Friction stir welding tool including an improved shoulder

Abstract

This description concerns a friction stir welding tool (1), the tool (1) comprising: - a rotating external pin (2); and - a body (5) having a shoulder surrounding the pin (2), the shoulder (3) comprising at least one face (30) configured to be in contact with parts (21, 22) to be welded, an arithmetic mean roughness of the face (30) being less than or equal to 0.8. Abstract: Figure 3a

Description

Title of the invention: Friction stir welding tool comprising an improved shoulder. Technical field

[0001] The present description relates to friction stir welding. STATE OF THE ART

[0002] Friction stir welding (FSW) has been used for several years to weld mechanical parts. The weld resulting from FSW is created by means of a welding tool comprising a pin and a shoulder, rotating or static depending on the welding configuration (materials, thicknesses, required rate) and the desired weld quality, which includes at least one face configured to be in contact with the parts. The pin rotates about its axis of revolution at a given rotational speed and penetrates the parts to be welded. The shoulder face is brought into contact with the parts to be welded. Once the pin has penetrated the parts and the shoulder face is in contact with the parts, the tool moves forward in a given direction in space to trace a predefined joint line.This process is particularly advantageous for low-melting-point alloys, such as aluminum alloys, because it does not cause them to melt. This avoids the problems of porosity and hot cracking inherent in fusion welding of alloys, especially aluminum alloys.

[0003] However, the shoulder in contact with the parts to be welded causes surface cracks in the weld as it passes through. Consequently, pieces of the parts, typically made of aluminum alloy, stick to part or even all of the face. The weld then exhibits a brittleness that compromises its quality. Another consequence of these cracks is the appearance of a significant drag force, oriented in the opposite direction to the tool's feed movement on the workpiece, which weakens the tool and, in some cases, causes premature breakage of the pin. GENERAL STATEMENT

[0004] One aim of the present presentation is therefore to improve friction stir welding.

[0005] To this end, according to a first aspect of this presentation, a friction stir welding tool is proposed, the tool comprising: - a rotating outer pawl; and - a body with a shoulder surrounding the pawn, the shoulder comprising at least one face configured to be in contact with parts to be welded, an arithmetic mean of face roughness being less than or equal to 0.8.

[0006] The tribological properties of the face are then improved.

[0007] Thus, reducing the average arithmetic roughness of the face has the effect of reducing the coefficient of friction and thereby improving the sliding of the shoulder on the parts to be welded, particularly when the shoulder is static relative to the pin. This results in a reduction of the drag force thanks to the improvement of the face's tribological properties. The weld quality is therefore improved. Furthermore, the reduction in drag force improves the lifespan of the welding tool, which is subjected to less stress, and allows for welding with reduced forging force and faster speeds, consequently improving both the quality and the welding rate.

[0008] It may be provided that the arithmetic mean of roughness is less than or equal to 0.4 or 0.2, or even 0.1, for example 0.05, or even 0.50, or even 0.10.

[0009] It can be expected that the arithmetic mean of roughness is less than or equal to 0.01.

[0010] It may be provided that the face carries a coating layer having a coefficient of friction less than or equal to 0.8.

[0011] It may be provided that the face bears a coating layer having a hardness greater than or equal to 1000 HV.

[0012] It may be provided that the face of the shoulder is a flat end face.

[0013] It may be provided that the shoulder face is an end face of the shape curved or radiating.

[0014] It may be provided that a maximum temperature resistance of the coating layer is greater than or equal to 200°C.

[0015] It may be provided that the coating layer has anti-sticking or anti-static properties of aluminum.

[0016] It may be provided that the coating layer is made of adamantine carbon.

[0017] It may be provided that the face is nitrided.

[0018] It may be provided that the shoulder is static and the pin is mounted movable in rotation relative to the shoulder.

[0019] It can be provided that a ratio between a diameter of the face and a diameter of the pin is less than or equal to 1.5.

[0020] It may be provided that the tool further includes means for lubricating the face.

[0021] It may be provided that the shoulder has several non-coplanar faces, each having an arithmetic mean roughness less than or equal to 0.8, for example less than or equal to 0.4 or 0.2, or even 0.1, for example 0.05, or even 0.50, or even 0.10.

[0022] It may be provided that the shoulder has several non-coplanar faces each having an arithmetic mean roughness less than or equal to 0.01.

[0023] According to a second aspect of the present exposition, a method for treating a shoulder of a welding tool by friction stir welding is proposed, the shoulder comprising at least one face configured to be in contact with parts to be welded, the process including a rectification of the face.

[0024] It may be provided that the grinding is implemented so that an arithmetic mean of face roughness is less than or equal to 0.8, preferably less than or equal to 0.01.

[0025] It may be provided that the rectification is implemented so that the arithmetic mean of the roughness of the face is less than or equal to 0.4 or 0.2, or even 0.1, for example 0.05 or even 0.50, or even 0.10.

[0026] It may be provided that the process further includes a step of coating the face after grinding.

[0027] It may be provided that the process further includes a nitriding step of the front face of the coating.

[0028] According to a third aspect of the present exposition, a process for welding parts is proposed, the process being implemented by a tool conforming to the first aspect.

[0029] It may be envisaged that the welding process is applied to parts juxtaposed field to field.

[0030] It may be envisaged that the welding process is applied to parts superimposed one on top of the other.

[0031] According to a fourth aspect, a welding process for a first part and a second part is provided. the process being implemented by a tool conforming to the first aspect, the shoulder having several non-coplanar faces each having an arithmetic mean roughness less than or equal to 0.8, for example less than or equal to 0.4 or 0.2, or even 0.1, for example 0.05, or even 0.50, or even 0.10 or having several non-coplanar faces each having an arithmetic mean roughness less than or equal to 0.01, and so that: - one face and a second face of the shoulder are in contact with the first piece; and - a third of the faces of the shoulder is in contact with the second piece, the first and second pieces being inclined relative to each other, for example being perpendicular to each other.

[0032] According to a fifth aspect, an assembly is provided comprising welded parts resulting from the implementation of a process according to the third or fourth aspect.

[0033] According to a sixth aspect, a battery tray is provided comprising at least one skin and at least one hollow profile, a weld of the skin to the profile resulting from an implementation of a process according to the third or fourth aspect.

[0034] According to a seventh aspect, an aircraft is planned comprising a fuselage skin and at least one stiffener, a weld of the stiffener to the fuselage skin resulting from the implementation of a process according to the fourth aspect.

[0035] For the sake of brevity, the average arithmetic roughness will be referred to as the roughness index in the rest of the description. DESCRIPTION OF THE FIGURES

[0036] Other features, purposes and advantages will become apparent from the following description, which is purely illustrative and not limiting, and which should be read in conjunction with the accompanying drawings on which:

[0037] Fig. 1 schematically illustrates a friction stir welding electrospindle mounted on a robot;

[0038] [Fig.2] is a schematic elevation view of a friction-stirring tool mounted on a friction-stirring welding electrospindle;

[0039] [Fig.3a] and [Fig.3b] are schematic perspective views of friction-mixing tools with a static shoulder;

[0040] Fig. 4a and Fig. 4b schematically illustrate friction-mixing tools;

[0041] [Fig.5a], [Fig.5b] and [Fig.5c] are photographs of welds with defects and produced by friction stir welding;

[0042] [Fig.6] is a close-up photograph of a weld showing surface material defects and produced by friction stir welding;

[0043] [Fig.7a] and [Fig.7b] are photographs of a weld with surface cracks produced by friction stir welding;

[0044] [Fig.7c] is a curve of the drag force suffered by the tool during a friction stir weld with a shoulder not showing any improvement in the tribological properties of the face;

[0045] [Fig.8] is a photograph of a weld without surface defects and produced by friction stir welding;

[0046] [Fig. 9] is a graph illustrating the evolution of a drag force as a function of time during a friction stir weld with a shoulder exhibiting a improvement of the tribological properties of the face;

[0047] [Fig.10a] is a photograph of a face of a shoulder showing pieces of weld glued on;

[0048] [Fig.10b] is a photograph of a face of a shoulder that has not been welded (new);

[0049] [Fig.10c] is a photograph of a face of a shoulder without aluminum bonding thanks to the improvement of the tribological properties of the face;

[0050] [Fig.1 1] is a flowchart illustrating a method of implementing a process for treating a face of a shoulder;

[0051] [Fig.12] is a flowchart illustrating a method of implementing a process for welding parts by friction stir welding;

[0052] [Fig. 13a], [Fig. 13b], [Fig. 13c], [Fig. 13d] and [Fig. 13e] schematically illustrate several ways of carrying out friction stir welding;

[0053] Figure 14 illustrates a drag effort with and without lubrication of the face of a shoulder; and

[0054] [Fig. 15] is a photograph of parts welded by friction stir welding;

[0055] [Fig. 16] is a micrograph of parts welded by friction stir;

[0056] [Fig. 17] schematically illustrates part of an aircraft;

[0057] [Fig. 18a], [Fig. 18b] and [Fig. 18c] schematically illustrate several ways of welding aircraft parts by friction stir welding;

[0058] Figure 19 schematically illustrates a welding configuration of an aluminum skin onto a hollow aluminum profile typical of an electric vehicle battery tray; and

[0059] [Fig.20a] and [Fig.20b] are photographs of a weld on a battery tray obtained by friction stir welding. DETAILED DESCRIPTION

[0060] An industrial robot 100 designed to move within a workspace to weld parts 21, 22 of an assembly 20 is illustrated by way of example in [Fig. 1]. The assembly 20 is further illustrated by way of example in [Fig. 13a]. The robot comprises at least one arm mounted on at least one axis. In the present application, each axis corresponds to one degree of freedom of the robot. In the embodiment illustrated in [Fig. 1], the robot 100 comprises six axes. The robot further comprises a free end 101 configured to receive a spindle, preferably an electrospindle 10, for performing the welding operation. Of course, the electrospindle 10 can be mounted on another device, for example, a machine tool, to perform the welding.

[0061] Parts 21, 22 are mounted in a tool 200 fixed to a table 300. According to one embodiment, notably illustrated in [Fig. 1], the tool 200 is placed and held in position on the table 300, typically by screws making it fixed to the table 300. The tooling 200 further includes means for clamping the parts 21, 22. According to one embodiment, the tooling 200 includes clamping flanges configured to hold the parts 21, 22 immobile during the friction stir welding operation.

[0062] In the present description, welding is carried out by friction stir welding. For this purpose, the electrospindle 10 includes a friction stir tool 1, illustrated in particular in [Fig. 2], mounted on a free end 4 of the electrospindle 10. The electrospindle 10 is known to those skilled in the art and will therefore not be described in further detail. Reference may be made to document FR-3 122 110, which describes an example of an electrospindle 10.

[0063] The friction-mixing tool 1 includes a rotating pin 2, i.e. mounted mobilely in rotation around a longitudinal axis Z of the electrospin.

[0064] It is agreed here that an axial direction corresponds to a direction collinear with the longitudinal axis Z and that a radial direction is a direction orthogonal to this axis and intersecting it. Furthermore, an axial plane is a plane defined along the longitudinal axis Z and a transverse plane is a plane perpendicular to the longitudinal axis Z. An oblique plane is a plane inclined with respect to the axial plane or the radial plane.

[0065] The friction-mixing tool 1 further comprises a body 5 separate from the pin 2. The body 5 can be fixed relative to the pin 2. The body 5 comprises a base 6 and a shoulder 3. The base 6 is mounted on the electrospindle 10, and the shoulder 3 is configured to be in contact with the parts 21, 22 during welding. The body 5 is axially delimited from the base 6 to the shoulder 3 and radially delimited by a lateral face 7 extending around the longitudinal axis Z. The shoulder 3 surrounds the pin 2 and has a diameter D2 greater than a diameter DI of the pin 2. Thus, the shoulder forms a variation in cross-section between the body 5 and the pin 2.

[0066] According to an example of an embodiment of the body 5, particularly illustrated in Figures 3a and 3b, the base 6 of the body 5 has a first cylindrical section 60 and a second cylindrical section 61 having a diameter greater than the diameter of the first cylindrical section 60. The first cylindrical section 60 includes flats 63 configured to prevent the body 5 from rotating within the electrospindle 10. Thus, when mounting the body 5 on the electrospindle 10, the body 5 is positioned with the electrospindle 10 by centering it on the first section 60 and providing a flat support on the second section 61. The body 5 is held in position by a clamping means that secures the body 5 to the electrospindle 10.

[0067] According to an exemplary embodiment of the lateral face 7, notably illustrated in [Fig. 4a], the lateral face 7 is cylindrical. It has a constant diameter D2 along the longitudinal axis Z, measured perpendicular to the longitudinal axis Z. Alternatively, the lateral face 7 may be non-cylindrical. For example, it may be frustoconical as illustrated in For example, see [Fig. 4b]. It has a diameter D2 measured perpendicular to the axis which is not constant and which, in this case, decreases as one moves towards the pin. The lateral face 7 can also be non-cylindrical on a first portion 70 and cylindrical on a second portion 71. For example, it is frustoconical on the first portion 70 as illustrated by [Fig. 3a] and [Fig. 3b].

[0068] The pin 2 can be mounted to move relative to the shoulder 3, which is then said to be fixed, for example by assembling the shoulder 3 to a base of the electrospindle 10. Thus, the tool 1 is more robust thanks to the fixed shoulder 3. In addition, the weld 23 has a better surface finish. It is therefore more resistant. Furthermore, the tool 1 welds faster. The cutting speed of the tool 1 is therefore improved. Alternatively, the pin 2 can be mounted to be rigidly fixed to the shoulder 3, for example by assembling the pin 2 and the shoulder 3 on the same axis of rotation of the electrospindle 10.

[0069] The shoulder 3 has at least one axial end face 30 of generally flat shape and configured to be in contact with the surface of the parts 21, 22 to be welded.

[0070] The axial end face 30 may have another shape. For example, a junction between the axial end face 30 and the lateral face may be rounded or chamfered. The face 30 may have a concave shape.

[0071] Thanks to the fixed shoulder, the shape of the shoulder can be particularly well adapted to the shape and configuration of the parts to be welded. This shoulder then constitutes a "counterform" of the parting line and contains the material being welded (see, for example, the embodiment of Figures 13d and 13e described below). For each particular welding configuration, it is possible to adapt the shape of the shoulder to that of the joint to be produced.

[0072] The device carrying the tool 1, for example the aforementioned robot, is configured to move the tool vertically, in order to bring the axial end face 30, typically flat, into contact with a portion of the parts 21, 22, and horizontally, in order to advance the tool along the parts to be welded. Thus, during welding, particularly when the shoulder is fixed, the face 30 slides on the portion of the parts 21, 22 and at the same time, the pin 2, rotating about its longitudinal axis, heats and mixes the joint surface to create a weld 23 of the parts 21, 22. The face 30 then serves to contain the material during the welding operation.

[0073] The shoulder 3 may further comprise several axial end faces, in particular planar, non-coplanar 30, 31, 32. Thus, it is possible to carry out the weld 23 between parts extending angularly, for example perpendicularly or presenting an angle less than 90°, such as 70°, to each other.

[0074] According to one embodiment, notably illustrated in [Fig.3b], the face 3 is decomposed into a first axial end face 30 extending in a transverse end plane and two other planar faces 31, 32 extending symmetrically from each other with respect to the axial plane of symmetry giving rise to two distinct oblique planes from the face 30. Alternatively, the two other planar faces 31, 32 extend asymmetrically from each other with respect to the axial plane of symmetry for welding parts not extending perpendicularly but having an angle of less than 90°, for example 70°.

[0075] Improving the tribological properties through contact of face 30 with the surface of parts 21, 22 improves the weld 23. To improve the tribological properties, the roughness index of face 30 is less than or equal to 0.8, for example, less than or equal to 0.4. Thus, face 30 has no machining marks, particularly in the form of bosses, that could adhere to parts 21, 22 in contact with face 30 during welding. Consequently, the coefficient of friction of face 30 with parts 21, 22 is improved.

[0076] Three welding configurations are distinguished in order to show the relevance of improving the tribological properties of face 30.

[0077] In a first example of the configuration, the body 5, in particular the shoulder 3 of the body 5, rotates about the longitudinal axis Z and does not slide on the parts 21, 22. In this example, the pin 2 is generally fixed to the body 5 and rotates in the same way. Figures 5a, 5b and 5c illustrate examples of defects encountered in this configuration, in particular weld bulges 24, more commonly called "weld flash" because of the relief formed by the projected pieces of material that agglomerate around the periphery of the weld during the rotation of the shoulder 3, and weld ridges 25. These defects reduce the mechanical properties of the assembly of the parts 21, 22 and also form corrosion initiation points for the parts 21, 22. In addition, the weld 23 is irregular. Indeed, as illustrated in the example in [Fig.[5a] The figure shows numerous raised areas within weld 23 due to weld ridges 25 and around the periphery of weld 23 due to weld flash 24. Consequently, weld 23 exhibits lower mechanical quality and is less resistant to corrosion. To limit weld flash 24 and weld ridges 25, a finishing step is necessary after welding, such as machining, brushing, or grinding. However, because of this finishing step, welding takes longer and the product is more expensive to manufacture. Furthermore, the rotational movement of the shoulder 3 on parts 21, 22 can generate sufficient heat to reduce the stiffness of parts 21, 22 to the point where they can no longer withstand the forging force applied by the welding tool 1 to parts 21, 22 along the longitudinal axis. Z. Tool 1 then penetrates deeply into parts 21, 22 and causes even more pronounced weld flashes 24 ([Fig. 5b]), or even a weld collapse 26, more commonly known as a "weld crash" ([Fig. 5c]). Parts 21, 22 are then discarded.

[0078] In a second example of the configuration, the pin 2 rotates about the longitudinal axis Z relative to the body 5, in particular relative to the shoulder 3, which is fixed in this example. It should be noted here that when the shoulder 3 is fixed, the axial end face 30 slides in translation on the parts 21, 22 to be welded. Also in this second configuration, the face 30 lacks any of the previously stated improvements to the tribological properties of the face 30. However, the weld 23 is still irregular. Indeed, it exhibits material defects on the surface 29 ([Fig. 6]) and fragments 28 of the parts 21, 22, typically made of aluminum alloy, clog the face 30 ([Fig. 10a]). Cracks 27 may even appear (Figures 7a and 7b). The weld is then of poor quality and industrially unacceptable. We have illustrated on the graph in [Fig.[7c] The evolution of the drag force exerted on tool 1, expressed in Newtons, over time, expressed in seconds. This graph shows that the drag force can reach up to 3500 N. Such a high drag force is a consequence of poor sliding of face 30 of body 5 on the surface of parts 21 and 22, which is the source of the aforementioned defects. Indeed, since the drag force opposes the feed movement of tool 1, its value increases when face 30 is not sufficiently smooth, and therefore has a high roughness coefficient, and / or when it is clogged. One solution is to reduce the feed and / or rotation speed of tool 1 to limit clogging. However, the low feed and / or rotation speeds are incompatible with industrial-scale manufacturing and severely degrade the mechanical properties of parts 21, 22 and the weld.

[0079] Thus, according to a third example of a configuration, in which the shoulder 3 is fixed and the pin 2 is movable, a roughness coefficient of the face 30 is less than or equal to 0.8. The face 30 therefore exhibits a tribological improvement here. Unlike the previous example configurations, the weld 23 has a better surface quality, as illustrated, for example, in [Fig. 8]. The weld meets the quality criteria required at the industrial level with a high-performance finish. Indeed, the weld 23 in [Fig. 8] shows no weld flash 24, no weld streaks 25, and no cracks 27. The resulting weld 23 is therefore smooth and clean in appearance. Furthermore, the reduction in the coefficient of friction between the face 30 and the surface of the parts 21, 22 allows for faster welding thanks to a reduced coefficient of friction. The drag force has been illustrated in [Fig.9] in the form of a graph showing as an example a welding test of parts 21, 22 and in which is represented in . The y-axis represents drag force, which can be expressed in Newtons, and the x-axis represents time, which can be expressed in seconds. The drag force is reduced to 1500 N, a 65% reduction compared to the second configuration. It is also much smoother, causing less stress on tool 1. Indeed, according to this graph, the evolution of the drag force 90 is centered on an average drag force value 91 during the weld. In this case, the drag force varies little around the average value 91, typically less than 5%, and generally forms a plateau. Thus, the tribological properties of face 30 significantly improve sliding, as evidenced by the considerably reduced drag force. Consequently, the tool life and throughput of tool 1 are improved. A finishing step, such as machining, grinding, or brushing, is no longer required.

[0080] Of course, tribological improvement 30 can also be advantageous in a rotating shoulder configuration.

[0081] The roughness index of face 30 can also be less than or equal to 0.01, so that the aforementioned advantages are further enhanced. This is then referred to as a mirror-polished surface because the roughness index is extremely low.

[0082] In the case where the face 3 comprises several faces, in particular several non-coplanar faces 30, 31, 32, all or some of the faces may have a roughness index less than or equal to 0.8, less than or equal to 0.4 or less than or equal to 0.01. A single face may also have a roughness index less than or equal to 0.8, less than or equal to 0.4, or less than or equal to 0.01. Similarly, each face may or may not include, or may independently include, a coating 33 having the aforementioned properties.

[0083] A measurement of the roughness index can be implemented by means known to a person skilled in the art, typically a roughness tester, and will therefore not be detailed further in this presentation.

[0084] The face 30 can carry a coating layer 33 having a coefficient of friction less than or equal to 0.8. Thus, the tribological properties of the face are further improved by reducing the coefficient of friction. Indeed, the layer 33 reduces the drag force and therefore improves sliding. In addition, the friction of the face 30 on the parts 21, 22 is reduced by up to 65% compared to a flat end face 30 having a roughness index greater than 0.8 and lacking the layer 33. Furthermore, the face 30 having a roughness coefficient less than or equal to 0.8 improves the adhesion of the layer 33 to the face 30, and therefore its lifespan, and even more so when it has a roughness coefficient less than or equal to 0.01.

[0085] The hardness of layer 33 may be greater than or equal to 1000 HV, preferably greater than or equal to 4000 HV in order to improve abrasion resistance. Having a low roughness index on face 30 improves the adhesion of layer 33 to face 30 and the lifespan of layer 33.

[0086] A measure of hardness expressed in HV, called Vickers hardness, can be implemented in a manner known to a person skilled in the art, typically by means of an optical measurement of a trace left by a standardized pyramidal diamond indenter, and will not be detailed further in this presentation.

[0087] The maximum temperature resistance of layer 33 is greater than or equal to 200°C, preferably greater than or equal to 1100°C. Thus, the temperature resistance of layer 33 during welding is improved and the tool life 1 is increased.

[0088] In order to improve the adhesion of layer 33 with face 30, face 30 can be nitrided by a nitriding treatment before application of layer 33 to face 30. Thus, the service life of layer 33 is further improved.

[0089] According to one embodiment of layer 33, layer 33 is made of diamond-like carbon (DLC). DLCs cover various amorphous carbon compounds based on their predominant bonding, namely sp2 trigonal or sp3 tetrahedral bonds, and their hydrogen content. In this application, "amorphous carbons" means that the carbon atoms of the compound do not form a crystalline structure.DLC can be a compound of hydrogenated amorphous carbons (known by the acronym "aC:H"), that is, a compound of amorphous carbons that have undergone a chemical reaction by the addition of gaseous dihydrogen molecules and exhibit between 40% and 60% of the total number of bonds in the compound, as well as between 30% and 50% of the total number of atoms in the compound; or of amorphous tetrahedral carbons (known by the acronym "ta-C"), exhibiting between 80% and 88% of the total number of bonds in the compound and zero hydrogen atoms. Furthermore, the terms sp2 and sp3 should be understood as defined in the modeling of hybrid orbitals in quantum chemistry and will not be further explained, as they are well-established.In this case, layer 33 also exhibits antistatic or anti-sticking properties of aluminum, which further reduce the sticking of parts 21, 22 to face 30 ([Fig. 10c]) and thus further improve the tool life 1. Alternatively, layer 33 can be composite, for example, comprising a first layer of adamantine carbon and a second layer of chromium nitride (CrN). Thus, in addition to benefiting from the antistatic or anti-sticking properties, the chromium nitride improves the lifespan of layer 33.

[0090] In the case where the shoulder 3 comprises several faces, in particular several non-coplanar faces 30, 31, 32, all the faces may carry a layer 33, or selectively certain faces or a single face. The layers 33 may independently one from the other, or independently one group of layers 33 with respect to another group of layers exhibit the aforementioned characteristics of coefficient of friction, hardness, temperature, and anti-sticking properties taken alone or in combination.

[0091] A total of the faces 30, 31, 32 can carry the layer 33.

[0092] According to one embodiment, in particular illustrated in [Fig. 3a], the layer 33 covers the entire face 30 so that the latter is in contact with the parts 21, 22 only via the layer 33. Alternatively to [Fig. 3b], a fraction of the faces 30, 31, 32 may carry the layer 33. According to one embodiment, in particular illustrated in [Fig. 3b], a fraction of each oblique face 31, 32 carries a layer 33.

[0093] In order to obtain an axial contact force of the shoulder 3 on the parts 21, 22 of less than 2,000 N, a ratio between a diameter, preferably a minimum diameter, of the shoulder 3 and a diameter of the pin 2 can be less than or equal to 1.5, preferably less than or equal to 1.3. Thus, the clogging of the welded material on the face 30, as well as the mechanical stresses experienced by the tool 1, are reduced, and therefore the tool life 1 is further improved. The parts 21, 22 will be subjected to less welding stress and therefore less geometric deformation after welding. In addition, reducing the axial force allows the tool 1 to experience less mechanical stress. The tool 1 is therefore also more precise during welding.

[0094] An implementation method for treating shoulder 3 is described with reference to [Fig. 11]. During a step E10, face 30 is ground. The ground face 30 can be seen as an example in [Fig. 10b]. This is also referred to as polishing the face.

[0095] Prior art finishing methods, for example conventional machining, allow a roughness coefficient to be obtained between 1.6 and 3.2, whereas the E10 grinding step makes it possible to obtain a roughness index less than or equal to 0.8, for example less than or equal to 0.4, preferably less than or equal to 0.01. Its implementation therefore makes it possible to considerably reduce the roughness index, at a minimum by halving it, generally by a factor of eight, up to a factor of more than three hundred. Furthermore, grinding makes it possible to remove the marks of conventional machining cutters or cutting tools and to have no bosses or machining marks on face 30.

[0096] Then, in a step E11, the flat end face 30 of the shoulder is nitrided. According to one embodiment, the nitriding extends over a portion of the face 3 including the end face 30. Then, in a step E12, the face is coated by the layer 33. In the case where the face 3 comprises several faces, in particular several non-coplanar faces 30, 31, 32, steps E10 to E12 can be carried out on all the faces, or selectively on certain faces, or on only one. face.

[0097] A method of implementing a welding process of a first part 21 and a second part 22 of an assembly 20 is described with reference to [Fig. 12].

[0098] The welding process is implemented by tool 1 of this presentation.

[0099] In the case of a removable tool 200, the tool 200 is fixed on a table 300 at During step E20, according to an example implementation of step E20, tooling 200 is placed and held in position on table 300, typically by screws. Alternatively, the tooling is part of table 300. In this case, tooling 200 is already mounted on table 300.

[0100] During a step E21, the parts 21, 22 to be welded are positioned in the tooling 200 and then held in position by fastening means, for example clamping flanges placed in the tooling 200. The parts 21, 22 can be positioned according to different configurations: - in juxtaposition field against field ([Fig. 13a]), the pieces 21, 22 then having coplanar main faces 210, 220; - superimposed one on top of the other parallel ([Fig. 13b]), one of the parts 21 then extending over the other part 22. The lower principal face 211 of the upper part 21 is in surface contact with the upper principal face 220 of the lower part 22; or - superimposed one on the other angularly, for example perpendicularly or at an angle less than 90° such as 70°, or face to face (Figures 13c, 13d and 13e), one of the parts 21 extending above the other part 22, the lower principal face 211 of the upper part 21 being in surface contact with a face 222 of the lower part 22 ([Fig. 13c]) or a face 212 of the upper part 21 being in contact with the upper principal face 220 of the lower part 22 ([Fig. 13d] and 13e). The principal faces 220, 221 of the latter are perpendicular to those of the upper part 21.

[0101] During a step E22, the tool 1 is moved in vertical translation until the end face 30 is in contact with at least one of the first and second parts 21, 22.

[0102] In juxtaposition, the end face 30 is in contact with both parts 21, 22 simultaneously. In superposition, the tool 1 can be in contact with one or both parts 21, 22. According to one embodiment, notably illustrated in [Fig. 13b], the parts are superimposed one on top of the other parallel to each other, and the end face 30 is in contact with the upper principal face 210 of the upper part 21.

[0103] According to another embodiment, notably illustrated in [Fig. 13c], one of the parts 21 extends perpendicularly above the other part 22, the lower principal face 211 of the upper part 21 being in surface contact with a field 222 of the lower part 22. Thus, the end face 30 is in contact with the upper main face 210 of the upper part 21.

[0104] Alternatively, as illustrated in particular in Figures 13d and 13e, the upper part 21 has a main flat portion 213, having principal faces extending parallel to each other, and a flared edge 214 in which the principal faces move away as one approaches the field. This field 212 of the upper part 21 is in contact with the upper principal face 220 of the lower part 22. Thus: - the axial end face 30 and the first oblique face 31 of the shoulder 3 are respectively in contact with the edge 214 and a flat face of the main part 213 of the upper piece 21; and - the second oblique face 32 of the shoulder 3 is in contact with the upper main face of the lower part 22.

[0105] Tool 1 is ready to weld. During a step E23, the pin 2 is rotated and tool 1 is moved in a direction in space, typically horizontal, to follow a joint line so as to make a pass and form the weld 23 of the first and second parts 21, 22. Several passes can be made to form the weld 23, typically two passes.

[0106] In juxtaposition, an example of which is illustrated in particular in [Fig. 13a], the end face 30 passes simultaneously over the coplanar principal faces 210, 220 of the parts 21, 22.

[0107] In the case where the parts 21, 22 are superimposed one on the other parallel, an example of which is illustrated in particular in [Fig.13b], the end face 30 passes over the main external face 210 of the upper part 21 and welds the two parts together.

[0108] In the case where one of the parts 21 extends angularly above the other part 22, for example perpendicularly in an example illustrated in [Fig. 13c] or presenting an angle less than 90° such as 70°, the lower principal face 211 of the upper part 21 being in surface contact with a field 222 of the lower part 22, the end face 30 passes over the upper principal face 210 of the upper part. Alternatively, illustrated in particular by way of example in figures 13d, the field 212 of the upper part 21 can be in contact with the upper main face 220 of the lower part 22, the end face 30 passes over the main face 214 of the upper part 21 and the oblique faces 31, 32 pass respectively over the main face 213 of the upper part 21 and the upper main face 220 of the lower part 22.

[0109] Parts 21 and 22 are then welded. Steps E20 to E23 can be repeated until assembly 20 is completely welded. Consequently, assembly 20 then comprises at least two parts.

[0110] The application of additional lubrication to parts 21, 22 reduces the drag force. The sliding of the end face 30 is then further improved. Indeed, as illustrated by example in [Fig. 14], which shows the evolution of the drag force experienced by tool 1 with and without lubrication over time (the force being expressed in Newtons and the time in seconds), this force falls below 1000 N in magnitude with the addition of lubrication for welding 23. It can therefore be planned that parts 21, 22 are lubricated during step E23. Tool 1 can then include lubrication means.

[0111] The assembly 20 resulting from the welding process implemented by tool 1 of this presentation is distinguished macroscopically by a weld 23 exhibiting a reduction, or even an elimination, of weld flash 24, weld streaks 25, cracks 27, and material defects 29. Furthermore, the weld 23 does not exhibit weld collapse 26. Indeed, the weld 23 obtained by tool 1 of this presentation, illustrated by way of example in Figures 8 and 15, does not exhibit weld flash 24, weld streaks 25, cracks 27, material defects 29, or weld collapse 26, whereas a weld 23 obtained by a tool known in the prior art, and in particular illustrated in Figures 5a, 5b, 5c, 6, 7a, and 7b, exhibits cracks 27, weld flash 24, and weld streaks. 25, material defects 29 and weld collapse 26.

[0112] The assembly 20 resulting from the process implemented by the tool 1 of this presentation is further distinguished microscopically by an overlap zone 40, illustrated in particular by way of example in [Fig. 16].

[0113] An aircraft fuselage is illustrated in [Fig. 17]. It comprises stringers 51 extending along a longitudinal direction of the fuselage, frames 55 extending in a transverse direction of the fuselage, and a skin 52 covering the stringers 51 and frames 55. The frames 55 and stringers 51 act here as stiffeners of the skin 52 of the fuselage.

[0114] In what follows, the present exposition will be detailed for frames 55 and applies mutatis mutandis to rails 51.

[0115] For the sake of brevity, frames 55 and rails 51 will be referred to as stiffeners in the remainder of this description

[0116] The stiffeners thus extend over an inner face 520 of the skin 52, an outer face 521 of the skin 52 being free and opposite the stiffeners. The skin and each stiffener are welded to each other by the welding process implemented by the tool 1. It is therefore not necessary to fasten them to each other by means of an assembly using added fasteners. Thus, the mass of the aircraft 50 is reduced and the efficiency of the aircraft 50 is improved. The aircraft 50 is also assembled more quickly.

[0117] According to a first embodiment, notably illustrated in [Fig. 18a], the stiffener has a wedge-shaped profile and includes a flange 53, the flange 53 being welded in overlap onto the fuselage skin 52. The welding takes place with the axial end face 30 in contact with the flange 53, on the side of the stiffener 51 opposite the skin 52.

[0118] According to a second embodiment, notably illustrated in [Fig. 18b], the stiffener 51 is welded in overlap onto the fuselage skin 52 and the tool is this time in contact with the fuselage skin 52 during welding, extending over the outer face 521 of the skin, opposite the stiffener 51. A field of the stiffener 513 is in contact with the inner face of the skin 52.

[0119] According to a third embodiment, notably illustrated in [Fig. 18c], the stiffener 51 is welded in overlap onto the fuselage skin 52, and the tool is in contact with both the fuselage skin 52 and the stiffener 51 during welding. The welding takes place from the inner, non-visible face 520 of the skin, representing a considerable advantage over the configuration of [Fig. 18b]. The welding takes place in the configuration shown in Figures 13d and 13e. The oblique faces 31, 32 of the shoulder 3 come into contact with both the main face of the stiffener 511 and the inner main face 520 of the skin 52, and the end face 30 of face 3 is in contact with the portion 512 of the stiffener 51. The tool 1 therefore performs the weld by simultaneously passing over the flat portions 511, 512 of the stiffener 51 as well as the inner face 520 of the skin 52, for example on the left in [Fig. 18c]. Another pass allows the same to be done on the right.Since the weld is performed on the internal side of the aircraft, a finishing step, such as machining or grinding the weld 23, is eliminated. There is also no longer a need for a base plate 53, which reduces the overall weight. Furthermore, the airtightness of the aircraft 50 is improved because there is no longer a residual interface with an overlap 40 between the two passes, as illustrated as an example in [Fig. 16]. The weld is also more robust thanks to the overlap zone 40, and there is no longer any lack of interface mixing.

[0120] The welding process implemented by tool 1 of this exposition also makes it possible to obtain an assembly 80 having a hollow welded structure, as illustrated in [Fig. 19]. This architecture is typical of the aluminum battery trays used in electric vehicles, which consist of welding a skin element 81 onto a hollow aluminum profile 82. The hollow profile 82 reduces weight in order to improve the power-to-weight ratio of the electric vehicle and to consume less energy. This is not possible with the prior art tool, with which weld collapse 26 occurs, as illustrated by way of example in [Fig. 5c].

[0121] According to one embodiment, notably illustrated in Figures 20a and 20b, the skin element 81 and the hollow aluminum profile 82 are placed one on top of the other parallel to each other, the skin element 81 then extends over the profile 82. The weld 23 of the skin 81 with the profile is then obtained by a passage of the tool on a main upper face 810 of the skin 81 opposite the hollow aluminium profile 82.

Claims

Demands

1. Friction stir welding tool (1), the tool (1) comprising: - a rotating external pin (2); and - a body (5) having a shoulder surrounding the pin (2), the shoulder (3) comprising at least one face (30) configured to be in contact with parts (21, 22) to be welded, an arithmetic mean roughness of the face (30) being less than or equal to 0.

8.

2. Tool (1) according to claim 1, wherein the arithmetic mean of roughness is less than or equal to 0.

01.

3. Tool (1) according to claim 1 or 2, wherein the face (30) carries a coating layer (33) having a coefficient of friction less than or equal to 0.

8.

4. Tool (1) according to any one of claims 1 to 3, wherein the face (30) carries a coating layer (33) having a hardness greater than or equal to 1000 HV.

5. Tool (1) according to any one of claims 3 or 4, wherein a maximum temperature resistance of the coating layer (33) is greater than or equal to 200°C.

6. Tool (1) according to any one of claims 3 to 5, wherein the coating layer (33) is made of adamantine carbon.

7. Tool (1) according to any one of claims 1 to 6, wherein the face (30) is nitrided.

8. Tool (1) according to any one of claims 1 to 7, wherein the shoulder (3) is static and the pin is mounted movable in rotation relative to the shoulder (3).

9. Tool (1) according to any one of claims 1 to 8, wherein a ratio between a diameter (D2) of the face (3) and a diameter (Dl) of the pin (2) is less than or equal to 1.

5.

10. Tool (1) according to any one of claims 1 to 9, further comprising means for lubricating the face (3).

11. Tool (1) according to any one of claims 1 to 10, wherein the shoulder (3) has several non-coplanar faces (30, 31, 32) each having an arithmetic mean roughness less than or equal to 0.

8.

12. A tool according to claim 11, wherein the shoulder (3) has several non-coplanar faces (30, 31, 32), each having a arithmetic mean roughness less than or equal to 0.

01.

13. Method of treating a shoulder (3) of a friction stir welding tool (1), the shoulder (3) comprising at least one face (30) configured to be in contact with parts to be welded, the method comprising a grinding (E10) of the face (30).

14. A method according to claim 13, wherein the grinding (E10) is carried out so that an arithmetic mean of roughness of the face (30) is less than or equal to 0.8, preferably less than or equal to 0.

01.

15. A method according to any one of claims 13 or 14, further comprising a coating step (E12) of the face (30) after the grinding (E10).

16. Method according to claim 15, further comprising a nitriding step (E11) of the face (30) before the coating (E12).

17. A method for welding parts, the method being carried out by a tool (1) according to any one of claims 1 to 12.

18. Method according to claim 17, applied to parts (21, 22) juxtaposed field to field.

19. Method according to claim 17, applied to parts (21, 22) superimposed one on top of the other.

20. A welding method for a first part (21) and a second part (22), the method being carried out by a tool (1) according to one of claims 11 or 12, and such that: - a first (30) of the faces and a second of the faces (31) of the shoulder (3) are in contact with the first part (21); and - a third (32) of the faces of the shoulder (3) is in contact with the second part (22), the first and second parts (21, 22) being inclined with respect to each other, for example being perpendicular to each other.

21. Assembly (20) comprising welded parts (21, 22) resulting from the implementation of a process according to any one of claims 17 to 20.

22. Battery tray (80) comprising at least one skin (81) and at least one hollow profile (82), a weld of the skin (81) to the profile (82) resulting from an implementation of a method according to any one of claims 17 to 20.

23. Aircraft (50) comprising a fuselage skin (52) and at least one stiffener (51), a weld of the stiffener (51) to the fuselage skin (52) resulting from an implementation of a process according to claim 20.

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