WO2014083270A1

WO2014083270A1 - Method for creating a power transmission casing using friction stir welding

Info

Publication number: WO2014083270A1
Application number: PCT/FR2013/052852
Authority: WO
Inventors: Baptiste Jean Patrice GUERIN
Original assignee: Hispano-Suiza
Priority date: 2012-11-27
Filing date: 2013-11-26
Publication date: 2014-06-05
Also published as: FR2998498B1; FR2998498A1

Abstract

The invention relates to a method for creating a power transmission casing (7), comprising the steps that involve machining at least a first and a second metal sheet in order respectively to form at least a first and a second hollow part (7a, 7b) to be assembled, then in assembling the two hollow parts (7a, 7b) by friction stir welding so as to form the casing (7), and fixing a third hollow part (7c), intended to form a reservoir, to at least one of the first and second hollow parts (7a, 7b) by friction stir welding, one of said first and second hollow parts (7a, 7b) forming a dividing partition between the space delimited by said first and second parts (7a, 7b) and that delimited by said third part (7c).

Description

METHOD FOR MAKING A TRANSMISSION CASE

POWER

USING FRICTION MIXING WELDING

The present invention relates to a method of producing a power transmission casing for a turbomachine.

A turbomachine, such as a turbojet engine or a turboprop engine, conventionally comprises, from upstream to downstream in the direction of flow of the gases, a fan, a low pressure compressor, a high pressure compressor, a combustion chamber, a high turbine pressure, a low pressure turbine, and a gas exhaust nozzle. Each compressor stage has a turbine stage, both of which are connected by a shaft so as to form a body, in particular a low pressure body and a high pressure body.

Part of the power generated by a turbomachine is used to supply energy to different equipment of the turbomachine. This power is taken mechanically on the shaft of the high pressure body of the turbomachine by a power take-off shaft which drives an input shaft of a power transmission.

Power transmission is also known as "Accessory Gearbox" or AGB. It is a housing comprising a gear mechanism connected to equipment or accessories, such as for example an electric generator, a choke, an alternator, hydraulic pumps, fuel or oil, etc.

The AGB generally comprises a casing manufactured by foundry, having a housing for accommodating the gear system for driving the accessories and closed by several lids. The various accessories driven by the AGB are mounted directly on the housing or on the covers, the drive shafts of the accessories passing through the wall of said housing.

The power transmission also comprises a lubrication system that supplies different parts of the turbomachine and ensures the lubrication of the internal organs of the power transmission. The lubrication circuit more specifically comprises an oil reservoir, a lubricating unit (which drives the circulating oil in the circuit) and oil transport lines to the lubrication units. The lubrication unit is usually mounted near the AGB and is driven by it.

In some turbomachines, for reasons of compactness and economy of pipes, it was chosen to mount the oil tank directly on the AGB. For this purpose, the oil reservoir can be formed by an outgrowth of the casting part forming the housing of the AGB. The disadvantage of this type of casting is the difficulty of its design and manufacture. The foundry is indeed a difficult technique to control and the cost of a complex piece with an outgrowth is relatively high.

In other turbomachines, it has been chosen to separate the oil reservoir from the AGB, which makes it possible to form the AGB directly by machining a metal billet. Such parts manufactured directly by machining are commonly designated by those skilled in the art by the expression of "machined-mass" or "cut-mass" parts. In general, such parts must be machined on last generation machining centers, for example comprising 5 axes.

The AGB can also be formed from a so-called "split-line" technology, in which two half-shells or two hollow parts are used to form the housing of the AGB. The two hollow portions are generally assembled by bolting, which requires to provide extra thickness in the bolted areas to limit the effects of stress concentrations due to the use of bolts. The oil tank is then removed from the AGB and connected to it by pipes. Such a solution generates a large mass and bulk. Patent application WO 2010/086422 discloses a technology similar to the "split-line" in which the AGB is formed by machining a metal block, an oil reservoir being also formed by machining a metal block, AGB and the tank are then assembled by screwing at the flanges by interposing an additional partition to prevent the oil contained in the tank flows unduly into the compartment of the AGB.

The invention aims in particular to provide a simple, effective and economical solution to the problems mentioned.

To this end, it proposes a method for producing a power transmission casing, characterized in that it comprises the steps of machining at least a first and a second sheet so as to form at least a first and a second sheet respectively. second hollow portions to be assembled, then to assemble the two hollow parts by friction-stir welding so as to form the housing, and in that a third hollow part, intended to form a reservoir, is fixed on at least one first and second hollow portions by friction stir welding, one of said first and second hollow portions forming a partition wall between the space defined by said first and second portions and that defined by said third portion.

The assembly of the two hollow parts by friction stir welding makes it possible, in a simple manner, a casing having complex shapes, without requiring extra thicknesses. Friction stir welding also avoids a significant reduction of the mechanical characteristics (behavior under static forces, fatigue behavior, hardness, etc.) compared to other welding processes. Such a welding process also makes it possible to assemble parts made of materials known to be difficult to weld.

In addition, as indicated above, the machining of two hollow parts which are subsequently assembled makes it possible to produce housings having very complex shapes. Each sheet may have a thickness between 80 and 160 mm for example. The supply of thicker sheets is generally difficult. Thus, for a casing having a thickness of the order of 200 mm, the realization of a housing in two parts assembled makes it possible to dispense with such supply constraints. The machining of each hollow portion can be performed on a traditional machining center, for example comprising 2 or 3 axes, less expensive and less complex than a last-generation machining center, comprising for example 5 axes.

In addition, according to the invention, the tank is integrated in the AGB, which reduces the mass and bulk of the assembly. Note that, according to the invention, it is not necessary to provide additional separate partition, to separate the inner space of the first and second hollow portions and that of the tank as is the case in the document WO 2010 / 086422. The realization of the power transmission casing is thus facilitated.

Friction Stir Welding (FSW) is known in particular from document EP 0 752 926, and involves the use of a rotating mobile welding head comprising a body and a kneading pin. protruding from the body.

This method consists of rotating the welding head and the kneading pin at a controlled speed and to penetrate the pin at an interface zone between two parts to be assembled. The friction thus generated causes, by heating, a softening of the material of the parts that enters the pasty phase. The corresponding edges of the pieces are then deformed plastically and the pasty material of these parts is mixed. The body generally forms with the pin a shoulder that prevents the brewed metal from moving away from the welding zone. The welding head is also moved along the area to be welded so as to form a weld bead by cooling and crystallization of the pasty material thus mixed. This pasty welding of the material is preferred for applications where it is important to maintain the original characteristics of the assembled parts. Indeed, because the material is in a pasty and non-liquid state (there is no fusion during such a welding process), the mechanical properties of said parts are slightly degraded. For example, there is a decrease of about 30% in elongation and yield strength for an aluminum alloy, which is relatively small compared to other welding processes.

Such a method makes it possible in particular to assemble parts of aluminum alloys known to be difficult to weld or very sensitive to cracking, to weld large thicknesses in a single pass and with a minimum of deformation of the parts, to obtain a microstructure to fine grains in the weld zone and minimize thermomechanical stresses and deformations during welding. It is then generally not necessary to perform a heat treatment and / or subsequent machining.

By way of comparison, the assembly of two pieces by TIG (Tungsten Inert Gas) welding generates a reduction of about 50% in mechanical characteristics after subsequent machining and heat treatment. Similarly, the assembly of two pieces by electron beam welding generates a reduction of about 40% in mechanical characteristics after subsequent machining and heat treatment.

The sheets can be made of an aluminum alloy, such as for example an alloy of the 2000 series or an alloy of the 7000 series.

This type of material has good mechanical properties and is easily weldable by the friction stir method.

According to a feature of the invention, before assembly of the first and second hollow parts by friction stir welding, they are pre-assembled by spot welding. This makes it possible to limit the deformation of the hollow parts during the subsequent welding and ensures better positioning of said parts so as to obtain a casing that complies with the dimensional specifications.

Preferably, during friction stir welding, a support member is mounted in opposition to a friction stir welding head.

At least two of the hollow parts are made of identical materials (homogeneous housing) or different (heterogeneous housing).

In addition, after assembly, at least one of said hollow portions can be machined at functional areas, such as bearing supports.

In addition, after assembly, at least a portion of the housing can undergo a complete heat treatment or local to restore the original mechanical characteristics of the material. In the case where the complete heat treatment of the part is performed, the material can be advantageously welded in the quenched and not returned state.

It will be noted, however, that the assembly using the friction-kneading welding method generally makes it possible to dispense with such heat treatment.

According to one embodiment, each of the first and second hollow portions may comprise at least one flange extending substantially perpendicular to a side wall of said portion, the first and second hollow portions being joined to each other by welding by friction-mixing at their flanges.

According to another embodiment, the first and second hollow portions may respectively comprise a first and a second edge zone extending in the extension of one another, said edge zones being assembled together by friction welding. -mixing.

The invention will be better understood and other details, features and advantages of the invention will become apparent on reading the following description given by way of non-limiting example with reference to the accompanying drawings in which:

- Figure 1 is a longitudinal sectional view of a portion of a friction stir welding head,

FIGS. 2 to 4 are diagrammatic views showing various steps of the friction stir assembly method,

- Figures 5 to 7 are views schematically illustrating the assembly of three types of different housings.

FIG. 1 represents a friction stir welding head 1 intended to equip a numerically controlled machine. The head 1 comprises a hollow body 2 in which a central rod 3 is displaceable in translation. The end of this rod comprises a peg of smaller diameter, forming a kneading pin 4 projecting from the body 2. A guiding member 5 of the pin 4 is fixed to the end of the body 2, between the latter and the peg 2. The rod 3 is movable along the axis A of the body 2, between an extended position in which the pin 4 protrudes out of the body 2 and the guide member 5, and a retracted position in which the pin 4 does not does not protrude out of the body 2 and the guide member 5. The body 2 or the guide member 5 (which form the same assembly) form a shoulder 6 with the pin 4.

The numerically controlled machine conventionally comprises means for moving the welding head 1 relative to the parts to be welded 7a, 7b, means for moving the rod 3 and the kneading pin 4 relative to the body 2, and means driving in rotation of the body 2 and the rod 3.

We will now describe a method of assembling two pieces by friction-stirring, with reference to Figures 2 to 4.

After assembling the parts 7a, 7b on a fixed support, the welding head 1 is rotated, for example at a speed of the order of 1000 revolutions per minute (FIG. 2). Meanwhile, it is moved along the axis A until the kneading pin 4 (which is in the deployed position) penetrates into the material of the parts 7a, 7b, at the region to be welded 8, and that the shoulder 6 bears on the outer surfaces of the corresponding ends of the parts 7a, 7b (Figure 3). At this moment, a force is applied by the welding head 1, so that the shoulder 6 rests on the aforementioned surfaces.

The penetration of the kneading pin 4 into the material at the region to be welded 8 and its controlled rotation within the material cause, by frictional heating, a softening of the material of the parts 7a, 7b which enters the paste phase. The corresponding ends of the parts 7a, 7b are then deformed plastically and the pasty material of these parts 7a, 7b is mixed. The shoulder 6 prevents the stirred metal from moving away from the welding zone 8.

The welding head 1 is moved progressively over the entire circumference of the zone to be welded 8 and over an additional overlap zone. Thus, a continuous weld bead 9 is formed (FIG. 4) by cooling with ambient air and crystallization of the mixed pasty material.

The tangential advance speed of the welding head 1 relative to the parts 7a, 7b is for example between 100 and 300 mm / min. At the end of the stroke, the pin 4 is moved relative to the body 1 in its retracted position, the shoulder 6 continuing to maintain the material at the welded zone 8 during the withdrawal of the pin 4 (FIG. ).

After completion of the weld bead 9, the welding head 1 is moved away from the area to be welded and the rotation of the welding head 1 is stopped.

As indicated above, such friction stir welding is particularly advantageous in the case of the repair or the production of an aluminum or aluminum alloy casing, since it does not cause a significant reduction in the mechanical characteristics. assembled parts 7a, 7b at the welded zone 8. In addition, the assembled parts 7a, 7b do not require treatment thermal or subsequent machining. Finally, such an assembly respects the thickness of the assembled parts 7a, 7b at the welded zone 8.

FIG. 5 illustrates a method of producing a power transmission casing 7, for a turbomachine such as a turbojet engine or a turboprop engine, according to a first embodiment.

This process comprises at least the following successive steps:

machining two hollow portions 7a, 7b, also called half-shells, in aluminum alloy sheets, for example in alloy sheets of the 2000 series or the 7000 series, preferably in the type of alloy 2618,

- Fixing the two hollow parts 7a, 7b in a welding machine, facing one another, so that they come into contact with each other at a surface to assemble 8,

pre-assembling the two hollow portions 7a, 7b by spot welding by friction-stirring, such a process also being referred to as Spot Welding Friction,

- Assembling the two hollow portions 7a, 7b by welding-mixing by producing a continuous weld bead 9 along the surface 8 to be assembled, so as to form the housing 7,

dismantling the casing 7 thus assembled from the welding machine,

machining the casing 7 assembled at the level of functional areas, such as bearing supports, equipment supports, or any other function necessary for a transmission of power,

optionally, performing a local or complete heat treatment of the assembled and machined housing 7, so as to restore the mechanical properties of the aluminum alloy.

In the embodiment of FIG. 5, each hollow portion 7a, 7b comprises at least one flange 1 1a, 1 1b extending substantially perpendicularly to a side wall of said portion 7a, 7b, the two hollow portions 7a, 7b being joined to one another by friction-stirring at their flanges 1 1a, 1 1b.

In this embodiment, the welding head 1 is brought perpendicularly to the flanges 1 1a, 1 1b, the kneading pin 4 passing through a first flange 1 1a and then sinking into the second opposite flange 1 1b. This second flange 1 1b is not traversed by the kneading pin 4 and thus acts as the metal bearing zone opposite the head 1, so as to limit the deformation of the welded zone.

Preferably, the friction stir welding is carried out by means of a welding head 1 comprising a retractable pin 4, so as to achieve a progressive start and end of the welding bead 9, as is known from FIG. prior art. Alternatively, if the welding head 1 has no retractable pin 4, the beginning and the end of the bead 9 may be located outside the surface to be assembled, in a zone intended to be weakly constrained.

The mounting of each hollow portion 7a, 7b on the welding machine can be achieved using mechanical flanges and / or using vacuum tables, for example.

FIG. 6 illustrates a second embodiment, in which the first and second hollow portions 7a, 7b respectively comprise a first and a second edge zone 12a, 12b extending in the extension of one another, said zones 12a, 12b are assembled together by friction stir welding.

In this case, a support element 13 is mounted opposite the welding head 1 so as to avoid the deformation of the hollow portions 7a, 7b at the assembled zone 8. This support element 13 is pressed against the edges 12a, 12b, inside the housing 7, and is intended to be removed before dismantling the casing 7 of the welding machine.

In this case also, the casing 7 preferably has a progressive geometry and large radii, at the edges 12a, 12b to assemble, so as to achieve a weld 9 around the housing 7 without degrading the quality of the weld bead 9 in the corners.

FIG. 7 illustrates a third embodiment, in accordance with the invention, distinguished from that of FIG. 6 in that a third hollow portion 7c, also produced by machining in a sheet made of an aluminum alloy of the aforementioned type, is fixed on one 7a of the hollow portions 7a, 7b by friction-stir welding. This part 7c may be pre-assembled by spot welding, and then be assembled by friction stir welding to form a continuous weld seam along the assembly zone 8b. In this embodiment, the third hollow portion 7c has a plated flange 11c against a surface of the hollow portion 7a, the contact surface between the portions 7a, 7c forming the weld zone 8b.

The parts 7a and 7b can be assembled by means of a first welding head 1a and the parts 7a and 7c can be assembled with the aid of a second welding head 1b. Alternatively, one and the same welding head 1 can be used to make each of the aforementioned assemblies.

Of course, it is also conceivable to assemble the parts 7a and 7b at the flanges 11a, 11b, similarly to what has been described with reference to Figure 5.

In this embodiment, the portions 7a and 7b define an internal volume 15 and the portion 7c defines an internal volume 16, separated from each other by a partition wall 14 formed by the portion 7a.

Moreover, at least one of the hollow parts 7a, 7b, 7c may have a functional zone, here an excess thickness 10 at the partition wall 14 and whose surface facing the internal volume 15 is machined after assembly of the parts. hollow 7a and 7b.

Claims

1. Process for producing a power transmission casing (7), characterized in that it comprises the steps of machining at least a first and a second plate so as to form at least a first and a second hollow part respectively ( 7a, 7b) to be assembled, then to assemble the two hollow portions (7a, 7b) by friction-stir welding to form the housing (7), and in that a third hollow portion (7c) for forming a reservoir, is fixed on at least one of the first and second hollow portions (7a, 7b) by friction stir welding, one of said first and second hollow portions (7a, 7b) forming a partition wall between the space delimited by said first and second parts (7a, 7b) and that delimited by said third part (7c).

2. Method according to claim 1, characterized in that the sheets are made of an aluminum alloy, such as for example an alloy of the 2000 series or an alloy of the 7000 series.

3. Method according to claim 1 or 2, characterized in that, before assembly of the first and second hollow portions (7a, 7b) by friction-stir welding, the latter (7a, 7b) are pre-assembled by welding by point.

4. Method according to one of claims 1 to 3, characterized in that, during the friction-stir welding, a support element (13) is mounted in opposition to a friction welding head (1). mixing.

5. Method according to one of claims 1 to 4, characterized in that at least two of the hollow portions (7a, 7b, 7c) are made of identical or different materials.

6. Method according to one of claims 1 to 5, characterized in that, after assembly, at least one of the hollow portions (7a, 7b, 7c) is machined at functional areas (10), such as bearing supports.

7. Method according to one of claims 1 to 5, characterized in that, after assembly, at least a portion of the housing (7) undergoes heat treatment.

8. Method according to one of claims 1 to 7, characterized in that each of the first and second hollow portions (7a, 7b) comprises at least one flange (1 1 a, 1 1 b) extending substantially perpendicular to a side wall of said portion (7a, 7b), the first and second hollow portions (7a, 7b) being joined to each other by friction stir welding at their flanges (11a, 11b). ).

9. Method according to one of claims 1 to 7, characterized in that the first and second hollow portions (7a, 7b) respectively comprise a first and a second edge zone (12a, 12b) extending in the extension l one of the other, said edge regions (12a, 12b) being joined together by friction stir welding.