Method for friction-stir welding between two parts forming a weld surface along a weld line

Abstract

The present application relates to a method for friction-stir welding between two parts jointly forming a weld surface (3) along a weld line (4), the method comprising: rotating a stirring pin (1), moving the stirring pin (1) in rotation along the weld line (4) so as to friction-stir weld the material of the two parts during a movement along the weld line (4), moving a shoulder (2) over the weld surface (3) so as to exert a forging force on the two parts along the weld line (4), the shoulder (2) surrounding the rotating stirring pin such that the stirring pin (1) is withdrawn at the end of movement so as to move the stirring pin (1) away from the weld line (4), wherein the stirring pin (1) is kept rotating during the step of withdrawing the stirring pin (1), and wherein the shoulder (2) is kept bearing against the weld surface (3) so as to exert the forging force on the two parts during the withdrawal of the stirring pin (1), the shoulder (2) being driven in rotation during the withdrawal of the stirring pin (1).

Description

Description Title of the invention: Welding process Technical Field [OOOlJThis presentation concerns a friction stir welding process, and more particularly a friction stir welding process for thin parts forming a closed loop. Previous technique

[0002] Friction stir welding (FSW) is a solid-state welding process that involves joining two parts by bringing them locally to a paste-like state using a retractable pin driven in high-speed rotation.

[0003] Friction stir welding utilizes the heat generated by a high-speed rotating pin along the contact line between the parts to be welded. This softens the materials, causing them to become pasty. The pin then penetrates the joint and thoroughly mixes the materials. The complete assembly is achieved as the pin progresses, gradually covering the entire area to be welded.

[0004] Friction stir welding is primarily used for joining aluminum alloys. It can now also be applied to titanium, copper, nickel, magnesium, steel, and stainless steel alloys. Thermoplastics and metal matrix composites (MMCs) can also be welded. Applications of friction stir welding are varied and include, for example, modern shipbuilding, trains, aerospace applications, and more.

[0005] Friction stir welding makes it possible to obtain a weld joint with good mechanical properties, including for alloys considered unweldable.

[0006] However, friction stir welding is complex to implement for thin parts such as, for example, thin sheets like those that can be used in the aeronautical field.

[0007] Indeed, the use of a retractable pin generates deformations that are problematic for welding thin sheets, especially when the weld must have strict sealing characteristics. These deformations prevent sufficient sealing reliability and therefore result in a high rate of welded parts being rejected.

[0008] Another friction stir welding process suitable for welding thin parts involves using a shoulder surrounding the rotating pin, which is held stationary as the pin moves along the weld line. This process, called SSFSW (Stationary Shoulder Friction Stir Welding), offers several advantages and is particularly well-suited for welding thin sheets because it allows for localized clamping of the thin and flexible sheets during welding, as well as more localized heat input and therefore limited post-weld distortion.

[0009] However, the SSFSW process leaves a hole at the end of the weld, typically at the end of the weld line at the point where the pin exits at the end of the weld.

[0010] In some cases, it is possible to remove the portion of the weld containing the end hole, typically by cutting out the welded section with the resulting hole. However, it is not always possible to remove the portion of the weld containing the hole. For example, in the aerospace industry, it is necessary to weld thin cylindrical sheets together in such a way that the weld is closed, meaning it runs around the entire circumference of the welded parts, and the entire weld must be preserved. In such a closed weld, it is not possible to remove the portion of the weld containing the end hole left at the pin exit. [001 l]In addition, the presence of a hole in a closed weld is also unacceptable for reasons of aerodynamic and mechanical performance and / or to ensure the sealing of the weld beads.

[0012] It is therefore necessary to develop a welding process that is free, at least in part, from the disadvantages inherent in the above processes. Description of the invention

[0013] One idea underlying the invention is to enable a weld of satisfactory quality between two thin pieces. In particular, one idea underlying the invention is to create a closed weld with sealing characteristics and satisfactory weld quality between thin pieces and without a pin exit hole at the end of the weld.

[0014] To this end, the invention provides a friction-stir welding process between two parts forming a weld surface along a weld line, the process comprising: - the rotation of a mixing pin, - the movement of said rotating mixing pin along the weld line so as to weld the material of said two parts by friction-mixing during movement along the weld line, - the displacement of a shoulder bearing on the weld surface so as to exert a forging force on said two parts along the weld line, said shoulder surrounding the mixing pin, - the removal of the mixing pin at the end of the movement so as to move said mixing pin away from the weld line, in which the mixing pin is kept in rotation during the removal of said mixing pin and in which the shoulder is kept in contact with the surface to be welded so as to exert the forging force on said two parts during the removal of the mixing pin.

[0015] This welding process allows the weld to be performed along the weld line while preventing the formation of a weld hole resulting from the withdrawal of the mixing pin. Indeed, the application of the forging force by the shoulder during the withdrawal of the mixing pin deforms the material in its slurry state and prevents the hole from forming during the pin's removal.

[0016] According to different embodiments, the process according to the invention may comprise one or more of the features below, alone or in combination.

[0017] In one embodiment, the two parts are thin sheets, for example, having a thickness between 0.5 mm and 5 mm. Such sheets can have many shapes. In one embodiment, these sheets are cylindrical, preferably of revolution. In another embodiment, these sheets are conical or frustoconical. In yet another embodiment, these sheets have a non-closed curved shape, for example, a half-cylinder or a semi-frustoconical shape.

[0018] According to one embodiment, the weld line is closed. Thus, according to one embodiment, the weld line is continuous such that the mixing pin makes at least two passes over an insertion point of said mixing pin in the two parts to be welded, typically once during insertion and at least once before or during the withdrawal of the mixing pin.

[0019] According to one embodiment, the shoulder is held fixed relative to a rotation axis of the mixing pin during the movement of the mixing pin along the weld line.

[0020] According to one embodiment, the shoulder is rotated during the removal of the mixing pin.

[0021] Activating the rotation of the shoulder during the retraction phase of the pin facilitates the flattening of the material during the removal of the mixing pin, thus allowing for an even more satisfactory weld quality despite the removal of the mixing pin.

[0022] According to one embodiment, the shoulder is rotated during the movement of the mixing pin along the weld line.

[0023] According to one embodiment, the mixing pin is in a fixed position along the weld line when said mixing pin is withdrawn.

[0024] In one embodiment, the mixing pin is withdrawn progressively as it is moved along the weld line. In other words, the mixing pin is withdrawn as it is moved along the weld line.

[0025] Such a withdrawal of the mixing pin during the movement of said mixing pin along the weld line therefore allows a progressive withdrawal of the pin and thus a reduction of the material to be flattened at the end of the weld.

[0026] In one embodiment, the axis of rotation of the mixing pin is inclined relative to the weld surface. In other words, both the mixing pin and the shoulder are inclined relative to the weld surface. Preferably, this inclination is opposite to the direction of movement of the mixing pin along the weld line. Thus, the shoulder bears more heavily on the material already mixed by the mixing pin than on the material that has not yet been mixed, ensuring better flattening of the material by the shoulder.

[0027] Such an inclination of the pin and shoulder is also particularly advantageous for welding curved surfaces because it helps to avoid interference between the welding tool carrying the mixing pin and shoulder and the area to be welded.

[0028] According to one embodiment, the mixing pin is movable between a developed position in which said mixing pin protrudes from an underside of the shoulder, typically the face applied against the weld surface, and a retracted position in which the mixing pin is retracted by the shoulder.

[0029] Such a retractable pin allows the shoulder support to be maintained against the welding surface independently of the retraction of the mixing pin.

[0030] According to one embodiment, the invention also provides a friction stir welding method between two parts jointly forming a weld surface along a weld line, the method comprising: - the rotation of a mixing pin, - the movement of said rotating mixing pin along the weld line so as to weld the material of said two parts by friction-mixing during movement along the weld line, -the displacement of a shoulder on the weld surface so as to exert a forging force on said two parts along the weld line, said shoulder surrounding the rotating mixing pin, - the progressive withdrawal of the mixing pin at the end of the movement of the mixing pin along the weld line so as to move said mixing pin away from the weld line, in which the mixing pin is kept in rotation during the step of withdrawing said mixing pin, and in which the shoulder is moved away from the weld surface during the withdrawal of the mixing pin.

[0031] This embodiment allows the weld to be performed along the weld line by applying a controlled forging force during the movement of the mixing pin, without creating a hole at the end of the weld. Furthermore, this embodiment does not require a retractable pin to achieve this result and is therefore simple to implement.

[0032] In one embodiment, the shoulder is rotated as it is moved away from the weld surface. In another embodiment, the shoulder is supported against the weld surface and preferably held fixed in rotation prior to the removal of the mixing pin so as to generate a forging force during the movement preceding the removal of the mixing pin.

[0033] The invention also provides a friction-stir welding device comprising - a mixing pin that is movable and rotates around an axis of rotation, said mixing pin being movable in translation along said axis of rotation and perpendicular to said axis of rotation, - a shoulder having a lower face perpendicular to the axis of rotation of the mixing pin, the shoulder further having an internal housing, the mixing pin being housed in said internal housing, the shoulder being movable in rotation around the axis of rotation of the mixing pin and in translation along said axis of rotation.

[0034] In one embodiment, the mixing pin is translationally movable along the axis of rotation relative to the shoulder between a retracted position in which the mixing pin is concealed by the shoulder and an extended position in which the mixing pin protrudes from the underside of the shoulder. In other words, the mixing pin is retractable into the internal housing of the shoulder.

[0035] The aforementioned features and advantages, as well as others, will become apparent upon reading the following detailed description of examples of the welding process according to different variants of the invention. This detailed description refers to the attached drawings. Brief description of the drawings

[0036] The attached drawings are schematic and are primarily intended to illustrate the principles of the presentation.

[0037] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference symbols. [Fig. 1] Figure 1 schematically represents a cross-sectional view of a welding device according to the invention during a weld according to a first embodiment; [Fig. 2] Figure 2 schematically represents a cross-sectional view of a welding device according to the invention during a weld according to a second embodiment. [Fig. 3] Figure 3 schematically represents a cross-sectional view of a welding device according to the invention during a weld according to a third embodiment. [Fig. 4] Figure 4 schematically represents a cross-sectional view of a welding device according to the invention during a weld according to a fourth embodiment Description of the implementation methods

[0038] Figure 1 illustrates a first embodiment of the invention in which a welding device comprises a mixing pin 1 and a shoulder 2 for welding together two adjoining pieces to jointly form a weld surface 3 along a weld line 4.

[0039] The mixing pin 1 is movable in rotation around an axis of rotation 5. This mixing pin 1 is also movable in translation along said axis of rotation 5. This mixing pin 1 is also movable in translation along the weld line 4.

[0040] In the embodiment illustrated in Figure 1, the shoulder has an internal cylindrical housing 6. The mixing pin 1 is housed in the internal housing 6. The shoulder 2 has a lower face 7. The mixing pin 1 is movable between an extended position illustrated on the left side of Figure 1 and a retracted position illustrated on the right side of Figure 1.

[0041] In the extended position, the mixing pin 1 protrudes from the lower face 7 of the shoulder 2. In the retracted position, the mixing pin 1 is inserted into the internal housing 6 and is therefore retracted by the shoulder 2.

[0042] To weld the two parts joined along the weld line 4, the mixing pin 1 is rotated 8 at high speed. The rotating mixing pin 1 is pressed 9 against the weld surface 3 of the two parts to be welded. Furthermore, the lower face 7 of the shoulder 2 is also pressed against the weld surface 3. During this initial contact of the mixing pin 1 and the lower face 7 against the weld surface 3, the mixing pin 1 is in a retracted position.

[0043] The contact of the mixing pin 1, rotating at high speed against the weld surface 3 of the two parts to be welded, allows, under the effect of the friction generated by this contact and the high-speed rotation of the mixing pin 1, the material forming the weld surface 3 to become pasty. The mixing pin 1 is moved into the developed position to be inserted into the material in the pasty state and penetrate into the weld surface 3, as illustrated on the left side of Figure 1.

[0044] Inserting the mixing pin 1 into the material in its paste-like state allows the material to be mixed and thus the two parts to be welded together. Furthermore, the pressure of the lower face 7 of the shoulder 2 on the weld surface 3 generates a forging force that flattens the material mixed by the mixing pin 1 and allows for a good quality weld, typically without the deformations related to the insertion and mixing caused by the rotation of the mixing pin 1.

[0045] The mixing pin 1 is kept rotating at high speed and moved along the weld line 4 in order to perform the weld over the entire length of said weld line 4. During this movement of the mixing pin 1 along the weld line 4, the lower face 7 of the shoulder 2 is also moved and kept in contact with the weld surface 3 in order to generate the forging force all along the weld line 4.

[0046] In the embodiment illustrated in Figure 1, the shoulder 2 is held fixed relative to the axis of rotation 5. Typically, only the mixing pin 1 rotates around the axis of rotation 5 during this movement along the weld line 4, while the shoulder 2 remains stationary. The rotation of the mixing pin 1 and the lack of rotation of the shoulder 2, while maintaining support on the lower face 7, allows for more precise weld localization by rendering the material into a paste-like state at the mixing pin 1 alone, while maintaining the forging force on the shoulder 2.

[0047] When the mixing pin 1 has moved all the way along the weld line 4, that is, when said mixing pin 1 is positioned at the end of the weld line 4, said mixing pin 1 is retracted 10 from its extended position to its retracted position so that it is no longer inserted into the material formed by the two parts to be welded. This retraction of the pin mixing 1 is carried out in the fixed position of said mixing pin 1, and therefore of the shoulder 2, along the weld line 4.

[0048] During the withdrawal of the mixing pin 1, the shoulder 2 is held against the weld surface 3 so as to maintain the forging force 11. Maintaining the forging force 11 during the withdrawal of the mixing pin 1 allows the material to be deformed at the point of exit of the mixing pin 1 to smooth the weld surface 3 and not leave a hole in said weld surface 3 despite the withdrawal of the mixing pin 1.

[0049] Figure 2 illustrates a first variant of the welding process according to the invention. This variant differs from the process described above with reference to Figure 1 in that the shoulder 2 is held fixed relative to the axis of rotation 5 during movement along the weld line 4 but is driven into rotation 12 at high speed around said axis of rotation 5 during the withdrawal of the mixing pin 1.

[0050] The rotational drive of the shoulder 2 during the withdrawal of the mixing pin 1 allows the material to remain in a pasty state at the exit point of the mixing pin 1. Maintaining the material in a pasty state at the exit of the mixing pin 1 facilitates the deformation of the material under the forging force of the shoulder 2 and thus allows for better mixing of the material and therefore a weld with no exit hole of the mixing pin 1 and better uniformity of the material at the exit of the mixing pin 1.

[0051] Figure 3 illustrates a second embodiment of the welding process according to the invention. This embodiment differs from the embodiments illustrated in Figures 1 and 2 in that the withdrawal of the mixing pin 1 is progressive during the movement of said mixing pin along the weld line 4. Thus, a trajectory 13 of the mixing pin 1 is such that a portion 14 of said mixing pin 1, inserted into the material of the two parts in order to mix said material and perform the weld, is progressively reduced at the end of the weld line 4.

[0052] In this embodiment, the lower face 7 of the shoulder 2 is held in support in order to generate the forging force during the withdrawal of the mixing pin 1.

[0053] In addition, the shoulder 2 is preferably driven in rotation around the axis of rotation 5 during the progressive withdrawal of the mixing pin 1. However, the shoulder 2 can also be held in a fixed position relative to the axis of rotation 5, i.e. without being driven in rotation, during the withdrawal of the mixing pin 1.

[0054] Figure 4 illustrates a third embodiment of the welding process according to the invention. Similar to the second embodiment shown in Figure 3, the withdrawal of the mixing pin 1 in this third embodiment of the process according to the invention is progressive and, in fact, follows a progressive withdrawal trajectory 13 at the end of the weld along the weld line 4. However, in this third embodiment, the shoulder 2 is fixed in movement along the axis of rotation 5 of the mixing pin 1. Thus, in this third embodiment, the shoulder 2 is moved away from the weld surface 3 during the withdrawal of the mixing pin 1.

[0055] Similar to the second variant, this third variant can be achieved by rotating the shoulder 2 when the mixing pin 1 is withdrawn, or conversely by keeping said shoulder 2 fixed around the axis of rotation 5.

[0056] In an embodiment not shown, the axis of rotation of the mixing pin, and optionally of the shoulder, is inclined relative to the weld line. Such an inclination of the axis of rotation of the mixing pin allows for better management of interference with the weld surface during movement along the weld line, particularly in the case of a curved weld surface, as is the case, for example, with two cylindrical parts, or any curved surfaces, to be welded together using the welding process according to the invention.

[0057] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense. [0058JII is also evident that all the characteristics described with reference to a process are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.

Claims

Demands

1. A friction stir welding method between two parts forming a weld surface (3) along a weld line (4), the method comprising: - the rotation of a mixing pin (1), - the movement of said mixing pin (1) in rotation along the weld line (4) so ​​as to weld by friction-mix the material of said two parts during a movement along the weld line (4), - the displacement of a shoulder (2) bearing on the weld surface (3) so as to exert a forging force on said two parts along the weld line (4), said shoulder (2) surrounding the rotating mixing pin, - the removal of the mixing pin (1) at the end of the movement so as to move said mixing pin (1) away from the weld line (4), in which the mixing pin (1) is kept in rotation during the removal of said mixing pin (1), and in which the shoulder (2) is kept in contact with the weld surface (3) so as to exert the forging force on said two parts during the removal of the mixing pin (1), the shoulder (2) being driven in rotation during the removal of the mixing pin (1).

2. A welding method according to claim 1, wherein the shoulder (2) is held fixed relative to a rotation axis (5) of the mixing pin (1) during the movement of said mixing pin (1) along the weld line (4).

3. Method according to claim 1 or 2, wherein the mixing pin (1) is in a fixed position along the weld line (4) when said mixing pin (1) is withdrawn.

4. A method according to any one of claims 1 to 3, wherein the retraction of the mixing pin (1) is progressive during the movement of said mixing pin (1) along the weld line (4).

5. A method according to any one of claims 1 to 4, wherein the axis of rotation (5) of the mixing pin (1) is inclined with respect to the weld surface (3).

6. A method according to any one of claims 1 to 5, wherein the mixing pin (1) is movable between a developed position in which said mixing pin (1) protrudes from an underside (7) of the shoulder (2) and a retracted position in which the mixing pin (1) is retracted by the shoulder (2).

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