 0.71%.

[0061] Figure 8 is a graph representing the distribution of measurement results of the diameter De, at a given location, on 18 samples, specifically the difference E in mm (millimeters) between the measured diameter De and the predetermined value of this diameter. In particular, the graph on the right represents the one on the left in more detail, with the x-axis scale enlarged.

[0062] The graph in [Fig. 8] indicates a lower dispersion of the measured diameter values ​​De compared to the result of the prior art process ([Fig. 4]) and the first embodiment ([Fig. 6]), and shows an even greater proportion of the measured deviations E below the tolerance interval I of 0.05 mm, with all the tested samples meeting this interval in this example. It should also be noted that the addition of step S140, in addition to the reversal of steps S210 and S220, makes it possible to obtain a rate of 96% of the ferrules exhibiting, after machining step S200, a circularity conforming to the quality requirements.

[0063] Furthermore, a holding heat treatment step S150 can be carried out after the expansion step S140, the step S150 being identical to the step S130 described previously with reference to the prior art process.

[0064] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than a restrictive sense.

Claims

Demands

1. A method for manufacturing a metallic annular part (10) comprising at least one diameter (De) having a predetermined value, the method comprising: - a forging step (S10) in which a rough blank of the annular part (10) is produced, - at least one heat treatment step (S120, S130) by quenching in a coolant, - a machining step (S200) comprising, on the one hand, the fit turning (S220') of the blank to adjust the diameter (De) of the blank to the predetermined value of the part to be manufactured, and on the other hand, the material removal (S210') of the blank in which at least 50% of the mass of the rough blank is removed and comprising at least the drilling and milling of holes (14) and / or a groove (17, 19) in the rough blank, the removal of material (S210') of the rough being made before the adjustment turning (S220').

2. A method according to claim 1, wherein, during the removal of material (S210') from the blank, at least 90% of an initial mass of the rough blank is removed.

3. A method according to claim 1 or 2, wherein the material removal (S210') comprises the formation of scallops (12) intended to be distributed circumferentially along an external face of the annular piece (10).

4. A method according to any one of claims 1 to 3, wherein the diameter of the annular piece (10) is greater than or equal to 50 cm.

5. A method according to any one of claims 1 to 4, comprising, after the forging step (SI 10) of the rough blank, and then heat treatment (S120) of the rough blank by quenching in a coolant, an expansion step (S 140), during which a diameter of the rough blank is increased relative to its initial diameter after quenching.

6. A method according to claim 5, wherein, during the expansion step (S140), the diameter of the rough blank is increased by a value between 0.1% and 0.8% of its initial diameter.

7. A method according to claim 5 or 6, wherein the expansion step (S140) is carried out by means of a jack pushing the rough blank radially outwards so as to enlarge said blank

8. raw. Method according to any one of claims 1 to 7, wherein the annular part (10) is a ferrule enabling the coupling of two aircraft engine modules.

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