BE1025078A1 - Method of designing a tool for friction welding, tool obtained by said method and use of the tool for friction welding blades on a rotor of a turbomachine - Google Patents

Abstract

The method comprising the following steps: - defining a form of tool (1) initaile; - defining a design space (2) for welding a blade (4) to the outer wall of the rotor (5); - define the parameters essential to the design of the tool (1): force imposed on the tool, geometry of the blade (4), modulus of elasticity of the material of the tool (1), a margin of deformation of the tool (1) tolerated; discretizing the initial shape of the tool (1) in finite elements; optimizing the initial shape of the tool (1) in the design space (2) by using a topological optimization method taking into account the parameters essential to the design of the tool (1).

Description

(30) Priority data:

(71) Applicant (s):

SAFRAN AERO BOOSTERS S.A.

4041, HERSTAL

Belgium (72) Inventor (s):

PIERRE Paul-André 4000 LIEGE Belgium

LAVIGNE Thierry 01600 TREVOUX France (54) Method for designing a tool for friction welding, tool obtained by said method and use of the tool for friction welding of blades on a rotor of a turbomachine (57) The method comprising the following steps: defining a form of tool (1) initial; - define a design space (2) for welding a blade (4) to the outer wall of the rotor (5); - define the parameters essential to the design of the tool (1): force imposed on the tool, geometry of the blade (4), modulus of elasticity of the tool material (1), a margin of deformation tool (1) tolerated; discretize the initial shape of the tool (1) into finite elements; - optimize the initial shape of the tool (1) in the design space (2) using a topological optimization method taking into account the parameters essential to the design of the tool (1).

BE2017 / 5194

Method for designing a tool for friction welding, tool obtained by said method and use of the tool for friction welding of blades on a rotor of a turbomachine

Technical area [0Ö01

The invention relates to a method of designing a tool, to the tool obtained and to the use of the tool for friction welding.

State of the art [0002] Friction welding is a process which uses the heat generated by friction between a first part and a second part to be assembled by applying a compressive force between them. The heat generated makes it possible to bring the parts in contact with the parts to be assembled in a pasty state allowing them to be welded.

The friction between a first part and a second part to be assembled can be applied in a linear, rotary, circular or orbital motion between ies two parts. Orbital friction welding is particularly suitable for welding between two parts having two assembly surfaces with close dimensions but having no rotational symmetry of their two assembly surfaces.

Welding by orbital friction requires putting one of the 20 parts to be welded in movement relative to the other. An orbital friction machine allows control of the friction movement and the compression force applied during orbital friction welding. An orbital friction machine is equipped with a tool which allows the first piece to be welded to be held on the friction machine, the second piece to be welded being held in a fixed position.

Welding by orbital friction of blades on a turbomachine rotor requires an outii which allows the blade to be welded to be welded without damaging it as well as a tool having a space requirement which allows the welding of blades on a turbomachine rotor, the blades being configured in close proximity to each other.

[Ü0D8] Poor quality orbital friction welding is obtained when the tool does not allow a good transfer of the movement generated by the

BE2017 / 5194 orbital friction machine to the workpiece, it appears that a tool which has a different transfer of movement in one direction than in another does not allow obtaining a weld of optimal quality.

Welding by orbital friction of a blade on a turbomachine rotor for the production of a monebloc bladed disc requires a tool adapted to the part to be welded and making it possible to obtain a high quality weld.

Summary of rsnvention [0008] In order to provide a tool which allows a good transfer of the movement generated by the welding machine to the workpiece (and in different directions in the case of orbital friction welding) as well as a space requirement. which allows the welding of blades on a turbomaohine rotor in close proximity, the inventors propose according to a first aspect, a method of designing a tool for ie friction welding, preferably orbital, of a blade on a rotor of '' a turbomachine, said turbomaohine comprising:

~ a rotor having an axis of symmetry of revolution and an outer wall;

- blades each comprising:

o an assembly surface;

o a profiled portion;

o a volume;

said vanes being intended to be welded to said outer wall by said assembly surface;

said blades being intended to be welded in a plane perpendicular to said axis of symmetry of revolution of said rotor so that they form a crown of blades;

said blades of said blade crown being spaced by inter-blade spacing;

said tool being intended to hold one of said blades during its friction welding on said rotor;

said method comprising the following steps:

BE2017 / 5194

at. define an initial tool form;

b. defining a movement of said tool during a friction welding operation;

vs. defining a design space for welding one of said blades by said assembly surface to said outer wall of said rotor;

d. said design space being defined by the available space defined by said volume of the blade to be welded and by the inter-blade spacing available on either side of the blade to be welded and by the space necessary for movement said tool during a friction welding operation;

e. define the essential parameters for the design of the following tool

- a parameter relating to a force imposed by a friction machine on said tool for fear of welding a blade on a rotor;

- said assembly surface of said blade;

- a modulus of elasticity of the material for manufacturing said tool;

a tolerated margin of deformation of the tool, this margin being defined by the difference between the displacement generated by said friction machine and the displacement actually transmitted by said tool to said assembly surface of said blade during friction welding ;

f. discretize said initial farm of said tool into finite elements;

g. optimize said initial shape of said tool in said topological design space by using a topological optimization method taking into account said parameters essential to the design of said tool.

An initial tool shape is a form of the tool that has not been optimized. For example, a form of tool that has not been optimized takes up a large part of the design space. A form of tool that has not been optimized has for example been defined taking only into account the

BE2017 / 5194 mechanical stresses that the part must be able to withstand without any consideration concerning the mass or the shape of the tool [0010] During a friction welding operation, the friction machine generates a displacement which is transmitted to FoutiL L 'tool being provided to maintain a blade so as to weld the blade on the drum of a rotor. The displacement of the tool generated by the friction machine is defined in a plane. The movement of the tool generated by the friction machine requires a space available around the tool so that the tool does not come into contact during the welding operation with an element of the rotor or an element welded with the rotor. The displacement of the tool generated by the friction machine is preferably defined in a plane.

Preferably, friction welding is obtained by a relative movement of the two parts. For example, a point situated on the assembly surface of the blade is subjected to a relative movement with respect to a point situated on the assembly surface of the rotor and vice versa, [0012] When welding a blade on the rotor drum, it is important to clearly define the design space available. The design space takes into account the projecting elements closest to the assembly surface located on the rotor. These elements are blades, blade stumps, wipers or any other element ... When it is a question of making a crown of blades, that is to say blades aligned in a plane and having equal inter-blade spacing, the space available for carrying out a weld aimed at welding a blade at a location intended to receive a blade is the space between two blades already welded, The space available is space to weld the last blade of a blade crown. The space available to weld a blade of a blade crown between two existing blade crowns is the space available between all adjacent blades. The design space is the available space reduced by the tool displacement space generated by the friction machine, preferably orbital friction. The design space also plans to be reduced by a margin of error. The design space takes into account the space available around the area to be welded, the displacement of the tool necessary for welding as well as a margin of error.

BE2017 / 5194 [0013] The design of the tool requires the definition of parameters specific to the tool. These parameters make it possible to define the design constraints of the tool.

One of the design parameters is the force imposed by a friction machine during the welding of a blade on a rotor.

This parameter takes into account the mass of the blade to be welded, the assembly surface of the blade, the assembly surface on the rotor, the type or materials of the blade and the rotor, the force of compression imposed by the friction machine between the blade and the rotor. These forces imposed by the friction machine 10 are defined in a plane. The forces imposed by the friction machine defined in a plan depend on the geometry of the assembly surfaces.

One of the design parameters is the assembly surface of a blade. This parameter can also define an area relating to a part of the blade intended to be clamped in the tool.

One of the design parameters is a modulus of elasticity of the material for making or manufacturing the tool. Preferably the tool is made of metallic material. The elastic modulus can also be defined by defining a specific material known to the skilled person.

[0Ô1 T] One of the design parameters is a tolerated tool deformation margin. This tolerated margin of deformation must make it possible to obtain a high quality weld. A high quality weld is preferably a weld having no point defect or having a homogeneous weld quality of the assembly surface. The topological optimization 2 5 makes it possible to find an optimal distribution of the material of the tool in a design space and taking into account one or more design parameters. Topological optimization makes it possible to obtain an optimal tool mass, that is to say preferably the smallest possible taking into account the parameters imposed.

3Ö [0018] The design of the tool requires the discretization of the shape of the initial tool into a mesh of points in three-dimensional space. The discretization in a mesh of points corresponds to the discretization in the form of finite elements of the initial form of the tool

BE2017 / 5194 [0019] The design of S’oiitH includes the optimization of the initial form of i'outii by a topological optimization method. The topological optimization method takes into account the design parameters of

I’m out.

Topological optimization consists of finding the ideal material distribution of an object subjected to constraints in a given volume in order to, for example, improve its characteristics and reduce the amount of material used.

Topological optimization makes it possible to assign a weight to each of the points of the tool in three-dimensional space by means of an optimization groove, for example, as a function of its importance for achieving the targeted characteristics. Topological optimization, depending on the weight to be assigned to each of the tool points, keeps the most important points and removes the least important points. Topological optimization makes it possible, thanks to an optimization loop, to repeat the optimization until a form of the tool is obtained having the defined technical characteristics and having the smallest possible mass. A smoothing step of the tool obtained can prove useful at the end of topological optimization in order to obtain a tool that is relatively easy to manufacture and for example without sharp edges or tips.

Topoiogical optimization aims to minimize or maximize an objective function while satisfying the constraints and displacements to which the object must respond. The objective function is for example a function defining the mass of the object to be optimized. Topoiogical optimization is different from shape optimization or dimensioning in that it allows a structure of the object to appear different from the initial structure, for example by making holes appear or disappear, reinforcements, changes in connection between elements.

The advantage of the tool design method is that it allows the design of a tool suitable for the manufacture of a type of one-piece bladed disc. For example, the method allows the design of a tool according to the space available between the blades of the one-piece bladed disc.

BE2017 / 5194

For example, the method allows the design of a tool according to the size of the blade to be assembled.

The tool which allows the first part to be welded to be held is designed so as to be able to transmit the friction movement with the least possible deformation.

Preferably, said tool comprises a fixed part and a mobile part, said fixed part and mobile part being mechanically coupled and in that said fixed part allows the maintenance of a blade during the welding operation, iü [ The advantage of having a tool having a fixed part and a mobile part is to be able to have a fixed part fixed to the friction machine and able to receive a mobile part intended to receive the blade. The fixed part and the mobile part are movable with respect to each other in one direction. In an orthogonal three-dimensional space, the fixed part and the mobile part are movable with respect to one another in one direction and are mechanically coupled in the other two directions. The movable part is for example connected to the friction machine in a mechanical and controllable manner, that is to say that the friction machine makes it possible to control the maintenance of the movable part with the fixed part during a welding operation. . The friction machine makes it possible to control the release of the movable part from the fixed part after the welding of a blade on the rotor in the direction where the fixed part and the mobile part are not mechanically coupled. The advantage of being able to release the movable part which holds the blade during the welding is that it allows the movable part and therefore the tool to be removed from the blade having just been welded to the rotor. The advantage is to be able to dispose of more space to release the clamping means allowing a blade to be very firmly held in the tool.

Preferably, said method comprises the following additional step after step f. :

adapting the tool obtained for machining said tool The advantage of carrying out an adaptation of the tool obtained for its machining is that it is easy to machine. Indeed, during topological optimization, sharp edges or spikes may remain and it is sometimes

BE2017 / 5194 necessary to smooth the object obtained. Smoothing should not be done at the expense of objective function, mechanical properties and design space. Adapting the tool for machining most of the time results in an increase in the mass of the object obtained by topological optimization.

Preferably, said deformation margin is defined in a plane.

The weld being produced by heating by friction generated in a yaw, the deformation of the tool which it is appropriate to control is a deformation in a plane.

[Ü031] Preferably, the topological optimization validates or removes the presence of each discretized element of said tool for all said parameters essential to the design of said tool.

The advantage of topoiogical optimization compared to other types of optimization is to be able to vary the mass of the tool by defining a weight for each of the discretized elements of the object. Thus the topological optimization makes it possible to validate the most important points of the tool to achieve an objective function for example and to delete the less important points in order to reduce the mass of the tool. The advantage of this method is to be able to delete points anywhere in the tool and not only near the edges of the tool as a shape optimization would allow for example.

The inventors propose, according to a second aspect, a tool obtained by the method of the invention.

The different variants and advantages described for the method according to the first aspect of the invention apply to the device of the second aspect, mutadis mutandis.

The inventors propose, according to a third aspect, a method for welding a blade to a rotor by friction, preferably orbital and comprising the following steps:

at. provide a tool;

b. providing a friction machine, preferably orbital, comprising a movable plate, said movable plate being defined by a plane;

BE2017 / 5194

vs. fixing said tool to said movable plate of said friction machine, preferably an orbital friction machine;

d. positioning a blade in said tool, said blade comprising:

- a basic portion;

- a profiled portion;

said base portion comprising an assembly portion; said assembly portion comprising an assembly surface;

said assembly surface being defined by a plane;

the blade being clamped in said tool by its said base portion such that the plane defined by said assembly surface of said blade is parallel to the plane defined by said movable plate of said friction machine, preferably orbital;

said assembly portion being located beyond the part of the base portion clamped in said tool;

e. providing a rotor comprising an outer wall, said outer wall comprising an assembly portion, said assembly portion comprising an assembly surface;

f. positioning said assembly surface of said blade in contact with said assembly surface of said rotor;

g. performing a friction weld, preferably by orbital friction of said blade on said rotor by bringing said assembly surfaces of said blade and said rotor into contact, by imposing a relative, preferably relative rotational movement between said assembly surfaces and by imposing a compressive force between said assembly surfaces so that the heat generated by your friction forces between said assembly surfaces makes it possible to reach a pasty state of said assembly portions;

h. releasing said tool from the assembly formed by said blade and said rotor. [ÖÖ36] The different variants and advantages described for the method according to the first aspect of the invention and for the device for the second aspect apply to the method of using the device of the third aspect, mutadis mutandis.

BE2017 / 5194 [0037] Preferably, the method comprises the following additional step before step a. :

by machining removing a blade to be replaced from a one-piece bladed disc comprising a rotor, said rotor comprising an outer wall, said outer wall comprising an assembly portion welded to said blade to be replaced, the machining making it possible to remove the blade to replace the assembly portion and form an assembly surface capable of receiving a blade by friction welding, preferably orbital.

Preferably, a turbomachine comprising a one-piece bladed disc obtained by the method described above,

Brief description of the figures

These aspects as well as other aspects of the invention will be clarified in the detailed description of particular embodiments of the invention, reference being made to the drawings of the figures, in which:

- Fig.1 shows a sectional view of the rotor of a turbomachine illustrating the design space allowing the welding by orbital friction of a blade on said rotor;

- Fig, 2 shows a sectional view of the rotor of a turbomachine having a location intended to weld a blade and also shows an orbital friction machine in which a blade is held by a tool and is presented at the location intended to weld a blade;

- Fig.3 shows a sectional view of the rotor of a turbomachine having a location intended to weld a blade and also shows an orbital friction machine in which a blade is held by a tool having a fixed part and a movable part, the blade being held by the movable part, the blade is presented as a replacement intended to weld a blade;

- Fig.4 shows a close-up view of a blade welded to a turbomachine rotor and representing the difference in areas and part concerned by the welding.

BE2017 / 5194 ~ Fig. 5 shows a 3D view of a monobioc bladed disc making it possible to visualize a design space situated between blades already welded to the turbomachine rotor.

The drawings of the figures are not to scale, Generally, similar elements are denoted by similar references in the figures. The presence of reference numbers in the drawings cannot be considered to be limiting, including when these numbers are indicated in the claims.

Detailed description of certain embodiments of the invention [0Ö39] FIG. 1 illustrates a section of a rotor 5 of a turbomachine of the bladed monobloc disc type 19 comprising vanes 4 welded directly to the drum 5. FIG. 1 illustrates a section longitudinal, that is to say in the direction of the length of the rotor 5. This sectional view also represents an axis of symmetry of revolution 3. The blades 4 feel welded around the rotor 5 15 on the outer surface 6 of the rotor 5. In this preferred embodiment, your blades 4 are welded radially around the rotor 5 and in three rows of blades 4. The rows of blades 4 are also called blade crowns 4. Figure 1 shows a design space 2 located on a row of blades between two rows of blades and on which at least one blade is missing. A blade 4 can be welded in a design space 2 on a turbomachine rotor 5 during the manufacture of a one-piece bladed disc or during the repair of such a one-piece bladed disc 19. The design space 2 takes counts the space available between already welded vanes 4 located on the same row of vanes 4 and or between vanes located on one or two adjacent rows of vanes. The design space 2 also takes into account the space occupied by replacement available to weld a blade 4 in the case of a blade 4 not present.

The location available for welding a blade preferably includes an assembly portion 16 projecting from the outer surface 6 of the rotor 30 5. This assembly portion 16 is also called a stump. An assembly portion 16 comprises an assembly surface 17 intended to be brought into contact with the assembly surface of the blade 12 and to be rubbed

BE2017 / 5194 until your assembly portions of rotor 16 and mole 12 reach a temperature sufficient to produce a weld between the assembly portion 15 of the blade 4 and the assembly portion 16 of the rotor 5 Once the desired temperature has been reached, the friction movement is stopped in a reference position and a forging force is exerted on the blade 4 towards the drum 5 in order to form the weld.

The design space 2 is defined taking into account the presence of the wipers 18, the presence of the blades already welded, the assembly portion 16 located on the rotor 5 and intended to receive a blade 4.

The design space 2 can also extend beyond the adjacent blades 4 by providing holes in the design space 2. The design space takes into account the curvature of the rotor 5. The curvature of the rotor 5 can be different depending on the row of dawn. The design space 2 is different depending on the row of blades on which it is desired to weld a blade 4. The blades 4 may be different depending on the row of blades on which they are intended to be welded.

A tool 1 can be designed by taking into account several different design spaces 2. Several design spaces 2 can be used to define a global design space 2 allowing the design of a tool 1 compatible with each of the rows of blades to be welded. A tool 1 can be designed for each of the rows of blades, A tool 1 can be designed for the blade welding on two rows of blades of the same single-piece bladed disc 19. A tool 1 can be designed for welding blades 4 of two rows of adjacent blades of the same single-piece bladed disc 19. A tool 1 25 can be designed for welding blades 4 of three rows of blades of the same single-bladed disc 19.

[0G42] FIG. 2 illustrates a one-piece bladed disc 19 comprising a location for welding a blade 4. The location for welding a blade 4 has an assembly portion 16. FIG. 2 illustrates an orbital friction machine 8 comprising a movable plate 7 on which the tool 1. The tool 1 is designed taking into account the design space 2 as well as the displacement generated by the orbital friction machine 8 and your mechanical constraints that Toutil 1 must be able to withstand. Tool 1 described in Figure 2

BE2017 / 5194 includes a part. The tool 1 has fixing means to be fixed to the orbital friction machine 8 and or to the movable plate 7. The tool 1 described in FIG. 2 presents means making it possible to maintain a blade 4 to be welded by the base portion 14 of this blade 4. The base portion 14 and the assembly portion 15 of the blade 4 can be partly combined. The tool 1 attached to the orbital friction machine 8 makes it possible to present the assembly surface 12 of the blade 4 to be welded opposite the assembly surface 17 situated on the rotor 5. Preferably, the surfaces of assemblies 12, 17 have similar topologies. Preferably, the assembly surfaces are each defined in a plane. Preferably when the assembly surfaces are brought into contact to rub them against each other, these are coplanar and or included in the same plane.

The tool 1 is designed so that the movable plate 7 or the orbital friction machine 8 cannot collide with one of the elements of the one-piece bladed disc 19, a blade 4 or the rotor 5.

FIG. 3 illustrates a one-piece bladed disc 19 as described in FIGS. 1 and 2, FIG. 3 also illustrates a tool 1 composed of a fixed part 9 and a movable part 10. The fixed part 9 of the tool 1 has fixing means which allow it to be fixed to the orbital friction machine 8 and or to the movable plate 7. The fixed part 9 and the mobile part 10 of the tool 1 are mechanically coupled in two directions that form a plan. The plane formed by these two directions is for example coplanar with the plane formed by the assembly surface 12 of the blade. The fixed part 9 and the mobile part 10 of the tool 1 are mechanically coupled by a system of pins present. on the fixed part and a system of holes present on the moving part 10. The pins and your holes make it possible to mechanically and playfully couple the fixed part 9 and the mobile part between it and in a plane. Preferably the plane in which the fixed 9 and mobile 10 parts of the tool 1 are blocked is perpendicular to the direction of assembly of the mobile part 10 on the fixed part 9.

FIG. 4 illustrates a blade 4 held by a tool 1, the blade 4 comprises a base portion 14, the base portion 14 comprises an assembly portion of the blade 15. The assembly portion has a blade assembly surface 15 which allows orbital friction welding of the blade

BE2017 / 5194 on the rotor 5. The tool 1 allows you to keep the blade 4 by its base portion and or by its assembly portion so that the blade 4 has no play with respect to the tool 1 during orbital friction welding, that is to say when applying a compressive force as well as by generating a friction force on the assembly surface 12 of the blade. The blade 4 is preferably held in the tool 1 by mechanical, hydraulic, or pneumatic clamping means of the base portion 14 of the blade. The profiled part of the blade is inserted into the tool 1 and is kept out of contact with the tool 1 during the orbital friction welding operation. The blade 4 is IG held in the tool 1 by its base portion 14 or by its assembly portion 15 but not by its profiled portion 11.

The rotor 5 has projecting from its outer surface 6 an assembly portion 16 which comprises an assembly surface 17. The assembly surfaces of the blade 15 and the rotor 17 are presented 15 parallel to each other. come out that when they are in contact and an orbital friction movement is generated, the friction forces on these two surfaces are generated in a homogeneous manner. The assembly surfaces of the blade 12 and the rotor 17, for example, have different shapes and different areas. The assembly surfaces of the blade 12 and the rotor 17 for example have identical shapes and identical areas.

[Ü047] FIG. 5 illustrates a one-piece bladed disc 19 comprising three rows of vanes arranged radially, author of the main part. Each row of dawn can be defined in a plan. A blade 4 to be welded can be located in the middle of other blades 4 on a bladed disc 25 in one piece 19 and the tool 1 necessary for its welding can be partly defined by the design space 2 available between the blades present on the monobioc bladed disc 19. The situation which requires welding a blade between two adjacent blades on the same row of blades arises when it is the last blade to be welded on a blade row or when replacing a 7G dawn. The replacement of a blade is necessary when a welded blade does not have the desired characteristics or when during the use of the one-piece bladed disc 19, a blade 4 is damaged and requires replacement. The replacement of a vane 4 requires prior

BE2017 / 5194 welding of a new blade, the machining of the damaged blade 4 in order to form an assembly surface 17 projecting from the exterior surface 6 of the rotor 5.

Welding by orbital friction is obtained by a relative rotation of the blade 4 and the rotor 5. For example, a point located on the assembly surface of the blade 12 is subjected to a relative rotation by relative to a point on the assembly surface of rotor 17 and vice zersa. The orbital friction movement can be defined as follows, two parallel straight lines, one located on the assembly surface of the blade 12 and the other on the assembly surface of the rotor 17 remain parallel to each other when a 10 orbital friction movement is applied between these two assembly surfaces.

The weld obtained by the orbital friction welding operation using the tool 1 has very good weld homogeneity, that is to say that the weld has no points of weakness.

The present invention has been described in connection with specific embodiments, which have a purely illustrative value and should not be considered as limiting. In general, the present invention is not limited to the examples illustrated and / or described above. The use of the verbs "understand", "include", "comprise", or any other variant, as well as their conjugations, cannot in any way exclude the presence of elements other than those mentioned. The use of the indefinite article "a", "an", or of the definite article "1e", "ia" or "Γ", to introduce an element does not exclude the presence of a plurality of these elements. Reference numbers in the claims do not limit their scope.

The description of the preferred embodiments relates to orbital friction. However, the invention can be applied to any friction welding method, for example ia linear friction.

In summary, the invention can also be described as follows.

The method comprising the following steps:

.3 O - define an initial tool form;

- define a design space for welding a blade to the outer wall of the rotor;

BE2017 / 5194 define the parameters essential to the design of the tool: force imposed on the tool, geometry of the blade, modulus of elasticity of the tool material, a margin of deformation of the tool! tolerated;

discretize the initial form of the tool into finite elements;

optimize the initial shape of the tool in the design space using a topological optimization method taking into account the parameters essential to the design of the tool.

BE2017 / 5194

Claims (8)

Claims 1. Method for designing a tool (1) for friction welding of a blade (4) on a rotor (5) of a turbomachine, said turbomachine comprising: - a rotor (5) having an axis of symmetry of revolution (3) and an outer wall (6); - vanes (4) each comprising: o an assembly surface (12); o a profiled portion (11); o a volume; said vanes (4) being intended to be welded to said outer wall (6) by said assembly surface (12); said blades (4) being intended to be welded in a plane perpendicular to said axis of symmetry of revolution (3) of said rotor (5) so that they form a crown of blades; said blades (4) of said blade ring being spaced by an inter-blade spacing (13); said tool (1) being intended to hold one of said blades (4) during its friction welding on said rotor (5); Said method comprising the following steps: at. define an initial tool form (1); b. define a displacement of said tool (1) during a friction welding operation; vs. defining a design space (2) for welding one of said blades (4) by said assembly surface (12) to said outer wall of said rotor (5); d. said design space (2) being defined by the available space defined by said volume of faube to be welded and by the inter-blade spacing (13) available on either side of faube to be welded and by the space required moving said tool (1) during a friction welding operation; e. define the essential parameters for the design of the following tool (1): BE2017 / 5194 - a parameter relating to a force imposed by a friction machine (8) on said tool for welding a blade (4) on a rotor (5); - said assembly surface of said blade (4); - a modulus of elasticity of the material for manufacturing said tool (1); a tolerated margin of deformation of the tool (1), this margin being defined by the difference between the displacement generated by said friction machine (8) and the displacement actually transmitted by said tool (1) to said surface of assembly (12) of said blade (4) during friction welding; f, discretizing said initial form of said tool (1) into finite elements; g. optimize said initial shape of said tool (1) in said topological design space (2) by using a topological optimization method taking into account said parameters essential to the design of said tool (1). 2. Method according to the preceding claim characterized in that the 20 friction is orbital friction and in that the step friction machine e. is an orbital friction machine .. 3. Method according to any one of the preceding claims, characterized in that said tool (1) comprises a fixed part (9) and a mobile part (10), said fixed part (9) and mobile part (10) being coupled mechanically and in that said fixed part (9) allows the maintenance of a blade (4) during the welding operation. 4. Method according to any one of the preceding claims comprising the following additional step after step f. : - adapt the tool (1) obtained for machining said tool (1). BE2017 / 5194 5. Seton method Any of the preceding claims characterized in that said deformation margin is defined in a plane. 5 6. Method according to any one of the preceding claims, characterized in that the topological optimization validates or eliminates the presence of each discretized element of said tool (1) for all of said essential parameters for the design of said tool (1). 10 15 7. Tool (1) obtained according to any one of the preceding claims. 8. Method for welding a blade (4) to a rotor (5) by friction and comprising the following steps: at. providing a tool (1) according to claim 7; b. providing a friction machine (8) comprising a movable plate (7), said movable plate (7) being defined by a plane; vs. fixing said tool (1) to said movable plate (7) of said friction machine (8); d. positioning a blade (4) in said tool (1), said blade (4) 20 including: - a base portion (14); - a profiled portion (11); said base portion (14) comprising an assembly portion (15); 3 said assembly portion (15) comprising an assembly surface (12); said assembly surface (12) being defined by a plane; the blade (4) being clamped in said tool (1) by its said base portion (14) such as the plane defined by said assembly surface (12) of 30 said blade (4) is parallel to the plane defined by said movable plate (7) of said friction machine (8); said assembly portion (15) being located beyond the part of the base portion (14) clamped in said tool (1); BE2017 / 5194 e. providing a rotor (5) comprising an outer wall (6), said outer wall (6) comprising an assembly portion (16), said assembly portion (16) comprising an assembly surface (17); f. position said assembly surface (12) of said blade (4) at 5 contact of said assembly surface (17) of said rotor (5); g. performing a friction weld of said blade (4) on said rotor (5) by bringing said assembly surfaces (12; 17) of said blade (4) and said rotor (5) into contact, by imposing a relative movement between said assembly surfaces (12; 17) and by imposing a force of 10 compression between said assembly surfaces (12; 17) so that the heat generated by your friction efforts between said assembly surfaces (12; 17) allow a pasty state of said assembly portions (15; 16) to be reached ); h. release said tool (1) from the assembly formed by said blade (4) and said 15 rotor (5), 9. Method according to the preceding claim and comprising the following additional step before step a. : - removing by machining a blade (4) to be replaced from a one-piece bladed disc comprising a rotor (5), said rotor (5) comprising an outer wall (6), said outer wall (6) comprising an assembly portion ( 16) welded to said blade (4) to be replaced, the machining making it possible to remove the blade (4) to be replaced from the assembly portion (16) and to form an assembly surface (17) suitable for 2 5 receive a blade (4) by friction welding. 10. Method according to any one of the two preceding claims characterized in that the friction is an orbital friction, in that said relative movement of step g. is a relative rotational movement, and in 30 what the friction machine of step b. is an orbital friction machine. BE2017 / 5194 11. Turbomachine comprising a one-piece bladed disc obtained by the method according to any one of the three preceding claims. BE2017 / 5194 BE2017 / 5194 BE2017 / 5194 \ BE2017 / 5194 Abridged Method for designing an outH for friction welding, tool obtained by said method and use of the tool for friction welding of blades on a rotor of a turbomachine The method comprising the following steps: - define an initial tool form (1); - define a design space (2) for welding a blade (4) to the outer wall of the rotor (5); - define the parameters essential to the design of the tool (1): force imposed on the tool, geometry of the blade (4), modulus of elasticity of the tool material (1), a margin of deformation tool (1) tolerated; - discretize the initial shape of the tool (1) into finite elements; - optimize the initial shape of the tool (1) in the design space (2) using a topologic optimization method taking into account the parameters essential to the design of the tool (1).