BE1031524A1 - METHOD FOR MODELING A BLADE JUNCTION TO A TURBOMACHINE ROTOR STUMP BY ORBITAL WELDING - Google Patents

Abstract

The invention proposes a method for modeling a junction (10) of a blade (4) to a stub (6) on a rotor (2) of a turbomachine, by orbital friction welding, comprising the following step: determining a material consumption rate VCA as a function of the following orbital friction welding parameters: eccentricity, frequency and pressure, and a geometric parameter z of the section of the blade and the stub at the junction; remarkable in that the method further comprises the following step: determining a maximum thickness emax of the junction as a function of the determined material consumption rate VCA, the geometric parameter z being an average of the mean radii zi sweeping the section at the junction at any point i of the periphery of said section.

Description

Description

METHOD FOR MODELING A BLADE JUNCTION TO A STUMP

TURBOMACHINE ROTOR BY ORBITAL WELDING

Technical field

The invention relates to a method for modeling a blade junction to a turbomachine rotor, and more particularly to a method for modeling a junction obtained by orbital friction welding of a blade to a stub on a turbomachine rotor.

Prior art

Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being or will be adopted by various states. In particular, an ambitious standard applies both to new types of aircraft but also to those in circulation requiring the implementation of technological solutions in order to make them compliant with current regulations. Civil aviation has been mobilizing for several years now to make a contribution to the fight against climate change.

Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft. The Applicant takes into consideration the impact factors in all phases of design and development to obtain less energy-intensive, more environmentally friendly aeronautical components and products whose integration and use in civil aviation have moderate environmental consequences with the aim of improving the energy efficiency of aircraft.

Consequently, the Applicant is constantly working to reduce its negative climate impact by using methods and operating virtuous development and manufacturing processes and minimizing greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of its activity.

This sustained research and development work covers new generations of aircraft engines, the weight reduction of aircraft, particularly through the materials used and the lighter on-board equipment, the development of the use of electrical technologies to provide propulsion, and, as an essential complement to technological progress, aeronautical biofuels.

To this end, the invention is the result of technological research aimed at significantly improving the performance of aircraft and, in this sense, contributes to reducing the environmental impact of aircraft.

In this context, the invention relates to a method of modeling and orbital friction welding for producing a bladed disk (commonly referred to as: "blisk") or a bladed drum (commonly referred to as "blum") for a turbomachine compressor.

Orbital friction welding is a welding process in which the parts to be assembled are brought into contact under stress and welded by a circular motion generally defined by an eccentric, and accompanied by a uniform tangential speed, so as to generate friction and homogeneous heating at a weld junction between the two parts.

It is also known to use linear friction welding, this is a welding process in which the necessary heat is created by a back and forth movement of the interfaces to be welded. However, orbital friction welding has several advantages over linear friction, for example, the relative movement between the two interfaces is continuous thanks to the circular friction movement, which provides better thermal homogeneity. Unlike linear movement for which the relative speed of the two parts becomes zero at each half-oscillation period. In addition, the cycle time of orbital welding is considerably lower than that of linear friction welding (respectively approximately 2 minutes compared to approximately 5 minutes).

Published patent document EP 2 535 516 A1 discloses a method of orbital friction welding of blades to a turbomachine rotor in which, once a material consumption is reached in a welding zone between the blade and the disk, the orbital movement is stopped at a reference position, and a forging force is exerted on the blade against the rotor in order to form the weld.

After welding, progressive machining adapting to the external surface of the blade is then carried out in order to remove the material from the interface which will have been pushed outwards during welding (commonly referred to as: "flash"), so as to avoid any projection linked to machining.

However, post-weld machining may reveal a weld junction of the blade with the rotor disc which may present structural defects and/or material health defects.

Summary of the invention

Technical problem

The invention aims to solve at least one of the problems posed by the prior art. More specifically, the invention aims to propose a simple and economical solution for controlling the structural and dimensional quality of the weld between the blade and the bladed disk.

Technical solution

The invention is the result of technological research aimed at very significantly improving the performance of aircraft and, in this sense, contributes to reducing the environmental impact of aircraft. For this purpose, the subject of the present invention is a method for modeling a blade-to-stub junction on a turbomachine rotor, by orbital friction welding, comprising the following step: determining a material consumption rate VCA as a function of the following orbital friction welding parameters: eccentricity, frequency and pressure, and a geometric parameter z of the section of the blade and the stub at the junction; remarkable in that the method further comprises the following step: determining a maximum thickness emax of the junction as a function of the determined material consumption rate VCA, the geometric parameter z being an average of the average radii z; scanning the section of the blade and the stub at the junction at any point/periphery of said section.

Advantageously, the pressure comprises a forging pressure and/or a pressure applied during an orbital movement of the orbital friction weld.

According to an advantageous embodiment of the invention, the maximum thickness emax determined and the material consumption rate VCA determined are all the greater as the geometric parameter z is small and vice versa.

According to an advantageous embodiment of the invention, the mean radii zi sweeping the section of the blade and the stump at the junction at any point i of the periphery of said section are strictly contained in said section.

According to an advantageous embodiment of the invention, the mean radii Z; scanning the section of the blade and the stump at the junction at any point i of the periphery of said section completely scan said section.

According to an advantageous embodiment of the invention, the maximum thickness emax determined and the material consumption rate VCA determined are all the smaller as the eccentricity decreases and vice versa.

According to an advantageous embodiment of the invention, the maximum thickness @max determined and the material consumption rate VCA determined are all the smaller as the frequency decreases and vice versa.

According to an advantageous embodiment of the invention, the determination of the maximum thickness @max and the material consumption rate VCA is based on experimental orbital friction welding data, where for each welding operation the material consumption rate VCA is measured and correlated with the eccentricity, the frequency, the pressure and the geometric parameter z.

According to an advantageous embodiment of the invention, the correlations of the experimental data are made so as to provide a model for determining the rate of consumption of material VCA and possibly the maximum thickness emax.

According to an advantageous embodiment of the invention, the model for determining the material consumption rate VCA and possibly the maximum thickness emax involves the use of artificial intelligence.

The invention also relates to a method of orbital friction welding of a blade to a stub on a turbomachine rotor to form a junction, comprising the following step: determining a material consumption rate VCA; characterized in that the method further comprises the following step: determining a maximum thickness E€max of the junction as a function of the determined material consumption rate VCA and as a function of a geometric parameter z corresponding to an average of the mean radii Zi scanning the section of the blade and the stub at the junction at any point i of the periphery of said section.

Advantageously, determination of a material consumption rate VCA corresponds to a measurement on the machine and/or the tooling performing the orbital welding. Preferably, the determination of the maximum thickness

Emax of the joint is also a function of the following orbital friction welding parameters: eccentricity, frequency and forging pressure, said parameters being determined by measurement on the machine and/or tooling performing the orbital welding.

According to an advantageous embodiment of the invention, the welding method further comprising a step of comparing the maximum thickness emax determined with an interval of values of the maximum thickness @max predefined during a modeling method of the blade junction to the stump, said modeling method being according to the invention.

The invention also relates to a method for dimensioning a blade and a corresponding stub on a turbomachine rotor, intended to be joined by orbital friction welding, according to a maximum thickness emax of the predetermined junction, remarkable in that the dimensioning method comprises an iteration of determining the maximum thickness @max of the junction according to different dimensions of the junction, according to a modeling method according to the invention.

According to an advantageous embodiment of the invention, the iteration of determining the maximum thickness emax of the junction according to different dimensions of the junction is carried out while the eccentricity, the frequency and the pressure remain constant. Preferably, the pressure comprises the pressure applied during the orbital movement and the forging pressure.

According to an advantageous embodiment of the invention, the different dimensions of the junction, in the iteration of determining the maximum thickness emax of the junction, are selected so as to correspond to different values of the geometric parameter z.

According to an advantageous embodiment of the invention, the iteration of determining the maximum thickness Emax of the junction according to different dimensions of the junction is stopped when the maximum thickness emax determined corresponds to the maximum thickness @max of the junction predetermined with a given tolerance.

The measures of the invention are particularly advantageous in that the determination of the material consumption rate VCA, in particular as a function of the geometric parameter z of the junction section, makes it possible to ensure an efficient and precise estimation of the maximum thickness emax of said junction.

The modeling of the junction by determining its maximum thickness emax, allows, from the design stage, to define an optimal dimensioning of the radial extents of the blades and the stubs so as to guarantee an optimal radial position of a welding plane of the junction before orbital welding. In addition, the contact section presented between the blades and the stubs is also dimensioned by means of a robust process so as to ensure homogeneity of the mixing of the material and thus obtain a healthy welded junction free of defects.

It is understood that each detail of an embodiment below can be combined with each other detail of the other embodiments.

Brief description of the drawings

Figure 1 schematically illustrates a side view of a blade joined to a stub extending radially from a turbomachine rotor, having an orbital friction welded junction comprising a maximum thickness

Emax determined by a junction modeling method according to the invention;

Figure 2 schematically illustrates a section of the blade and/or stump at the junction visible in Figure 1;

Figure 3 illustrates the junction section of Figure 2 when determining a mean radius Za sweeping said section from a point A on the periphery of said section;

Figure 4 illustrates the junction section of Figure 2 when determining a mean radius za sweeping said section from a point B on its periphery.

Detailed description of the embodiments

In the following description, the terms “internal” and “external” refer to a positioning relative to the axis of rotation of an axial turbomachine.

The axial direction is the direction along the axis of rotation of the turbomachine, with lengths measured axially. Widths are measured circumferentially. The radial direction is perpendicular to the axis of rotation. Upstream and downstream refer to the main flow direction of the flow in the turbomachine.

The dimensions of the figures are not to scale and in particular the thicknesses or radial dimensions are exaggerated to facilitate reading of the figures.

Figure 1 schematically illustrates a side view of a blade 4 joined to a stub 6 extending radially from an external surface 8 of a turbomachine rotor 2, having a junction 10 welded by orbital friction comprising a maximum thickness @max determined by a method of modeling the junction according to the invention.

It can be observed that the junction 10 has a diabolo or butterfly shape, with a wider peripheral end (in the radial direction) than its inner central part, this is due to a concentration of the excess material displaced during orbital welding. For this purpose, the maximum thickness

Emax Se Measured at the peripheral end of junction 10.

The present invention proposes a modeling method and a method of dimensioning the blades 4 and the stubs 6 so as to allow the manufacture of a bladed disk for a turbomachine.

Preferably, the bladed disc is a mobile wheel intended to be arranged upstream of an air flow separation nozzle in a turbomachine.

For this purpose, the external surface 8 corresponds to an air guiding surface of a fluid stream along the turbomachine. Alternatively, the bladed disk may correspond to a drum-type rotor belonging to a high-pressure or low-pressure compressor.

Preferably, the bladed disk is a so-called “bi-material” disk comprising two different titanium alloys. For example, the blades 4 can be made from a Ta6v alloy, and the rotor disk 2 from one of the following alloys: Ti17, Ti575, Ti1023.

Advantageously, the mixture of the two different titanium alloys (Ta6v and Ti17) presents easier machinability, and makes it possible to achieve a gain in mass compared to a solution based, for example, solely on a Ti17 alloy, this is notably due to a density of Ta6v which is slightly lower than that of Ti17.

In fact, the Ti17 alloy was preferentially chosen for the disc part for its good HCF fatigue characteristics (English acronym for: “High Cycle

Fatigue”) and LFC (“Low Cycle Fatigue”). A Ti17 disc will also show a greater margin in burst speed than a Ta6v disc.

For the blades, the Ta6v alloy was chosen because it provides the blades with a higher elongation at break (better impact resistance), and better crack propagation behavior which results in better durability to low energy impacts.

It can be seen in Figure 1 that the junction 10 comprises a weld plane 10.1 illustrated in a central position relative to the maximum thickness emax of said junction 10.

Advantageously, the determination of the emax makes it possible to control the radial position h of the weld plane 10.1 from the external surface 8 of the rotor 2, as well as to size the radial extent of the blade 4 and the stub 6, prior to the manufacture of the bladed disk.

In this regard, the method of modeling the junction 10 comprises a step of determining the maximum thickness emax as a function of a material consumption rate VCA (which can be expressed in mm/s) which is presented at the contact interface between the blade 4 and the stub 6 during orbital friction welding.

The method of the invention makes it possible to determine the rate of material consumption VCA analytically by an estimation as a function of a geometric parameter z of the section of the blade 4 and the stub 6 at the junction 10, and also as a function of the following orbital friction welding parameters: eccentricity (corresponding to the eccentric e of the orbital oscillation movement during welding); frequency (oscillation speed); and the pressure applied during the maximum axial consumption phase during the orbital movement. Advantageously, the welding parameters can be predefined as input instructions on a welding machine prior to the execution of said welding.

Preferably, the analytical estimation of the material consumption rate

VCA is based on experimental orbital friction welding data, for example by means of test specimens using the same orbital welding parameters, where for each welding operation the actual VCA speed is measured and correlated with the eccentricity, frequency, forging pressure and the geometric parameter z. Preferably by means of artificial intelligence. Thus, a model for determining the VCA speed can be defined.

It has been established that the maximum thickness @max and the determined material consumption rate VCA are all the greater as the geometric parameter z is small and the eccentricity and/or frequency increases and vice versa.

Advantageously, the maximum thickness Eemax determined by means of the modeling method of the invention makes it possible, prior to orbital welding, to control the radial position h of the welding plane 10.1, and thus to size the radial extent of each of the blade 4 and the stub 6.

Figure 2 schematically illustrates the section 11 of the blade 4 and/or the stub 6 at the weld junction 10 visible in Figure 1.

Preferably, section 11 is identical for blade 4 and for stub 6 of rotor 2.

Section 11 is modeled from an aerodynamic profile 4.1 of the blade 4, preferably, the latter includes a section widening by means of an excess thickness e corresponding, more preferably, to the eccentric e of the orbital oscillation movement during welding. However, the excess thickness e is not necessarily constant around the profile 4.1, it may present variations around said profile 4.1.

It should be noted that prior to orbital friction welding, a sacrificial volume of material (extending essentially radially) is provided on each of the blades 4 and the stubs 6 to be assembled. This sacrificial volume is caused to be extruded outside the contact interface between the sections 11, thus forming a burr, commonly referred to as: "flash", which will then be eliminated, to reach the profile 4.1 of the blade. However, a non-homogeneous ejection of the flash along the periphery of the section to be welded risks causing the recirculation of local material inside the section to be welded and can prevent complete ejection of the contaminants created at the first moments of the weld and risks creating recesses in the welded joint, which is detrimental to the quality of the weld.

Advantageously, the widening of the contact section makes it possible to avoid the recirculation of the material (potentially harmful because it prevents the evacuation of impurities) towards narrower regions of the section of the final aerodynamic profile 4.1 of the blade and thus to ensure thermal homogeneity during welding, precisely in the final section 4.1 of the blade 4. Indeed, if we add an excess thickness e at least equal to the value of the eccentric, this means that the points of the final aerodynamic surface 4.1 are always in contact during welding (between the stump and the blade).

Unlike the points in this excess thickness e which, by the orbital movement, are in contact with the opposite surface only during part of the orbit.

Thus, during welding, at section 11, the resulting local VCA speeds are more homogeneous, which allows the blade profile 4.1 to be preserved more and a more resistant joint to be obtained.

The modeled section 11 makes it possible to determine the geometric parameter z. Indeed, z is an average of the mean radii zi sweeping the section 11 at any point on its periphery 11.1.

Each of the mean rays z; corresponds to an average length Zi of rays

Zia Extending entirely in section 11 from a point / to the periphery 11.1 and sweeping said section 11. Preferably, the Zia rays correspond to projections of the point / onto an entire portion of the periphery 11.1 which is opposite said point /.

Advantageously, the evolution of the mean radii zi on the periphery of the section 11 to be welded physically represents the homogeneity of the length to be sheared during rotation (orbital movement during welding) and therefore the homogeneity of the material flow rate expelled in the flash along the contour of the blade. It is representative of the homogeneity of ejection of contaminants from the weld.

In this regard, the determination of the geometric parameter z includes the determination of the mean radius z; for the plurality of points / over the entire periphery 11.1.

Preferably, the determination of the geometric parameter z is an automated process using a computer algorithm. In this regard, a “ray tracing” type algorithm can be adapted.

Figures 3 and 4 illustrate an example of projection of rays ZAa and ZB,a, respectively, from points A and B of the periphery 11.1.

Figure 3 illustrates section 11 when determining a mean radius za sweeping said section 11 from a point A of the periphery 11.1.

It can be seen that from point A, a plurality of rays Za are projected onto a portion of the periphery 11.1 visible from said point A. In this configuration, the rays zac can be included between two rays Zaa tangent to the periphery 11.1.

The number of rays Za, projected can depend on the angle a chosen, the latter allows to establish the precision of determination of the average radius za. For this purpose, the angle a can be between 0.001° and 10°.

The mean radius Za thus corresponds to the average of all the projections ZA, a.

Figure 4 illustrates section 11 when determining a mean radius ze sweeping said section 11 from a point B of the periphery 11.1.

Preferably, the angle a is identical for all projections of the rays

Zia for the plurality of points / of the periphery 11.1. Preferably, the number of points / of the periphery 11.1 from which the rays will be projected, is approximately 2000 points, this number being able to vary according to the desired calculation precision.

Similarly to point A, the rays Zes are projected from point B onto a portion of the periphery 11.1 visible at said point B. The mean radius Zs corresponds to the average of all the projections Zsa.

The geometric parameter z is therefore the average of all the mean radii Zi (including the mean radii za and Zs) of the points / of the entire periphery 11.1.

The geometric parameter z corresponds to a geometric dimension that can be expressed in mm. Advantageously, this parameter z is the optimal dimension that best distinguishes the geometric shape of the section 11 and thus ensures a precise correlation between the weld parameters and the VCA speed. Indeed, the surfaces of the section 11 comprising the projected rays Zia from each point / can be assimilated to the mixing surface of the material during orbital friction welding (without being limited by a particular theory).

The geometric parameter z allows to take into account the specificities of orbital friction welding in the manufacturing process. Indeed, the friction force provided during welding rotates cyclically, which implies that a weld point at the end of section 11 (e.g. point A or B) sees a fraction of section 11 of the blade between the two extreme projected radii (ZA a OR ZB,a), the latter can therefore be assimilated to equivalent lengths of material to be sheared.

Moreover, the parameter z is relevant because it allows to take into account more the camber of the specific shape of the periphery 11.1, in a better way than the area of said section 11 or the chord of its profile.

In order to further optimize the dimensions of the blade and the rotor stubs, the dimensioning method of the present invention makes it possible to act iteratively on the shape of the section 11 so as to reach a predefined maximum thickness emax, while the parameters of the orbital friction welding from which the VCA speed is predetermined remain constant.

Preferably, the shape of the section 11 is modified by acting on the excess thickness. For example, with reference to FIG. 2, the excess thickness e can be retained, and a second excess thickness can further widen the narrowest regions of the section 11, i.e. widening at the ends 11.2, 11.3. The modification of the section 11 can be carried out manually by means of modeling software, or in an automated manner by a specific computer algorithm.

The modification of section 11 causes a change in the value of the geometric parameter z, which influences the determined VCA speed as well as the Emax. In this configuration, for each new junction section established, the maximum thickness @max is determined, and this iteratively until said determined @max corresponds to the initially predefined emax, with a tolerance of +5%.

The last joint section modeled before stopping the iteration is the one that will be used for orbital welding of the blade to the disk, said section will be widened enough with respect to the blade profile to ensure constant material mixing and VCA speed during welding, thus obtaining a welded joint with better structural quality and free of recesses and contaminants.

Advantageously, the dimensioning method of the invention therefore makes it possible to define both an optimal radial position of the weld plane and an ideal junction section. This is done prior to the manufacture of the bladed disk, so as to allow anticipation of the stresses that may be exerted on the junction following possible impacts of debris on the blades.

Thus, the bladed disc obtained by orbital welding of the blades to the stubs sized by the process, comprises junctions positioned radially in an optimal manner, each of said junctions advantageously comprising an improved structural and dimensional quality.

Advantageously, the welding method of the invention makes it possible, during the manufacture of the turbomachine bladed disk, to estimate the maximum thickness €max for each orbital weld made between the blade and the stub, from the geometric parameter z, and by measuring the VCA speed and the forging pressure directly on the welding machine used.

The geometric parameter z can be the one used when modeling the section to be welded, or measured on the blade and/or on the stump before the welding operation, for example, by means of an image recognition measurement.

Advantageously, the welding method of the invention makes it possible to validate the value of the maximum thickness Emax estimated during each weld without requiring a physical inspection of the part (e.g. by making cuts and micrographs), thus ensuring efficiency and considerable time savings during the manufacture of the bladed disc.

Preferably, the validation includes a comparison of the estimated maximum thickness Emax with thickness values between predetermined limit boundaries, for example, when modeling the junction. Advantageously, these limit boundaries make it possible to comply with certain design criteria (e.g. critical threshold N1/N2 for crack propagation, tolerance interval involving parametric and/or height and/or inclination variabilities of the junction, etc.).

Alternatively, the comparison of the emax determined (by measuring the VCA and the z parameter) during orbital welding can be carried out with the emax calculated during modeling, which makes it possible to quantify the influence of the real welding parameters (measured on the machine) on the thickness of the modeled junction and thus validate the welds during the manufacture of the bladed disc without requiring destructive cutting of the bladed disc.

Claims (15)

Claims 1. Method for modeling a junction (10) of a blade (4) to a stub (6) on a rotor (2) of a turbomachine, by orbital friction welding, comprising the following step: determining a material consumption rate BOR as a function of the following orbital friction welding parameters: eccentricity, frequency and pressure, and a geometric parameter z of the section (11) of the blade (4) and the stub (6) at the junction (10); characterized in that the method further comprises the following step: determining a maximum thickness emax of the junction (10) as a function of the determined material consumption rate VCA, the geometric parameter z being an average of the mean radii z; scanning the section (11) of the blade (4) and the stub (6) at the junction (10) at any point / of the periphery (11.1) of said section (11). 2. Modeling method according to claim 1, in which the determined maximum thickness @max and the determined material consumption rate VCA are all the greater as the geometric parameter z is small and vice versa. 3. Modeling method according to one of claims 1 and 2, in which the mean radii z; scanning the section (11) of the blade (4) and the stump (6) at the junction (10) at any point / of the periphery (11.1) of said section (11) are strictly contained in said section (11). 4. Modeling method according to one of claims 1 to 3, in which the mean rays z; scanning the section (11) of the blade (4) and the stub (6) at the junction (10) at any point i of the periphery (11.1) of said section (11) completely scan said section (11). 5. Modeling method according to one of claims 1 to 4, in which the determined maximum thickness emax and the determined material consumption rate VCA are all the smaller as the eccentricity decreases and vice versa. 6. Modeling method according to one of claims 1 to 5, in which the determined maximum thickness @max and the determined material consumption rate VCA are all the smaller as the frequency decreases and vice versa. 7. Modeling method according to one of claims 1 to 6, in which the determination of the maximum thickness emax and the material consumption rate VCA is based on experimental orbital friction welding data, where for each welding operation the material consumption rate VCA is measured and correlated with the eccentricity, the frequency, the pressure and the geometric parameter z. 8. Modeling method according to claim 7, in which the correlations of the experimental data are made so as to provide a model for determining the rate of material consumption VCA and possibly the maximum thickness Gmax. 9. Modeling method according to claim 8, in which the model for determining the material consumption rate VCA and possibly the maximum thickness emax involves the use of artificial intelligence. 10. Method for orbital friction welding of a blade (4) to a stub (6) on a turbomachine rotor (2) to form a junction (10), comprising the following step: determining a material consumption rate VCA; characterized in that the method further comprises the following step: determining a maximum thickness Emax of the junction (10) as a function of the determined material consumption rate VCA and as a function of a geometric parameter z corresponding to an average of the mean radii zi sweeping the section (11) of the blade (4) and the stub (6) at the junction (10) at any point/of the periphery (11.1) of said section (11). 11. Welding method according to claim 10, further comprising a step of comparing the maximum thickness emax determined with a range of values of the maximum thickness emax predefined during a modeling method of the junction (10) of the blade (4) to the stump (6), said modeling method being according to one of claims 1 to 9. 12. Method for dimensioning a blade (4) and a corresponding stub (6) on a turbomachine rotor (2), intended to be joined by orbital friction welding, according to a predetermined maximum thickness emax of the junction (10), characterized in that the dimensioning method comprises an iteration of determining the maximum thickness Emax of the junction (10) according to different dimensions of the junction (10), according to a modeling method according to one of claims 1 to 9. 13. Sizing method according to claim 12, wherein the determination of the maximum thickness @max of the junction (10) according to different dimensions of the junction (10) is carried out while the eccentricity, the frequency and the pressure remain constant. 14. Dimensioning method according to one of claims 12 and 13, in which the different dimensions of the junction (10), in the iteration of determining the maximum thickness emax of the junction (10), are selected so as to correspond to different values of the geometric parameter Z. 15. Sizing method according to one of claims 12 to 14, in which the iteration of determining the maximum thickness emax of the junction (10) according to different dimensions of the junction (10) is stopped when the maximum thickness emax determined corresponds to the maximum thickness @max of the junction (10) predetermined with a given tolerance.