Friction stir welding tool including improved shoulder

Abstract

The present disclosure relates to 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: figure 3a

Description

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

[0001] This disclosure relates to friction stir welding. STATE OF THE ART

[0002] Friction stir welding (known by the English acronym "FSW" for Friction Stir Welding) has been used for several years to weld mechanical parts. The weld, resulting from FSW welding, is created by means of a welding tool comprising a pin and a shoulder, rotating or static depending on the welding configurations (materials, thicknesses, required rate) and the desired weld quality, which comprises at least one face configured to be in contact with the parts. The pin is mobile in rotation around its axis of revolution at a given rotation speed and penetrates the parts to be welded. As for the face of the shoulder, it is brought into contact with the parts to be welded. Once the pin has penetrated the parts and the face of the shoulder is in contact with the parts, the tool is driven by a forward movement in a given direction in space in order to travel along a previously defined joint line.This process is particularly advantageous for an alloy with a low melting point, for example an aluminum alloy, because it does not cause it to melt. This circumvents the problems of porosity and hot cracking inherent in fusion welding of alloys, particularly aluminum alloys.

[0003] However, the shoulder in contact with the parts to be welded causes cracks on the surface of the weld as it passes. As a result, pieces of the parts, typically made of aluminum alloy, stick to part or even the entire face. The weld then becomes fragile, compromising its quality. Another consequence of these cracks is the appearance of a significant drag force, oriented in a direction opposite to the feed movement of the tool on the part, which weakens the tool to the point of causing premature breakage of the pin in certain cases. GENERAL STATEMENT

[0004] An aim of the present disclosure is therefore to improve friction stir welding.

[0005] For this purpose, according to a first aspect of the present disclosure, a friction stir welding tool is proposed, the tool comprising: - a rotating external pawn; 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 arithmetic mean roughness of the face has the effect of reducing the coefficient of friction and thus making the shoulder slide better on the parts to be welded, in particular when the shoulder is static relative to the pin. This results in a reduction in the drag force thanks to the improvement in the tribological properties of the face. The quality of the weld is therefore improved. The reduction in the drag force also makes it possible to improve the service life of the welding tool which is less stressed, to weld with a reduced forging force and this, more quickly, consequently improving the quality and the rate of the welding.

[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 may be provided 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 carries 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 planar end face.

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

[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 the 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 mobile in rotation relative to the shoulder.

[0019] It may 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 comprises 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 disclosure, there is provided a method of treating a shoulder of a friction stir welding tool, the shoulder comprising at least one face configured to be in contact with parts to be welded, the process comprising a grinding of the face.

[0024] It may be provided that the rectification is implemented so that an arithmetic mean roughness of the face 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 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 method further comprises a step of coating the face after grinding.

[0027] It may be provided that the method further comprises a step of nitriding the face before coating.

[0028] According to a third aspect of the present disclosure, there is provided a method of welding parts, the method being implemented by a tool according to the first aspect.

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

[0030] It may be provided that the welding process is applied to parts superimposed on each other.

[0031] According to a fourth aspect, there is provided a method of welding a first part and a second part, the method 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: - a first of the faces and a second of the faces of the shoulder are in contact with the first part; and - a third of the faces of the shoulder is in contact with the second part, the first and second parts being inclined relative to each other, for example being perpendicular to each other.

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

[0033] According to a sixth aspect, there is provided a battery tray 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 method according to the third aspect or the fourth aspect.

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

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

[0036] Other characteristics, aims and advantages will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

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

[0038] [Fig.2] is a schematic elevation view of a friction stir tool mounted on a friction stir 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 made by friction stir;

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

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

[0044] [Fig.7c] is a curve of the drag force experienced by the tool during a weld carried out by friction stir 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;

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

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

[0048] [Fig.10b] is a photograph of one face of a shoulder that has not undergone any welding (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.l 1] is a flowchart illustrating a mode of implementation of a method for treating a face of a shoulder;

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

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

[0053] [Fig. 14] illustrates a drag force with and without lubrication of the face of a shoulder; and

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

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

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

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

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

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

[0060] Illustrated by way of example in [Fig.l] is an industrial robot 100 intended to move in a workspace to weld parts 21, 22 of an assembly 20. 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 a degree of freedom of the robot. In the exemplary embodiment illustrated in [Fig.l], the robot 100 comprises six axes. The robot further comprises a free end 101 configured to receive a spindle, preferably an electrospindle 10 to carry out the welding operation. Of course, the electrospindle 10 can be mounted on another device, for example a machine tool, to carry out the welding.

[0061] The parts 21, 22 are mounted in a tool 200 fixed to a table 300. According to an exemplary embodiment, notably illustrated in [Fig.l], the tool 200 is placed and held in position on the table 300, typically by screws making it integral with the table 300. The tool 200 further comprises means for clamping the parts 21, 22. According to an exemplary embodiment, the tool 200 comprises clamping flanges configured to keep the parts 21, 22 stationary during the friction stir welding operation.

[0062] In the present disclosure, the welding is implemented by friction stir. To do this, the electrospindle 10 comprises 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 a person skilled in the art and will therefore not be detailed further. Reference may be made to document FR-3 122 110 which describes an example of an electrospindle 10.

[0063] The friction-mixing tool 1 comprises a rotating pin 2, i.e. mounted to move in rotation around a longitudinal axis Z of the electrospindle.

[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 the latter. 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 relative to the axial plane or the radial plane.

[0065] The friction-stirring tool 1 further comprises a body 5 distinct from the pin 2. The body 5 can be mounted 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 delimited axially from the base 6 to the shoulder 3 and radially 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 exemplary embodiment of the body 5, notably 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 comprises flats 63 configured to lock the body 5 in rotation in the electrospindle 10. Thus, when mounting the body 5 on the electrospindle 10, the body 5 is put in position with the electrospindle 10 by centering on the first section 60 and a flat support on the second section 61. The body 5 is held in position by a clamping means making it possible to make the body 5 integral with 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. It is for example frustoconical as illustrated in as an example in [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 may also be non-cylindrical on a first portion 70 and cylindrical on a second portion 71. It is for example frustoconical on the first portion 70 as illustrated as an example in [Fig.3a] and in [Fig.3b].

[0068] The pin 2 can be mounted so as to be movable 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 quality. It is therefore more resistant. In addition, the tool 1 welds more quickly. A rate of the tool 1 is therefore improved. Alternatively, the pin 2 can be mounted by being rigidly fixed to the shoulder 3, for example by assembling the pin 2 and the shoulder 3 to the same axis of rotation of the electrospindle 10.

[0069] The shoulder 3 has at least one axial end face 30 of generally planar 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 side 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 joint plane and contains the material being welded (see for example on this subject the embodiment of figures 13d and 13e described later.) 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 in vertical translation, in order to bring the axial end face 30, typically planar, into contact with a portion of the parts 21, 22, and in horizontal translation, in order to advance the tool along the parts to be welded. Thus, during welding, in particular 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 driven by a rotational movement around the longitudinal axis heats and kneads the joint plane, to create a weld 23 of the parts 21, 22. The face 30 then makes it possible 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 produce the weld 23 between parts extending angularly, for example perpendicularly or presenting an angle of less than 90°, such as 70°, relative to each other.

[0074] According to an exemplary 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 flat faces 31, 32 extending symmetrically from one another with respect to the axial plane of symmetry giving rise to two distinct oblique planes from the face 30. As a variant, the two other flat faces 31, 32 extend asymmetrically from one another with respect to the axial plane of symmetry to weld parts not extending perpendicularly but having an angle of less than 90°, for example 70°.

[0075] The improvement of the tribological properties by the contact of the face 30 with the surface of the parts 21, 22 makes it possible to improve the weld 23. In order to improve the tribological properties, a roughness index of the face 30 is less than or equal to 0.8, for example less than or equal to 0.4. Thus, the face 30 does not have any machining grooves, in particular in the form of bosses, likely to adhere to the parts 21, 22 in contact with the face 30 during the welding. Consequently, the coefficient of friction of the face 30 with the parts 21, 22 is improved.

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

[0077] In a first configuration example, the body 5, in particular the shoulder 3 of the body 5, is driven by a rotational movement around the longitudinal axis Z and does not slide on the parts 21, 22. In this example, the pin 2 is generally integral with the body 5 and is driven by the same rotational movement. Figures 5a, 5b and 5c illustrate examples of defects encountered in this configuration, in particular beads 24, more commonly called “weld flash” due to the relief formed by the projected pieces of material which agglomerate at the periphery of the weld during the rotation of the shoulder 3, and welding streaks 25. However, 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 reliefs within the weld 23 because of the welding striations 25 and on the periphery of the weld 23 because of the welding flashes 24. Consequently, the weld 23 has a lower mechanical quality and is less resistant to corrosion phenomena. To limit the welding flashes 24 and the welding striations 25, a finishing step is necessary after welding, for example machining, brushing or grinding. However, because of the finishing step, welding is longer and the production of the product is more expensive. The rotary movement of the shoulder 3 on the parts 21, 22 can also create sufficient heating to reduce the stiffness of the parts 21, 22 to the point that it can no longer withstand a forging force applied by the welding tool 1 on the parts 21, 22 along the longitudinal axis. Z. The tool 1 then penetrates deeply into the parts 21, 22 and causes even more pronounced weld flashes 24 ([Fig.5b]), or even a weld collapse 26, more commonly called “weld crash” ([Fig.5c]). The parts 21, 22 are then scrapped.

[0078] In a second configuration example, the pin 2 is driven by a rotational movement along the longitudinal axis Z relative to the body 5, in particular relative to the shoulder 3 which is fixed in this example. It is recalled here that when the shoulder 3 is fixed, the axial end face 30 slides in translation on the parts 21, 22 to be welded. Still in this second configuration, the face 30 is devoid of any improvement in the tribological properties of the face 30 stated previously. However, the weld 23 is always irregular. Indeed, it has material gaps on the surface 29 ([Fig. 6]) and pieces 28 of the parts 21, 22, typically made of aluminum alloy, seal the face 30 ([Fig. 10a]). Cracks 27 may even appear (Figures 7a and 7b). The weld is then of poor quality and not industrially acceptable. This is illustrated on the graph in [Fig.7c] an evolution of a drag force undergone by the tool 1 which can be expressed in Newtons over time which can be expressed in seconds. On this graph, it can be seen that the drag force can reach up to 3500 N. However, such a value of the drag force is a consequence of poor sliding of the face 30 of the body 5 on the surface of the parts 21, 22 at the origin of the aforementioned defects. Indeed, the drag force opposing the advance movement of the tool 1, its value increases when the face 30 is not sufficiently smooth, and therefore has a high roughness coefficient, and / or when it is clogged. One solution consists of reducing the advance and / or rotation speed of the tool 1 in order to limit clogging. But the low feed and / or rotation speeds are incompatible with industrial-scale manufacturing and significantly degrade the mechanical properties of the parts 21, 22 and the weld.

[0079] Thus, according to a third configuration example, in which the shoulder 3 is fixed and the pin 2 is mobile, a roughness coefficient of the face 30 is less than or equal to 0.8. The face 30 therefore presents a tribological improvement here. Unlike the previous configuration examples, the weld 23 presents a better surface quality as illustrated for example in [Fig. 8]. The weld meets the quality criteria necessary at the industrial level with a high-performance finish. Indeed, the weld 23 of [Fig. 8] has neither weld flash 24, nor weld streaks 25, nor cracks 27. The weld 23 obtained therefore has a smooth and clean appearance. In addition, the reduction in the coefficient of friction between the face 30 and the surface of the parts 21, 22 makes it possible to weld more quickly 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 the parts 21, 22 and in which is represented in . ordinate the drag force which can be expressed in Newton and on the abscissa a duration which can be expressed in seconds. The drag force is reduced to 1500 N, a gain of 65% compared to the second configuration. It is also much smoother, causing less stress on the tool 1. Indeed, still according to this graph, an evolution of the drag force 90 is centered on an average value of the drag force 91 during the welding. 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 improve sliding as evidenced by the considerably reduced drag force. Consequently, the tool life and throughput of tool 1 are improved. A finishing step, for example machining, grinding or brushing, is no longer necessary.

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

[0081] The roughness index of the face 30 may furthermore be less than or equal to 0.01 so that the aforementioned advantages are further accentuated. 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 the faces or certain 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. In the same way, each face may or may not comprise, or may independently comprise, 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 meter, and will therefore not be detailed further in the present disclosure.

[0084] The face 30 may carry a coating layer 33 having a friction coefficient less than or equal to 0.8. Thus, the tribological properties of the face are further improved by reducing the friction coefficient. Indeed, the layer 33 reduces the drag force and therefore improves sliding. In addition, 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 devoid of the layer 33. In addition, the face 30 having a roughness coefficient less than or equal to 0.8 improves the adhesion of the layer 33 on the face 30, therefore its lifetime, and even more so when it has a roughness coefficient less than or equal to 0.01.

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

[0086] A measurement of the 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 pyramid-shaped diamond indenter, and will not be detailed further in the present disclosure.

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

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

[0089] According to an exemplary embodiment of layer 33, layer 33 is made of adamantine carbon (better known by the English acronym “DLC” for diamond-like carbon). DLCs cover different amorphous carbon compounds according to their predominant bonds, namely sp2 trigonal or sp3 tetrahedral bonds and their hydrogen content. In the present application, “amorphous carbons” means that the carbon atoms of the compound do not form a crystalline structure.The 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 that have a number of sp3 bonds between 40% and 60% of a total number of bonds of the compound and a quantity of hydrogen atoms between 30% and 50% of a total quantity of atoms of the compound, or amorphous tetrahedral carbons (known by the acronym "ta-C"), that have a number of sp3 bonds between 80% and 88% of a total number of bonds of the compound and a zero quantity of hydrogen atoms. Furthermore, the names sp2 and sp3 are to be understood as they are defined in the modeling of hybrid orbitals in quantum chemistry and will not be detailed further because they are known.In this case, the layer 33 also has antistatic or anti-sticking properties of the aluminum which will further reduce sticking of pieces of parts 21, 22 on the face 30 ([Fig. 10c]) and thus further improve the service life of the tool 1. Alternatively, the layer 33 may be composite, for example by 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 service life of the 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 can carry a layer 33, or selectively certain faces or a single face. The layers 33 can independently from each other, or independently a 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] All of the faces 30, 31, 32 can carry the layer 33.

[0092] According to an exemplary embodiment, notably 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. As a variant of [Fig.3b], a fraction of the faces 30, 31, 32 can carry the layer 33. According to an exemplary embodiment, notably 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 may 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 undergone by the tool 1 are reduced and therefore the service life of the tool 1 is further improved. The parts 21, 22 will undergo less welding stresses and therefore less geometric deformation after welding. In addition, reducing the axial force allows the tool 1 to undergo less mechanical stresses. The tool 1 is therefore also more precise during welding.

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

[0095] The finishing methods known in the state of the art, for example by conventional machining, make it possible to obtain a roughness coefficient between 1.6 and 3.2, while the grinding step E10 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 least by dividing it by two, generally by eight, up to dividing it beyond three hundred. In addition, the grinding makes it possible to remove the marks of conventional machining cutters or cutting tools and to have no bosses or machining striations on the face 30.

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

[0097] A mode of implementing a method of welding 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 the present disclosure.

[0099] In the case of a removable tool 200, the tool 200 is fixed on a table 300 at during a step E20. According to an exemplary implementation of step E20, the tool 200 is placed and held in position on the table 300, typically by screws. Alternatively, the tool is part of the table 300. The tool 200 is then already mounted on the table 300.

[0100] During a step E21, the parts 21, 22 to be welded are placed in position in the tool 200 and then held in position by fixing means, for example clamping flanges placed in the tool 200. The parts 21, 22 can be placed in position according to different configurations: - in juxtaposition field against field ([Fig. 13a]), the parts 21, 22 then having coplanar main faces 210, 220; - superimposed on each other in parallel ([Fig.13b]), one of the parts 21 then extending above the other part 22. The lower main face 211 of the upper part 21 is in surface contact with the upper main face 220 of the lower part 22; or - superimposed on each other angularly, for example perpendicularly or at an angle less than 90° such as 70°, or face against field (figures 13c, 13d and 13e), one of the parts 21 extending above the other part 22, the lower main face 211 of the upper part 21 being in surface contact with a field 222 of the lower part 22 ([Fig. 13c]) or a field 212 of the upper part 21 being in contact with the upper main face 220 of the lower part 22 ([Fig.l3d] and 13e). The main 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 comes into contact with at least one of the first and second parts 21, 22.

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

[0103] According to another exemplary embodiment, notably illustrated in [Fig. 13c], one of the parts 21 extends perpendicularly above the other part 22, the lower main 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] As a variant, notably illustrated in figures 13d and 13e, the upper part 21 has a main planar portion 213, having main faces extending parallel, and a flared edge 214 in which the main faces move away as one approaches the field. This field 212 of the upper part 21 is in contact with the upper main 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 part 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] The tool 1 is ready to weld. During a step E23, the pin 2 is rotated and the tool 1 is moved in a spatial direction, 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 notably illustrated in [Fig. 13a], the end face 30 passes simultaneously over the coplanar main faces 210, 220 of the parts 21, 22.

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

[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 main 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 main face 210 of the upper part. As a variant, notably illustrated 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] The parts 21, 22 are then welded. Steps E20 to E23 can be repeated until the assembly 20 is entirely welded. Consequently, the assembly 20 then comprises at least two parts.

[0110] The supply of additional lubrication to the parts 21, 22 makes it possible to reduce the drag force. The sliding of the end face 30 is then further improved. Indeed, as illustrated by way of example in [Fig. 14] illustrating a change in the drag force experienced by the tool 1 with and without the supply of lubrication as a function of time, the force being able to be expressed in Newtons and the time in seconds, this force drops below 1000 N in modulus with the supply of lubrication for the production of the weld 23. It can then be provided that the parts 21, 22 are lubricated during step E23. The tool 1 can then comprise lubrication means.

[0111] The assembly 20 resulting from the welding method implemented by the tool 1 of the present disclosure is distinguished macroscopically by a weld 23 having a reduction, or even an elimination, of the weld flashes 24, the weld streaks 25, the cracks 27 and the material deficiencies 29. In addition, the weld 23 does not have any weld collapse 26. Indeed, the weld 23 obtained by the tool 1 of the present disclosure illustrated by way of example in FIGS. 8 and 15 does not have any weld flash 24, welding streaks 25, cracks 27, material deficiencies 29 and weld collapse 26 while a weld 23 obtained by a tool known from the prior art and in particular illustrated in FIGS. 5a, 5b, 5c, 6, 7a and 7b has cracks 27, weld flash 24, weld streaks 25, cracks 27, material deficiencies 29 and weld collapse 26. welding 25, material failures 29 and weld collapse 26.

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

[0113] [Fig. 17] illustrates an aircraft fuselage. It comprises stringers 51 extending in 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 the following, the present description will be detailed for the frames 55 and applies mutatis mutandis to the rails 51.

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

[0116] The stiffeners therefore extend over an internal face 520 of the skin 52, an external 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 method implemented by the tool 1. It is therefore not necessary to fix them to each other by means of an assembly by added fixing members. Thus, a 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 exemplary embodiment, notably illustrated in [Fig. 18a], the stiffener has a wedge-shaped profile and comprises a flange 53, the flange 53 being welded superimposed on 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 exemplary embodiment, notably illustrated in [Fig. 18b], the stiffener 51 is welded superimposed on the fuselage skin 52 and the tool is this time in contact with the fuselage skin 52 during welding, extending over the external face 521 of the skin, opposite the stiffener 51. A field of the stiffener 513 is in contact with the internal face of the skin 52.

[0119] According to a third exemplary embodiment, notably illustrated in [Fig. 18c], the stiffener 51 is welded superimposed on 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 internal and non-visible face 520 of the skin, representing a considerable advantage compared to the configuration of [Fig. 18b]. The welding takes place in the configuration of 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 main internal face 520 of the skin 52 and the end face 30 of the face 3 is in contact with the portion 512 of the stiffener 51. The tool 1 therefore performs the weld by passing simultaneously over the flat portions 511, 512 of the stiffener 51 as well as the internal 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 welding is carried out on the internal side of the aircraft, a finishing step, for example by machining or grinding the weld 23, is then eliminated. There is also no longer any need for a sole 53, which reduces the weight of the assembly. In addition, the sealing of the aircraft 50 is improved because there is no longer any residual interface remaining with an overlap 40 between the two passes illustrated as an example in [Fig. 16]. The welding is also more robust thanks to the overlap zone 40 and there is no longer any lack of mixing of the interface.

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

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

Claims

Claims

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 roughness is less than or equal to 0.

01.

3. Tool (1) according to claim 1 or 2, in which 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 one of claims 1 to 3, in which the face (30) carries a coating layer (33) having a hardness greater than or equal to 1000 HV.

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

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

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

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

9. Tool (1) according to one of claims 1 to 8, in which 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 one of claims 1 to 9, further comprising means for lubricating the face (3).

11. Tool (1) according to one of claims 1 to 10, in which 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. Tool according to claim 11, in which 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 for 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. Method according to claim 13, wherein the grinding (E10) is carried out so that an arithmetic mean roughness of the face (30) is less than or equal to 0.8, preferably less than or equal to 0.

01.

15. Method according to one of claims 13 or 14, further comprising a step of coating (El2) the face (30) after the grinding (E10).

16. Method according to claim 15, further comprising a step of nitriding (El 1) the face (30) before the coating (E12).

17. Method of welding parts, the method being implemented by a tool (1) according to one of claims 1 to 12.

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

19. Method according to claim 17, applied to parts (21, 22) superimposed on each other.

20. A method of welding 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 relative to each other, for example being perpendicular to each other.

21. Assembly (20) comprising welded parts (21, 22) resulting from the implementation of a method according to 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 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 method according to claim 20.

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